Internet Research Task Force (IRTF) M. Mosko
Request for Comments: 8609 PARC, Inc.
Category: Experimental I. Solis
ISSN: 2070-1721 LinkedIn
C. Wood
University of California, Irvine
May
July 2019
Content-Centric Networking (CCNx) Messages in TLV Format
Abstract
Content-Centric Networking (CCNx) is a network protocol that uses a
hierarchical name to forward requests and to match responses to
requests. This document specifies the encoding of CCNx messages in a
TLV packet format, including the TLV types used by each message
element and the encoding of each value. The semantics of CCNx
messages follow the encoding-independent CCNx Semantics
specification.
This document is a product of the Information Centric Networking
research group (ICNRG). The document received wide review among
ICNRG participants and has two full implementations currently in
active use, which have informed the technical maturity of the
protocol specification.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Research Task
Force (IRTF). The IRTF publishes the results of Internet-related
research and development activities. These results might not be
suitable for deployment. This RFC represents the consensus of the
Information-Centric Networking Research Group of the Internet
Research Task Force (IRTF). Documents approved for publication by
the IRSG are not candidates for any level of Internet Standard; see
Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8609.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Type-Length-Value (TLV) Packets . . . . . . . . . . . . . . . 5
3.1. Overall Packet Format . . . . . . . . . . . . . . . . . . 6 7
3.2. Fixed Headers . . . . . . . . . . . . . . . . . . . . . . 7 8
3.2.1. Interest Fixed Header . . . . . . . . . . . . . . . . 8 9
3.2.1.1. Interest HopLimit . . . . . . . . . . . . . . . . 9
3.2.2. Content Object Fixed Header . . . . . . . . . . . . . 9
3.2.3. InterestReturn Interest Return Fixed Header . . . . . . . . . . . . . 9 10
3.2.3.1. InterestReturn Interest Return HopLimit . . . . . . . . . . . . . 10
3.2.3.2. InterestReturn Interest Return Flags . . . . . . . . . . . . . . 10
3.2.3.3. Return Code . . . . . . . . . . . . . . . . . . . 10
3.3. Global Formats . . . . . . . . . . . . . . . . . . . . . 11
3.3.1. Pad . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3.2. Organization-Specific TLVs . . . . . . . . . . . . . 12
3.3.3. Hash Format . . . . . . . . . . . . . . . . . . . . . 12
3.3.4. Link . . . . . . . . . . . . . . . . . . . . . . . . 13
3.4. Hop-by-Hop TLV Headers . . . . . . . . . . . . . . . . . 14
3.4.1. Interest Lifetime . . . . . . . . . . . . . . . . . . 14
3.4.2. Recommended Cache Time . . . . . . . . . . . . . . . 15
3.4.3. Message Hash . . . . . . . . . . . . . . . . . . . . 15 16
3.5. Top-Level Types . . . . . . . . . . . . . . . . . . . . . 16 17
3.6. CCNx Message TLV . . . . . . . . . . . . . . . . . . . . . . 17 18
3.6.1. Name . . . . . . . . . . . . . . . . . . . . . . . . 18 19
3.6.1.1. Name Segments . . . . . . . . . . . . . . . . . . 19 20
3.6.1.2. Interest Payload ID . . . . . . . . . . . . . . . 20
3.6.2. Message TLVs . . . . . . . . . . . . . . . . . . . . 21
3.6.2.1. Interest Message TLVs . . . . . . . . . . . . . . 21
3.6.2.2. Content Object Message TLVs . . . . . . . . . . . 22 23
3.6.3. Payload . . . . . . . . . . . . . . . . . . . . . . . 24 25
3.6.4. Validation . . . . . . . . . . . . . . . . . . . . . 24 25
3.6.4.1. Validation Algorithm . . . . . . . . . . . . . . 24 25
3.6.4.2. Validation Payload . . . . . . . . . . . . . . . 30 32
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 33
4.1. Packet Type Registry . . . . . . . . . . . . . . . . . . 31 33
4.2. Interest Return Code Registry . . . . . . . . . . . . . . 31 34
4.3. Hop-by-Hop Type Registry . . . . . . . . . . . . . . . . 33 35
4.4. Top-Level Type Registry . . . . . . . . . . . . . . . . . 34 36
4.5. Name Segment Type Registry . . . . . . . . . . . . . . . 34 37
4.6. Message Type Registry . . . . . . . . . . . . . . . . . . 35 37
4.7. Payload Type Registry . . . . . . . . . . . . . . . . . . 37 38
4.8. Validation Algorithm Type Registry . . . . . . . . . . . 37 39
4.9. Validation-Dependent Data Type Registry . . . . . . . . . 39 40
4.10. Hash Function Type Registry . . . . . . . . . . . . . . . 40
5. Security Considerations . . . . . . . . . . . . . . . . . . . 41
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 44
6.1. Normative References . . . . . . . . . . . . . . . . . . 44
6.2. Informative References . . . . . . . . . . . . . . . . . 44
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46
1. Introduction
This document specifies a Type-Length-Value (TLV) packet format and
the TLV type and value encodings for CCNx messages. A full
description of the CCNx network protocol, providing an encoding-free
description of CCNx messages and message elements, may be found in
[RFC8569]. CCNx is a network protocol that uses a hierarchical name
to forward requests and to match responses to requests. It does not
use endpoint addresses; the Internet Protocol does. Restrictions in
a request can limit the response by the public key of the response's
signer or the cryptographic hash of the response. Every CCNx
forwarder along the path does the name matching and restriction
checking. The CCNx protocol fits within the broader framework of
Information-Centric Networking (ICN) protocols [RFC7927].
This document describes a TLV scheme using a fixed 2-byte T and a
fixed 2-byte L field. The rational for this choice is described in
Section 5. Briefly, this choice avoids multiple encodings of the
same value (aliases) and reduces the work of a validator to ensure
compliance. Unlike some uses of TLV in networking, each network hop
must evaluate the encoding, so even small validation latencies at
each hop could add up to a large overall forwarding delay. For very
small packets or low-throughput links, where the extra bytes may
become a concern, one may use a TLV compression protocol, for
example, [compress] and [CCNxz].
This document uses the terms CCNx Packet, CCNx Message, and CCNx
Message TLV. A CCNx Packet refers to the entire Layer 3 datagram as
specified in Section 3.1. A CCNx Message is the ABNF token defined
in the CCNx Semantics document [RFC8569]. A CCNx Message TLV refers
to the encoding of a CCNx Message as specified in Section 3.6.
This document specifies:
o the TLV packet CCNx Packet format,
o the overall packet format for CCNx messages, Message TLV format,
o the TLV types used by CCNx messages,
o the encoding of values for each type,
o top-level types that exist at the outermost containment,
o Interest TLVs that exist within Interest containment, and
o Content Object TLVs that exist within Content Object containment.
This document is supplemented by these documents:
o [RFC8569], which covers message semantics and the protocol
operation regarding Interest and Content Object, including the
Interest Return protocol.
o [CCNxURI], which covers the CCNx URI notation.
The type values in Section 4 conform to the IANA-assigned numbers for
the CCNx protocol. This document uses the symbolic names defined in
that section. All TLV type values are relative to their parent
containers. For example, each level of a nested TLV structure might
define a "type = 1" with a completely different meaning.
Packets are represented as 32-bit wide words using ASCII art. Due to
the nested levels of TLV encoding and the presence of optional fields
and variable sizes, there is no concise way to represent all
possibilities. We use the convention that ASCII art fields enclosed
by vertical bars "|" represent exact bit widths. Fields with a
forward slash "/" are variable bit widths, which we typically pad out
to word alignment for picture readability.
The document represents the consensus of the ICN RG. It is the first
ICN protocol from the RG, created from the early CCNx protocol [nnc]
with significant revision and input from the ICN community and RG
members. The document has received critical reading by several
members of the ICN community and the RG. The authors and RG chairs
approve of the contents. The document is sponsored under the IRTF
and is not issued by the IETF and is not an IETF standard. This is
an experimental protocol and may not be suitable for any specific
application and the specification may change in the future.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Definitions
These definitions summarize items defined in [RFC8569]. This
document defines their encodings.
o Name: A hierarchically structured variable-length identifier. It
is an ordered list of path segments, which are variable-length
octet strings. In human-readable form, it is represented in URI
format as "ccnx:/path/part". There is no host or query string.
See [CCNxURI] for complete details.
o Interest: A message requesting a Content Object with a matching
Name and other optional selectors to choose from multiple objects
with the same Name. Any Content Object with a Name and attributes
that matches the Name and optional selectors of the Interest is
said to satisfy the Interest.
o Content Object: A data object sent in response to an Interest
request. It has an optional Name and a content payload that are
bound together via cryptographic means.
3. Type-Length-Value (TLV) Packets
We use 16-bit Type and 16-bit Length fields to encode TLV-based
packets. This provides 64,000 65,536 different possible types and value
field lengths of up to 64 KiB. With 64,000 65,536 possible types at each
level of TLV encoding, there should be sufficient space for basic
protocol types, while also allowing ample room for experimentation,
application use, vendor extensions, and growth. This encoding does
not allow for jumbo packets beyond 64 KiB total length. If used on a
media that allows for jumbo frames, we suggest defining a media
adaptation envelope that allows for multiple smaller frames.
