From: Ben Laurie <ben@links.org>
Date: Mon, 28 Jan 2013 18:24:55 +0000 (+0000)
Subject: Oops. Add missing file.
X-Git-Tag: OpenSSL_0_9_8y~17
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=a33e6702a0db1b9f4648d247b8b28a5c0e42ca13;p=oweals%2Fopenssl.git

Oops. Add missing file.
(cherry picked from commit 014265eb02e26f35c8db58e2ccbf100b0b2f0072)
(cherry picked from commit 7721c53e5e9fe4c90be420d7613559935a96a4fb)
---

diff --git a/ssl/s3_cbc.c b/ssl/s3_cbc.c
new file mode 100644
index 0000000000..e9b112c1b5
--- /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);
+	}