markus reichelt wrote: > Hi, > > I need to create a moderate amount of v3 keys for loop-aes and wonder > how/if the "openssl rand" implementation differs significantly from > /dev/random concerning entropy. > > In case /dev/random and "openssl rand" are somewhat comparable, I > would just use the latter to create the keys. > > Openssl actually uses /dev/urandom to generate random bytes on Linux and other systems that support it, possibly with some further filtering. On systems without a random device, a configuration file is used instead, since openssl is supposed to be compatible over a wide range of systems. Openssl rand should therefore be equivalent with the non-blocking /dev/urandom on Linux. from openssl crypto/rand/rand_unix.c: /* Use a random entropy pool device. Linux, FreeBSD and OpenBSD * have this. Use /dev/urandom if you can as /dev/random may block * if it runs out of random entries. */ > However, I certainly don't want to use a /dev/urandom look-alike. > > Whether the blocking behaviour of /dev/random is desirable is a matter of discussion. Some people argue that a periodically reseeded cryptographic-quality random number generator is as secure as a true random number generator for all practical purposes. It does then not make sense with a blocking generator like /dev/random. This view is much disputed, as can be seen if you read the archives of the Linux kernel mailing list. I personally can't think of any realistic scenario where /dev/random would make you safe while /dev/urandom would make you sorry. Some people seem to think differently, including you apparently :-) , while the openssl people seem more concerned about the blocking behaviour of /dev/random. -Gisle - Linux-crypto: cryptography in and on the Linux system Archive: http://mail.nl.linux.org/linux-crypto/
