/* 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 "../crypto/constant_time_locl.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

/*-

 * 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 constant_time_select_int(good, 1, -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 (SSL_USE_EXPLICIT_IV(s)) {

        /*

         * 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 ((CRYPTO_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_8(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.

     */

    good = constant_time_eq(0xff, good & 0xff);

    padding_length = good & (padding_length + 1);

    rec->length -= padding_length;

    rec->type |= padding_length << 8; /* kludge: pass padding length */

    return constant_time_select_int(good, 1, -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_8(i, mac_start);

        unsigned char mac_ended = constant_time_ge_8(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. )

 * Returns 1 on success or 0 on error

 */

int 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:

        if (MD5_Init((MD5_CTX *)md_state.c) <= 0)

            return 0;

        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:

        if (SHA1_Init((SHA_CTX *)md_state.c) <= 0)

            return 0;

        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:

        if (SHA224_Init((SHA256_CTX *)md_state.c) <= 0)

            return 0;

        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:

        if (SHA256_Init((SHA256_CTX *)md_state.c) <= 0)

            return 0;

        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:

        if (SHA384_Init((SHA512_CTX *)md_state.c) <= 0)

            return 0;

        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:

        if (SHA512_Init((SHA512_CTX *)md_state.c) <= 0)

            return 0;

        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 = 0;

        return 0;

    }

    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) {

            unsigned overhang;

            /*

             * 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). There are no

             * ciphersuites in SSLv3 that are not SHA1 or MD5 based and

             * therefore we can be confident that the header_length will be

             * greater than |md_block_size|. However we add a sanity check just

             * in case

             */

            if (header_length <= md_block_size) {

                /* Should never happen */

                return 0;

            }

            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_8(j, c);

            is_past_cp1 = is_block_a & constant_time_ge_8(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 = constant_time_select_8(is_past_c, 0x80, b);

            /*

             * 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 = constant_time_select_8(is_block_b,

                                           length_bytes[j -

                                                        (md_block_size -

                                                         md_length_size)], b);

            }

            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);

    if (EVP_DigestInit_ex(&md_ctx, ctx->digest, NULL /* engine */ ) <= 0)

        goto err;

    if (is_sslv3) {

        /* We repurpose |hmac_pad| to contain the SSLv3 pad2 block. */

        memset(hmac_pad, 0x5c, sslv3_pad_length);

        if (EVP_DigestUpdate(&md_ctx, mac_secret, mac_secret_length) <= 0

                || EVP_DigestUpdate(&md_ctx, hmac_pad, sslv3_pad_length) <= 0

                || EVP_DigestUpdate(&md_ctx, mac_out, md_size) <= 0)

            goto err;

    } else {

        /* Complete the HMAC in the standard manner. */

        for (i = 0; i < md_block_size; i++)

            hmac_pad[i] ^= 0x6a;

        if (EVP_DigestUpdate(&md_ctx, hmac_pad, md_block_size) <= 0

                || EVP_DigestUpdate(&md_ctx, mac_out, md_size) <= 0)

            goto err;

    }

    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);

    return 1;

err:

    EVP_MD_CTX_cleanup(&md_ctx);

    return 0;

}

#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