diff --git a/crypto/cipher/CMakeLists.txt b/crypto/cipher/CMakeLists.txt
index 40e239c..3b7135c 100644
--- a/crypto/cipher/CMakeLists.txt
+++ b/crypto/cipher/CMakeLists.txt
@@ -16,6 +16,8 @@
 	e_des.c
 	e_aes.c
 	e_chacha20poly1305.c
+
+	tls_cbc.c
 )
 
 add_executable(
diff --git a/crypto/cipher/internal.h b/crypto/cipher/internal.h
index d46a9e6..e73d4a1 100644
--- a/crypto/cipher/internal.h
+++ b/crypto/cipher/internal.h
@@ -130,6 +130,76 @@
               const uint8_t *ad, size_t ad_len);
 };
 
+
+/* EVP_ssl3_cbc_remove_padding determines the padding from the decrypted, SSLv3,
+ * CBC record in |in|. It sets |*out_len| to the length with the padding removed
+ * or |in_len| if invalid.
+ *
+ * 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 EVP_ssl3_cbc_remove_padding(unsigned *out_len,
+                                const uint8_t *in, unsigned in_len,
+                                unsigned block_size, unsigned mac_size);
+
+/* EVP_tls1_cbc_get_padding determines the padding from the decrypted, TLS, CBC
+ * record in |in|. This decrypted record should not include any "decrypted"
+ * explicit IV. It sets |*out_len| to the length with the padding removed or
+ * |in_len| if invalid.
+ *
+ * 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 EVP_tls1_cbc_remove_padding(unsigned *out_len,
+                                const uint8_t *in, unsigned in_len,
+                                unsigned block_size, unsigned mac_size);
+
+/* EVP_ssl3_cbc_copy_mac copies |md_size| bytes from the end of the first
+ * |in_len| bytes of |in| to |out| in constant time (independent of the concrete
+ * value of |in_len|, which may vary within a 256-byte window). |in| must point
+ * to a buffer of |orig_len| bytes.
+ *
+ * On entry:
+ *   orig_len >= in_len >= md_size
+ *   md_size <= EVP_MAX_MD_SIZE */
+void EVP_ssl3_cbc_copy_mac(uint8_t *out, unsigned md_size,
+                           const uint8_t *in, unsigned in_len,
+                           unsigned orig_len);
+
+/* EVP_ssl3_cbc_record_digest_supported returns 1 iff |md| is a hash function
+ * which EVP_ssl3_cbc_digest_record supports. */
+int EVP_ssl3_cbc_record_digest_supported(const EVP_MD *md);
+
+/* EVP_ssl3_cbc_digest_record computes the MAC of a decrypted, padded SSLv3/TLS
+ * record.
+ *
+ *   md: the hash function used in the SSLv3 MAC or HMAC.
+ *     ssl3_cbc_record_digest_supported must return true for this hash.
+ *   md_out: the digest output. At most EVP_MAX_MD_SIZE bytes will be written.
+ *   md_out_size: the number of output bytes is written here.
+ *   header: the 13-byte, TLS record header.
