patches/0002-Make-CBC-decoding-constant-time.patch

From fb402b7cdeffc907a9464cb84aa1311b1f77832a Mon Sep 17 00:00:00 2001
From: Adam Langley <agl@chromium.org>
Date: Wed, 16 Jan 2013 11:18:19 -0500
Subject: [PATCH 2/2] Make CBC decoding constant time.

This patch makes the decoding of SSLv3 and TLS CBC records constant
time. Without this, a timing side-channel can be used to build a padding
oracle and mount Vaudenay's attack.

This patch also disables the stitched AESNI+SHA mode pending a similar
fix to that code.

In order to be easy to backport, this change is implemented in ssl/,
rather than as a generic AEAD mode. In the future this should be changed
around so that HMAC isn't in ssl/, but crypto/ as FIPS expects.
---
 crypto/evp/c_allc.c |   2 +
 ssl/Makefile        |   4 +-
 ssl/d1_enc.c        |  59 ++---
 ssl/d1_pkt.c        |  87 ++++---
 ssl/s3_cbc.c        | 696 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 ssl/s3_enc.c        | 119 +++++----
 ssl/s3_pkt.c        |  94 +++----
 ssl/ssl3.h          |   4 +
 ssl/ssl_algs.c      |   3 +
 ssl/ssl_locl.h      |  34 +++
 ssl/t1_enc.c        | 144 +++++------
 11 files changed, 993 insertions(+), 253 deletions(-)
 create mode 100644 ssl/s3_cbc.c

diff --git a/crypto/evp/c_allc.c b/crypto/evp/c_allc.c
index 2a45d43..e230e60 100644
--- a/crypto/evp/c_allc.c
+++ b/crypto/evp/c_allc.c
@@ -195,11 +195,13 @@ void OpenSSL_add_all_ciphers(void)
 	EVP_add_cipher(EVP_aes_256_xts());
 	EVP_add_cipher_alias(SN_aes_256_cbc,"AES256");
 	EVP_add_cipher_alias(SN_aes_256_cbc,"aes256");
+#if 0  /* Disabled because of timing side-channel leaks. */
 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
 	EVP_add_cipher(EVP_aes_128_cbc_hmac_sha1());
 	EVP_add_cipher(EVP_aes_256_cbc_hmac_sha1());
 #endif
 #endif
+#endif
 
 #ifndef OPENSSL_NO_CAMELLIA
 	EVP_add_cipher(EVP_camellia_128_ecb());
diff --git a/ssl/Makefile b/ssl/Makefile
index feaf3e3..bdb49e2 100644
--- a/ssl/Makefile
+++ b/ssl/Makefile
@@ -22,7 +22,7 @@ LIB=$(TOP)/libssl.a
 SHARED_LIB= libssl$(SHLIB_EXT)
 LIBSRC=	\
 	s2_meth.c   s2_srvr.c s2_clnt.c  s2_lib.c  s2_enc.c s2_pkt.c \
-	s3_meth.c   s3_srvr.c s3_clnt.c  s3_lib.c  s3_enc.c s3_pkt.c s3_both.c \
+	s3_meth.c   s3_srvr.c s3_clnt.c  s3_lib.c  s3_enc.c s3_pkt.c s3_both.c s3_cbc.c \
 	s23_meth.c s23_srvr.c s23_clnt.c s23_lib.c          s23_pkt.c \
 	t1_meth.c   t1_srvr.c t1_clnt.c  t1_lib.c  t1_enc.c \
 	d1_meth.c   d1_srvr.c d1_clnt.c  d1_lib.c  d1_pkt.c \
@@ -33,7 +33,7 @@ LIBSRC=	\
 	bio_ssl.c ssl_err.c kssl.c tls_srp.c t1_reneg.c
 LIBOBJ= \
 	s2_meth.o  s2_srvr.o  s2_clnt.o  s2_lib.o  s2_enc.o s2_pkt.o \
-	s3_meth.o  s3_srvr.o  s3_clnt.o  s3_lib.o  s3_enc.o s3_pkt.o s3_both.o \
+	s3_meth.o  s3_srvr.o  s3_clnt.o  s3_lib.o  s3_enc.o s3_pkt.o s3_both.o s3_cbc.o \
 	s23_meth.o s23_srvr.o s23_clnt.o s23_lib.o          s23_pkt.o \
 	t1_meth.o   t1_srvr.o t1_clnt.o  t1_lib.o  t1_enc.o \
 	d1_meth.o   d1_srvr.o d1_clnt.o  d1_lib.o  d1_pkt.o \
diff --git a/ssl/d1_enc.c b/ssl/d1_enc.c
index 07a5e97..712c464 100644
--- a/ssl/d1_enc.c
+++ b/ssl/d1_enc.c
@@ -126,20 +126,28 @@
 #include <openssl/des.h>
 #endif
 
+/* dtls1_enc encrypts/decrypts the record in |s->wrec| / |s->rrec|, respectively.
+ *
+ * Returns:
+ *   0: (in non-constant time) if the record is publically invalid (i.e. too
+ *       short etc).
+ *   1: if the record's padding is valid / the encryption was successful.
+ *   -1: if the record's padding/AEAD-authenticator is invalid or, if sending,
+ *       an internal error occured. */
 int dtls1_enc(SSL *s, int send)
 	{
 	SSL3_RECORD *rec;
 	EVP_CIPHER_CTX *ds;
 	unsigned long l;
-	int bs,i,ii,j,k,n=0;
+	int bs,i,j,k,mac_size=0;
 	const EVP_CIPHER *enc;
 
 	if (send)
 		{
 		if (EVP_MD_CTX_md(s->write_hash))
 			{
-			n=EVP_MD_CTX_size(s->write_hash);
-			if (n < 0)
+			mac_size=EVP_MD_CTX_size(s->write_hash);
+			if (mac_size < 0)
 				return -1;
 			}
 		ds=s->enc_write_ctx;
@@ -164,9 +172,8 @@ int dtls1_enc(SSL *s, int send)
 		{
 		if (EVP_MD_CTX_md(s->read_hash))
 			{
-			n=EVP_MD_CTX_size(s->read_hash);
-			if (n < 0)
-				return -1;
+			mac_size=EVP_MD_CTX_size(s->read_hash);
+			OPENSSL_assert(mac_size >= 0);
 			}
 		ds=s->enc_read_ctx;
 		rec= &(s->s3->rrec);
@@ -231,7 +238,7 @@ int dtls1_enc(SSL *s, int send)
 		if (!send)
 			{
 			if (l == 0 || l%bs != 0)
-				return -1;
+				return 0;
 			}
 		
 		EVP_Cipher(ds,rec->data,rec->input,l);
@@ -246,43 +253,7 @@ int dtls1_enc(SSL *s, int send)
 #endif	/* KSSL_DEBUG */
 
 		if ((bs != 1) && !send)
-			{
-			ii=i=rec->data[l-1]; /* padding_length */
-			i++;
-			if (s->options&SSL_OP_TLS_BLOCK_PADDING_BUG)
-				{
-				/* First packet is even in size, so check */
-				if ((memcmp(s->s3->read_sequence,
-					"\0\0\0\0\0\0\0\0",8) == 0) && !(ii & 1))
-					s->s3->flags|=TLS1_FLAGS_TLS_PADDING_BUG;
-				if (s->s3->flags & TLS1_FLAGS_TLS_PADDING_BUG)
-					i--;
-				}
-			/* TLS 1.0 does not bound the number of padding bytes by the block size.
-			 * All of them must have value 'padding_length'. */
-			if (i + bs > (int)rec->length)
-				{
-				/* Incorrect padding. SSLerr() and ssl3_alert are done
-				 * by caller: we don't want to reveal whether this is
-				 * a decryption error or a MAC verification failure
-				 * (see http://www.openssl.org/~bodo/tls-cbc.txt) 
-				 */
-				return -1;
-				}
-			for (j=(int)(l-i); j<(int)l; j++)
-				{
-				if (rec->data[j] != ii)
-					{
-					/* Incorrect padding */
-					return -1;
-					}
-				}
-			rec->length-=i;
-
-			rec->data += bs;    /* skip the implicit IV */
-			rec->input += bs;
-			rec->length -= bs;
-			}
+			return tls1_cbc_remove_padding(s, rec, bs, mac_size);
 		}
 	return(1);
 	}
diff --git a/ssl/d1_pkt.c b/ssl/d1_pkt.c
index 5e2c56c..02c881a 100644
--- a/ssl/d1_pkt.c
+++ b/ssl/d1_pkt.c
@@ -376,15 +376,11 @@ static int
 dtls1_process_record(SSL *s)
 {
 	int i,al;
-	int clear=0;
 	int enc_err;
 	SSL_SESSION *sess;
 	SSL3_RECORD *rr;
 	unsigned int mac_size;
 	unsigned char md[EVP_MAX_MD_SIZE];
-	int decryption_failed_or_bad_record_mac = 0;
-	unsigned char *mac = NULL;
-
 
 	rr= &(s->s3->rrec);
 	sess = s->session;
@@ -414,14 +410,19 @@ dtls1_process_record(SSL *s)
 
