/*
- * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 1995-2019 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
int i;
/* |em| is the encoded message, zero-padded to exactly |num| bytes */
unsigned char *em = NULL;
- unsigned int good, found_zero_byte;
+ unsigned int good, found_zero_byte, mask;
int zero_index = 0, msg_index, mlen = -1;
if (tlen < 0 || flen < 0)
* section 7.2.2.
*/
- if (flen > num)
- goto err;
-
- if (num < 11)
- goto err;
+ if (flen > num || num < 11) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,
+ RSA_R_PKCS_DECODING_ERROR);
+ return -1;
+ }
- if (flen != num) {
- em = OPENSSL_zalloc(num);
- if (em == NULL) {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE);
- return -1;
- }
- /*
- * 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_TYPE_2, ERR_R_MALLOC_FAILURE);
+ return -1;
+ }
+ /*
+ * 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;
}
- good = constant_time_is_zero(from[0]);
- good &= constant_time_eq(from[1], 2);
+ good = constant_time_is_zero(em[0]);
+ good &= constant_time_eq(em[1], 2);
+ /* scan over padding data */
found_zero_byte = 0;
for (i = 2; i < num; i++) {
- unsigned int equals0 = constant_time_is_zero(from[i]);
- zero_index =
- constant_time_select_int(~found_zero_byte & equals0, i,
- zero_index);
+ unsigned int equals0 = constant_time_is_zero(em[i]);
+
+ zero_index = constant_time_select_int(~found_zero_byte & equals0,
+ i, zero_index);
found_zero_byte |= equals0;
}
/*
- * PS must be at least 8 bytes long, and it starts two bytes into |from|.
+ * PS must be at least 8 bytes long, and it starts two bytes into |em|.
* If we never found a 0-byte, then |zero_index| is 0 and the check
* also fails.
*/
- good &= constant_time_ge((unsigned int)(zero_index), 2 + 8);
+ good &= constant_time_ge(zero_index, 2 + 8);
/*
* Skip the zero byte. This is incorrect if we never found a zero-byte
mlen = num - msg_index;
/*
- * For good measure, do this check in constant time as well; it could
- * leak something if |tlen| was assuming valid padding.
+ * For good measure, do this check in constant time as well.
*/
- good &= constant_time_ge((unsigned int)(tlen), (unsigned int)(mlen));
+ good &= constant_time_ge(tlen, mlen);
/*
- * We can't continue in constant-time because we need to copy the result
- * and we cannot fake its length. This unavoidably leaks timing
- * information at the API boundary.
+ * 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)).
*/
- if (!good) {
- mlen = -1;
- goto err;
+ tlen = constant_time_select_int(constant_time_lt(num - 11, tlen),
+ num - 11, tlen);
+ 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]);
}
- memcpy(to, from + msg_index, mlen);
-
- err:
OPENSSL_clear_free(em, num);
- if (mlen == -1)
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,
- RSA_R_PKCS_DECODING_ERROR);
- return mlen;
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, RSA_R_PKCS_DECODING_ERROR);
+ err_clear_last_constant_time(1 & good);
+
+ return constant_time_select_int(good, mlen, -1);
}
projects / openssl.git / blobdiff