File openssl-rewrite-RSA-padding-checks.patch of Package compat-openssl098.29205
From 294d1e36c2495ff00e697c9ff622856d3114f14f Mon Sep 17 00:00:00 2001
From: Emilia Kasper <emilia@openssl.org>
Date: Thu, 28 Aug 2014 19:43:49 +0200
Subject: [PATCH] RT3066: rewrite RSA padding checks to be slightly more
constant time.
Also tweak s3_cbc.c to use new constant-time methods.
Also fix memory leaks from internal errors in RSA_padding_check_PKCS1_OAEP_mgf1
This patch is based on the original RT submission by Adam Langley <agl@chromium.org>,
as well as code from BoringSSL and OpenSSL.
Reviewed-by: Kurt Roeckx <kurt@openssl.org>
---
crypto/constant_time_locl.h | 36 ++++++++-
crypto/constant_time_test.c | 118 ++++++++++++++++++++++++----
crypto/rsa/Makefile | 5 +-
crypto/rsa/rsa.h | 3 +-
crypto/rsa/rsa_err.c | 1 +
crypto/rsa/rsa_oaep.c | 149 +++++++++++++++++++++---------------
crypto/rsa/rsa_pk1.c | 103 ++++++++++++++++++-------
ssl/s3_cbc.c | 9 ++-
8 files changed, 307 insertions(+), 117 deletions(-)
Index: openssl-0.9.8j/crypto/rsa/Makefile
===================================================================
--- openssl-0.9.8j.orig/crypto/rsa/Makefile
+++ openssl-0.9.8j/crypto/rsa/Makefile
@@ -189,7 +189,7 @@ rsa_oaep.o: ../../include/openssl/openss
rsa_oaep.o: ../../include/openssl/rand.h ../../include/openssl/rsa.h
rsa_oaep.o: ../../include/openssl/safestack.h ../../include/openssl/sha.h
rsa_oaep.o: ../../include/openssl/stack.h ../../include/openssl/symhacks.h
-rsa_oaep.o: ../cryptlib.h rsa_oaep.c
+rsa_oaep.o: ../constant_time_locl.h ../cryptlib.h rsa_oaep.c
rsa_pk1.o: ../../e_os.h ../../include/openssl/asn1.h
rsa_pk1.o: ../../include/openssl/bio.h ../../include/openssl/bn.h
rsa_pk1.o: ../../include/openssl/buffer.h ../../include/openssl/crypto.h
@@ -198,7 +198,8 @@ rsa_pk1.o: ../../include/openssl/lhash.h
rsa_pk1.o: ../../include/openssl/opensslv.h ../../include/openssl/ossl_typ.h
rsa_pk1.o: ../../include/openssl/rand.h ../../include/openssl/rsa.h
rsa_pk1.o: ../../include/openssl/safestack.h ../../include/openssl/stack.h
-rsa_pk1.o: ../../include/openssl/symhacks.h ../cryptlib.h rsa_pk1.c
+rsa_pk1.o: ../../include/openssl/symhacks.h ../constant_time_locl.h
+rsa_pk1.o: ../cryptlib.h rsa_pk1.c
rsa_pss.o: ../../e_os.h ../../include/openssl/asn1.h
rsa_pss.o: ../../include/openssl/bio.h ../../include/openssl/bn.h
rsa_pss.o: ../../include/openssl/buffer.h ../../include/openssl/crypto.h
Index: openssl-0.9.8j/crypto/rsa/rsa.h
===================================================================
--- openssl-0.9.8j.orig/crypto/rsa/rsa.h
+++ openssl-0.9.8j/crypto/rsa/rsa.h
@@ -510,6 +510,7 @@ void ERR_load_RSA_strings(void);
#define RSA_R_OAEP_DECODING_ERROR 121
#define RSA_R_OPERATION_NOT_ALLOWED_IN_FIPS_MODE 142
#define RSA_R_PADDING_CHECK_FAILED 114
+#define RSA_R_PKCS_DECODING_ERROR 159
#define RSA_R_P_NOT_PRIME 128
#define RSA_R_Q_NOT_PRIME 129
#define RSA_R_RSA_OPERATIONS_NOT_SUPPORTED 130
@@ -518,6 +519,7 @@ void ERR_load_RSA_strings(void);
#define RSA_R_SSLV3_ROLLBACK_ATTACK 115
#define RSA_R_THE_ASN1_OBJECT_IDENTIFIER_IS_NOT_KNOWN_FOR_THIS_MD 116
#define RSA_R_UNKNOWN_ALGORITHM_TYPE 117
+#define RSA_R_UNKNOWN_DIGEST 166
#define RSA_R_UNKNOWN_PADDING_TYPE 118
#define RSA_R_WRONG_SIGNATURE_LENGTH 119