 	/* decrypt in place in 'rr->input' */
 	rr->data=rr->input;
+	rr->orig_len=rr->length;
 
 	enc_err = s->method->ssl3_enc->enc(s,0);
-	if (enc_err <= 0)
+	/* enc_err is:
+	 *    0: (in non-constant time) if the record is publically invalid.
+	 *    1: if the padding is valid
+	 *    -1: if the padding is invalid */
+	if (enc_err == 0)
 		{
-		/* To minimize information leaked via timing, we will always
-		 * perform all computations before discarding the message.
-		 */
-		decryption_failed_or_bad_record_mac = 1;
+		/* For DTLS we simply ignore bad packets. */
+		rr->length = 0;
+		s->packet_length = 0;
+		goto err;
 		}
 
 #ifdef TLS_DEBUG
@@ -431,45 +432,59 @@ printf("\n");
 #endif
 
 	/* r->length is now the compressed data plus mac */
-	if (	(sess == NULL) ||
-		(s->enc_read_ctx == NULL) ||
-		(s->read_hash == NULL))
-		clear=1;
-
-	if (!clear)
+	if ((sess != NULL) &&
+	    (s->enc_read_ctx != NULL) &&
+	    (EVP_MD_CTX_md(s->read_hash) != NULL))
 		{
-		/* !clear => s->read_hash != NULL => mac_size != -1 */
-		int t;
-		t=EVP_MD_CTX_size(s->read_hash);
-		OPENSSL_assert(t >= 0);
-		mac_size=t;
-
-		if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+mac_size)
+		/* s->read_hash != NULL => mac_size != -1 */
+		unsigned char *mac = NULL;
+		unsigned char mac_tmp[EVP_MAX_MD_SIZE];
+		mac_size=EVP_MD_CTX_size(s->read_hash);
+		OPENSSL_assert(mac_size <= EVP_MAX_MD_SIZE);
+
+		/* orig_len is the length of the record before any padding was
+		 * removed. This is public information, as is the MAC in use,
+		 * therefore we can safely process the record in a different
+		 * amount of time if it's too short to possibly contain a MAC.
+		 */
+		if (rr->orig_len < mac_size ||
+		    /* CBC records must have a padding length byte too. */
+		    (EVP_CIPHER_CTX_mode(s->enc_read_ctx) == EVP_CIPH_CBC_MODE &&
+		     rr->orig_len < mac_size+1))
 			{
-#if 0 /* OK only for stream ciphers (then rr->length is visible from ciphertext anyway) */
-			al=SSL_AD_RECORD_OVERFLOW;
-			SSLerr(SSL_F_DTLS1_PROCESS_RECORD,SSL_R_PRE_MAC_LENGTH_TOO_LONG);
+			al=SSL_AD_DECODE_ERROR;
+			SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_LENGTH_TOO_SHORT);
 			goto f_err;
-#else
-			decryption_failed_or_bad_record_mac = 1;
-#endif			
 			}
-		/* check the MAC for rr->input (it's in mac_size bytes at the tail) */
-		if (rr->length >= mac_size)
+
+		if (EVP_CIPHER_CTX_mode(s->enc_read_ctx) == EVP_CIPH_CBC_MODE)
 			{
+			/* We update the length so that the TLS header bytes
+			 * can be constructed correctly but we need to extract
+			 * the MAC in constant time from within the record,
+			 * without leaking the contents of the padding bytes.
+			 * */
+			mac = mac_tmp;
+			ssl3_cbc_copy_mac(mac_tmp, rr, mac_size);
 			rr->length -= mac_size;
-			mac = &rr->data[rr->length];
 			}
 		else
-			rr->length = 0;
-		i=s->method->ssl3_enc->mac(s,md,0);
-		if (i < 0 || mac == NULL || CRYPTO_memcmp(md,mac,mac_size) != 0)
 			{
-			decryption_failed_or_bad_record_mac = 1;
+			/* In this case there's no padding, so |rec->orig_len|
+			 * equals |rec->length| and we checked that there's
+			 * enough bytes for |mac_size| above. */
+			rr->length -= mac_size;
+			mac = &rr->data[rr->length];
 			}
+
+		i=s->method->ssl3_enc->mac(s,md,0 /* not send */);
+		if (i < 0 || mac == NULL || CRYPTO_memcmp(md, mac, (size_t)mac_size) != 0)
+			enc_err = -1;
+		if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+mac_size)
+			enc_err = -1;
 		}
 
