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-rw-r--r--crypto/rsa/rsa_oaep.c48
1 files changed, 24 insertions, 24 deletions
diff --git a/crypto/rsa/rsa_oaep.c b/crypto/rsa/rsa_oaep.c
index 689e6dc22292..48b888bf27ad 100644
--- a/crypto/rsa/rsa_oaep.c
+++ b/crypto/rsa/rsa_oaep.c
@@ -1,5 +1,5 @@
/*
- * Copyright 1999-2018 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 1999-2019 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
@@ -143,7 +143,7 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
* |num| is the length of the modulus; |flen| is the length of the
* encoded message. Therefore, for any |from| that was obtained by
* decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
- * num < 2 * mdlen + 2 must hold for the modulus irrespective of
+ * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of
* the ciphertext, see PKCS #1 v2.2, section 7.1.2.
* This does not leak any side-channel information.
*/
@@ -179,17 +179,16 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
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
* Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
*/
- good = constant_time_is_zero(from[0]);
+ good = constant_time_is_zero(em[0]);
- maskedseed = from + 1;
- maskeddb = from + 1 + mdlen;
+ maskedseed = em + 1;
+ maskeddb = em + 1 + mdlen;
if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
goto cleanup;
@@ -230,29 +229,30 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
mlen = dblen - msg_index;
/*
- * For good measure, do this check in constant tine as well.
+ * For good measure, do this check in constant time 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.
+ * 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, 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]);
+ tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),
+ dblen - mdlen - 1, tlen);
+ 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]);
}
/*