There are several global TLV definitions that we reserve at all
hierarchical contexts. The TLV types in the range 0x1000 - 0x1FFF
are Reserved for Experimental Use. The TLV type T_ORG is also
Reserved for Vendor Extensions (see Section 3.3.2). The TLV type
T_PAD is used to optionally pad a field out to some desired
alignment.
+--------+------------------+---------------------------------------+
| Abbrev | Name | Description |
+--------+------------------+---------------------------------------+
| T_ORG | Vendor Specific | Information specific to a vendor |
| | Information | implementation (Section 3.3.2). |
| | | |
| T_PAD | Padding | Adds padding to a field (Section |
| | | 3.3.1). |
| | | |
| n/a | Experimental | Experimental use. |
+--------+------------------+---------------------------------------+
Table 1: Reserved TLV Types
There are several global TLV definitions that we reserve at all
hierarchical contexts. The TLV types in the range 0x1000 - 0x1FFF
are Reserved for Experimental Use. The TLV type T_ORG is also
Reserved for Vendor Extensions (see Section 3.3.2). The TLV type
T_PAD is used to optionally pad a field out to some desired
alignment.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Type | Length |
+---------------+---------------+---------------+---------------+
Figure 1: Type and Length encoding
The Length field contains the length of the Value field in octets.
It does not include the length of the Type and Length fields. The
Length MAY be zero.
TLV structures are nestable, allowing the Value field of one TLV
structure to contain additional TLV structures. The enclosing TLV
structure is called the container of the enclosed TLV.
Type values are context dependent. Within a TLV container, one may
reuse previous type values for new context-dependent purposes.
3.1. Overall Packet Format
Each packet CCNx Packet includes the 8-byte fixed header, described below,
followed by a set of TLV fields. These fields are optional hop-by-
hop headers and the Packet Payload.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PacketType | PacketLength |
+---------------+---------------+---------------+---------------+
| PacketType-specific fields | HeaderLength |
+---------------+---------------+---------------+---------------+
/ Optional hop-by-hop header TLVs /
+---------------+---------------+---------------+---------------+
/ PacketPayload TLVs /
+---------------+---------------+---------------+---------------+
Figure 2: Overall Packet Format
The packet payload is PacketPayload of a TLV encoding CCNx Packet is the protocol message itself.
The Content Object Hash is computed over the PacketPayload only,
excluding the fixed and hop-by-hop headers, as those might change
from hop to hop. Signed information or similarity hashes should not
include any of the CCNx message, followed by
optional Validation TLVs.
1 2 3
0 1 2 3 4 fixed or hop-by-hop headers. The PacketPayload
should be self-sufficient in the event that the fixed and hop-by-hop
headers are removed. See Message Hash (Section 3.4.3).
Following the CCNx Message TLV, the PacketPayload may include
optional Validation TLVs.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| CCNx Message TLV /
+---------------+---------------+---------------+---------------+
/ Optional CCNx ValidationAlgorithm TLV /
+---------------+---------------+---------------+---------------+
/ Optional CCNx ValidationPayload TLV (ValidationAlg required) /
+---------------+---------------+---------------+---------------+
This document describes the Version "1" TLV encoding.
Figure 3: PacketPayload TLVs
After discarding the fixed and hop-by-hop headers, the remaining
PacketPayload should be a valid protocol message. Therefore, the
PacketPayload always begins with 4 bytes of type-length that
specifies the protocol message (whether it is an Interest, Content
Object, or other message type) and its total length. The embedding
of a self-sufficient protocol data unit inside the fixed and hop-by-
hop headers allows a network stack to discard the headers and operate
only on the embedded message. It also decouples the PacketType field
-- which specifies how to forward the packet -- from the
PacketPayload.
The range of bytes protected by the Validation includes the CCNx
Message TLV and the ValidationAlgorithm TLV.
The ContentObjectHash begins with the CCNx Message TLV and ends at
the tail of the packet. CCNx Packet.
3.2. Fixed Headers
CCNx messages begin with an 8-byte fixed header (non-TLV format).
The HeaderLength field represents the combined length of the fixed
and hop-by-hop headers. The PacketLength field represents the entire
packet length from the first byte of Version to the last byte of the
packet.
A specific PacketType may assign meaning to the "PacketType-specific
fields," which are otherwise reserved. For the three defined
PacketTypes (Interest, ContentObject, and InterestReturn), we define
those values in this document.
The PacketPayload of a CCNx packet is the protocol message itself.
The Content Object Hash is computed over the PacketPayload only,
excluding the fixed and hop-by-hop headers, as those might change
from hop to hop. Signed information or similarity hashes should not
include any of the fixed or hop-by-hop headers. The PacketPayload
should be self-sufficient in the event that
In Figure 2, the fixed and hop-by-hop
headers are removed.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PacketType | PacketLength |
+---------------+---------------+---------------+---------------+
| PacketType-specific header fields | HeaderLength |
+---------------+---------------+---------------+---------------+ are:
o Version: defines the version of the packet. packet, which MUST be 1.
o HeaderLength: The length of the fixed header (8 bytes) and hop-by-
hop headers. The minimum value MUST be 8.
o PacketType: describes forwarder actions to take on the packet.
o PacketLength: Total octets of packet including all headers (fixed
header plus hop-by-hop headers) and protocol message.
o PacketType-specific Fields: specific PacketTypes define the use of
these bits.
The PacketType field indicates how the forwarder should process the
packet. A Request Packet (Interest) has PacketType PT_INTEREST, a
Response (Content Object) has PacketType PT_CONTENT, and an
InterestReturn Interest
Return has PacketType PT_RETURN.
HeaderLength is the number of octets from the start of the packet CCNx
Packet (Version) to the end of the hop-by-hop headers. PacketLength
is the number of octets from the start of the packet to the end of
the packet. Both lengths have a minimum value of 8 (the fixed header
itself).
The PacketType-specific fields are reserved bits whose use depends on
the PacketType. They are used for network-level signaling.
3.2.1. Interest Fixed Header
If the PacketType is PT_INTEREST, it indicates that the PacketPayload packet should
be processed as an forwarded following the Interest message. pipeline in Section 2.4.4 of
[RFC8569]. For this type of packet, the Fixed Header includes a
field for a HopLimit as well as Reserved and Flags fields. The
Reserved field MUST be set to 0 in an Interest
-- this field will be set to a return code in the case of an Interest
Return. Interest. There are currently
no flags defined, so the Flags field MUST be set to 0.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PT_INTEREST | PacketLength |
+---------------+---------------+---------------+---------------+
| HopLimit | Reserved | Flags | HeaderLength |
+---------------+---------------+---------------+---------------+
Figure 4: Interest Header
3.2.1.1. Interest HopLimit
For an Interest message, the HopLimit is a counter that is
decremented with each hop. It limits the distance an Interest may
travel on the network. The node originating the Interest MAY put in
any value up to the maximum of 255. Each node that receives an
Interest with a HopLimit decrements the value upon reception. If the
value is 0 after the decrement, the Interest MUST NOT be forwarded
off the node.
It is an error to receive an Interest from a remote node with the
HopLimit field set to
0 from a remote node. 0.
3.2.2. Content Object Fixed Header
If the PacketType is PT_CONTENT, it indicates that the PacketPayload packet should
be processed as a forwarded following the Content Object message. pipeline in Section 2.4.4
of [RFC8569]. A Content Object defines a Flags field; however, there
are currently no flags defined, so the Flags field must be set to 0.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PT_CONTENT | PacketLength |
+---------------+---------------+---------------+---------------+
| Reserved | Flags | HeaderLength |
+---------------+---------------+---------------+---------------+
Figure 5: Content Object Header
3.2.3. InterestReturn Interest Return Fixed Header
If the PacketType is PT_RETURN, it indicates that the PacketPayload packet should
be processed as a returned following the Interest message. Return rules in Section 10 of
[RFC8569]. The only difference between this InterestReturn Interest Return message
and the original Interest is that the PacketType is changed to
PT_RETURN and a ReturnCode is put into the ReturnCode field. All
other fields are unchanged from the Interest packet. The purpose of
this encoding is to prevent packet length changes so no additional
bytes are needed to return an Interest to the previous hop. See [RFC8569] for a protocol
description of this packet type.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PT_RETURN | PacketLength |
+---------------+---------------+---------------+---------------+
| HopLimit | ReturnCode | Flags | HeaderLength |
+---------------+---------------+---------------+---------------+
Figure 6: Interest Return Header
3.2.3.1. InterestReturn Interest Return HopLimit
This is the original Interest's HopLimit, as received. It is the
value received before being decremented
decrement at the current node (i.e., sending the
received value). Interest Return.
3.2.3.2. InterestReturn Interest Return Flags
These are the original Flags as set in the Interest.
3.2.3.3. Return Code
The return types are listed below;
This section maps the numeric values assigned Return Code name [RFC8569] to the
return types are listed in TLV symbolic
name. Section 4.2. 4.2 maps the symbolic names to numeric values. This value
field is set by the node creating the Interest Return.
A return code of "0" MUST NOT be used, as it indicates that the
returning system did not modify the Return Code field.
