diff options
author | Bernd Edlinger <bernd.edlinger@hotmail.de> | 2019-03-20 22:02:58 +0100 |
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committer | Bernd Edlinger <bernd.edlinger@hotmail.de> | 2019-03-22 14:48:24 +0100 |
commit | 8f58aa0a5edad245e7103449b1639b4b9d4233ea (patch) | |
tree | e41288ebdecc0214b989b5d7a8a9a94c1d2c8ea1 /crypto/rsa/rsa_pk1.c | |
parent | 2a483a87e74ec33bfcd904dbaeaa017c658f0389 (diff) |
Modify the RSA_private_decrypt functions to check the padding in
constant time with a memory access pattern that does not depend
on secret information.
[extended tests]
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8543)
(cherry picked from commit 9c0cf214e7836eb5aaf1ea5d3cbf6720533f86b5)
Diffstat (limited to 'crypto/rsa/rsa_pk1.c')
-rw-r--r-- | crypto/rsa/rsa_pk1.c | 32 |
1 files changed, 16 insertions, 16 deletions
diff --git a/crypto/rsa/rsa_pk1.c b/crypto/rsa/rsa_pk1.c index f63c65b01b..745d22eaf1 100644 --- a/crypto/rsa/rsa_pk1.c +++ b/crypto/rsa/rsa_pk1.c @@ -226,25 +226,25 @@ int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen, good &= constant_time_ge(tlen, mlen); /* - * Even though we can't fake result's length, we can pretend copying - * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num| - * bytes are viewed as circular buffer with start at |tlen|-|mlen'|, - * where |mlen'| is "saturated" |mlen| value. Deducing information - * about failure or |mlen| would take attacker's ability to observe - * memory access pattern with byte granularity *as it occurs*. It - * should be noted that failure is indistinguishable from normal - * operation if |tlen| is fixed by protocol. + * Move the result in-place by |num|-11-|mlen| bytes to the left. + * Then if |good| move |mlen| bytes from |em|+11 to |to|. + * Otherwise leave |to| unchanged. + * Copy the memory back in a way that does not reveal the size of + * the data being copied via a timing side channel. This requires copying + * parts of the buffer multiple times based on the bits set in the real + * length. Clear bits do a non-copy with identical access pattern. + * The loop below has overall complexity of O(N*log(N)). */ tlen = constant_time_select_int(constant_time_lt(num - 11, tlen), num - 11, tlen); - msg_index = constant_time_select_int(good, msg_index, num - tlen); - mlen = num - msg_index; - for (mask = good, i = 0; i < tlen; i++) { - unsigned int equals = constant_time_eq(msg_index, num); - - msg_index -= tlen & equals; /* rewind at EOF */ - mask &= ~equals; /* mask = 0 at EOF */ - to[i] = constant_time_select_8(mask, em[msg_index++], to[i]); + for (msg_index = 1; msg_index < num - 11; msg_index <<= 1) { + mask = ~constant_time_eq(msg_index & (num - 11 - mlen), 0); + for (i = 11; i < num - msg_index; i++) + em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]); + } + for (i = 0; i < tlen; i++) { + mask = good & constant_time_lt(i, mlen); + to[i] = constant_time_select_8(mask, em[i + 11], to[i]); } OPENSSL_clear_free(em, num); |