On Wed, 2011-09-07 at 13:38 -0400, Jarod Wilson wrote: > Certain security-related certifications and their respective review > bodies have said that they find use of /dev/urandom for certain > functions, such as setting up ssh connections, is acceptable, but if and > only if /dev/urandom can block after a certain threshold of bytes have > been read from it with the entropy pool exhausted. Initially, we were > investigating increasing entropy pool contributions, so that we could > simply use /dev/random, but since that hasn't (yet) panned out, and > upwards of five minutes to establsh an ssh connection using an > entropy-starved /dev/random is unacceptable, we started looking at the > blocking urandom approach. Can't you accomplish this in userspace by trying to read as much as you can out of /dev/random without blocking, then reading out of /dev/urandom the minimum between allowed threshold and remaining bytes, and then blocking on /dev/random? For example, lets say you need 100 bytes of randomness, and your threshold is 30 bytes. You try reading out of /dev/random and get 50 bytes, at that point you'll read another 30 (=threshold) bytes out /dev/urandom and then you'll need to block on /dev/random until you get the remaining 20 bytes. -- Sasha. -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