-	if (decryption_failed_or_bad_record_mac)
+	if (enc_err < 0)
 		{
 		/* decryption failed, silently discard message */
 		rr->length = 0;
diff --git a/ssl/s3_cbc.c b/ssl/s3_cbc.c
new file mode 100644
index 0000000..e9b112c
--- /dev/null
+++ b/ssl/s3_cbc.c
@@ -0,0 +1,696 @@
+/* ssl/s3_cbc.c */
+/* ====================================================================
+ * Copyright (c) 2012 The OpenSSL Project.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * 3. All advertising materials mentioning features or use of this
+ *    software must display the following acknowledgment:
+ *    "This product includes software developed by the OpenSSL Project
+ *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
+ *
+ * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
+ *    endorse or promote products derived from this software without
+ *    prior written permission. For written permission, please contact
+ *    openssl-core@openssl.org.
+ *
+ * 5. Products derived from this software may not be called "OpenSSL"
+ *    nor may "OpenSSL" appear in their names without prior written
+ *    permission of the OpenSSL Project.
+ *
+ * 6. Redistributions of any form whatsoever must retain the following
+ *    acknowledgment:
+ *    "This product includes software developed by the OpenSSL Project
+ *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
+ * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ * ====================================================================
+ *
+ * This product includes cryptographic software written by Eric Young
+ * (eay@cryptsoft.com).  This product includes software written by Tim
+ * Hudson (tjh@cryptsoft.com).
+ *
+ */
+
+#include <stdint.h>
+
+#include "ssl_locl.h"
+
+#include <openssl/md5.h>
+#include <openssl/sha.h>
+
+/* MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's length
+ * field. (SHA-384/512 have 128-bit length.) */
+#define MAX_HASH_BIT_COUNT_BYTES 16
+
+/* MAX_HASH_BLOCK_SIZE is the maximum hash block size that we'll support.
+ * Currently SHA-384/512 has a 128-byte block size and that's the largest
+ * supported by TLS.) */
+#define MAX_HASH_BLOCK_SIZE 128
+
+/* Some utility functions are needed:
+ *
+ * These macros return the given value with the MSB copied to all the other
+ * bits. They use the fact that arithmetic shift shifts-in the sign bit.
+ * However, this is not ensured by the C standard so you may need to replace
+ * them with something else on odd CPUs. */
+#define DUPLICATE_MSB_TO_ALL(x) ( (unsigned)( (int)(x) >> (sizeof(int)*8-1) ) )
+#define DUPLICATE_MSB_TO_ALL_8(x) ((unsigned char)(DUPLICATE_MSB_TO_ALL(x)))
+
+/* constant_time_ge returns 0xff if a>=b and 0x00 otherwise. */
+static unsigned constant_time_ge(unsigned a, unsigned b)
+	{
+	a -= b;
+	return DUPLICATE_MSB_TO_ALL(~a);
+	}
+
+/* constant_time_eq_8 returns 0xff if a==b and 0x00 otherwise. */
+static unsigned char constant_time_eq_8(unsigned char a, unsigned char b)
+	{
+	unsigned c = a ^ b;
+	c--;
+	return DUPLICATE_MSB_TO_ALL_8(c);
+	}
+
+/* ssl3_cbc_remove_padding removes padding from the decrypted, SSLv3, CBC
+ * record in |rec| by updating |rec->length| in constant time.
+ *
+ * block_size: the block size of the cipher used to encrypt the record.
+ * returns:
+ *   0: (in non-constant time) if the record is publicly invalid.
+ *   1: if the padding was valid
+ *  -1: otherwise. */
+int ssl3_cbc_remove_padding(const SSL* s,
+			    SSL3_RECORD *rec,
+			    unsigned block_size,
+			    unsigned mac_size)
+	{
+	unsigned padding_length, good;
+	const unsigned overhead = 1 /* padding length byte */ + mac_size;
+
+	/* These lengths are all public so we can test them in non-constant
+	 * time. */
+	if (overhead > rec->length)
+		return 0;
+
+	padding_length = rec->data[rec->length-1];
+	good = constant_time_ge(rec->length, padding_length+overhead);
+	/* SSLv3 requires that the padding is minimal. */
+	good &= constant_time_ge(block_size, padding_length+1);
+	rec->length -= good & (padding_length+1);
+	return (int)((good & 1) | (~good & -1));
+}
+
+/* tls1_cbc_remove_padding removes the CBC padding from the decrypted, TLS, CBC
+ * record in |rec| in constant time and returns 1 if the padding is valid and
+ * -1 otherwise. It also removes any explicit IV from the start of the record
+ * without leaking any timing about whether there was enough space after the
+ * padding was removed.
+ *
+ * block_size: the block size of the cipher used to encrypt the record.
+ * returns:
+ *   0: (in non-constant time) if the record is publicly invalid.
+ *   1: if the padding was valid
+ *  -1: otherwise. */
+int tls1_cbc_remove_padding(const SSL* s,
+			    SSL3_RECORD *rec,
+			    unsigned block_size,
+			    unsigned mac_size)
+	{
+	unsigned padding_length, good, to_check, i;
+	const char has_explicit_iv =
+		s->version >= TLS1_1_VERSION || s->version == DTLS1_VERSION;
+	const unsigned overhead = 1 /* padding length byte */ +
+				  mac_size +
+				  (has_explicit_iv ? block_size : 0);
+
+	/* These lengths are all public so we can test them in non-constant
+	 * time. */
+	if (overhead > rec->length)
+		return 0;
+
+	padding_length = rec->data[rec->length-1];
+
+	/* NB: if compression is in operation the first packet may not be of
+	 * even length so the padding bug check cannot be performed. This bug
+	 * workaround has been around since SSLeay so hopefully it is either
+	 * fixed now or no buggy implementation supports compression [steve]
+	 */
+	if ( (s->options&SSL_OP_TLS_BLOCK_PADDING_BUG) && !s->expand)
+		{
+		/* First packet is even in size, so check */
+		if ((memcmp(s->s3->read_sequence, "\0\0\0\0\0\0\0\0",8) == 0) &&
+		    !(padding_length & 1))
+			{
+			s->s3->flags|=TLS1_FLAGS_TLS_PADDING_BUG;
+			}
+		if ((s->s3->flags & TLS1_FLAGS_TLS_PADDING_BUG) &&
+		    padding_length > 0)
+			{
+			padding_length--;
+			}
+		}
+
+	good = constant_time_ge(rec->length, overhead+padding_length);
+	/* The padding consists of a length byte at the end of the record and
+	 * then that many bytes of padding, all with the same value as the
+	 * length byte. Thus, with the length byte included, there are i+1
+	 * bytes of padding.
+	 *
+	 * We can't check just |padding_length+1| bytes because that leaks
+	 * decrypted information. Therefore we always have to check the maximum
+	 * amount of padding possible. (Again, the length of the record is
+	 * public information so we can use it.) */
+	to_check = 255; /* maximum amount of padding. */
+	if (to_check > rec->length-1)
+		to_check = rec->length-1;
+
+	for (i = 0; i < to_check; i++)
+		{
+		unsigned char mask = constant_time_ge(padding_length, i);
+		unsigned char b = rec->data[rec->length-1-i];
+		/* The final |padding_length+1| bytes should all have the value
+		 * |padding_length|. Therefore the XOR should be zero. */
+		good &= ~(mask&(padding_length ^ b));
+		}
+
+	/* If any of the final |padding_length+1| bytes had the wrong value,
+	 * one or more of the lower eight bits of |good| will be cleared. We
+	 * AND the bottom 8 bits together and duplicate the result to all the
+	 * bits. */
+	good &= good >> 4;
+	good &= good >> 2;
+	good &= good >> 1;
+	good <<= sizeof(good)*8-1;
+	good = DUPLICATE_MSB_TO_ALL(good);
+
+	rec->length -= good & (padding_length+1);
+
+	/* We can always safely skip the explicit IV. We check at the beginning
+	 * of this function that the record has at least enough space for the
+	 * IV, MAC and padding length byte. (These can be checked in
+	 * non-constant time because it's all public information.) So, if the
+	 * padding was invalid, then we didn't change |rec->length| and this is
+	 * safe. If the padding was valid then we know that we have at least
+	 * overhead+padding_length bytes of space and so this is still safe
+	 * because overhead accounts for the explicit IV. */
+	if (has_explicit_iv)
+		{
+		rec->data += block_size;
+		rec->input += block_size;
+		rec->length -= block_size;
+		rec->orig_len -= block_size;
+		}
+
+	return (int)((good & 1) | (~good & -1));
+	}
+
+#if defined(_M_AMD64) || defined(__x86_64__)
+#define CBC_MAC_ROTATE_IN_PLACE
+#endif
+
+/* ssl3_cbc_copy_mac copies |md_size| bytes from the end of |rec| to |out| in
