RAND_BYTES(3) | Library Functions Manual | RAND_BYTES(3)

# NAME

`RAND_bytes`, `RAND_pseudo_bytes` — generate random data

# SYNOPSIS

library “libcrypto”
`#include <openssl/rand.h>`

int
`RAND_bytes`(unsigned char *buf, int num);

int
`RAND_pseudo_bytes`(unsigned char *buf, int num);

# DESCRIPTION

These functions are deprecated and only retained for compatibility with legacy application programs. Use arc4random_buf(3) instead.

`RAND_bytes`() puts num cryptographically strong pseudo-random bytes into buf.

`RAND_pseudo_bytes`() puts num pseudo-random bytes into buf. Pseudo-random byte sequences generated by `RAND_pseudo_bytes`() will be unique if they are of sufficient length, but are not necessarily unpredictable. They can be used for non-cryptographic purposes and for certain purposes in cryptographic protocols, but usually not for key generation etc.

# RETURN VALUES

`RAND_bytes`() returns 1. `RAND_pseudo_bytes`() returns 1.

# HISTORY

`RAND_bytes`() first appeared in SSLeay 0.5.1 and has been available since OpenBSD 2.4. It has a return value since OpenSSL 0.9.5 and OpenBSD 2.7.

`RAND_pseudo_bytes`() first appeared in OpenSSL 0.9.5 and has been available since OpenBSD 2.7.

June 8, 2025 | Debian