+-------------------------------------+-----------------------------+
| Type | Return Type | Name in RFC 8569 |
+-------------------------------------+-----------------------------+
| T_RETURN_NO_ROUTE | No Route |
| | |
| T_RETURN_LIMIT_EXCEEDED | Hop Limit Exceeded |
| | |
| T_RETURN_NO_RESOURCES | No Resources |
| | |
| T_RETURN_PATH_ERROR | Path Error |
| | |
| T_RETURN_PROHIBITED | Prohibited |
| | |
| T_RETURN_CONGESTED | Congested |
| | |
| T_RETURN_MTU_TOO_LARGE | MTU too large |
| | |
| T_RETURN_UNSUPPORTED_HASH_RESTRICTI | Unsupported ContentObjectHa |
| ON | shRestriction |
| | |
| T_RETURN_MALFORMED_INTEREST | Malformed Interest |
+-------------------------------------+-----------------------------+
Table 2: Return Codes
3.3. Global Formats
This section defines global formats that may be nested within other
TLVs.
3.3.1. Pad
The pad type may be used by protocols sources that prefer word-aligned data.
The size of the word may be defined by the protocol.
Padding 4-byte words, for example, would use a 1-byte, 2-byte, and
3-byte Length. Padding 8-byte words would use a (0, 1, 2, 3, 5, 6,
7)-byte Length.
One MUST NOT pad inside a Name. Apart from that, a pad MAY be
inserted after any other TLV in the CCNx Message TLV or in the
Validation-Dependent Data
ValidationAlgorithm TLV. In the remainder of this document, we will
not show optional Pad TLVs.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_PAD | Length |
+---------------+---------------+---------------+---------------+
/ variable-length pad MUST be zeros /
+---------------+---------------+---------------+---------------+
Figure 7: Pad Encoding
3.3.2. Organization-Specific TLVs
Organization-specific TLVs (also known as Vendor TLVs) MUST use the
T_ORG type. The Length field is the length of the organization-
specific information plus 3. The Value begins with the 3 byte
organization number derived from the last three digits network byte order encoding of
the IANA "Private Enterprise Numbers" registry [IANA-PEN], followed
by the organization-specific information.
A T_ORG MAY be used as a path segment in a Name, in which case it Name. It is
a regular treated like
any other path segment and is part of the regular name matching. segment.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_ORG | Length (3+value length) |
+---------------+---------------+---------------+---------------+
| PEN[0] | PEN[1] | PEN[2] | /
+---------------+---------------+---------------+ +
/ Vendor-Specific Vendor Specific Value /
+---------------+---------------+---------------+---------------+
Figure 8: Organization-Specific TLVs
3.3.3. Hash Format
Hash values are used in several fields throughout a packet. This TLV
encoding is commonly embedded inside those fields to specify the
specific hash function used and it's its value. Note that the reserved
TLV types are also reserved here for user-defined experimental
functions.
The LENGTH field of the hash value MUST be less than or equal to the
hash function length. If the LENGTH is less than the full length, it
is taken as the left LENGTH bytes of the hash function output. Only
specified truncations are allowed, not arbitrary truncations.
This nested format is used because it allows binary comparison of
hash values for certain fields without a router needing to understand
a new hash function. For example, the KeyIdRestriction is bit-wise
compared between an Interest's KeyIdRestriction field and a
ContentObject's KeyId field. This format means the outer field
values do not change with differing hash functions so a router can
still identify those fields and do a binary comparison of the hash
TLV without need to understand the specific hash used. An
alternative approach, such as using T_KEYID_SHA512-256, would require
each router keep keeps an up-to-date parser and supporting user-defined
hash functions here would explode the parsing state-space.
A CCNx entity MUST support the hash type T_SHA-256. An entity MAY
support the remaining hash types.
+-----------+------------------------+
| Abbrev | Lengths (octets) |
+-----------+------------------------+
| T_SHA-256 | 32 |
| | |
| T_SHA-512 | 64, 32 |
| | |
| n/a | Experimental TLV types |
+-----------+------------------------+
Table 3: CCNx Hash Functions
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_FOO | 36 |
+---------------+---------------+---------------+---------------+
| T_SHA512 | 32 |
+---------------+---------------+---------------+---------------+
/ 32-byte hash value /
+---------------+---------------+---------------+---------------+
Figure 9: Example nesting inside type T_FOO
3.3.4. Link
A Link is the tuple: {Name, [KeyIdRestr], [ContentObjectHashRestr]}.
It is a general encoding that is used in both the payload of a
Content Object with PayloadType = "Link" and in the KeyLink field in a KeyLocator. Content Object's
KeyLink field. A Link is essentially the body of an Interest.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+
+---------------+---------------+---------------+---------------+
/ Mandatory CCNx Name /
+---------------+---------------+-------------------------------+
+---------------+---------------+---------------+---------------+
/ Optional KeyIdRestriction /
+---------------------------------------------------------------+
+---------------+---------------+---------------+---------------+
/ Optional ContentObjectHashRestriction /
+---------------------------------------------------------------+
+---------------+---------------+---------------+---------------+
Figure 10: Link Encoding
3.4. Hop-by-Hop TLV Headers
Hop-by-hop TLV headers are unordered and meaning MUST NOT be attached
to their ordering. Three hop-by-hop headers are described in this
document:
+-------------+-----------------+-----------------------------------+
+-------------+--------------------+--------------------------------+
| Abbrev | Name | Description |
+-------------+-----------------+-----------------------------------+
+-------------+--------------------+--------------------------------+
| T_INTLIFE | Interest Lifetime | The time an Interest should stay |
| | Lifetime (Section 3.4.1) | stay pending at an intermediate node. |
| | (Section 3.4.1) | intermediate node. |
| | | |
| T_CACHETIME | Recommended Cache | The Recommended Cache Time for |
| | Cache Time (Section | Content Objects. |
| | (Section 3.4.2) | |
| | | |
| T_MSGHASH | Message Hash | The A cryptographic hash of the CCNx Message to |
| | (Section 3.4.3) | end of packet using the format |
| | (Section 3.4.3) | specified in Section 3.3.3. 3.3.3). |
+-------------+-----------------+-----------------------------------+
+-------------+--------------------+--------------------------------+
Table 4: Hop-by-Hop Header Types
Additional hop-by-hop headers are defined in higher level
specifications such as the fragmentation specification.
3.4.1. Interest Lifetime
The Interest Lifetime is the time that an Interest should stay
pending at an intermediate node. It is expressed in milliseconds as
an unsigned integer in network byte order.
A value of 0 (encoded as 1 byte %x00) 0x00) indicates the Interest does not
elicit a Content Object response. It should still be forwarded, but
no reply is expected and a forwarder could skip creating a PIT entry.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_INTLIFE | Length |
+---------------+---------------+---------------+---------------+
/ /
/ Lifetime (length (Length octets) /
/ /
+---------------+---------------+---------------+---------------+
Figure 11: Interest Lifetime Encoding
3.4.2. Recommended Cache Time
The Recommended Cache Time (RCT) is a measure of the useful lifetime
of a Content Object as assigned by a content producer or upstream
node. It serves as a guideline to the Content Store cache in
determining how long to keep the Content Object. It is a
recommendation only and may be ignored by the cache. This is in
contrast to the ExpiryTime (described in Section 3.6.2.2.2) which
takes precedence over the RCT and must be obeyed.
Because the Recommended Cache Time is an optional hop-by-hop header
and not a part of the signed message, a content producer may re-issue
a previously signed Content Object with an updated RCT without
needing to re-sign the message. There is little ill effect from an
attacker changing the RCT as the RCT serves as a guideline only.
The Recommended Cache Time (a millisecond timestamp) is an unsigned
integer in network byte order that indicates the time when the
payload expires (as the number of milliseconds since the epoch in
UTC). It is a 64-bit field.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_CACHETIME | 8 |
+---------------+---------------+---------------+---------------+
/ /
/ Recommended Cache Time /
/ /
+---------------+---------------+---------------+---------------+
Figure 12: Recommended Cache Time Encoding
3.4.3. Message Hash
Within a trusted domain, an operator may calculate the message hash
at a border device and insert that value into the hop-by-hop headers
of a message. An egress device should remove the value. This
permits intermediate devices within that trusted domain to match
against a ContentObjectHashRestriction without calculating it at
every hop.
The message hash is a cryptographic hash from the start of the CCNx
Message TLV to the end of the packet. It is used to match against
the ContentObjectHashRestriction (Section 3.6.2.1.2). The Message
Hash may be of longer length than an Interest's restriction, in which
case the device should use the left bytes of the Message Hash to
check against the Interest's value.
The Message Hash may only carry one hash type and there may only be
one Message Hash header.
The Message Hash header is unprotected, so this header is only of
practical use within a trusted domain, such as an operator's
autonomous system.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_MSGHASH | (length + 4) |
+---------------+---------------+---------------+---------------+
| (hash type) hash type | length |
+---------------+---------------+---------------+---------------+
/ hash value /
+---------------+---------------+---------------+---------------+
Figure 13: Message Hash Header
3.5. Top-Level Types
The top-level TLV types listed below exist at the outermost level of
a CCNx protocol message. Message TLV.