+ * constant time (independent of the concrete value of rec->length, which may
+ * vary within a 256-byte window).
+ *
+ * ssl3_cbc_remove_padding or tls1_cbc_remove_padding must be called prior to
+ * this function.
+ *
+ * On entry:
+ *   rec->orig_len >= md_size
+ *   md_size <= EVP_MAX_MD_SIZE
+ *
+ * If CBC_MAC_ROTATE_IN_PLACE is defined then the rotation is performed with
+ * variable accesses in a 64-byte-aligned buffer. Assuming that this fits into
+ * a single cache-line, then the variable memory accesses don't actually affect
+ * the timing. This has been tested to be true on Intel amd64 chips.
+ */
+void ssl3_cbc_copy_mac(unsigned char* out,
+		       const SSL3_RECORD *rec,
+		       unsigned md_size)
+	{
+#if defined(CBC_MAC_ROTATE_IN_PLACE)
+	unsigned char rotated_mac_buf[EVP_MAX_MD_SIZE*2];
+	unsigned char *rotated_mac;
+#else
+	unsigned char rotated_mac[EVP_MAX_MD_SIZE];
+#endif
+
+	/* mac_end is the index of |rec->data| just after the end of the MAC. */
+	unsigned mac_end = rec->length;
+	unsigned mac_start = mac_end - md_size;
+	/* scan_start contains the number of bytes that we can ignore because
+	 * the MAC's position can only vary by 255 bytes. */
+	unsigned scan_start = 0;
+	unsigned i, j;
+	unsigned div_spoiler;
+	unsigned rotate_offset;
+
+	OPENSSL_assert(rec->orig_len >= md_size);
+	OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE);
+
+#if defined(CBC_MAC_ROTATE_IN_PLACE)
+	rotated_mac = (unsigned char*) (((intptr_t)(rotated_mac_buf + 64)) & ~63);
+#endif
+
+	/* This information is public so it's safe to branch based on it. */
+	if (rec->orig_len > md_size + 255 + 1)
+		scan_start = rec->orig_len - (md_size + 255 + 1);
+	/* div_spoiler contains a multiple of md_size that is used to cause the
+	 * modulo operation to be constant time. Without this, the time varies
+	 * based on the amount of padding when running on Intel chips at least.
+	 *
+	 * The aim of right-shifting md_size is so that the compiler doesn't
+	 * figure out that it can remove div_spoiler as that would require it
+	 * to prove that md_size is always even, which I hope is beyond it. */
+	div_spoiler = md_size >> 1;
+	div_spoiler <<= (sizeof(div_spoiler)-1)*8;
+	rotate_offset = (div_spoiler + mac_start - scan_start) % md_size;
+
+	memset(rotated_mac, 0, md_size);
+	for (i = scan_start; i < rec->orig_len;)
+		{
+		for (j = 0; j < md_size && i < rec->orig_len; i++, j++)
+			{
+			unsigned char mac_started = constant_time_ge(i, mac_start);
+			unsigned char mac_ended = constant_time_ge(i, mac_end);
+			unsigned char b = 0;
+			b = rec->data[i];
+			rotated_mac[j] |= b & mac_started & ~mac_ended;
+			}
+		}
+
+	/* Now rotate the MAC */
+#if defined(CBC_MAC_ROTATE_IN_PLACE)
+	j = 0;
+	for (i = 0; i < md_size; i++)
+		{
+		unsigned char offset = (div_spoiler + rotate_offset + i) % md_size;
+		out[j++] = rotated_mac[offset];
+		}
+#else
+	memset(out, 0, md_size);
+	for (i = 0; i < md_size; i++)
+		{
+		unsigned char offset = (div_spoiler + md_size - rotate_offset + i) % md_size;
+		for (j = 0; j < md_size; j++)
+			out[j] |= rotated_mac[i] & constant_time_eq_8(j, offset);
+		}
+#endif
+	}
+
+/* These functions serialize the state of a hash and thus perform the standard
+ * "final" operation without adding the padding and length that such a function
+ * typically does. */
+static void tls1_md5_final_raw(void* ctx, unsigned char *md_out)
+	{
+	MD5_CTX *md5 = ctx;
+	l2n(md5->A, md_out);
+	l2n(md5->B, md_out);
+	l2n(md5->C, md_out);
+	l2n(md5->D, md_out);
+	}
+
+static void tls1_sha1_final_raw(void* ctx, unsigned char *md_out)
+	{
+	SHA_CTX *sha1 = ctx;
+	l2n(sha1->h0, md_out);
+	l2n(sha1->h1, md_out);
+	l2n(sha1->h2, md_out);
+	l2n(sha1->h3, md_out);
+	l2n(sha1->h4, md_out);
+	}
+
+static void tls1_sha256_final_raw(void* ctx, unsigned char *md_out)
+	{
+	SHA256_CTX *sha256 = ctx;
+	unsigned i;
+
+	for (i = 0; i < 8; i++)
+		{
+		l2n(sha256->h[i], md_out);
+		}
+	}
+
+static void tls1_sha512_final_raw(void* ctx, unsigned char *md_out)
+	{
+	SHA512_CTX *sha512 = ctx;
+	unsigned i;
+
+	for (i = 0; i < 8; i++)
+		{
+		l2n8(sha512->h[i], md_out);
+		}
+	}
+
+/* ssl3_cbc_record_digest_supported returns 1 iff |ctx| uses a hash function
+ * which ssl3_cbc_digest_record supports. */
+char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx)
+	{
+	switch (ctx->digest->type)
+		{
+		case NID_md5:
+		case NID_sha1:
+		case NID_sha224:
+		case NID_sha256:
+		case NID_sha384:
+		case NID_sha512:
+			return 1;
+		default:
+			return 0;
+		}
+	}
+
+/* ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
+ * record.
+ *
+ *   ctx: the EVP_MD_CTX from which we take the hash function.
+ *     ssl3_cbc_record_digest_supported must return true for this EVP_MD_CTX.
+ *   md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written.
+ *   md_out_size: if non-NULL, the number of output bytes is written here.
+ *   header: the 13-byte, TLS record header.
+ *   data: the record data itself, less any preceeding explicit IV.
+ *   data_plus_mac_size: the secret, reported length of the data and MAC
+ *     once the padding has been removed.
+ *   data_plus_mac_plus_padding_size: the public length of the whole
+ *     record, including padding.
+ *   is_sslv3: non-zero if we are to use SSLv3. Otherwise, TLS.
+ *
+ * On entry: by virtue of having been through one of the remove_padding
+ * functions, above, we know that data_plus_mac_size is large enough to contain
+ * a padding byte and MAC. (If the padding was invalid, it might contain the
+ * padding too. ) */
+void ssl3_cbc_digest_record(
+	const EVP_MD_CTX *ctx,
+	unsigned char* md_out,
+	size_t* md_out_size,
+	const unsigned char header[13],
+	const unsigned char *data,
+	size_t data_plus_mac_size,
+	size_t data_plus_mac_plus_padding_size,
+	const unsigned char *mac_secret,
+	unsigned mac_secret_length,
+	char is_sslv3)
+	{
+	unsigned char md_state[sizeof(SHA512_CTX)];
+	void (*md_final_raw)(void *ctx, unsigned char *md_out);
+	void (*md_transform)(void *ctx, const unsigned char *block);
+	unsigned md_size, md_block_size = 64;
+	unsigned sslv3_pad_length = 40, header_length, variance_blocks,
+		 len, max_mac_bytes, num_blocks,
+		 num_starting_blocks, k, mac_end_offset, c, index_a, index_b;
+	uint64_t bits;
+	unsigned char length_bytes[MAX_HASH_BIT_COUNT_BYTES];
+	/* hmac_pad is the masked HMAC key. */
+	unsigned char hmac_pad[MAX_HASH_BLOCK_SIZE];
+	unsigned char first_block[MAX_HASH_BLOCK_SIZE];
+	unsigned char mac_out[EVP_MAX_MD_SIZE];
+	unsigned i, j, md_out_size_u;
+	EVP_MD_CTX md_ctx;
+	/* mdLengthSize is the number of bytes in the length field that terminates
+	* the hash. */
+	unsigned md_length_size = 8;
+
+	/* This is a, hopefully redundant, check that allows us to forget about
+	 * many possible overflows later in this function. */
+	OPENSSL_assert(data_plus_mac_plus_padding_size < 1024*1024);
+
+	switch (ctx->digest->type)
+		{
+		case NID_md5:
+			MD5_Init((MD5_CTX*)md_state);
+			md_final_raw = tls1_md5_final_raw;
+			md_transform = (void(*)(void *ctx, const unsigned char *block)) MD5_Transform;
+			md_size = 16;
+			sslv3_pad_length = 48;
+			break;
+		case NID_sha1:
+			SHA1_Init((SHA_CTX*)md_state);
+			md_final_raw = tls1_sha1_final_raw;
+			md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA1_Transform;
+			md_size = 20;
+			break;
+		case NID_sha224:
+			SHA224_Init((SHA256_CTX*)md_state);
+			md_final_raw = tls1_sha256_final_raw;
+			md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform;
+			md_size = 224/8;
+			break;
+		case NID_sha256:
+			SHA256_Init((SHA256_CTX*)md_state);
+			md_final_raw = tls1_sha256_final_raw;
+			md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform;
+			md_size = 32;
+			break;
+		case NID_sha384:
+			SHA384_Init((SHA512_CTX*)md_state);
+			md_final_raw = tls1_sha512_final_raw;
+			md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform;
+			md_size = 384/8;
+			md_block_size = 128;
+			md_length_size = 16;
+			break;
+		case NID_sha512:
+			SHA512_Init((SHA512_CTX*)md_state);
+			md_final_raw = tls1_sha512_final_raw;
+			md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA512_Transform;
+			md_size = 64;
+			md_block_size = 128;
+			md_length_size = 16;