+ *   data: the record data itself
+ *   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. ) */
+int EVP_ssl3_cbc_digest_record(const EVP_MD *md, uint8_t *md_out,
+                               size_t *md_out_size, const uint8_t header[13],
+                               const uint8_t *data, size_t data_plus_mac_size,
+                               size_t data_plus_mac_plus_padding_size,
+                               const uint8_t *mac_secret,
+                               unsigned mac_secret_length, char is_sslv3);
+
 #if defined(__cplusplus)
 } /* extern C */
 #endif
diff --git a/crypto/cipher/tls_cbc.c b/crypto/cipher/tls_cbc.c
new file mode 100644
index 0000000..ecff605
--- /dev/null
+++ b/crypto/cipher/tls_cbc.c
@@ -0,0 +1,556 @@
+/* ====================================================================
+ * 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 <assert.h>
+
+#include <openssl/digest.h>
+#include <openssl/obj.h>
+#include <openssl/sha.h>
+
+#include "../internal.h"
+
+
+/* TODO(davidben): unsigned should be size_t. The various constant_time
+ * functions need to be switched to size_t. */
+
+/* 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
+
+int EVP_ssl3_cbc_remove_padding(unsigned *out_len,
+                                const uint8_t *in, unsigned in_len,
+                                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 > in_len) {
+    return 0;
+  }
+
+  padding_length = in[in_len - 1];
+  good = constant_time_ge(in_len, 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);
+  *out_len = in_len - padding_length;
+  return constant_time_select_int(good, 1, -1);
+}
+
+int EVP_tls1_cbc_remove_padding(unsigned *out_len,
+                                const uint8_t *in, unsigned in_len,
+                                unsigned block_size, unsigned mac_size) {
+  unsigned padding_length, good, to_check, i;
+  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 > in_len) {
+    return 0;
+  }
+
+  padding_length = in[in_len - 1];
+
+  good = constant_time_ge(in_len, 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 = 256; /* maximum amount of padding, inc length byte. */
+  if (to_check > in_len) {
+    to_check = in_len;
+  }
+
+  for (i = 0; i < to_check; i++) {
+    uint8_t mask = constant_time_ge_8(padding_length, i);
+    uint8_t b = in[in_len - 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);
+  *out_len = in_len - padding_length;
+
+  return constant_time_select_int(good, 1, -1);
+}
+
+/* If CBC_MAC_ROTATE_IN_PLACE is defined then EVP_ssl3_cbc_copy_mac 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 EVP_ssl3_cbc_copy_mac(uint8_t *out, unsigned md_size,
+                           const uint8_t *in, unsigned in_len,
+                           unsigned orig_len) {
+#if defined(CBC_MAC_ROTATE_IN_PLACE)
+  uint8_t rotated_mac_buf[64 + EVP_MAX_MD_SIZE];
+  uint8_t *rotated_mac;
+#else
+  uint8_t rotated_mac[EVP_MAX_MD_SIZE];
+#endif
+
+  /* mac_end is the index of |in| just after the end of the MAC. */
+  unsigned mac_end = in_len;
+  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;
+
+  assert(orig_len >= in_len);
+  assert(in_len >= md_size);
+  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++) {
+    uint8_t mac_started = constant_time_ge_8(i, mac_start);
+    uint8_t mac_ended = constant_time_ge_8(i, mac_end);
+    uint8_t b = in[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 uint8_t *)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
+}
+
+/* u32toBE serialises an unsigned, 32-bit number (n) as four bytes at (p) in
+ * big-endian order. The value of p is advanced by four. */
+#define u32toBE(n, p) \
+  (*((p)++)=(uint8_t)(n>>24), \
+   *((p)++)=(uint8_t)(n>>16), \
+   *((p)++)=(uint8_t)(n>>8), \
+   *((p)++)=(uint8_t)(n))
+
+/* u64toBE serialises an unsigned, 64-bit number (n) as eight bytes at (p) in
+ * big-endian order. The value of p is advanced by eight. */
+#define u64toBE(n, p) \
+  (*((p)++)=(uint8_t)(n>>56), \
+   *((p)++)=(uint8_t)(n>>48), \
+   *((p)++)=(uint8_t)(n>>40), \
+   *((p)++)=(uint8_t)(n>>32), \
+   *((p)++)=(uint8_t)(n>>24), \
