# Generating Secure Random Numbers in R

#### 2019-07-16

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] 25 6f fc 3f 2c a7 36 3e 30 ab

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

    as.numeric(rnd)

     [1]  37 111 252  63  44 167  54  62  48 171

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

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

    [1] FALSE  TRUE  TRUE  TRUE FALSE  TRUE FALSE FALSE

## 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] 0.7709538 0.6803416 0.2199021 0.5627981 0.8837980 0.4052726 0.1712342
     [8] 0.7817140 0.1486292 0.8552378

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))