+----------------------+------------+-------------------------------+
| Abbrev | Name | Description |
+----------------------+------------+-------------------------------+
| T_INTEREST | Interest | An Interest MessageType. |
| | (Section | |
| | 3.6) | |
| | | |
| T_OBJECT | Content | A Content Object MessageType |
| | Object | |
| | (Section | |
| | 3.6) | |
| | | |
| T_VALIDATION_ALG | Validation | The method of message |
| | Algorithm | verification such as a |
| | (Section | Message Integrity Check |
| | 3.6.4.1) | (MIC), Message Authentication |
| | | Code (MAC), or cryptographic |
| | | signature. |
| | | |
| T_VALIDATION_PAYLOAD | Validation | The validation output, such |
| | Payload | as the CRC32C code or the RSA |
| | (Section | signature. |
| | 3.6.4.2) | |
+----------------------+------------+-------------------------------+
Table 5: CCNx Top Level Types
3.6. CCNx Message TLV
This is the format for the CCNx protocol message Message itself. The CCNx
message Message TLV
is the portion of the packet CCNx Packet between the hop-by-hop headers and
the Validation TLVs. The figure below is an expansion of the "CCNx
Message TLV" depicted in the beginning of Section 3. The CCNx
message
Message TLV begins with MessageType and runs through the optional
Payload. The same general format is used for both Interest and
Content Object messages which are differentiated by the MessageType
field. The first enclosed TLV of a CCNx Message TLV is always the
Name
TLV. TLV, if present. This is followed by an optional Message TLVs
and an optional Payload TLV.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| MessageType | MessageLength |
+---------------+---------------+---------------+---------------+
|
/ Name TLV (Type = T_NAME) | /
+---------------+---------------+---------------+---------------+
/ Optional Message TLVs (Various Types) /
+---------------+---------------+---------------+---------------+
/ Optional Payload TLV (Type = T_PAYLOAD) /
+---------------+---------------+---------------+---------------+
Figure 14: CCNx Message TLV Encoding
+-----------+---------------+---------------------------------------+
| Abbrev | Name | Description |
+-----------+---------------+---------------------------------------+
| T_NAME | Name (Section | The CCNx Name requested in an |
| | 3.6.1) | Interest or published in a Content |
| | | Object. |
| | | |
| T_PAYLOAD | Payload | The message payload. |
| | (Section | |
| | 3.6.3) | |
+-----------+---------------+---------------------------------------+
Table 6: CCNx Message TLV Types
3.6.1. Name
A Name is a TLV encoded sequence of segments. The table below lists
the type values appropriate for these Name name segments. A Name MUST NOT
include Pad TLVs.
As described in CCNx Semantics [RFC8569], using the CCNx URI
[CCNxURI] notation, a T_NAME with zero length corresponds to "ccnx:/"
(the default route) and is distinct from a route). The message grammar does not allow the first
name with one zero-length
segment, such as "ccnx:/NAME=". segment to have zero length in a CCNx Message TLV Name. In the
TLV encoding, "ccnx:/" corresponds to T_NAME with zero length, while "ccnx:/NAME="
corresponds to T_NAME with a length of 4 bytes and T_NAMESEGMENT with
zero length.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name segment TLVs /
+---------------+---------------+---------------+---------------+
Figure 15: Name Encoding
+---------------+-------------+-------------------------------------+
| Symbolic Name | Name | Description |
+---------------+-------------+-------------------------------------+
| T_NAMESEGMENT | Name | A generic name Segment. segment. |
| | segment | |
| | (Section | |
| | 3.6.1.1) | |
| | | |
| T_IPID | Interest | An identifier that represents the |
| | Payload ID | Interest Payload field. As an |
| | (Section | example, the Payload ID might be a |
| | 3.6.1.2) | hash of the Interest Payload. This |
| | | provides a way to differentiate |
| | | between Interests based on their |
| | | payloads without having to parse |
| | | all the bytes of the payload |
| | | itself, and instead using only this |
| | | Payload ID Name name segment. |
| | | |
| T_APP:00 - | Application | Application-specific payload in a |
| T_APP:4096 | Components | name segment. An application may |
| | (Section | apply its own semantics to the 4096 |
| | 3.6.1.1) | reserved types. |
+---------------+-------------+-------------------------------------+
Table 7: CCNx Name Types
3.6.1.1. Name Segments
4096 special application payload name segments are allocated. These
have application semantics applied to them. A good convention is to
put the application's identity in the name prior to using these name
segments.
For example, a name like "ccnx:/foo/bar/hi" would be encoded as:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| (T_NAME) | %x14 0x14 (20) |
+---------------+---------------+---------------+---------------+
| (T_NAME_SEGMENT) | %x03 0x03 (3) |
+---------------+---------------+---------------+---------------+
| f o o |(T_NAME_SEGMENT)
+---------------+---------------+---------------+---------------+
| | %x03 0x03 (3) | b |
+---------------+---------------+---------------+---------------+
| a r | (T_NAME_SEGMENT) |
+---------------+---------------+---------------+---------------+
| %x02 0x02 (2) | h | i |
+---------------+---------------+---------------+---------------+
Figure 16: Name Encoding Example
3.6.1.2. Interest Payload ID
The InterestPayloadID is a name segment created by the origin of an
Interest to represent the Interest Payload. This allows the proper
multiplexing of Interests based on their name if they have different
payloads. A common representation is to use a hash of the Interest
Payload as the InterestPayloadID.
As part of the Value of the TLV, the InterestPayloadID contains a
one-octet identifier of the method used to create the
InterestPayloadID followed by a variable-length octet string. An
implementation is not required to implement any of the methods to
receive an Interest; the InterestPayloadID may be treated only as an
opaque octet string for the purposes of multiplexing Interests with
different payloads. Only a device creating an InterestPayloadID name
segment or a device verifying such a segment needs to implement the
algorithms.
It uses the encoding of hash values specified in Section 3.3.3.
In normal operations, we recommend displaying the InterestPayloadID
as an opaque octet string in a CCNx URI, as this is the common
denominator for implementation parsing.
The InterestPayloadID, even if it is a hash, should not convey any
security context. If a system requires confirmation that a specific
entity created the InterestPayload, it should use a cryptographic
signature on the Interest via the ValidationAlgorithm and
ValidationPayload or use its own methods inside the Interest Payload.
3.6.2. Message TLVs
Each message type (Interest or Content Object) is associated with a
set of optional Message TLVs. Additional specification documents may
extend the types associated with each.
3.6.2.1. Interest Message TLVs
There are two Message TLVs currently associated with an Interest
message: the KeyIdRestriction selector and the ContentObjectHashRestr
selector are used to narrow the universe of acceptable Content
Objects that would satisfy the Interest.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| MessageType | MessageLength |
+---------------+---------------+---------------+---------------+
| Name TLV |
+---------------+---------------+---------------+---------------+
/ Optional KeyIdRestriction TLV /
+---------------------------------------------------------------+
/ Optional ContentObjectHashRestriction TLV /
+---------------------------------------------------------------+
Figure 17: Interest Message TLVs
+----------------+------------------------------+-------------------+
| Abbrev | Name | Description |
+----------------+------------------------------+-------------------+
| T_KEYIDRESTR | KeyIdRestriction (Section | A representation |
| | 3.6.2.1.1) | (as per Section |
| | | 3.3.3) of the |
| | | KeyId |
| | | |
| T_OBJHASHRESTR | ContentObjectHashRestriction | A representation |
| | (Section 3.6.2.1.2) | (as per Section |
| | | 3.3.3) of the |
| | | hash of the |
| | | specific Content |
| | | Object that would |
| | | satisfy the |
| | | Interest. |
+----------------+------------------------------+-------------------+
Table 8: CCNx Interest Message TLV Types
3.6.2.1.1. KeyIdRestriction
An Interest MAY include a KeyIdRestriction selector. This ensures
that only Content Objects with matching KeyIds will satisfy the
Interest. See Section 3.6.4.1.4.1 for the format of a KeyId.
3.6.2.1.2. ContentObjectHashRestriction
An Interest MAY contain a ContentObjectHashRestriction selector.
This is the hash of the Content Object -- the self-certifying name
restriction that must be verified in the network, if an Interest
carried this restriction. It is calculated from the beginning of the
CCNx restriction (see Message to the end of the packet. Hash (Section 3.4.3)). The
LENGTH MUST be from one of the allowed values for that hash (see
Section 3.3.3).
The ContentObjectHashRestriction SHOULD be of type T_SHA-256 and of
length 32 bytes.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_OBJHASHRESTR | LENGTH+4 (LENGTH+4) |
+---------------+---------------+---------------+---------------+
| <hash type> hash type | LENGTH |
+---------------+---------------+---------------+---------------+
/ LENGTH octets of hash /
+---------------+---------------+---------------+---------------+
Figure 18: ContentObjectHashRestriction Encoding
3.6.2.2. Content Object Message TLVs
The following message TLVs are currently defined for Content Objects:
PayloadType (optional) and ExpiryTime (optional).
