3.7. RandomnessCryptographic algorithms and protocols require a good source of random bits, or entropy. Randomness is used in various ways:
These files should be kept protected, since they contain sensitive information that can weaken SSH's security if disclosed to an attacker, although SSH takes steps to reduce that possibility. The seed information is always mixed with some new entropy before being used, and only half the pool is ever saved to disk, to reduce its predictive value if stolen.In SSH1 and SSH2, all this happens automatically and invisibly. When compiling OpenSSH on platform without /dev/random, you have a choice. If you have installed an add-on randomness source, such as the OpenSSH-recommended " Entropy Gathering Daemon" (EGD, http://www.lothar.com/tech/crypto/), you can tell OpenSSH to use it with the switch -- with-egd-pool. If you don't specify a pool, OpenSSH uses an internal entropy-gathering mechanism. You can tailor which programs are run to gather entropy and "how random" they're considered to be, by editing the file /etc/ssh_prng_cmds. Also, note that OpenSSH random seed is kept in the ~/.ssh/prng_seed file, even the daemon's, which is just the root user's seed file.
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