+			break;
+		default:
+			/* ssl3_cbc_record_digest_supported should have been
+			 * called first to check that the hash function is
+			 * supported. */
+			OPENSSL_assert(0);
+			if (md_out_size)
+				*md_out_size = -1;
+			return;
+		}
+
+	OPENSSL_assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES);
+	OPENSSL_assert(md_block_size <= MAX_HASH_BLOCK_SIZE);
+	OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE);
+
+	header_length = 13;
+	if (is_sslv3)
+		{
+		header_length =
+			mac_secret_length +
+			sslv3_pad_length +
+			8 /* sequence number */ +
+			1 /* record type */ +
+			2 /* record length */;
+		}
+
+	/* variance_blocks is the number of blocks of the hash that we have to
+	 * calculate in constant time because they could be altered by the
+	 * padding value.
+	 *
+	 * In SSLv3, the padding must be minimal so the end of the plaintext
+	 * varies by, at most, 15+20 = 35 bytes. (We conservatively assume that
+	 * the MAC size varies from 0..20 bytes.) In case the 9 bytes of hash
+	 * termination (0x80 + 64-bit length) don't fit in the final block, we
+	 * say that the final two blocks can vary based on the padding.
+	 *
+	 * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not
+	 * required to be minimal. Therefore we say that the final six blocks
+	 * can vary based on the padding.
+	 *
+	 * Later in the function, if the message is short and there obviously
+	 * cannot be this many blocks then variance_blocks can be reduced. */
+	variance_blocks = is_sslv3 ? 2 : 6;
+	/* From now on we're dealing with the MAC, which conceptually has 13
+	 * bytes of `header' before the start of the data (TLS) or 71/75 bytes
+	 * (SSLv3) */
+	len = data_plus_mac_plus_padding_size + header_length;
+	/* max_mac_bytes contains the maximum bytes of bytes in the MAC, including
+	* |header|, assuming that there's no padding. */
+	max_mac_bytes = len - md_size - 1;
+	/* num_blocks is the maximum number of hash blocks. */
+	num_blocks = (max_mac_bytes + 1 + md_length_size + md_block_size - 1) / md_block_size;
+	/* In order to calculate the MAC in constant time we have to handle
+	 * the final blocks specially because the padding value could cause the
+	 * end to appear somewhere in the final |variance_blocks| blocks and we
+	 * can't leak where. However, |num_starting_blocks| worth of data can
+	 * be hashed right away because no padding value can affect whether
+	 * they are plaintext. */
+	num_starting_blocks = 0;
+	/* k is the starting byte offset into the conceptual header||data where
+	 * we start processing. */
+	k = 0;
+	/* mac_end_offset is the index just past the end of the data to be
+	 * MACed. */
+	mac_end_offset = data_plus_mac_size + header_length - md_size;
+	/* c is the index of the 0x80 byte in the final hash block that
+	 * contains application data. */
+	c = mac_end_offset % md_block_size;
+	/* index_a is the hash block number that contains the 0x80 terminating
+	 * value. */
+	index_a = mac_end_offset / md_block_size;
+	/* index_b is the hash block number that contains the 64-bit hash
+	 * length, in bits. */
+	index_b = (mac_end_offset + md_length_size) / md_block_size;
+	/* bits is the hash-length in bits. It includes the additional hash
+	 * block for the masked HMAC key, or whole of |header| in the case of
+	 * SSLv3. */
+
+	/* For SSLv3, if we're going to have any starting blocks then we need
+	 * at least two because the header is larger than a single block. */
+	if (num_blocks > variance_blocks + (is_sslv3 ? 1 : 0))
+		{
+		num_starting_blocks = num_blocks - variance_blocks;
+		k = md_block_size*num_starting_blocks;
+		}
+
+	bits = 8*mac_end_offset;
+	if (!is_sslv3)
+		{
+		/* Compute the initial HMAC block. For SSLv3, the padding and
+		 * secret bytes are included in |header| because they take more
+		 * than a single block. */
+		bits += 8*md_block_size;
+		memset(hmac_pad, 0, md_block_size);
+		OPENSSL_assert(mac_secret_length <= sizeof(hmac_pad));
+		memcpy(hmac_pad, mac_secret, mac_secret_length);
+		for (i = 0; i < md_block_size; i++)
+			hmac_pad[i] ^= 0x36;
+
+		md_transform(md_state, hmac_pad);
+		}
+
+	j = 0;
+	if (md_length_size == 16)
+		{
+		memset(length_bytes, 0, 8);
+		j = 8;
+		}
+	for (i = 0; i < 8; i++)
+		length_bytes[i+j] = bits >> (8*(7-i));
+
+	if (k > 0)
+		{
+		if (is_sslv3)
+			{
+			/* The SSLv3 header is larger than a single block.
+			 * overhang is the number of bytes beyond a single
+			 * block that the header consumes: either 7 bytes
+			 * (SHA1) or 11 bytes (MD5). */
+			unsigned overhang = header_length-md_block_size;
+			md_transform(md_state, header);
+			memcpy(first_block, header + md_block_size, overhang);
+			memcpy(first_block + overhang, data, md_block_size-overhang);
+			md_transform(md_state, first_block);
+			for (i = 1; i < k/md_block_size - 1; i++)
+				md_transform(md_state, data + md_block_size*i - overhang);
+			}
+		else
+			{
+			/* k is a multiple of md_block_size. */
+			memcpy(first_block, header, 13);
+			memcpy(first_block+13, data, md_block_size-13);
+			md_transform(md_state, first_block);
+			for (i = 1; i < k/md_block_size; i++)
+				md_transform(md_state, data + md_block_size*i - 13);
+			}
+		}
+
+	memset(mac_out, 0, sizeof(mac_out));
+
+	/* We now process the final hash blocks. For each block, we construct
+	 * it in constant time. If the |i==index_a| then we'll include the 0x80
+	 * bytes and zero pad etc. For each block we selectively copy it, in
+	 * constant time, to |mac_out|. */
+	for (i = num_starting_blocks; i <= num_starting_blocks+variance_blocks; i++)
+		{
+		unsigned char block[MAX_HASH_BLOCK_SIZE];
+		unsigned char is_block_a = constant_time_eq_8(i, index_a);
+		unsigned char is_block_b = constant_time_eq_8(i, index_b);
+		for (j = 0; j < md_block_size; j++)
+			{
+			unsigned char b = 0, is_past_c, is_past_cp1;
+			if (k < header_length)
+				b = header[k];
+			else if (k < data_plus_mac_plus_padding_size + header_length)
+				b = data[k-header_length];
+			k++;
+
+			is_past_c = is_block_a & constant_time_ge(j, c);
+			is_past_cp1 = is_block_a & constant_time_ge(j, c+1);
+			/* If this is the block containing the end of the
+			 * application data, and we are at the offset for the
+			 * 0x80 value, then overwrite b with 0x80. */
+			b = (b&~is_past_c) | (0x80&is_past_c);
+			/* If this the the block containing the end of the
+			 * application data and we're past the 0x80 value then
+			 * just write zero. */
+			b = b&~is_past_cp1;
+			/* If this is index_b (the final block), but not
+			 * index_a (the end of the data), then the 64-bit
+			 * length didn't fit into index_a and we're having to
+			 * add an extra block of zeros. */
+			b &= ~is_block_b | is_block_a;
+
+			/* The final bytes of one of the blocks contains the
+			 * length. */
+			if (j >= md_block_size - md_length_size)
+				{
+				/* If this is index_b, write a length byte. */
+				b = (b&~is_block_b) | (is_block_b&length_bytes[j-(md_block_size-md_length_size)]);
+				}
+			block[j] = b;
+			}
+
+		md_transform(md_state, block);
+		md_final_raw(md_state, block);
+		/* If this is index_b, copy the hash value to |mac_out|. */
+		for (j = 0; j < md_size; j++)
+			mac_out[j] |= block[j]&is_block_b;
+		}
+
+	EVP_MD_CTX_init(&md_ctx);
+	EVP_DigestInit_ex(&md_ctx, ctx->digest, NULL /* engine */);
+	if (is_sslv3)
+		{
+		/* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */
+		memset(hmac_pad, 0x5c, sslv3_pad_length);
+
+		EVP_DigestUpdate(&md_ctx, mac_secret, mac_secret_length);
+		EVP_DigestUpdate(&md_ctx, hmac_pad, sslv3_pad_length);
+		EVP_DigestUpdate(&md_ctx, mac_out, md_size);
+		}
+	else
+		{
+		/* Complete the HMAC in the standard manner. */
+		for (i = 0; i < md_block_size; i++)
+			hmac_pad[i] ^= 0x6a;
+
+		EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size);
+		EVP_DigestUpdate(&md_ctx, mac_out, md_size);
+		}
+	EVP_DigestFinal(&md_ctx, md_out, &md_out_size_u);
+	if (md_out_size)
+		*md_out_size = md_out_size_u;
+	EVP_MD_CTX_cleanup(&md_ctx);
+	}
diff --git a/ssl/s3_enc.c b/ssl/s3_enc.c
index c5df2cb..a0eac77 100644
--- a/ssl/s3_enc.c
+++ b/ssl/s3_enc.c
@@ -466,12 +466,21 @@ void ssl3_cleanup_key_block(SSL *s)
 	s->s3->tmp.key_block_length=0;
 	}
 