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| MessageType | MessageLength |
+---------------+---------------+---------------+---------------+
| Name TLV |
+---------------+---------------+---------------+---------------+
/ Optional PayloadType TLV /
+---------------------------------------------------------------+
/ Optional ExpiryTime TLV /
+---------------------------------------------------------------+
Figure 19: Content Object Message TLVs
+-------------+-------------+---------------------------------------+
| Abbrev | Name | Description |
+-------------+-------------+---------------------------------------+
| T_PAYLDTYPE | PayloadType | Indicates the type of Payload |
| | (Section | contents. |
| | 3.6.2.2.1) | |
| | | |
| T_EXPIRY | ExpiryTime | The time at which the Payload |
| | (Section | expires, as expressed in the number |
| | 3.6.2.2.2) | of milliseconds since the epoch in |
| | | UTC. If missing, Content Object may |
| | | be used as long as desired. |
+-------------+-------------+---------------------------------------+
Table 9: CCNx Content Object Message TLV Types
3.6.2.2.1. PayloadType
The PayloadType is an integer in network byte order octet representing the general type of the
Payload TLV.
o T_PAYLOADTYPE_DATA: Data (possibly encrypted)
o T_PAYLOADTYPE_KEY: Key
o T_PAYLOADTYPE_LINK: Link
The Data type indicates that the Payload of the ContentObject is
opaque application bytes. The Key type indicates that the Payload is
a DER-encoded public key. The Link type indicates that the Payload
is one or more Links (Section 3.3.4). If this field is missing, a
Data type is assumed.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_PAYLDTYPE | Length 1 |
+---------------+---------------+---------------+---------------+
| PayloadType / |
+---------------+
Figure 20: PayloadType Encoding
3.6.2.2.2. ExpiryTime
The ExpiryTime is the time at which the Payload expires, as expressed
by a timestamp containing the number of milliseconds since the epoch
in UTC. It is a network byte order unsigned integer in a 64-bit
field. A cache or end system should not respond with a Content
Object past its ExpiryTime. Routers forwarding a Content Object do
not need to check the ExpiryTime. If the ExpiryTime field is
missing, the Content Object has no expressed expiration, and a cache
or end system may use the Content Object for as long as desired.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_EXPIRY | 8 |
+---------------+---------------+---------------+---------------+
/ ExpiryTime /
/ /
+---------------+---------------+---------------+---------------+
Figure 21: ExpiryTime encoding
3.6.3. Payload
The Payload TLV contains the content of the packet. It MAY be of
zero length. If a packet does not have any payload, this field MAY
SHOULD be omitted, rather than being of zero length.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_PAYLOAD | Length |
+---------------+---------------+---------------+---------------+
/ Payload Contents /
+---------------+---------------+---------------+---------------+
Figure 22: Payload Encoding
3.6.4. Validation
Both Interests and Content Objects have the option to include
information about how to validate the CCNx message. Message. This information
is contained in two TLVs: the ValidationAlgorithm TLV and the
ValidationPayload TLV. The ValidationAlgorithm TLV specifies the
mechanism to be used to verify the CCNx message. Message. Examples include
verification with a Message Integrity Check (MIC), a Message
Authentication Code (MAC), or a cryptographic signature. The
ValidationPayload TLV contains the validation output, such as the
CRC32C code or the RSA signature.
An Interest would most likely only use a MIC type of validation -- a
CRC, checksum, or digest.
3.6.4.1. Validation Algorithm
The ValidationAlgorithm is a set of nested TLVs containing all of the
information needed to verify the message. The outermost container
has type = T_VALIDATION_ALG. The first nested TLV defines the
specific type of validation to be performed on the message. The type
is identified with the "ValidationType" as shown in the figure below
and elaborated in the table below. Nested within that container are
the TLVs for any ValidationType-dependent data -- for example, a Key
Id, Key Locator, etc.
Complete examples of several types may be found in Section 3.6.4.1.5 3.6.4.1.5.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_VALIDATION_ALG | ValidationAlgLength |
+---------------+---------------+---------------+---------------+
| ValidationType | Length |
+---------------+---------------+---------------+---------------+
/ ValidationType-dependent data /
+---------------+---------------+---------------+---------------+
+---------------+----------------+----------------------------------+
Figure 23: Validation Algorithm Encoding
+-----------------+---------------+---------------------------------+
| Abbrev | Name | Description |
+---------------+----------------+----------------------------------+
+-----------------+---------------+---------------------------------+
| T_CRC32C | CRC32C | Castagnoli CRC32 (iSCSI, ext4, |
| | (Section | etc.) with normal form |
| | 3.6.4.1.1) | polynomial 0x1EDC6F41. |
| | | |
| T_HMAC-SHA256 | HMAC-SHA256 | HMAC (RFC 2104) using SHA256 |
| | (Section | hash. |
| | 3.6.4.1.2) | |
| | | |
| T_RSA-SHA256 | RSA-SHA256 | RSA public-key signature using |
| | (Section | SHA256 digest. |
| | 3.6.4.1.3) | |
| | | |
| EC-SECP-256K1 T_EC-SECP-256K1 | SECP-256K1 | Elliptic Curve signature with |
| | (Section | SECP-256K1 parameters (see |
| | 3.6.4.1.3) | [ECC]). |
| | | |
| EC-SECP-384R1 T_EC-SECP-384R1 | SECP-384R1 | Elliptic Curve signature with |
| | (Section | SECP-384R1 parameters (see |
| | 3.6.4.1.3) | [ECC]). |
+---------------+----------------+----------------------------------+
+-----------------+---------------+---------------------------------+
Table 10: CCNx Validation Types
3.6.4.1.1. Message Integrity Checks
MICs do not require additional data in order to perform the
verification. An example is CRC32C that has a zero-length value.
3.6.4.1.2. Message Authentication Codes
MACs are useful for communication between two trusting parties who
have already shared secret keys. An example is the HMAC algorithm.
A MAC uses the KeyId field to identify which shared secret is in use.
The meaning of the KeyId is specific to the two parties involved and
could be simply an integer to enumerate keys. If a new MAC requires
an additional field, such as an Initialization Vector, that field
would need to be defined as part of the updated specification.
3.6.4.1.3. Signature
Signature type Validators specify a digest mechanism and a signing
algorithm to verify the message. Examples include an RSA signature
on a SHA256 digest, an Elliptic Curve signature with SECP-256K1
parameters, etc. These Validators require a KeyId and a mechanism
for locating the publisher's public key (a KeyLocator) -- and
optionally a PublicKey or Certificate or KeyLink.
3.6.4.1.4. Validation-Dependent Data
Different Validation Algorithms require access to different pieces of
data contained in the ValidationAlgorithm TLV. As described above,
Key Ids, Key Locators, Public Keys, Certificates, Links, and Key
Names all play a role in different Validation Algorithms. Any number
of Validation-Dependent Data containers can be present in a
Validation Algorithm TLV.
Below is a table of CCNx ValidationType-dependent data types:
+-------------+-----------------+-----------------------------------+
| Abbrev | Name | Description |
+-------------+-----------------+-----------------------------------+
| T_KEYID | SignerKeyId | An identifier of the shared |
| | (Section | secret or public key associated |
| | 3.6.4.1.4.1) | with a MAC or Signature. |
| | | |
| T_PUBLICKEY | Public Key | DER-encoded public key. |
| | (Section | |
| | 3.6.4.1.4.2) | |
| | | |
| T_CERT | Certificate | DER-encoded X.509 certificate. |
| | (Section | |
| | 3.6.4.1.4.3) | |
| | | |
| T_KEYLINK | KeyLink | A CCNx Link object. |
| | (Section | |
| | 3.6.4.1.4.4) | |
| | | |
| T_SIGTIME | SignatureTime | A millisecond timestamp |
| | (Section | indicating the time when the |
| | 3.6.4.1.4.5) | signature was created. |
+-------------+-----------------+-----------------------------------+
Table 11: CCNx Validation-Dependent Data Types
3.6.4.1.4.1. KeyId
The KeyId for a signature is the publisher key identifier. It is
similar to a Subject Key Identifier from X.509 (see Section 4.2.1.2
of [RFC5280]). It should be derived from the key used to sign, such
as from the SHA-256 hash of the key. It applies to both public and
private key systems and to symmetric key systems.
The KeyId is represented using the hash format in Section 3.3.3. If
a
an application protocol uses a non-hash identifier, it should use one
of the reserved values.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_KEYID | LENGTH+4 |
+---------------+---------------+---------------+---------------+
| <hash type> | LENGTH |
+---------------+---------------+---------------+---------------+
/ LENGTH octets of hash /
+---------------+---------------+---------------+---------------+
Figure 24: KeyId Encoding
3.6.4.1.4.2. Public Key
A Public Key is a DER-encoded Subject Public Key Info block, as in an
X.509 certificate.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_PUBLICKEY | Length |
+---------------+---------------+---------------+---------------+
/ Public Key (DER-encoded SPKI) /
+---------------+---------------+---------------+---------------+
Figure 25: Public Key Encoding
3.6.4.1.4.3. Certificate
A Certificate is a DER-encoded X.509 certificate. The KeyId
(Section 3.6.4.1.4.1) is derived from this encoding.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_CERT | Length |
+---------------+---------------+---------------+---------------+
/ Certificate (DER-encoded X.509) /
+---------------+---------------+---------------+---------------+
Figure 26: Certificate Encoding
3.6.4.1.4.4. KeyLink
A KeyLink type KeyLocator is a Link.
The KeyLink ContentObjectHashRestr, if included, is the digest of the
Content Object identified by KeyLink, not the digest of the public
key. Likewise, the KeyIdRestr of the KeyLink is the KeyId of the
ContentObject, not necessarily of the wrapped key.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+
| T_KEYLINK | Length |
+---------------+---------------+-------------------------------+
/ Link /
+---------------------------------------------------------------+
Figure 27: KeyLink Encoding
3.6.4.1.4.5. SignatureTime
The SignatureTime is a millisecond timestamp indicating the time at
which a signature was created. The signer sets this field to the
current time when creating a signature. A verifier may use this time
to determine whether or not the signature was created during the
validity period of a key, or if it occurred in a reasonable sequence
with other associated signatures. The SignatureTime is unrelated to
any time associated with the actual CCNx Message, which could have
been created long before the signature. The default behavior is to
always include a SignatureTime when creating an authenticated message
(e.g., HMAC or RSA).
