cherry pick bugfixes for http://www.openssl.org/news/secadv_20130205.txt

from the openssl git (changes between openssl 1.0.1c and 1.0.1d).
ok djm@

1 files changed, 790 insertions, 0 deletions

diff --git a/src/lib/libssl/s3_cbc.c b/src/lib/libssl/s3_cbc.c
new file mode 100644
index 0000000000..443a31e746
--- /dev/null
+++ b/src/lib/libssl/s3_cbc.c
@@ -0,0 +1,790 @@
+/* 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 "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_lt returns 0xff if a<b and 0x00 otherwise. */
+static unsigned constant_time_lt(unsigned a, unsigned b)
+        {
+        a -= b;
+        return DUPLICATE_MSB_TO_ALL(a);
+        }
+
+/* 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 a, unsigned 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);
+        padding_length = good & (padding_length+1);
+        rec->length -= padding_length;
+        rec->type |= padding_length<<8; /* kludge: pass padding length */
+        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 unsigned overhead = 1 /* padding length byte */ + mac_size;
+        /* Check if version requires explicit IV */
+        if (s->version >= TLS1_1_VERSION || s->version == DTLS1_BAD_VER)
+                {
+                /* These lengths are all public so we can test them in
+                 * non-constant time.
+                 */
+                if (overhead + block_size > rec->length)
+                        return 0;
+                /* We can now safely skip explicit IV */
+                rec->data += block_size;
+                rec->input += block_size;
+                rec->length -= block_size;
+                }
+        else 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--;
+                        }
+                }
+
+        if (EVP_CIPHER_flags(s->enc_read_ctx->cipher)&EVP_CIPH_FLAG_AEAD_CIPHER)
+                {
+                /* padding is already verified */
+                rec->length -= padding_length + 1;
+                return 1;
+                }
+
+        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);
+
+        padding_length = good & (padding_length+1);
+        rec->length -= padding_length;
+        rec->type |= padding_length<<8; /* kludge: pass padding length */
+
+        return (int)((good & 1) | (~good & -1));
+        }
+
+/* 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 or pair of cache-lines, then the variable memory accesses don't
+ * actually affect the timing. CPUs with smaller cache-lines [if any] are
+ * not multi-core and are not considered vulnerable to cache-timing attacks.
+ */
+#define CBC_MAC_ROTATE_IN_PLACE
+
+void ssl3_cbc_copy_mac(unsigned char* out,
+                       const SSL3_RECORD *rec,
+                       unsigned md_size,unsigned orig_len)
+        {
+#if defined(CBC_MAC_ROTATE_IN_PLACE)
+        unsigned char rotated_mac_buf[64+EVP_MAX_MD_SIZE];
+        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(orig_len >= md_size);
+        OPENSSL_assert(md_size <= EVP_MAX_MD_SIZE);
+
+#if defined(CBC_MAC_ROTATE_IN_PLACE)
+        rotated_mac = rotated_mac_buf + ((0-(size_t)rotated_mac_buf)&63);
+#endif
+
+        /* This information is public so it's safe to branch based on it. */
+        if (orig_len > md_size + 255 + 1)
+                scan_start = 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, j = 0; i < orig_len; i++)
+                {
+                unsigned char mac_started = constant_time_ge(i, mac_start);
+                unsigned char mac_ended = constant_time_ge(i, mac_end);
+                unsigned char b = rec->data[i];
+                rotated_mac[j++] |= b & mac_started & ~mac_ended;
+                j &= constant_time_lt(j,md_size);
+                }
+
+        /* Now rotate the MAC */
+#if defined(CBC_MAC_ROTATE_IN_PLACE)
+        j = 0;
+        for (i = 0; i < md_size; i++)
+                {
+                /* in case cache-line is 32 bytes, touch second line */
+                ((volatile unsigned char *)rotated_mac)[rotate_offset^32];
+                out[j++] = rotated_mac[rotate_offset++];
+                rotate_offset &= constant_time_lt(rotate_offset,md_size);
+                }
+#else
+        memset(out, 0, md_size);
+        rotate_offset = md_size - rotate_offset;
+        rotate_offset &= constant_time_lt(rotate_offset,md_size);
+        for (i = 0; i < md_size; i++)
+                {
+                for (j = 0; j < md_size; j++)
+                        out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset);
+                rotate_offset++;
+                rotate_offset &= constant_time_lt(rotate_offset,md_size);
+                }
+#endif
+        }
+
+/* u32toLE serialises an unsigned, 32-bit number (n) as four bytes at (p) in
+ * little-endian order. The value of p is advanced by four. */
+#define u32toLE(n, p) \
+        (*((p)++)=(unsigned char)(n), \
+         *((p)++)=(unsigned char)(n>>8), \
+         *((p)++)=(unsigned char)(n>>16), \
+         *((p)++)=(unsigned char)(n>>24))
+
+/* 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;
+        u32toLE(md5->A, md_out);
+        u32toLE(md5->B, md_out);
+        u32toLE(md5->C, md_out);
+        u32toLE(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);
+        }
+#define LARGEST_DIGEST_CTX SHA_CTX
+
+#ifndef OPENSSL_NO_SHA256
+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);
+                }
+        }
+#undef  LARGEST_DIGEST_CTX
+#define LARGEST_DIGEST_CTX SHA256_CTX
+#endif
+
+#ifndef OPENSSL_NO_SHA512
+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);
+                }
+        }
+#undef  LARGEST_DIGEST_CTX
+#define LARGEST_DIGEST_CTX SHA512_CTX
+#endif
+
+/* 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)
+        {
+#ifdef OPENSSL_FIPS
+        if (FIPS_mode())
+                return 0;
+#endif
+        switch (EVP_MD_CTX_type(ctx))
+                {
+                case NID_md5:
+                case NID_sha1:
+#ifndef OPENSSL_NO_SHA256
+                case NID_sha224:
+                case NID_sha256:
+#endif
+#ifndef OPENSSL_NO_SHA512
+                case NID_sha384:
+                case NID_sha512:
+#endif
+                        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)
+        {
+        union { double align;
+                unsigned char c[sizeof(LARGEST_DIGEST_CTX)]; } md_state;
+        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;
+        unsigned int bits;      /* at most 18 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;
+        char length_is_big_endian = 1;
+
+        /* 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 (EVP_MD_CTX_type(ctx))
+                {
+                case NID_md5:
+                        MD5_Init((MD5_CTX*)md_state.c);
+                        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;
+                        length_is_big_endian = 0;
+                        break;
+                case NID_sha1:
+                        SHA1_Init((SHA_CTX*)md_state.c);
+                        md_final_raw = tls1_sha1_final_raw;
+                        md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA1_Transform;
+                        md_size = 20;
+                        break;
+#ifndef OPENSSL_NO_SHA256
+                case NID_sha224:
+                        SHA224_Init((SHA256_CTX*)md_state.c);
+                        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.c);
+                        md_final_raw = tls1_sha256_final_raw;
+                        md_transform = (void(*)(void *ctx, const unsigned char *block)) SHA256_Transform;
+                        md_size = 32;
+                        break;
+#endif
+#ifndef OPENSSL_NO_SHA512
+                case NID_sha384:
+                        SHA384_Init((SHA512_CTX*)md_state.c);
+                        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.c);
+                        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;
+#endif
+                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.c, hmac_pad);
+                }
+
+        if (length_is_big_endian)
+                {
+                memset(length_bytes,0,md_length_size-4);
+                length_bytes[md_length_size-4] = (unsigned char)(bits>>24);
+                length_bytes[md_length_size-3] = (unsigned char)(bits>>16);
+                length_bytes[md_length_size-2] = (unsigned char)(bits>>8);
+                length_bytes[md_length_size-1] = (unsigned char)bits;
+                }
+        else
+                {
+                memset(length_bytes,0,md_length_size);
+                length_bytes[md_length_size-5] = (unsigned char)(bits>>24);
+                length_bytes[md_length_size-6] = (unsigned char)(bits>>16);
+                length_bytes[md_length_size-7] = (unsigned char)(bits>>8);
+                length_bytes[md_length_size-8] = (unsigned char)bits;
+                }
+
+        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.c, header);
+                        memcpy(first_block, header + md_block_size, overhang);
+                        memcpy(first_block + overhang, data, md_block_size-overhang);
+                        md_transform(md_state.c, first_block);
+                        for (i = 1; i < k/md_block_size - 1; i++)
+                                md_transform(md_state.c, 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.c, first_block);
+                        for (i = 1; i < k/md_block_size; i++)
+                                md_transform(md_state.c, 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.c, block);
+                md_final_raw(md_state.c, 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);
+        }
+
+#ifdef OPENSSL_FIPS
+
+/* Due to the need to use EVP in FIPS mode we can't reimplement digests but
+ * we can ensure the number of blocks processed is equal for all cases
+ * by digesting additional data.
+ */
+
+void tls_fips_digest_extra(
+        const EVP_CIPHER_CTX *cipher_ctx, EVP_MD_CTX *mac_ctx,
+        const unsigned char *data, size_t data_len, size_t orig_len)
+        {
+        size_t block_size, digest_pad, blocks_data, blocks_orig;
+        if (EVP_CIPHER_CTX_mode(cipher_ctx) != EVP_CIPH_CBC_MODE)
+                return;
+        block_size = EVP_MD_CTX_block_size(mac_ctx);
+        /* We are in FIPS mode if we get this far so we know we have only SHA*
+         * digests and TLS to deal with.
+         * Minimum digest padding length is 17 for SHA384/SHA512 and 9
+         * otherwise.
+         * Additional header is 13 bytes. To get the number of digest blocks
+         * processed round up the amount of data plus padding to the nearest
+         * block length. Block length is 128 for SHA384/SHA512 and 64 otherwise.
+         * So we have:
+         * blocks = (payload_len + digest_pad + 13 + block_size - 1)/block_size
+         * equivalently:
+         * blocks = (payload_len + digest_pad + 12)/block_size + 1
+         * HMAC adds a constant overhead.
+         * We're ultimately only interested in differences so this becomes
+         * blocks = (payload_len + 29)/128
+         * for SHA384/SHA512 and
+         * blocks = (payload_len + 21)/64
+         * otherwise.
+         */
+        digest_pad = block_size == 64 ? 21 : 29;
+        blocks_orig = (orig_len + digest_pad)/block_size;
+        blocks_data = (data_len + digest_pad)/block_size;
+        /* MAC enough blocks to make up the difference between the original
+         * and actual lengths plus one extra block to ensure this is never a
+         * no op. The "data" pointer should always have enough space to
+         * perform this operation as it is large enough for a maximum
+         * length TLS buffer. 
+         */
+        EVP_DigestSignUpdate(mac_ctx, data,
+                                (blocks_orig - blocks_data + 1) * block_size);
+        }
+#endif