+/* ssl3_enc encrypts/decrypts the record in |s->wrec| / |s->rrec|, respectively.
+ *
+ * Returns:
+ *   0: (in non-constant time) if the record is publically invalid (i.e. too
+ *       short etc).
+ *   1: if the record's padding is valid / the encryption was successful.
+ *   -1: if the record's padding is invalid or, if sending, an internal error
+ *       occured.
+ */
 int ssl3_enc(SSL *s, int send)
 	{
 	SSL3_RECORD *rec;
 	EVP_CIPHER_CTX *ds;
 	unsigned long l;
-	int bs,i;
+	int bs,i,mac_size=0;
 	const EVP_CIPHER *enc;
 
 	if (send)
@@ -522,32 +531,16 @@ int ssl3_enc(SSL *s, int send)
 		if (!send)
 			{
 			if (l == 0 || l%bs != 0)
-				{
-				SSLerr(SSL_F_SSL3_ENC,SSL_R_BLOCK_CIPHER_PAD_IS_WRONG);
-				ssl3_send_alert(s,SSL3_AL_FATAL,SSL_AD_DECRYPTION_FAILED);
 				return 0;
-				}
 			/* otherwise, rec->length >= bs */
 			}
 		
 		EVP_Cipher(ds,rec->data,rec->input,l);
 
+		if (EVP_MD_CTX_md(s->read_hash) != NULL)
+			mac_size = EVP_MD_CTX_size(s->read_hash);
 		if ((bs != 1) && !send)
-			{
-			i=rec->data[l-1]+1;
-			/* SSL 3.0 bounds the number of padding bytes by the block size;
-			 * padding bytes (except the last one) are arbitrary */
-			if (i > bs)
-				{
-				/* Incorrect padding. SSLerr() and ssl3_alert are done
-				 * by caller: we don't want to reveal whether this is
-				 * a decryption error or a MAC verification failure
-				 * (see http://www.openssl.org/~bodo/tls-cbc.txt) */
-				return -1;
-				}
-			/* now i <= bs <= rec->length */
-			rec->length-=i;
-			}
+			return ssl3_cbc_remove_padding(s, rec, bs, mac_size);
 		}
 	return(1);
 	}
@@ -716,7 +709,7 @@ int n_ssl3_mac(SSL *ssl, unsigned char *md, int send)
 	EVP_MD_CTX md_ctx;
 	const EVP_MD_CTX *hash;
 	unsigned char *p,rec_char;
-	unsigned int md_size;
+	size_t md_size;
 	int npad;
 	int t;
 
@@ -741,28 +734,68 @@ int n_ssl3_mac(SSL *ssl, unsigned char *md, int send)
 	md_size=t;
 	npad=(48/md_size)*md_size;
 
-	/* Chop the digest off the end :-) */
-	EVP_MD_CTX_init(&md_ctx);
-
-	EVP_MD_CTX_copy_ex( &md_ctx,hash);
-	EVP_DigestUpdate(&md_ctx,mac_sec,md_size);
-	EVP_DigestUpdate(&md_ctx,ssl3_pad_1,npad);
-	EVP_DigestUpdate(&md_ctx,seq,8);
-	rec_char=rec->type;
-	EVP_DigestUpdate(&md_ctx,&rec_char,1);
-	p=md;
-	s2n(rec->length,p);
-	EVP_DigestUpdate(&md_ctx,md,2);
-	EVP_DigestUpdate(&md_ctx,rec->input,rec->length);
-	EVP_DigestFinal_ex( &md_ctx,md,NULL);
-
-	EVP_MD_CTX_copy_ex( &md_ctx,hash);
-	EVP_DigestUpdate(&md_ctx,mac_sec,md_size);
-	EVP_DigestUpdate(&md_ctx,ssl3_pad_2,npad);
-	EVP_DigestUpdate(&md_ctx,md,md_size);
-	EVP_DigestFinal_ex( &md_ctx,md,&md_size);
-
-	EVP_MD_CTX_cleanup(&md_ctx);
+	if (!send &&
+	    EVP_CIPHER_CTX_mode(ssl->enc_read_ctx) == EVP_CIPH_CBC_MODE &&
+	    ssl3_cbc_record_digest_supported(hash))
+		{
+		/* This is a CBC-encrypted record. We must avoid leaking any
+		 * timing-side channel information about how many blocks of
+		 * data we are hashing because that gives an attacker a
+		 * timing-oracle. */
+
+		/* npad is, at most, 48 bytes and that's with MD5:
+		 *   16 + 48 + 8 (sequence bytes) + 1 + 2 = 75.
+		 *
+		 * With SHA-1 (the largest hash speced for SSLv3) the hash size
+		 * goes up 4, but npad goes down by 8, resulting in a smaller
+		 * total size. */
+		unsigned char header[75];
+		unsigned j = 0;
+		memcpy(header+j, mac_sec, md_size);
+		j += md_size;
+		memcpy(header+j, ssl3_pad_1, npad);
+		j += npad;
+		memcpy(header+j, seq, 8);
+		j += 8;
+		header[j++] = rec->type;
+		header[j++] = rec->length >> 8;
+		header[j++] = rec->length & 0xff;
+
+		ssl3_cbc_digest_record(
+			hash,
+			md, &md_size,
+			header, rec->input,
+			rec->length + md_size, rec->orig_len,
+			mac_sec, md_size,
+			1 /* is SSLv3 */);
+		}
+	else
+		{
+		unsigned int md_size_u;
+		/* Chop the digest off the end :-) */
+		EVP_MD_CTX_init(&md_ctx);
+
+		EVP_MD_CTX_copy_ex( &md_ctx,hash);
+		EVP_DigestUpdate(&md_ctx,mac_sec,md_size);
+		EVP_DigestUpdate(&md_ctx,ssl3_pad_1,npad);
+		EVP_DigestUpdate(&md_ctx,seq,8);
+		rec_char=rec->type;
+		EVP_DigestUpdate(&md_ctx,&rec_char,1);
+		p=md;
+		s2n(rec->length,p);
+		EVP_DigestUpdate(&md_ctx,md,2);
+		EVP_DigestUpdate(&md_ctx,rec->input,rec->length);
+		EVP_DigestFinal_ex( &md_ctx,md,NULL);
+
+		EVP_MD_CTX_copy_ex( &md_ctx,hash);
+		EVP_DigestUpdate(&md_ctx,mac_sec,md_size);
+		EVP_DigestUpdate(&md_ctx,ssl3_pad_2,npad);
+		EVP_DigestUpdate(&md_ctx,md,md_size);
+		EVP_DigestFinal_ex( &md_ctx,md,&md_size_u);
+		md_size = md_size_u;
+
+		EVP_MD_CTX_cleanup(&md_ctx);
+	}
 
 	ssl3_record_sequence_update(seq);
 	return(md_size);
diff --git a/ssl/s3_pkt.c b/ssl/s3_pkt.c
index 3e11140..dba6653 100644
--- a/ssl/s3_pkt.c
+++ b/ssl/s3_pkt.c
@@ -290,11 +290,8 @@ static int ssl3_get_record(SSL *s)
 	unsigned char *p;
 	unsigned char md[EVP_MAX_MD_SIZE];
 	short version;
-	int mac_size;
-	int clear=0;
+	unsigned mac_size;
 	size_t extra;
-	int decryption_failed_or_bad_record_mac = 0;
-	unsigned char *mac = NULL;
 
 	rr= &(s->s3->rrec);
 	sess=s->session;
@@ -401,19 +398,18 @@ fprintf(stderr, "Record type=%d, Length=%d\n", rr->type, rr->length);
 
 	/* decrypt in place in 'rr->input' */
 	rr->data=rr->input;
+	rr->orig_len=rr->length;
 
 	enc_err = s->method->ssl3_enc->enc(s,0);
-	if (enc_err <= 0)
+	/* enc_err is:
+	 *    0: (in non-constant time) if the record is publically invalid.
+	 *    1: if the padding is valid
+	 *    -1: if the padding is invalid */
+	if (enc_err == 0)
 		{
-		if (enc_err == 0)
-			/* SSLerr() and ssl3_send_alert() have been called */
-			goto err;
-
-		/* Otherwise enc_err == -1, which indicates bad padding
-		 * (rec->length has not been changed in this case).
-		 * To minimize information leaked via timing, we will perform
-		 * the MAC computation anyway. */
-		decryption_failed_or_bad_record_mac = 1;
+		al=SSL_AD_DECRYPTION_FAILED;
+		SSLerr(SSL_F_TLS1_ENC,SSL_R_BLOCK_CIPHER_PAD_IS_WRONG);
+		goto f_err;
 		}
 
 #ifdef TLS_DEBUG
@@ -423,53 +419,59 @@ printf("\n");
 #endif
 
 	/* r->length is now the compressed data plus mac */
-	if (	(sess == NULL) ||
-		(s->enc_read_ctx == NULL) ||
-		(EVP_MD_CTX_md(s->read_hash) == NULL))
-		clear=1;
-
-	if (!clear)
+	if ((sess != NULL) &&
+	    (s->enc_read_ctx != NULL) &&
+	    (EVP_MD_CTX_md(s->read_hash) != NULL))
 		{
-		/* !clear => s->read_hash != NULL => mac_size != -1 */
+		/* s->read_hash != NULL => mac_size != -1 */
+		unsigned char *mac = NULL;
+		unsigned char mac_tmp[EVP_MAX_MD_SIZE];
 		mac_size=EVP_MD_CTX_size(s->read_hash);
-		OPENSSL_assert(mac_size >= 0);
+		OPENSSL_assert(mac_size <= EVP_MAX_MD_SIZE);
 
