commit 3843c6615c7f62606973fef9068bbb7be58ff243 Author: Nick Mathewson <nickm@torproject.org> Date: Wed Dec 9 09:15:57 2015 -0500 Small cleanups and comment fixes to rng functions. --- src/common/crypto.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/src/common/crypto.c b/src/common/crypto.c index 675fe7a..1897946 100644 --- a/src/common/crypto.c +++ b/src/common/crypto.c @@ -2344,14 +2344,18 @@ void crypto_strongest_rand(uint8_t *out, size_t out_len) { const unsigned DLEN = SHA512_DIGEST_LENGTH; + /* We're going to hash DLEN bytes from the system RNG together with some + * bytes from the openssl PRNG, in order to yield DLEN bytes. + */ uint8_t inp[DLEN*2]; uint8_t tmp[DLEN]; tor_assert(out); while (out_len) { - crypto_rand((char*) inp+DLEN, DLEN); - if (crypto_strongest_rand_raw(inp, DLEN) < 0) { + crypto_rand((char*) inp, DLEN); + if (crypto_strongest_rand_raw(inp+DLEN, DLEN) < 0) { log_err(LD_CRYPTO, "Failed to load strong entropy when generating an " "important key. Exiting."); + /* Die with an assertion so we get a stack trace. */ tor_assert(0); } if (out_len >= DLEN) { @@ -2368,10 +2372,8 @@ crypto_strongest_rand(uint8_t *out, size_t out_len) } memwipe(tmp, 0, sizeof(tmp)); memwipe(inp, 0, sizeof(inp)); - } - /** Seed OpenSSL's random number generator with bytes from the operating * system. <b>startup</b> should be true iff we have just started Tor and * have not yet allocated a bunch of fds. Return 0 on success, -1 on failure. @@ -2430,6 +2432,9 @@ crypto_rand_unmocked(char *to, size_t n) tor_assert(n < INT_MAX); tor_assert(to); r = RAND_bytes((unsigned char*)to, (int)n); + /* We consider a PRNG failure non-survivable. Let's assert so that we get a + * stack trace about where it happened. + */ tor_assert(r >= 0); }