+   *((p)++)=(uint8_t)(n>>16), \
+   *((p)++)=(uint8_t)(n>>8), \
+   *((p)++)=(uint8_t)(n))
+
+/* 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_sha1_final_raw(void *ctx, uint8_t *md_out) {
+  SHA_CTX *sha1 = ctx;
+  u32toBE(sha1->h0, md_out);
+  u32toBE(sha1->h1, md_out);
+  u32toBE(sha1->h2, md_out);
+  u32toBE(sha1->h3, md_out);
+  u32toBE(sha1->h4, md_out);
+}
+#define LARGEST_DIGEST_CTX SHA_CTX
+
+static void tls1_sha256_final_raw(void *ctx, uint8_t *md_out) {
+  SHA256_CTX *sha256 = ctx;
+  unsigned i;
+
+  for (i = 0; i < 8; i++) {
+    u32toBE(sha256->h[i], md_out);
+  }
+}
+#undef  LARGEST_DIGEST_CTX
+#define LARGEST_DIGEST_CTX SHA256_CTX
+
+static void tls1_sha512_final_raw(void *ctx, uint8_t *md_out) {
+  SHA512_CTX *sha512 = ctx;
+  unsigned i;
+
+  for (i = 0; i < 8; i++) {
+    u64toBE(sha512->h[i], md_out);
+  }
+}
+#undef  LARGEST_DIGEST_CTX
+#define LARGEST_DIGEST_CTX SHA512_CTX
+
+int EVP_ssl3_cbc_record_digest_supported(const EVP_MD *md) {
+  switch (EVP_MD_type(md)) {
+    case NID_sha1:
+    case NID_sha256:
+    case NID_sha384:
+      return 1;
+
+    default:
+      return 0;
+  }
+}
+
+int EVP_ssl3_cbc_digest_record(const EVP_MD *md, uint8_t *md_out,
+                               size_t *md_out_size, const uint8_t header[13],
+                               const uint8_t *data, size_t data_plus_mac_size,
+                               size_t data_plus_mac_plus_padding_size,
+                               const uint8_t *mac_secret,
+                               unsigned mac_secret_length, char is_sslv3) {
+  union {
+    double align;
+    uint8_t c[sizeof(LARGEST_DIGEST_CTX)];
+  } md_state;
+  void (*md_final_raw)(void *ctx, uint8_t *md_out);
+  void (*md_transform)(void *ctx, const uint8_t *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 */
+  uint8_t length_bytes[MAX_HASH_BIT_COUNT_BYTES];
+  /* hmac_pad is the masked HMAC key. */
+  uint8_t hmac_pad[MAX_HASH_BLOCK_SIZE];
+  uint8_t first_block[MAX_HASH_BLOCK_SIZE];
+  uint8_t 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. */
+  assert(data_plus_mac_plus_padding_size < 1024 * 1024);
+
+  switch (EVP_MD_type(md)) {
+    case NID_sha1:
+      SHA1_Init((SHA_CTX *)md_state.c);
+      md_final_raw = tls1_sha1_final_raw;
+      md_transform =
+          (void (*)(void *ctx, const uint8_t *block))SHA1_Transform;
+      md_size = 20;
+      break;
+
+    case NID_sha256:
+      SHA256_Init((SHA256_CTX *)md_state.c);
+      md_final_raw = tls1_sha256_final_raw;
+      md_transform =
+          (void (*)(void *ctx, const uint8_t *block))SHA256_Transform;
+      md_size = 32;
+      break;
+
+    case NID_sha384:
+      SHA384_Init((SHA512_CTX *)md_state.c);
+      md_final_raw = tls1_sha512_final_raw;
+      md_transform =
+          (void (*)(void *ctx, const uint8_t *block))SHA512_Transform;
+      md_size = 384 / 8;
+      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. */
+      assert(0);
+      *md_out_size = 0;
+      return 0;
+  }
+
+  assert(md_length_size <= MAX_HASH_BIT_COUNT_BYTES);
+  assert(md_block_size <= MAX_HASH_BLOCK_SIZE);
+  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);
+    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);
+  }
+
+  memset(length_bytes, 0, md_length_size - 4);
+  length_bytes[md_length_size - 4] = (uint8_t)(bits >> 24);
+  length_bytes[md_length_size - 3] = (uint8_t)(bits >> 16);
+  length_bytes[md_length_size - 2] = (uint8_t)(bits >> 8);
+  length_bytes[md_length_size - 1] = (uint8_t)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: 7 bytes (SHA1). */
+      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++) {
+    uint8_t block[MAX_HASH_BLOCK_SIZE];
+    uint8_t is_block_a = constant_time_eq_8(i, index_a);
+    uint8_t is_block_b = constant_time_eq_8(i, index_b);
+    for (j = 0; j < md_block_size; j++) {
+      uint8_t 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, md, NULL /* engine */)) {
+    EVP_MD_CTX_cleanup(&md_ctx);
+    return 0;
+  }
+
+  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);
+  *md_out_size = md_out_size_u;
+  EVP_MD_CTX_cleanup(&md_ctx);
+
+  return 1;
+}