Date: 2025-05-26

# Generating Secure Random Numbers in R

#### 2025-05-26

The `rand_bytes` function binds to RAND_bytes in OpenSSL to generate cryptographically strong pseudo-random bytes. See the OpenSSL documentation for what this means.

    rnd <- rand_bytes(10)
    print(rnd)

     [1] d7 98 fd 91 0d 4a ba 23 6d 95

Bytes are 8 bit and hence can have `2^8 = 256` possible values.

    as.numeric(rnd)

     [1] 215 152 253 145  13  74 186  35 109 149

Each random byte can be decomposed into 8 random bits (booleans)

    x <- rand_bytes(1)
    as.logical(rawToBits(x))

    [1] FALSE  TRUE FALSE FALSE  TRUE  TRUE  TRUE  TRUE

## Secure Random Numbers

`rand_num` is a simple (2 lines) wrapper to `rand_bytes` to generate random numbers (doubles) between 0 and 1.

    rand_num(10)

     [1] 0.911241455 0.307891847 0.329681882 0.047568901 0.586398884 0.767603851
     [7] 0.085784320 0.002575604 0.538053861 0.503014223

To map random draws from [0,1] into a probability density, we can use a Cumulative Distribution Function. For example we can combine `qnorm` and `rand_num` to simulate `rnorm`:

    # Secure rnorm
    x <- qnorm(rand_num(1000), mean = 100, sd = 15)
    hist(x)

Same for discrete distributions:

    # Secure rbinom
    y <- qbinom(rand_num(1000), size = 20, prob = 0.1)
    hist(y, breaks = -.5:(max(y)+1))