Index: openssl-0.9.8j/crypto/rsa/rsa_err.c
===================================================================
--- openssl-0.9.8j.orig/crypto/rsa/rsa_err.c
+++ openssl-0.9.8j/crypto/rsa/rsa_err.c
@@ -154,6 +154,7 @@ static ERR_STRING_DATA RSA_str_reasons[]
{ERR_REASON(RSA_R_OAEP_DECODING_ERROR) ,"oaep decoding error"},
{ERR_REASON(RSA_R_OPERATION_NOT_ALLOWED_IN_FIPS_MODE),"operation not allowed in fips mode"},
{ERR_REASON(RSA_R_PADDING_CHECK_FAILED) ,"padding check failed"},
+{ERR_REASON(RSA_R_PKCS_DECODING_ERROR) ,"pkcs decoding error"},
{ERR_REASON(RSA_R_P_NOT_PRIME) ,"p not prime"},
{ERR_REASON(RSA_R_Q_NOT_PRIME) ,"q not prime"},
{ERR_REASON(RSA_R_RSA_OPERATIONS_NOT_SUPPORTED),"rsa operations not supported"},
Index: openssl-0.9.8j/crypto/rsa/rsa_oaep.c
===================================================================
--- openssl-0.9.8j.orig/crypto/rsa/rsa_oaep.c
+++ openssl-0.9.8j/crypto/rsa/rsa_oaep.c
@@ -18,6 +18,7 @@
* an equivalent notion.
*/
+#include "../constant_time_locl.h"
#if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
#include <stdio.h>
@@ -120,12 +121,13 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(un
const unsigned char *param, int plen,
const EVP_MD *md, const EVP_MD *mgf1md)
{
- int i, dblen, mlen = -1;
- const unsigned char *maskeddb;
- int lzero;
- unsigned char *db = NULL, seed[EVP_MAX_MD_SIZE], phash[EVP_MAX_MD_SIZE];
- unsigned char *padded_from;
- int bad = 0;
+ int i, dblen, mlen = -1, one_index = 0, msg_index;
+ unsigned int good, found_one_byte;
+ const unsigned char *maskedseed, *maskeddb;
+ /* |em| is the encoded message, zero-padded to exactly |num| bytes:
+ * em = Y || maskedSeed || maskedDB */
+ unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
+ phash[EVP_MAX_MD_SIZE];
int mdlen;
if (md == NULL)
@@ -135,85 +137,108 @@ int RSA_padding_check_PKCS1_OAEP_mgf1(un
mdlen = EVP_MD_size(md);
- if (--num < 2 * mdlen + 1)
- /* 'num' is the length of the modulus, i.e. does not depend on the
- * particular ciphertext. */
+ if (tlen <= 0 || flen <= 0)
+ return -1;
+ /*
+ * |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
+ * 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;
- lzero = num - flen;
- if (lzero < 0)
- {
- /* signalling this error immediately after detection might allow
- * for side-channel attacks (e.g. timing if 'plen' is huge
- * -- cf. James H. Manger, "A Chosen Ciphertext Attack on RSA Optimal
- * Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001),
- * so we use a 'bad' flag */
- bad = 1;
- lzero = 0;
- flen = num; /* don't overflow the memcpy to padded_from */
- }
-
- dblen = num - mdlen;
- db = OPENSSL_malloc(dblen + num);
- if (db == NULL)
+ dblen = num - mdlen - 1;
+ db = OPENSSL_malloc(dblen);
+ em = OPENSSL_malloc(num);
+ if (db == NULL || em == NULL)
{
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
- return -1;
+ goto cleanup;
}
- /* Always do this zero-padding copy (even when lzero == 0)
- * to avoid leaking timing info about the value of lzero. */
- padded_from = db + dblen;
- memset(padded_from, 0, lzero);
- memcpy(padded_from + lzero, from, flen);
+ /*
+ * Always do this zero-padding copy (even when num == flen) 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|.