SignatureTime is an unsigned integer in network byte order that is
indicates when the signature was created (as the number of
milliseconds since the epoch in UTC when the signature
was created. UTC). It is a fixed 64-bit field.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+
| T_SIGTIME | 8 |
+---------------+---------------+-------------------------------+
/ SignatureTime /
+---------------------------------------------------------------+
Figure 28: SignatureTime Encoding
3.6.4.1.5. Validation Examples
As an example of a MIC-type validation, the encoding for CRC32C
validation would be:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_VALIDATION_ALG | 4 |
+---------------+---------------+---------------+---------------+
| T_CRC32C | 0 |
+---------------+---------------+---------------+---------------+
Figure 29: CRC32C Encoding Example
As an example of a MAC-type validation, the encoding for an HMAC
using a SHA256 hash would be:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_VALIDATION_ALG | 40 |
+---------------+---------------+---------------+---------------+
| T_HMAC-SHA256 | 36 |
+---------------+---------------+---------------+---------------+
| T_KEYID | 32 |
+---------------+---------------+---------------+---------------+
/ KeyId /
/---------------+---------------+-------------------------------+
Figure 30: HMAC-SHA256 Encoding Example
As an example of a Signature-type validation, the encoding for an RSA
public-key signature using a SHA256 digest and Public Key would be:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_VALIDATION_ALG | 44 octets + Variable Length |
+---------------+---------------+---------------+---------------+
| T_RSA-SHA256 | 40 octets + Variable Length |
+---------------+---------------+---------------+---------------+
| T_KEYID | 32 |
+---------------+---------------+---------------+---------------+
/ KeyId /
/---------------+---------------+-------------------------------+
| T_PUBLICKEY | Variable Length (~160 octets)|
+---------------+---------------+---------------+---------------+
/ Public Key (DER-encoded SPKI) /
+---------------+---------------+---------------+---------------+
Figure 31: RSA-SHA256 Encoding Example
3.6.4.2. Validation Payload
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_VALIDATION_PAYLOAD | ValidationPayloadLength |
+---------------+---------------+---------------+---------------+
/ Type-dependent data /
+---------------+---------------+---------------+---------------+
Figure 32: Validation Payload Encoding
The ValidationPayload contains the validation output, such as the
CRC32C code or the RSA signature.
4. IANA Considerations
This section details each kind of CCNx protocol value that can be
registered. Each type registry can be updated by incrementally
expanding the type space, i.e., by allocating and reserving new
types. As per [RFC8126], this section details the creation of the
"Content-Centric Networking (CCNx)" registry and several
subregistries.
+----------+-----------------------------------+
| Property | Value |
+----------+-----------------------------------+
| Name | Content-Centric Networking (CCNx) |
| | |
| Abbrev | CCNx |
+----------+-----------------------------------+
Registry Creation
4.1. Packet Type Registry
IANA has created the "CCNx Packet Types" registry and allocated the
packet types described below.
+----------------+-----------------------------------+
| Property | Value |
+----------------+-----------------------------------+
| Name | CCNx Packet Types |
| | |
| Parent | Content-Centric Networking (CCNx) |
| | |
| Review process | The registration procedure is RFC Required |
| | |
| Syntax |
Required. The Type value is 1 octet |
+----------------+-----------------------------------+
Registry Creation octet. The range is 0x00-0xFF.
+------+-------------+----------------------------------+
| Type | Name | Reference |
+------+-------------+----------------------------------+
| %x00 0x00 | PT_INTEREST | Fixed Header Types (Section 3.2) |
| | | |
| %x01 0x01 | PT_CONTENT | Fixed Header Types (Section 3.2) |
| | | |
| %x02 0x02 | PT_RETURN | Fixed Header Types (Section 3.2) |
+------+-------------+----------------------------------+
Packet Types
4.2. Interest Return Code Registry
IANA has created the "CCNx InterestReturn Interest Return Code Types" registry and
allocated the InterestReturn Interest Return code types described below.
+----------------+-----------------------------------+
| Property | Value |
+----------------+-----------------------------------+
| Name | CCNx InterestReturn Code Types |
| | |
| Parent | Content-Centric Networking (CCNx) |
| | |
| Review process | The
registration procedure is Specification Required |
| | |
| Syntax | Required. The Type value is
1 octet |
+----------------+-----------------------------------+
Registry Creation octet. The range is 0x00-0xFF.
+------+---------------------------------------+--------------------+
| Type | Name | Reference |
+------+---------------------------------------+--------------------+
| %x00 0x00 | Reserved | |
| | | |
| %x01 0x01 | T_RETURN_NO_ROUTE | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x02 0x02 | T_RETURN_LIMIT_EXCEEDED | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x03 0x03 | T_RETURN_NO_RESOURCES | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x04 0x04 | T_RETURN_PATH_ERROR | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x05 0x05 | T_RETURN_PROHIBITED | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x06 0x06 | T_RETURN_CONGESTED | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x07 0x07 | T_RETURN_MTU_TOO_LARGE | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x08 0x08 | T_RETURN_UNSUPPORTED_HASH_RESTRICTION | Fixed Header Types |
| | | (Section 3.2.3.3) |
| | | |
| %x09 0x09 | T_RETURN_MALFORMED_INTEREST | Fixed Header Types |
| | | (Section 3.2.3.3) |
+------+---------------------------------------+--------------------+
CCNx Interest Return Types
4.3. Hop-by-Hop Type Registry
IANA has created the "CCNx Hop-by-Hop Types" registry and allocated
the hop-by-hop types described below.
+----------------+-----------------------------------+
| Property | Value |
+----------------+-----------------------------------+
| Name | CCNx Hop-by-Hop Types |
| | |
| Parent | Content-Centric Networking (CCNx) |
| | |
| Review process | The registration procedure is
RFC Required |
| | |
| Syntax | 2-octet TLV type |
+----------------+-----------------------------------+
Registry Creation Required. The Type value is 2 octets. The range is
0x0000-0xFFFF.
+---------------+-------------+-------------------------------------+
| Type | Name | Reference |
+---------------+-------------+-------------------------------------+
| %x0000 0x0000 | Reserved | |
| | | |
| %x0001 0x0001 | T_INTLIFE | Hop-by-hop TLV headers (Section |
| | | 3.4) |
| | | |
| %x0002 0x0002 | T_CACHETIME | Hop-by-hop TLV headers (Section |
| | | 3.4) |
| | | |
| %x0003 0x0003 | T_MSGHASH | Hop-by-hop TLV headers (Section |
| | | 3.4) |
| | | |
| %x0004 0x0004 - | Reserved | |
| %x0007 0x0007 | | |
| | | |
| %x0FFE 0x0FFE | T_PAD | Pad (Section 3.3.1) |
| | | |
| %x0FFF 0x0FFF | T_ORG | Organization-Specific TLVs (Section |
| | | 3.3.2) |
| | | |
| %x1000-%x1FFF 0x1000-0x1FFF | Reserved | Experimental Use (Section 3) |
+---------------+-------------+-------------------------------------+
CCNx Hop-by-Hop Types
4.4. Top-Level Type Registry
IANA has created the "CCNx Top-Level Types" registry and allocated
the top-level types described below.
+----------------+-----------------------------------+
| Property | Value |
+----------------+-----------------------------------+
| Name | CCNx Top-Level Types |
| | |
| Parent | Content-Centric Networking (CCNx) |
| | |
| Review process | The registration procedure is
RFC Required |
| | |
| Syntax | 2-octet TLV type |
+----------------+-----------------------------------+
Registry Creation Required. The Type value is 2 octets. The range is
0x0000-0xFFFF.
+--------+----------------------+-------------------------------+
| Type | Name | Reference |
+--------+----------------------+-------------------------------+
| %x0000 0x0000 | Reserved | |
| | | |
| %x0001 0x0001 | T_INTEREST | Top-Level Types (Section 3.5) |
| | | |
| %x0002 0x0002 | T_OBJECT | Top-Level Types (Section 3.5) |
| | | |
| %x0003 0x0003 | T_VALIDATION_ALG | Top-Level Types (Section 3.5) |
| | | |
| %x0004 0x0004 | T_VALIDATION_PAYLOAD | Top-Level Types (Section 3.5) |
+--------+----------------------+-------------------------------+
CCNx Top-Level Types
4.5. Name Segment Type Registry
IANA has created the "CCNx Name Segment Types" registry and allocated
the name segment types described below.
+----------------+-----------------------------------+
| Property | Value |
+----------------+-----------------------------------+
| Name | CCNx Name Segment Types |
| | |
| Parent | Content-Centric Networking (CCNx) |
| | |
| Review process | The registration procedure
is Specification Required |
| | |
| Syntax | 2-octet TLV type |
+----------------+-----------------------------------+
Registry Creation Required. The Type value is 2 octets. The range is
0x0000-0xFFFF.
