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Never allow OpenSSL engines to replace the RAND_SSLeay method 

This fixes bug 10402, where the rdrand engine would use the rdrand
instruction, not as an additional entropy source, but as a replacement
for the entire userspace PRNG.  That's obviously stupid: even if you
don't think that RDRAND is a likely security risk, the right response
to an alleged new alleged entropy source is never to throw away all
previously used entropy sources.

Thanks to coderman and rl1987 for diagnosing and tracking this down.
This commit is contained in:
Nick Mathewson 2013-12-18 11:49:44 -05:00
parent 561d9880f8
commit 7b87003957
2 changed files with 21 additions and 3 deletions
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11
changes/bug10402 Normal file
View File

@ -0,0 +1,11 @@
o Major bugfixes:
- Do not allow OpenSSL engines to replace the PRNG, even when
HardwareAccel is set. The only default builtin PRNG engine uses
the Intel RDRAND instruction to replace the entire PRNG, and
ignores all attempts to seed it with more entropy. That's
cryptographically stupid: the right response to a new alleged
entropy source is never to discard all previously used entropy
sources. Fixes bug 10402; works around behavior introduced in
OpenSSL 1.0.0. Diagnosis and investigation thanks to "coderman"
and "rl1987".

13
src/common/crypto.c
View File

@ -169,8 +169,8 @@ log_engine(const char *fn, ENGINE *e)
const char *name, *id;
name = ENGINE_get_name(e);
id = ENGINE_get_id(e);
log_notice(LD_CRYPTO, "Using OpenSSL engine %s [%s] for %s",
name?name:"?", id?id:"?", fn);
log_notice(LD_CRYPTO, "Default OpenSSL engine for %s is %s [%s]",
fn, name?name:"?", id?id:"?");
} else {
log_info(LD_CRYPTO, "Using default implementation for %s", fn);
}
@ -288,7 +288,7 @@ crypto_global_init(int useAccel, const char *accelName, const char *accelDir)
}
log_engine("RSA", ENGINE_get_default_RSA());
log_engine("DH", ENGINE_get_default_DH());
log_engine("RAND", ENGINE_get_default_RAND());
log_engine("RAND (which we will not use)", ENGINE_get_default_RAND());
log_engine("SHA1", ENGINE_get_digest_engine(NID_sha1));
log_engine("3DES", ENGINE_get_cipher_engine(NID_des_ede3_ecb));
log_engine("AES", ENGINE_get_cipher_engine(NID_aes_128_ecb));
@ -297,6 +297,13 @@ crypto_global_init(int useAccel, const char *accelName, const char *accelDir)
log_info(LD_CRYPTO, "NOT using OpenSSL engine support.");
}
if (RAND_get_rand_method() != RAND_SSLeay()) {
log_notice(LD_CRYPTO, "It appears that one of our engines has provided "
"a replacement the OpenSSL RNG. Resetting it to the default "
"implementation.");
RAND_set_rand_method(RAND_SSLeay());
}
evaluate_evp_for_aes(-1);
evaluate_ctr_for_aes();