ggentropy

on Windows/macOS/Linux

ggentropy is a liberally licensed and cross platform entropy library. You can use it to generate cryptographically secure random numbers, safe for use as nonces and keys in cryptographic operations.

ggentropy supports Windows, Apple platforms, Linux, FreeBSD, OpenBSD and NetBSD.

Version history

• v1.0 19th Jul 2021:
  • Use arc4random_buf on Apple platforms
  • Drop /dev/urandom fallback on Linux because all versions that require it have been EOL for years
  • Drop Solaris support

Usage

ggentropy has one function:

bool ggentropy( void * buf, size_t n );

which writes n bytes of crytographically secure random data to buf. It returns true on success and false on failure. Some platforms place a length restriction on n, so the library will exit on all platforms if n is greater than 256.

Basic usage looks like this:

#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>
#include "ggentropy.h"

int main() {
	uint8_t entropy[ 16 ];
	if( !ggentropy( entropy, sizeof( entropy ) ) )
		return 1;

	for( size_t i = 0; i < sizeof( entropy ); i++ ) {
		printf( "%02" PRIx8, entropy[ i ] );
	}
	printf( "\n" );

	return 0;
}

ggentropy can fail. In long lived programs you should use it to seed a userspace cryptographically secure psuedo-random number generator once at program startup and use that for all future cryptographically secure random data. For example, you can encrypt a stream of zeroes using a key chosen by ggentropy, and use the output of the cipher as a random number source.

Implementation details

ggentropy uses the following functionality:

OS	Implementation
Windows	BCryptGenRandom
Linux	getrandom
macOS/iOS/BSD	arc4random_buf