-		if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+extra+mac_size)
+		/* orig_len is the length of the record before any padding was
+		 * removed. This is public information, as is the MAC in use,
+		 * therefore we can safely process the record in a different
+		 * amount of time if it's too short to possibly contain a MAC.
+		 */
+		if (rr->orig_len < mac_size ||
+		    /* CBC records must have a padding length byte too. */
+		    (EVP_CIPHER_CTX_mode(s->enc_read_ctx) == EVP_CIPH_CBC_MODE &&
+		     rr->orig_len < mac_size+1))
 			{
-#if 0 /* OK only for stream ciphers (then rr->length is visible from ciphertext anyway) */
-			al=SSL_AD_RECORD_OVERFLOW;
-			SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_PRE_MAC_LENGTH_TOO_LONG);
+			al=SSL_AD_DECODE_ERROR;
+			SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_LENGTH_TOO_SHORT);
 			goto f_err;
-#else
-			decryption_failed_or_bad_record_mac = 1;
-#endif			
 			}
-		/* check the MAC for rr->input (it's in mac_size bytes at the tail) */
-		if (rr->length >= (unsigned int)mac_size)
+
+		if (EVP_CIPHER_CTX_mode(s->enc_read_ctx) == EVP_CIPH_CBC_MODE)
 			{
+			/* We update the length so that the TLS header bytes
+			 * can be constructed correctly but we need to extract
+			 * the MAC in constant time from within the record,
+			 * without leaking the contents of the padding bytes.
+			 * */
+			mac = mac_tmp;
+			ssl3_cbc_copy_mac(mac_tmp, rr, mac_size);
 			rr->length -= mac_size;
-			mac = &rr->data[rr->length];
 			}
 		else
 			{
-			/* record (minus padding) is too short to contain a MAC */
-#if 0 /* OK only for stream ciphers */
-			al=SSL_AD_DECODE_ERROR;
-			SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_LENGTH_TOO_SHORT);
-			goto f_err;
-#else
-			decryption_failed_or_bad_record_mac = 1;
-			rr->length = 0;
-#endif
+			/* In this case there's no padding, so |rec->orig_len|
+			 * equals |rec->length| and we checked that there's
+			 * enough bytes for |mac_size| above. */
+			rr->length -= mac_size;
+			mac = &rr->data[rr->length];
 			}
-		i=s->method->ssl3_enc->mac(s,md,0);
+
+		i=s->method->ssl3_enc->mac(s,md,0 /* not send */);
 		if (i < 0 || mac == NULL || CRYPTO_memcmp(md, mac, (size_t)mac_size) != 0)
-			{
-			decryption_failed_or_bad_record_mac = 1;
-			}
+			enc_err = -1;
+		if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+extra+mac_size)
+			enc_err = -1;
 		}
 
-	if (decryption_failed_or_bad_record_mac)
+	if (enc_err < 0)
 		{
 		/* A separate 'decryption_failed' alert was introduced with TLS 1.0,
 		 * SSL 3.0 only has 'bad_record_mac'.  But unless a decryption
diff --git a/ssl/ssl3.h b/ssl/ssl3.h
index 247e88c..87d3e0f 100644
--- a/ssl/ssl3.h
+++ b/ssl/ssl3.h
@@ -355,6 +355,10 @@ typedef struct ssl3_record_st
 /*r */	unsigned char *comp;    /* only used with decompression - malloc()ed */
 /*r */  unsigned long epoch;    /* epoch number, needed by DTLS1 */
 /*r */  unsigned char seq_num[8]; /* sequence number, needed by DTLS1 */
+/*rw*/	unsigned int orig_len;  /* How many bytes were available before padding
+				   was removed? This is used to implement the
+				   MAC check in constant time for CBC records.
+				 */
 	} SSL3_RECORD;
 
 typedef struct ssl3_buffer_st
diff --git a/ssl/ssl_algs.c b/ssl/ssl_algs.c
index d443143..41ccbaa 100644
--- a/ssl/ssl_algs.c
+++ b/ssl/ssl_algs.c
@@ -90,11 +90,14 @@ int SSL_library_init(void)
 	EVP_add_cipher(EVP_aes_256_cbc());
 	EVP_add_cipher(EVP_aes_128_gcm());
 	EVP_add_cipher(EVP_aes_256_gcm());
+#if 0 /* Disabled because of timing side-channel leaks. */
 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
 	EVP_add_cipher(EVP_aes_128_cbc_hmac_sha1());
 	EVP_add_cipher(EVP_aes_256_cbc_hmac_sha1());
 #endif
 #endif
+
+#endif
 #ifndef OPENSSL_NO_CAMELLIA
 	EVP_add_cipher(EVP_camellia_128_cbc());
 	EVP_add_cipher(EVP_camellia_256_cbc());
diff --git a/ssl/ssl_locl.h b/ssl/ssl_locl.h
index 0572e10..dd8388c 100644
--- a/ssl/ssl_locl.h
+++ b/ssl/ssl_locl.h
@@ -215,6 +215,15 @@
 			 *((c)++)=(unsigned char)(((l)>> 8)&0xff), \
 			 *((c)++)=(unsigned char)(((l)    )&0xff))
 
+#define l2n8(l,c)	(*((c)++)=(unsigned char)(((l)>>56)&0xff), \
+			 *((c)++)=(unsigned char)(((l)>>48)&0xff), \
+			 *((c)++)=(unsigned char)(((l)>>40)&0xff), \
+			 *((c)++)=(unsigned char)(((l)>>32)&0xff), \
+			 *((c)++)=(unsigned char)(((l)>>24)&0xff), \
+			 *((c)++)=(unsigned char)(((l)>>16)&0xff), \
+			 *((c)++)=(unsigned char)(((l)>> 8)&0xff), \
+			 *((c)++)=(unsigned char)(((l)    )&0xff))
+
 #define n2l6(c,l)	(l =((BN_ULLONG)(*((c)++)))<<40, \
 			 l|=((BN_ULLONG)(*((c)++)))<<32, \
 			 l|=((BN_ULLONG)(*((c)++)))<<24, \
@@ -1133,4 +1142,29 @@ int ssl_parse_clienthello_use_srtp_ext(SSL *s, unsigned char *d, int len,int *al
 int ssl_add_serverhello_use_srtp_ext(SSL *s, unsigned char *p, int *len, int maxlen);
 int ssl_parse_serverhello_use_srtp_ext(SSL *s, unsigned char *d, int len,int *al);
 
+/* s3_cbc.c */
+void ssl3_cbc_copy_mac(unsigned char* out,
+		       const SSL3_RECORD *rec,
+		       unsigned md_size);
+int ssl3_cbc_remove_padding(const SSL* s,
+			    SSL3_RECORD *rec,
+			    unsigned block_size,
+			    unsigned mac_size);
+int tls1_cbc_remove_padding(const SSL* s,
+			    SSL3_RECORD *rec,
+			    unsigned block_size,
+			    unsigned mac_size);
+char ssl3_cbc_record_digest_supported(const EVP_MD_CTX *ctx);
+void ssl3_cbc_digest_record(
+	const EVP_MD_CTX *ctx,
+	unsigned char* md_out,
+	size_t* md_out_size,
+	const unsigned char header[13],
+	const unsigned char *data,
+	size_t data_plus_mac_size,
+	size_t data_plus_mac_plus_padding_size,
+	const unsigned char *mac_secret,
+	unsigned mac_secret_length,
+	char is_sslv3);
+
 #endif
diff --git a/ssl/t1_enc.c b/ssl/t1_enc.c
index b37678f..bb46f7f 100644
--- a/ssl/t1_enc.c
+++ b/ssl/t1_enc.c
@@ -667,12 +667,21 @@ err:
 	return(ret);
 	}
 
+/* tls1_enc encrypts/decrypts the record in |s->wrec| / |s->rrec|, respectively.
+ *
+ * Returns:
+ *   0: (in non-constant time) if the record is publically invalid (i.e. too
+ *       short etc).
+ *   1: if the record's padding is valid / the encryption was successful.
+ *   -1: if the record's padding/AEAD-authenticator is invalid or, if sending,
+ *       an internal error occured.
+ */
 int tls1_enc(SSL *s, int send)
 	{
 	SSL3_RECORD *rec;
 	EVP_CIPHER_CTX *ds;
 	unsigned long l;
-	int bs,i,ii,j,k,pad=0;
+	int bs,i,j,k,pad=0,ret,mac_size=0;
 	const EVP_CIPHER *enc;
 
 	if (send)
@@ -729,11 +738,11 @@ int tls1_enc(SSL *s, int send)
 	printf("tls1_enc(%d)\n", send);
 #endif    /* KSSL_DEBUG */
 