+--------------+------------------+---------------------------------+
| Type | Name | Reference |
+--------------+------------------+---------------------------------+
| %x0000 0x0000 | Reserved | |
| | | |
| %x0001 0x0001 | T_NAMESEGMENT | Name (Section 3.6.1) |
| | | |
| %x0002 0x0002 | T_IPID | Name (Section 3.6.1) |
| | | |
| %x0010 0x0010 - | Reserved | Used in other documents RFC 8609 |
| %x0013 0x0013 | | |
| | | |
| %x0FFF 0x0FFF | T_ORG | Organization-Specific TLVs |
| | | (Section 3.3.2) |
| | | |
| %x1000 0x1000 - | T_APP:00 - | Application Components (Section |
| %x1FFF | T_APP:4096 | 3.6.1) |
+--------------+------------------+---------------------------------+
CCNx Name Segment Types
4.6. Message Type Registry
IANA has creaed the "CCNx Message Types" registry and registered the
message segment types described below.
+----------------+-----------------------------------+
| Property | Value |
+----------------+-----------------------------------+
| Name | CCNx Message Types |
| | |
| Parent | Content-Centric Networking (CCNx) |
| | |
| Review process | RFC Required |
| Application Components (Section |
| 0x1FFF | Syntax T_APP:4096 | 2-octet TLV type 3.6.1) |
+----------------+-----------------------------------+
+--------------+------------------+---------------------------------+
CCNx Name Segment Types
4.6. Message Type Registry Creation
IANA has created the "CCNx Message Types" registry and registered the
message segment types described below. The registration procedure is
RFC Required. The Type value is 2 octets. The range is
0x0000-0xFFFF.
+---------------+----------------+----------------------------------+
| Type | Name | Reference |
+---------------+----------------+----------------------------------+
| %x0000 0x0000 | T_NAME | Message Types (Section 3.6) |
| | | |
| %x0001 0x0001 | T_PAYLOAD | Message Types (Section 3.6) |
| | | |
| %x0002 0x0002 | T_KEYIDRESTR | Message Types (Section 3.6) |
| | | |
| %x0003 0x0003 | T_OBJHASHRESTR | Message Types (Section 3.6) |
| | | |
| %x0005 0x0005 | T_PAYLDTYPE | Content Object Message Types |
| | | (Section 3.6.2.2) |
| | | |
| %x0006 0x0006 | T_EXPIRY | Content Object Message Types |
| | | (Section 3.6.2.2) |
| | | |
| %x0007 0x0007 - | Reserved | Used in other documents RFC 8609 |
| %x000C 0x000C | | |
| | | |
| %x0FFE 0x0FFE | T_PAD | Pad (Section 3.3.1) |
| | | |
| %x0FFF 0x0FFF | T_ORG | Organization-Specific TLVs |
| | | (Section 3.3.2) |
| | | |
| %x1000-%x1FFF 0x1000-0x1FFF | Reserved | Experimental Use (Section 3) |
+---------------+----------------+----------------------------------+
CCNx Message Types
4.7. Payload Type Registry
IANA has created the "CCNx Payload Types" registry and allocated the
payload types described below.
+----------------+-----------------------------------+
| Property | Value |
+----------------+-----------------------------------+
| Name | CCNx Payload Types |
| | |
| Parent | Content-Centric Networking (CCNx) |
| | |
| Review process | The registration procedure is
Specification Required |
| | |
| Syntax | Variable-length unsigned integer |
+----------------+-----------------------------------+
Registry Creation Required. The Type value is 1 octet. The range is
0x00-0xFF.
+------+--------------------+-----------------------------------+
| Type | Name | Reference |
+------+--------------------+-----------------------------------+
| %x00 0x00 | T_PAYLOADTYPE_DATA | Payload Types (Section 3.6.2.2.1) |
| | | |
| %x01 0x01 | T_PAYLOADTYPE_KEY | Payload Types (Section 3.6.2.2.1) |
| | | |
| %x02 0x02 | T_PAYLOADTYPE_LINK | Payload Types (Section 3.6.2.2.1) |
+------+--------------------+-----------------------------------+
CCNx Payload Types
4.8. Validation Algorithm Type Registry
IANA has created the "CCNx Validation Algorithm Types" registry and
allocated the validation algorithm types described below.
+----------------+-----------------------------------+
| Property | Value |
+----------------+-----------------------------------+
| Name | CCNx Validation Algorithm Types |
| | |
| Parent | Content-Centric Networking (CCNx) |
| | |
| Review process | The
registration procedure is Specification Required |
| | |
| Syntax | 2-octet TLV type |
+----------------+-----------------------------------+
Registry Creation Required. The Type value is
2 octets. The range is 0x0000-0xFFFF.
+---------------+-----------------+---------------------------------+
| Type | Name | Reference |
+---------------+-----------------+---------------------------------+
| %x0000 0x0000 | Reserved | |
| | | |
| %x0002 0x0002 | T_CRC32C | Validation Algorithm (Section |
| | | 3.6.4.1) |
| | | |
| %x0004 0x0004 | T_HMAC-SHA256 | Validation Algorithm (Section |
| | | 3.6.4.1) |
| | | |
| %x0005 0x0005 | T_RSA-SHA256 | Validation Algorithm (Section |
| | | 3.6.4.1) |
| | | |
| %x0006 0x0006 | T_EC-SECP-256K1 | Validation Algorithm (Section |
| | | 3.6.4.1) |
| | | |
| %x0007 0x0007 | T_EC-SECP-384R1 | Validation Algorithm (Section |
| | | 3.6.4.1) |
| | | |
| %x0FFE 0x0FFE | T_PAD | Pad (Section 3.3.1) |
| | | |
| %x0FFF 0x0FFF | T_ORG | Organization-Specific TLVs |
| | | (Section 3.3.2) |
| | | |
| %x1000-%x1FFF 0x1000-0x1FFF | Reserved | Experimental Use (Section 3) |
+---------------+-----------------+---------------------------------+
CCNx Validation Algorithm Types
4.9. Validation-Dependent Data Type Registry
IANA has created the "CCNx Validation-Dependent Data Types" registry
and allocated the validation-dependent data types described below.
+----------------+--------------------------------------+
| Property | Value |
+----------------+--------------------------------------+
| Name | CCNx Validation-Dependent Data Types |
| | |
| Parent | Content-Centric Networking (CCNx) |
| | |
| Review process |
The registration procedure is RFC Required |
| | |
| Syntax | 2-octet TLV type |
+----------------+--------------------------------------+
Registry Creation Required. The Type value is 2
octets. The range is 0x0000-0xFFFF.
+---------------+----------------+----------------------------------+
| Type | Name | Reference |
+---------------+----------------+----------------------------------+
| %x0000 0x0000 | Reserved | |
| | | |
| %x0009 0x0009 | T_KEYID | Validation-Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x000A 0x000A | T_PUBLICKEYLOC | Validation-Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x000B 0x000B | T_PUBLICKEY | Validation-Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x000C 0x000C | T_CERT | Validation-Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x000D 0x000D | T_LINK | Validation-Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x000E 0x000E | T_KEYLINK | Validation-Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x000F 0x000F | T_SIGTIME | Validation-Dependent Data |
| | | (Section 3.6.4.1.4) |
| | | |
| %x0FFF 0x0FFF | T_ORG | Organization-Specific TLVs |
| | | (Section 3.3.2) |
| | | |
| %x1000-%x1FFF 0x1000-0x1FFF | Reserved | Experimental Use (Section 3) |
+---------------+----------------+----------------------------------+
CCNx Validation-Dependent Data Types
4.10. Hash Function Type Registry
IANA has created the "CCNx Hash Function Types" registry and
allocated the hash function types described below.
+----------------+-----------------------------------+
| Property | Value |
+----------------+-----------------------------------+
| Name | CCNx Hash Function Types |
| | |
| Parent | Content-Centric Networking (CCNx) |
| | |
| Review process | The registration
procedure is Specification Required |
| | |
| Syntax | 2-octet TLV type |
+----------------+-----------------------------------+
Registry Creation Required. The Type value is 2 octets.
The range is 0x0000-0xFFFF.
+---------------+-----------+---------------------------------------+
| Type | Name | Reference |
+---------------+-----------+---------------------------------------+
| %x0000 0x0000 | Reserved | |
| | | |
| %x0001 0x0001 | T_SHA-256 | Hash Format (Section 3.3.3) |
| | | |
| %x0002 0x0002 | T_SHA-512 | Hash Format (Section 3.3.3) |
| | | |
| %x0FFF 0x0FFF | T_ORG | Organization-Specific TLVs (Section |
| | | 3.3.2) |
| | | |
| %x1000-%x1FFF 0x1000-0x1FFF | Reserved | Experimental Use (Section 3) |
+---------------+-----------+---------------------------------------+
CCNx Hash Function Types
5. Security Considerations
The CCNx protocol is a Layer 3 network protocol, which may also
operate as an overlay using other transports such as UDP or other
tunnels. It includes intrinsic support for message authentication
via a signature (e.g., RSA or elliptic curve) or Message
Authentication Code (e.g., HMAC). In lieu of an authenticator, it
may instead use a Message Integrity Check (e.g., SHA or CRC). CCNx
does not specify an encryption envelope; that function is left to a
high-layer protocol (e.g., Encrypted Sessions in CCNx [esic]).
