# Generating Secure Random Numbers in R
Date: 2024-05-16

#### 2024-05-16

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] 90 fb a3 3c ef e0 00 b7 1a a1

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

    as.numeric(rnd)

     [1] 144 251 163  60 239 224   0 183  26 161

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

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

    [1]  TRUE FALSE  TRUE FALSE  TRUE FALSE FALSE  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] 0.9205410 0.7308148 0.2313601 0.5938068 0.8053278 0.2574549 0.8968282
     [8] 0.1798682 0.1427893 0.3694836

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))