-	if ((s->session == NULL) || (ds == NULL) ||
-		(enc == NULL))
+	if ((s->session == NULL) || (ds == NULL) || (enc == NULL))
 		{
 		memmove(rec->data,rec->input,rec->length);
 		rec->input=rec->data;
+		ret = 1;
 		}
 	else
 		{
@@ -797,13 +806,13 @@ int tls1_enc(SSL *s, int send)
 
 #ifdef KSSL_DEBUG
 		{
-                unsigned long ui;
+		unsigned long ui;
 		printf("EVP_Cipher(ds=%p,rec->data=%p,rec->input=%p,l=%ld) ==>\n",
-                        ds,rec->data,rec->input,l);
+			ds,rec->data,rec->input,l);
 		printf("\tEVP_CIPHER_CTX: %d buf_len, %d key_len [%d %d], %d iv_len\n",
-                        ds->buf_len, ds->cipher->key_len,
-                        DES_KEY_SZ, DES_SCHEDULE_SZ,
-                        ds->cipher->iv_len);
+			ds->buf_len, ds->cipher->key_len,
+			DES_KEY_SZ, DES_SCHEDULE_SZ,
+			ds->cipher->iv_len);
 		printf("\t\tIV: ");
 		for (i=0; i<ds->cipher->iv_len; i++) printf("%02X", ds->iv[i]);
 		printf("\n");
@@ -816,13 +825,7 @@ int tls1_enc(SSL *s, int send)
 		if (!send)
 			{
 			if (l == 0 || l%bs != 0)
-				{
-				if (s->version >= TLS1_1_VERSION)
-					return -1;
-				SSLerr(SSL_F_TLS1_ENC,SSL_R_BLOCK_CIPHER_PAD_IS_WRONG);
-				ssl3_send_alert(s,SSL3_AL_FATAL,SSL_AD_DECRYPTION_FAILED);
 				return 0;
-				}
 			}
 		
 		i = EVP_Cipher(ds,rec->data,rec->input,l);
@@ -839,68 +842,24 @@ int tls1_enc(SSL *s, int send)
 
 #ifdef KSSL_DEBUG
 		{
-                unsigned long i;
-                printf("\trec->data=");
+		unsigned long i;
+		printf("\trec->data=");
 		for (i=0; i<l; i++)
-                        printf(" %02x", rec->data[i]);  printf("\n");
-                }
+			printf(" %02x", rec->data[i]);  printf("\n");
+		}
 #endif	/* KSSL_DEBUG */
 
+		ret = 1;
+		if (EVP_MD_CTX_md(s->read_hash) != NULL)
+			mac_size = EVP_MD_CTX_size(s->read_hash);
 		if ((bs != 1) && !send)
-			{
-			ii=i=rec->data[l-1]; /* padding_length */
-			i++;
-			/* NB: if compression is in operation the first packet
-			 * may not be of even length so the padding bug check
-			 * cannot be performed. This bug workaround has been
-			 * around since SSLeay so hopefully it is either fixed
-			 * now or no buggy implementation supports compression 
-			 * [steve]
-			 */
-			if ( (s->options&SSL_OP_TLS_BLOCK_PADDING_BUG)
-				&& !s->expand)
-				{
-				/* First packet is even in size, so check */
-				if ((memcmp(s->s3->read_sequence,
-					"\0\0\0\0\0\0\0\0",8) == 0) && !(ii & 1))
-					s->s3->flags|=TLS1_FLAGS_TLS_PADDING_BUG;
-				if (s->s3->flags & TLS1_FLAGS_TLS_PADDING_BUG)
-					i--;
-				}
-			/* TLS 1.0 does not bound the number of padding bytes by the block size.
-			 * All of them must have value 'padding_length'. */
-			if (i > (int)rec->length)
-				{
-				/* Incorrect padding. SSLerr() and ssl3_alert are done
-				 * by caller: we don't want to reveal whether this is
-				 * a decryption error or a MAC verification failure
-				 * (see http://www.openssl.org/~bodo/tls-cbc.txt) */
-				return -1;
-				}
-			for (j=(int)(l-i); j<(int)l; j++)
-				{
-				if (rec->data[j] != ii)
-					{
-					/* Incorrect padding */
-					return -1;
-					}
-				}
-			rec->length -=i;
-			if (s->version >= TLS1_1_VERSION
-				&& EVP_CIPHER_CTX_mode(ds) == EVP_CIPH_CBC_MODE)
-				{
-				if (bs > (int)rec->length)
-					return -1;
-				rec->data += bs;    /* skip the explicit IV */
-				rec->input += bs;
-				rec->length -= bs;
-				}
-			}
+			ret = tls1_cbc_remove_padding(s, rec, bs, mac_size);
 		if (pad && !send)
 			rec->length -= pad;
 		}
-	return(1);
+	return ret;
 	}
+
 int tls1_cert_verify_mac(SSL *s, int md_nid, unsigned char *out)
 	{
 	unsigned int ret;
@@ -993,7 +952,7 @@ int tls1_mac(SSL *ssl, unsigned char *md, int send)
 	size_t md_size;
 	int i;
 	EVP_MD_CTX hmac, *mac_ctx;
-	unsigned char buf[5]; 
+	unsigned char header[13];
 	int stream_mac = (send?(ssl->mac_flags & SSL_MAC_FLAG_WRITE_MAC_STREAM):(ssl->mac_flags&SSL_MAC_FLAG_READ_MAC_STREAM));
 	int t;
 
@@ -1014,12 +973,6 @@ int tls1_mac(SSL *ssl, unsigned char *md, int send)
 	OPENSSL_assert(t >= 0);
 	md_size=t;
 
-	buf[0]=rec->type;
-	buf[1]=(unsigned char)(ssl->version>>8);
-	buf[2]=(unsigned char)(ssl->version);
-	buf[3]=rec->length>>8;
-	buf[4]=rec->length&0xff;
-
 	/* I should fix this up TLS TLS TLS TLS TLS XXXXXXXX */
 	if (stream_mac) 
 		{
@@ -1038,17 +991,44 @@ int tls1_mac(SSL *ssl, unsigned char *md, int send)
 		s2n(send?ssl->d1->w_epoch:ssl->d1->r_epoch, p);
 		memcpy (p,&seq[2],6);
 
-		EVP_DigestSignUpdate(mac_ctx,dtlsseq,8);
+		memcpy(header, dtlsseq, 8);
 		}
 	else
-		EVP_DigestSignUpdate(mac_ctx,seq,8);
+		memcpy(header, seq, 8);
 
-	EVP_DigestSignUpdate(mac_ctx,buf,5);
-	EVP_DigestSignUpdate(mac_ctx,rec->input,rec->length);
-	t=EVP_DigestSignFinal(mac_ctx,md,&md_size);
-	OPENSSL_assert(t > 0);
+	header[8]=rec->type;
+	header[9]=(unsigned char)(ssl->version>>8);
+	header[10]=(unsigned char)(ssl->version);
+	header[11]=(rec->length)>>8;
+	header[12]=(rec->length)&0xff;
+
+	if (!send &&
+	    EVP_CIPHER_CTX_mode(ssl->enc_read_ctx) == EVP_CIPH_CBC_MODE &&
+	    ssl3_cbc_record_digest_supported(mac_ctx))
+		{
+		/* This is a CBC-encrypted record. We must avoid leaking any
+		 * timing-side channel information about how many blocks of
+		 * data we are hashing because that gives an attacker a
+		 * timing-oracle. */
+		ssl3_cbc_digest_record(
+			mac_ctx,
+			md, &md_size,
+			header, rec->input,
+			rec->length + md_size, rec->orig_len,
+			ssl->s3->read_mac_secret,
+			ssl->s3->read_mac_secret_size,
+			0 /* not SSLv3 */);
+		}
+	else
+		{
+		EVP_DigestSignUpdate(mac_ctx,header,sizeof(header));
+		EVP_DigestSignUpdate(mac_ctx,rec->input,rec->length);
+		t=EVP_DigestSignFinal(mac_ctx,md,&md_size);
+		OPENSSL_assert(t > 0);
+		}
 		
-	if (!stream_mac) EVP_MD_CTX_cleanup(&hmac);
+	if (!stream_mac)
+		EVP_MD_CTX_cleanup(&hmac);
 #ifdef TLS_DEBUG
 printf("sec=");
 {unsigned int z; for (z=0; z<md_size; z++) printf("%02X ",mac_sec[z]); printf("\n"); }
-- 
1.8.1