The CCNx message Packet format includes the ability to attach MICs (e.g.,
SHA-256 or CRC), MACs (e.g., HMAC), and Signatures (e.g., RSA or
ECDSA) to all packet types. Because Interest packets can be sent at
will, an application should carefully select when to use a given
ValidationAlgorithm in an Interest to avoid DoS attacks. MICs, for
example, are inexpensive and could be used as desired, whereas MACs
and Signatures are more expensive and their inappropriate use could
open a computational DoS attack surface. Applications should use an
explicit protocol to guide their use of packet signatures. As a
general guideline, an application might use a MIC on an Interest to
detect unintentionally corrupted packets. If one wishes to secure an
Interest, one should consider using an encrypted wrapper and a
protocol that prevents replay attacks, especially if the Interest is
being used as an actuator. Simply using an authentication code or
signature does not make an Interest secure. There are several
examples in the literature on how to secure ICN-style messaging
[mobile] [ace].
As a Layer 3 protocol, this document does not describe how one
arrives at keys or how one trusts keys. The CCNx content object may
include a public key embedded in the object or may use the
PublicKeyLocator field to point to a public key (or public-key
certificate) that authenticates the message. One key exchange
specification is CCNxKE [ccnxke] [mobile], which is similar to the
TLS 1.3 key exchange except it is over the CCNx Layer 3 messages.
Trust is beyond the scope of a Layer 3 protocol and is left to
applications or application frameworks.
The combination of an ephemeral key exchange (e.g., CCNxKE [ccnxke])
and an encapsulating encryption (e.g., [esic]) provides the
equivalent of a TLS tunnel. Intermediate nodes may forward the
Interests and Content Objects but have no visibility inside. It also
completely hides the internal names in those used by the encryption
layer. This type of tunneling encryption is useful for content that
has little or no cacheability, as it can only be used by someone with
the ephemeral key. Short-term caching may help with lossy links or
mobility, but long-term caching is usually not of interest.
Broadcast encryption or proxy re-encryption may be useful for content
with multiple uses over time or many consumers. There is currently
no recommendation for this form of encryption.
The specific encoding of messages will have security implications.
This document uses a Type-Length-Value (TLV) encoding. We chose to
compromise between extensibility and unambiguous encodings of types
and lengths. Some TLVs TLV encodings use variable-length T and variable-length variable-
length L fields to accommodate a wide gamut of values while trying to
be byte efficient. Our TLV encoding uses a fixed length 2-byte T and
2-byte L. Using fixed-length T and L fields solves two problems.
The first is aliases. If one is able to encode the same value, such
as 0x2 0x02 and
0x02, 0x0002, in different byte lengths, then one must decide
if they mean the same thing, if they are different, or if one is
illegal. If they are different, then one must always compare on the
buffers not the integer equivalents. If one is illegal, then one
must validate the TLV encoding -- every field of every packet at
every hop. If they are the same, then one has the second problem:
how to specify packet filters. For example, if a name has 6 name
components, then there are 7 T fields and 7 L fields, each of which
might have up to 4 representations of the same value. That would be
14 fields with 4 encodings each, or 1001 combinations. It also means
that one cannot compare, for example, a name via a memory function,
as one needs to consider that any embedded T or L might have a
different format.
The Interest Return message has no authenticator from the previous
hop. Therefore, the payload of the Interest Return should only be
used locally to match an Interest. A node should never forward that
Interest payload as an Interest. It should also verify that it sent
the Interest in the Interest Return to that node and not allow anyone
to negate Interest messages.
Caching nodes must take caution when processing content objects. It
is essential that the Content Store obey the rules outlined in
[RFC8569] to avoid certain types of attacks. Unlike Named Data
Networking (NDN), CCNx 1.0 has no
mechanism to work around an undesired result from the network (there
are no "excludes"), so if a cache becomes poisoned with bad content
it might cause problems retrieving content. There are three types of
access to content from a Content Store: unrestricted, signature
restricted, and hash restricted. If an Interest has no restrictions,
then the requester is not particular about what they get back, so any
matching cached object is OK. In the hash restricted case, the
requester is very specific about what they want, and the Content
Store (and every forward hop) can easily verify that the content
matches the request. In the case of signature verification restricted case (which is
often used for initial manifest discovery), the requester only knows
the KeyId that signed the content. This case requires the closest
attention in the Content Store to avoid amplifying bad data. The
Content Store must only respond with a content object if it can
verify the signature -- this means either the content object carries
the public key inside it or the Interest carries the public key in
addition to the KeyId. If that is not the case, then the Content
Store should treat the Interest as a cache miss and let an endpoint
respond.
A user-level cache could perform full signature verification by
fetching a public key according to the PublicKeyLocator. However,
that is not a burden we wish to impose on the forwarder. A user-
level cache could also rely on out-of-band attestation, such as the
cache operator only inserting content that it knows has the correct
signature.
The CCNx grammar allows for hash algorithm agility via the HashType.
It specifies a short list of acceptable hash algorithms that should
be implemented at each forwarder. Some hash values only apply to end
systems, so updating the hash algorithm does not affect forwarders --
they would simply match the buffer that includes the type-length-hash
buffer. Some fields, such as the ConObjHash, must be verified at
each hop, so a forwarder (or related system) must know the hash
algorithm, and it could cause backward compatibility problems if the
hash type is updated.
A CCNx name uses binary matching, whereas a URI uses a case-
insensitive hostname. Some systems may also use case-insensitive
matching of the URI path to a resource. An implication of this is
that human-entered CCNx names will likely have case or non-ASCII
symbol mismatches unless one uses a consistent URI normalization for
the CCNx name. It also means that an entity that registers a CCNx-
routable prefix -- say, "ccnx:/example.com" -- would need separate
registrations for simple variations like "ccnx:/Example.com". Unless
this is addressed in URI normalization and routing protocol
conventions, there could be phishing attacks.
For a more general introduction to ICN-related security concerns and
approaches, see [RFC7927] and [RFC7945].
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
6.2. Informative References
[ace] Shang, W., Yu, Y., Liang, T., Zhang, B., and L. Zhang,
"NDN-ACE: Access control for constrained environments over
named data networking", NDN Technical Report NDN-0036,
2015, <http://new.named-
data.net/wp-content/uploads/2015/12/
ndn-0036-1-ndn-ace.pdf>. <http://new.named-data.net/wp-content/uploads/2015/
12/ndn-0036-1-ndn-ace.pdf>.
[ccnxke] Mosko, M., Uzun, E., and C. Wood, "CCNx Key Exchange
Protocol Version 1.0", Work in Progress, draft-wood-icnrg-
ccnxkeyexchange-02, March 2017.
[CCNxURI] Mosko, M. and C. Wood, "The CCNx URI Scheme", Work in
Progress, draft-mosko-icnrg-ccnxurischeme-01, April 2016.
[CCNxz] Mosko, M., "CCNxz TLV Header Compression Experimental
Code", commit f1093a2, March 2018,
<https://github.com/PARC/CCNxz>.
[compress] Mosko, M., "Header Compression for TLV-based Packets",
ICNRG Interim Meeting, 2016,
<https://datatracker.ietf.org/meeting/interim-2016-icnrg-
02/materials/slides-interim-2016-icnrg-2-7>.
[ECC] Certicom Research, "SEC 2: Recommended Elliptic Curve
Domain Parameters", 2010,
<http://www.secg.org/sec2-v2.pdf>.
[esic] Mosko, M. and C. Wood, "Encrypted Sessions In CCNx
(ESIC)", Work in Progress, draft-wood-icnrg-esic-01,
September 2017.
[IANA-PEN] IANA, "Private Enterprise Numbers",
<http://www.iana.org/assignments/enterprise-numbers>.
[mobile] Mosko, M., Uzun, E., and C. Wood, "Mobile Sessions in
Content-Centric Networks", IFIP Networking, 2017,
<http://dl.ifip.org/db/conf/networking/
networking2017/1570334964.pdf>.
[nnc] Jacobson, V., Smetters, D., Thornton, J., Plass, M.,
Briggs, N., and R. Braynard, "Networking Named Content",
Proceedings of the 5th international conference on
Emerging networking experiments and technologies (CoNEXT
'09), 2009, <http://dx.doi.org/10.1145/1658939.1658941>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC7927] Kutscher, D., Ed., Eum, S., Pentikousis, K., Psaras, I.,
Corujo, D., Saucez, D., Schmidt, T., and M. Waehlisch,
"Information-Centric Networking (ICN) Research
Challenges", RFC 7927, DOI 10.17487/RFC7927, July 2016,
<https://www.rfc-editor.org/info/rfc7927>.
[RFC7945] Pentikousis, K., Ed., Ohlman, B., Davies, E., Spirou, S.,
and G. Boggia, "Information-Centric Networking: Evaluation
and Security Considerations", RFC 7945,
DOI 10.17487/RFC7945, September 2016,
<https://www.rfc-editor.org/info/rfc7945>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8569] Mosko, M., Solis, I., and C. Wood, "Content-Centric
Networking (CCNx) Semantics", RFC 8569,
DOI 10.17487/RFC8569, May July 2019,
<https://www.rfc-editor.org/info/rfc8569>.
Authors' Addresses
Marc Mosko
PARC, Inc.
Palo Alto, California 94304
United States of America
Phone: +01 650-812-4405
Email: marc.mosko@parc.com mmosko@parc.com
Ignacio Solis
LinkedIn
Mountain View, California 94043
United States of America
Email: nsolis@linkedin.com
Christopher A. Wood
University of California, Irvine
Irvine, California 92697
United States of America
Phone: +01 315-806-5939
Email: woodc1@uci.edu