The Tor Browser: security/nss/lib/freebl/hmacct.c@b8a032363ba2 (annotated)

security/nss/lib/freebl/hmacct.c@b8a032363ba2 (annotated)

security/nss/lib/freebl/hmacct.c

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #ifdef FREEBL_NO_DEPEND
 #include "stubs.h"
 #endif
 #include "secport.h"
 #include "hasht.h"
 #include "blapit.h"
 #include "hmacct.h"
 #include "secerr.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
 /* 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 an 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.
  *
  * Note: the argument to these macros must be an unsigned int.
  * */
 #define DUPLICATE_MSB_TO_ALL(x) ( (unsigned int)( (int)(x) >> (sizeof(int)*8-1) ) )
 #define DUPLICATE_MSB_TO_ALL_8(x) ( (unsigned char)(DUPLICATE_MSB_TO_ALL(x)) )
 /* constantTimeGE returns 0xff if a>=b and 0x00 otherwise, where a, b <
  * MAX_UINT/2. */
 static unsigned char
 constantTimeGE(unsigned int a, unsigned int b)
 {
     a -= b;
     return DUPLICATE_MSB_TO_ALL(~a);
 }
 /* constantTimeEQ8 returns 0xff if a==b and 0x00 otherwise. */
 static unsigned char
 constantTimeEQ8(unsigned char a, unsigned char b)
 {
     unsigned int c = a ^ b;
     c--;
     return DUPLICATE_MSB_TO_ALL_8(c);
 }
 /* MAC performs a constant time SSLv3/TLS MAC of |dataLen| bytes of |data|,
  * where |dataLen| includes both the authenticated bytes and the MAC tag from
  * the sender. |dataLen| must be >= the length of the MAC tag.
  *
  * |dataTotalLen| is >= |dataLen| and also accounts for any padding bytes
  * that may follow the sender's MAC. (Only a single block of padding may
  * follow in SSLv3, or up to 255 bytes in TLS.)
  *
  * Since the results of decryption are secret information (otherwise a
  * padding-oracle is created), this function is constant-time with respect to
  * |dataLen|.
  *
  * |header| contains either the 13-byte TLS header (containing the sequence
  * number, record type etc), or it contains the SSLv3 header with the SSLv3
  * padding bytes etc. */
 static SECStatus
 MAC(unsigned char *mdOut,
     unsigned int *mdOutLen,
     unsigned int mdOutMax,
     const SECHashObject *hashObj,
     const unsigned char *macSecret,
     unsigned int macSecretLen,
     const unsigned char *header,
     unsigned int headerLen,
     const unsigned char *data,
     unsigned int dataLen,
     unsigned int dataTotalLen,
     unsigned char isSSLv3)
 {
     void *mdState = hashObj->create();
     const unsigned int mdSize = hashObj->length;
     const unsigned int mdBlockSize = hashObj->blocklength;
     /* mdLengthSize is the number of bytes in the length field that terminates
      * the hash.
      *
      * This assumes that hash functions with a 64 byte block size use a 64-bit
      * length, and otherwise they use a 128-bit length. This is true of {MD5,
      * SHA*} (which are all of the hash functions specified for use with TLS
      * today). */
     const unsigned int mdLengthSize = mdBlockSize == 64 ? 8 : 16;
     const unsigned int sslv3PadLen = hashObj->type == HASH_AlgMD5 ? 48 : 40;
     /* varianceBlocks 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 varianceBlocks can be reduced. */
     unsigned int varianceBlocks = isSSLv3 ? 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) */
     const unsigned int len = dataTotalLen + headerLen;
     /* maxMACBytes contains the maximum bytes of bytes in the MAC, including
      * |header|, assuming that there's no padding. */
     const unsigned int maxMACBytes = len - mdSize - 1;
     /* numBlocks is the maximum number of hash blocks. */
     const unsigned int numBlocks =
 	(maxMACBytes + 1 + mdLengthSize + mdBlockSize - 1) / mdBlockSize;
     /* macEndOffset is the index just past the end of the data to be
