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rsa/rsa_oaep.c: remove memcpy calls from RSA_padding_check_PKCS1_OAEP.

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And make RSAErr call unconditional.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
This commit is contained in:
Andy Polyakov 2018-09-06 21:54:23 +02:00 committed by Matt Caswell
parent e875b0cf2f
commit 75f5e944be
1 changed files with 52 additions and 32 deletions
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84
crypto/rsa/rsa_oaep.c
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@ -120,7 +120,7 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
const EVP_MD *mgf1md)
{
int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
unsigned int good, found_one_byte;
unsigned int good = 0, found_one_byte, mask;
const unsigned char *maskedseed, *maskeddb;
/*
* |em| is the encoded message, zero-padded to exactly |num| bytes: em =
@ -147,8 +147,11 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
* the ciphertext, see PKCS #1 v2.2, section 7.1.2.
* This does not leak any side-channel information.
*/
if (num < flen || num < 2 * mdlen + 2)
goto decoding_err;
if (num < flen || num < 2 * mdlen + 2) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
RSA_R_OAEP_DECODING_ERROR);
return -1;
}
dblen = num - mdlen - 1;
db = OPENSSL_malloc(dblen);
@ -157,26 +160,27 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
goto cleanup;
}
if (flen != num) {
em = OPENSSL_zalloc(num);
if (em == NULL) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
ERR_R_MALLOC_FAILURE);
goto cleanup;
}
/*
* Caller is encouraged to pass zero-padded message created with
* BN_bn2binpad, but if it doesn't, we do this zero-padding copy
* to avoid leaking that information. The copy still leaks some
* side-channel information, but it's impossible to have a fixed
* memory access pattern since we can't read out of the bounds of
* |from|.
*/
memcpy(em + num - flen, from, flen);
from = em;
em = OPENSSL_malloc(num);
if (em == NULL) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
ERR_R_MALLOC_FAILURE);
goto cleanup;
}
/*
* Caller is encouraged to pass zero-padded message created with
* BN_bn2binpad. Trouble is that since we can't read out of |from|'s
* bounds, it's impossible to have an invariant memory access pattern
* in case |from| was not zero-padded in advance.
*/
for (from += flen, em += num, i = 0; i < num; i++) {
mask = ~constant_time_is_zero(flen);
flen -= 1 & mask;
from -= 1 & mask;
*--em = *from & mask;
}
from = em;
/*
* The first byte must be zero, however we must not leak if this is
* true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
@ -222,32 +226,48 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
* so plaintext-awareness ensures timing side-channels are no longer a
* concern.
*/
if (!good)
goto decoding_err;
msg_index = one_index + 1;
mlen = dblen - msg_index;
if (tlen < mlen) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
mlen = -1;
} else {
memcpy(to, db + msg_index, mlen);
goto cleanup;
/*
* For good measure, do this check in constant tine as well.
*/
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 |dblen|
* 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.
*/
tlen = constant_time_select_int(constant_time_lt(dblen, tlen), dblen, tlen);
msg_index = constant_time_select_int(good, msg_index, dblen - tlen);
mlen = dblen - msg_index;
for (from = db + msg_index, mask = good, i = 0; i < tlen; i++) {
unsigned int equals = constant_time_eq(i, mlen);
from -= dblen & equals; /* if (i == dblen) rewind */
mask &= mask ^ equals; /* if (i == dblen) mask = 0 */
to[i] = constant_time_select_8(mask, from[i], to[i]);
}
decoding_err:
/*
* To avoid chosen ciphertext attacks, the error message should not
* reveal which kind of decoding error happened.
*/
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
RSA_R_OAEP_DECODING_ERROR);
err_clear_last_constant_time(1 & good);
cleanup:
OPENSSL_cleanse(seed, sizeof(seed));
OPENSSL_clear_free(db, dblen);
OPENSSL_clear_free(em, num);
return mlen;
return constant_time_select_int(good, mlen, -1);
}
int PKCS1_MGF1(unsigned char *mask, long len,