+ *
+ * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
+ */
+ memset(em, 0, num);
+ memcpy(em + num - flen, from, flen);
+
+ /*
+ * 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(em[0]);
- maskeddb = padded_from + mdlen;
+ maskedseed = em + 1;
+ maskeddb = em + 1 + mdlen;
if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
- return -1;
+ goto cleanup;
for (i = 0; i < mdlen; i++)
- seed[i] ^= padded_from[i];
-
+ seed[i] ^= maskedseed[i];
+
if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
- return -1;
+ goto cleanup;
for (i = 0; i < dblen; i++)
db[i] ^= maskeddb[i];
if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
- return -1;
+ goto cleanup;
+
+ good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
- if (CRYPTO_memcmp(db, phash, mdlen) != 0 || bad)
+ found_one_byte = 0;
+ for (i = mdlen; i < dblen; i++)
+ {
+ /* Padding consists of a number of 0-bytes, followed by a 1. */
+ unsigned int equals1 = constant_time_eq(db[i], 1);
+ unsigned int equals0 = constant_time_is_zero(db[i]);
+ one_index = constant_time_select_int(~found_one_byte & equals1,
+ i, one_index);
+ found_one_byte |= equals1;
+ good &= (found_one_byte | equals0);
+ }
+
+ good &= found_one_byte;
+
+ /*
+ * At this point |good| is zero unless the plaintext was valid,
+ * 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
{
- for (i = mdlen; i < dblen; i++)
- if (db[i] != 0x00)
- break;
- if (i == dblen || db[i] != 0x01)
- goto decoding_err;
- else
- {
- /* everything looks OK */
-
- mlen = dblen - ++i;
- if (tlen < mlen)
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
- mlen = -1;
- }
- else
- memcpy(to, db + i, mlen);
- }
+ memcpy(to, db + msg_index, mlen);
+ goto cleanup;
}
- OPENSSL_free(db);
- return mlen;
decoding_err:
- /* to avoid chosen ciphertext attacks, the error message should not reveal
- * which kind of decoding error happened */
+ /* 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);
+cleanup:
if (db != NULL) OPENSSL_free(db);
- return -1;
+ if (em != NULL) OPENSSL_free(em);
+ return mlen;
}
int PKCS1_MGF1(unsigned char *mask, long len,
Index: openssl-0.9.8j/crypto/rsa/rsa_pk1.c
===================================================================
--- openssl-0.9.8j.orig/crypto/rsa/rsa_pk1.c
+++ openssl-0.9.8j/crypto/rsa/rsa_pk1.c
@@ -56,6 +56,8 @@
* [including the GNU Public Licence.]
*/
+#include "../constant_time_locl.h"
+
#include <stdio.h>
#include "cryptlib.h"
#include <openssl/bn.h>
@@ -181,44 +183,87 @@ int RSA_padding_add_PKCS1_type_2(unsigne
int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
const unsigned char *from, int flen, int num)
{
- int i,j;
- const unsigned char *p;
-
- p=from;
- if ((num != (flen+1)) || (*(p++) != 02))
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,RSA_R_BLOCK_TYPE_IS_NOT_02);
- return(-1);
- }
-#ifdef PKCS1_CHECK
- return(num-11);
-#endif
-
- /* scan over padding data */
- j=flen-1; /* one for type. */
- for (i=0; i<j; i++)
- if (*(p++) == 0) break;
-
- if (i == j)
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,RSA_R_NULL_BEFORE_BLOCK_MISSING);
- return(-1);
- }
-
- if (i < 8)
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,RSA_R_BAD_PAD_BYTE_COUNT);
- return(-1);
- }
- i++; /* Skip over the '\0' */
- j-=i;
- if (j > tlen)
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,RSA_R_DATA_TOO_LARGE);
- return(-1);
- }
- memcpy(to,p,(unsigned int)j);
-
- return(j);
+ int i;
+ /* |em| is the encoded message, zero-padded to exactly |num| bytes */
+ unsigned char *em = NULL;
+ unsigned int good, found_zero_byte;
+ int zero_index = 0, msg_index, mlen = -1;
+
+ if (tlen < 0 || flen < 0)
+ return -1;
+
+ /* PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography
+ * Standard", section 7.2.2. */
+
+ if (flen > num)
+ goto err;
+
+ if (num < 11)
+ goto err;
+
+ em = OPENSSL_malloc(num);
+ if (em == NULL)
+ {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE);
+ return -1;
+ }
+ memset(em, 0, num);
+ /*
+ * Always do this zero-padding copy (even when num == flen) 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|.
+ *
+ * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
+ */
+ memcpy(em + num - flen, from, flen);
+
+ good = constant_time_is_zero(em[0]);
+ good &= constant_time_eq(em[1], 2);
+
+ found_zero_byte = 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;
+ }
+
+ /*
+ * 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);
+
+ /* 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; it could
+ * leak something if |tlen| was assuming valid padding. */
+ good &= constant_time_ge((unsigned int)(tlen), (unsigned int)(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.
+ * TODO(emilia): this could be addressed at the call site,
+ * see BoringSSL commit 0aa0767340baf925bda4804882aab0cb974b2d26.
+ */
+ if (!good)
+ {
+ mlen = -1;
+ goto err;
+ }
+
+ memcpy(to, em + msg_index, mlen);
+
+err:
+ if (em != NULL)
+ OPENSSL_free(em);
+ if (mlen == -1)
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, RSA_R_PKCS_DECODING_ERROR);
+ return mlen;
}
-
