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Modify the RSA_private_decrypt functions to check the padding in

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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)
This commit is contained in:
Bernd Edlinger 2019-03-20 22:02:58 +01:00
parent 94dc53a3f7
commit 9c0cf214e7
3 changed files with 48 additions and 48 deletions
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32
crypto/rsa/rsa_oaep.c
View file

@ -234,25 +234,25 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(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 |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.
* Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.
* Then if |good| move |mlen| bytes from |db|+|mdlen|+1 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(dblen - mdlen - 1, tlen),
dblen - mdlen - 1, tlen);
msg_index = constant_time_select_int(good, msg_index, dblen - tlen);
mlen = dblen - msg_index;
for (mask = good, i = 0; i < tlen; i++) {
unsigned int equals = constant_time_eq(msg_index, dblen);
msg_index -= tlen & equals; /* rewind at EOF */
mask &= ~equals; /* mask = 0 at EOF */
to[i] = constant_time_select_8(mask, db[msg_index++], to[i]);
for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {
mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);
for (i = mdlen + 1; i < dblen - msg_index; i++)
db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);
}
for (i = 0; i < tlen; i++) {
mask = good & constant_time_lt(i, mlen);
to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);
}
/*

32
crypto/rsa/rsa_pk1.c
View file

@ -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);

32
crypto/rsa/rsa_ssl.c
View file

@ -141,25 +141,25 @@ int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
/*
* 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);