most libraries use some form of specialized crypto random number generator (openssl uses the ssleay random number generator, JDK has the same schema for java.se

most libraries use some form of specialized crypto random number generator (openssl uses the ssleay random number generator, JDK has the same schema for java.security.SecureRandom): /dev/rand is used to seed it with some random numbers, each iteration computes the SHA1 checksum of the previous state, the algorithm returns part of the state as random number output. The assumption here is that the initial state can't be guessed, i guess you would rather use /dev/random for that, even if it blocks. Now be careful with the initialization step of your favorite crypto library, most inconsistencies /fishy tricks do happen right here ! Also another issue is that that such a random number generator introduces locks; I have a small program that encrypts everything with RSA, and uses multiprocessing to speed up the process; RSA encryption is supposed to use padding schema that needs to generate random numbers, so it locks, however you don't have this problem with decryption - that's where it counts because RSA decryption is much slower than encryption. here is my project: http://mosermichael.github.io/cstuff/all/projects/2014/02/24/openssl.html http://mosermichael.github.io/cstuff/all/projects/2014/02/24...