/*
- * Copyright 1995-2017 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
#include <openssl/bn.h>
#include <openssl/rsa.h>
#include <openssl/rand.h>
+#include "internal/constant_time_locl.h"
int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
const unsigned char *from, int flen)
return 1;
}
+/*
+ * Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding
+ * if nul delimiter is not preceded by 8 consecutive 0x03 bytes. It also
+ * preserves error code reporting for backward compatibility.
+ */
int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
const unsigned char *from, int flen, int num)
{
- int i, j, k;
- const unsigned char *p;
+ int i;
+ /* |em| is the encoded message, zero-padded to exactly |num| bytes */
+ unsigned char *em = NULL;
+ unsigned int good, found_zero_byte, mask, threes_in_row;
+ int zero_index = 0, msg_index, mlen = -1, err;
- p = from;
- if (flen < 10) {
+ if (tlen <= 0 || flen <= 0)
+ return -1;
+
+ if (flen > num || num < 11) {
RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
return -1;
}
- if ((num != (flen + 1)) || (*(p++) != 02)) {
- RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_BLOCK_TYPE_IS_NOT_02);
+
+ em = OPENSSL_malloc(num);
+ if (em == NULL) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, 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(em[0]);
+ good &= constant_time_eq(em[1], 2);
+ err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
+ mask = ~good;
/* scan over padding data */
- j = flen - 1; /* one for type */
- for (i = 0; i < j; i++)
- if (*(p++) == 0)
- break;
-
- if ((i == j) || (i < 8)) {
- RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23,
- RSA_R_NULL_BEFORE_BLOCK_MISSING);
- return -1;
+ found_zero_byte = 0;
+ threes_in_row = 0;
+ for (i = 2; i < num; i++) {
+ 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;
+
+ threes_in_row += 1 & ~found_zero_byte;
+ threes_in_row &= found_zero_byte | constant_time_eq(em[i], 3);
}
- for (k = -9; k < -1; k++) {
- if (p[k] != 0x03)
- break;
+
+ /*
+ * 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(zero_index, 2 + 8);
+ err = constant_time_select_int(mask | good, err,
+ RSA_R_NULL_BEFORE_BLOCK_MISSING);
+ mask = ~good;
+
+ good &= constant_time_ge(threes_in_row, 8);
+ err = constant_time_select_int(mask | good, err,
+ RSA_R_SSLV3_ROLLBACK_ATTACK);
+ mask = ~good;
+
+ /*
+ * Skip the zero byte. This is incorrect if we never found a zero-byte
+ * but in this case we also do not copy the message out.
+ */
+ msg_index = zero_index + 1;
+ mlen = num - msg_index;
+
+ /*
+ * For good measure, do this check in constant time as well.
+ */
+ good &= constant_time_ge(tlen, mlen);
+ err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
+
+ /*
+ * 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);
+ 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]);
}
- if (k == -1) {
- RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_SSLV3_ROLLBACK_ATTACK);
- return -1;
+ 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]);
}
- i++; /* Skip over the '\0' */
- j -= i;
- if (j > tlen) {
- RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_LARGE);
- return -1;
- }
- memcpy(to, p, (unsigned int)j);
+ OPENSSL_clear_free(em, num);
+ RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);
+ err_clear_last_constant_time(1 & good);
- return j;
+ return constant_time_select_int(good, mlen, -1);
}
projects / oweals / openssl.git / blobdiff