April 15, 1997 ARC4RANDOM 9

### NAME

arc4random - arc4 random number generator

### SYNOPSIS

```uint32_t` arc4random(```void`)

### DESCRIPTION

The arc4random(``) function provides a high quality 32-bit pseudo-random number very quickly. arc4random(``) seeds itself on a regular basis from the kernel strong random number subsystem described in rnd(4). On each call, an ARC4 generator is used to generate a new result. The arc4random(``) function uses the ARC4 cipher key stream generator, which uses 8*8 8 bit S-Boxes. The S-Boxes can be in about (2**1700) states.

arc4random(``) fits into a middle ground not covered by other subsystems such as the strong, slow, and resource expensive random devices described in rnd(4) versus the fast but poor quality interfaces such as random(``).

### SEE ALSO

arc4random(3), rnd(4)

### HISTORY

An algorithm called ```RC4` was designed by RSA Data Security, Inc. It was considered a trade secret, but not trademarked. Because it was a trade secret, it obviously could not be patented. A clone of this was posted anonymously to USENET and confirmed to be equivalent by several sources who had access to the original cipher. Because of the trade secret situation, RSA Data Security, Inc. can do nothing about the release of the ARC4 algorithm. Since ```RC4` used to be a trade secret, the cipher is now referred to as ```ARC4`.

These functions first appeared in OpenBSD2.1.