      * MACed. */
     const unsigned int macEndOffset = dataLen + headerLen - mdSize;
     /* c is the index of the 0x80 byte in the final hash block that
      * contains application data. */
     const unsigned int c = macEndOffset % mdBlockSize;
     /* indexA is the hash block number that contains the 0x80 terminating
      * value. */
     const unsigned int indexA = macEndOffset / mdBlockSize;
     /* indexB is the hash block number that contains the 64-bit hash
      * length, in bits. */
     const unsigned int indexB = (macEndOffset + mdLengthSize) / mdBlockSize;
     /* 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. */
     unsigned int bits;
     /* 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 |varianceBlocks| blocks and we
      * can't leak where. However, |numStartingBlocks| worth of data can
      * be hashed right away because no padding value can affect whether
      * they are plaintext. */
     unsigned int numStartingBlocks = 0;
     /* k is the starting byte offset into the conceptual header||data where
      * we start processing. */
     unsigned int k = 0;
     unsigned char lengthBytes[MAX_HASH_BIT_COUNT_BYTES];
     /* hmacPad is the masked HMAC key. */
     unsigned char hmacPad[HASH_BLOCK_LENGTH_MAX];
     unsigned char firstBlock[HASH_BLOCK_LENGTH_MAX];
     unsigned char macOut[HASH_LENGTH_MAX];
     unsigned i, j;
     /* 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 (numBlocks > varianceBlocks + (isSSLv3 ? 1 : 0)) {
 	numStartingBlocks = numBlocks - varianceBlocks;
 	k = mdBlockSize*numStartingBlocks;
     }
     bits = 8*macEndOffset;
     hashObj->begin(mdState);
     if (!isSSLv3) {
 	/* 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*mdBlockSize;
 	memset(hmacPad, 0, mdBlockSize);
 	PORT_Assert(macSecretLen <= sizeof(hmacPad));
 	memcpy(hmacPad, macSecret, macSecretLen);
 	for (i = 0; i < mdBlockSize; i++)
 	    hmacPad[i] ^= 0x36;
 	hashObj->update(mdState, hmacPad, mdBlockSize);
     }
     j = 0;
     memset(lengthBytes, 0, sizeof(lengthBytes));
     if (mdLengthSize == 16) {
 	j = 8;
     }
     if (hashObj->type == HASH_AlgMD5) {
 	/* MD5 appends a little-endian length. */
 	for (i = 0; i < 4; i++) {
 	    lengthBytes[i+j] = bits >> (8*i);
 	}
     } else {
 	/* All other TLS hash functions use a big-endian length. */
 	for (i = 0; i < 4; i++) {
 	    lengthBytes[4+i+j] = bits >> (8*(3-i));
 	}
     }
     if (k > 0) {
 	if (isSSLv3) {
 	    /* 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). */
 	    const unsigned int overhang = headerLen-mdBlockSize;
 	    hashObj->update(mdState, header, mdBlockSize);
 	    memcpy(firstBlock, header + mdBlockSize, overhang);
 	    memcpy(firstBlock + overhang, data, mdBlockSize-overhang);
 	    hashObj->update(mdState, firstBlock, mdBlockSize);
 	    for (i = 1; i < k/mdBlockSize - 1; i++) {
 		hashObj->update(mdState, data + mdBlockSize*i - overhang,
 				mdBlockSize);
 	    }
 	} else {
 	    /* k is a multiple of mdBlockSize. */
 	    memcpy(firstBlock, header, 13);
 	    memcpy(firstBlock+13, data, mdBlockSize-13);
 	    hashObj->update(mdState, firstBlock, mdBlockSize);
 	    for (i = 1; i < k/mdBlockSize; i++) {
 		hashObj->update(mdState, data + mdBlockSize*i - 13,
 				mdBlockSize);
 	    }
 	}
     }
     memset(macOut, 0, sizeof(macOut));
     /* We now process the final hash blocks. For each block, we construct
      * it in constant time. If i == indexA then we'll include the 0x80
      * bytes and zero pad etc. For each block we selectively copy it, in
      * constant time, to |macOut|. */
     for (i = numStartingBlocks; i <= numStartingBlocks+varianceBlocks; i++) {
 	unsigned char block[HASH_BLOCK_LENGTH_MAX];
 	unsigned char isBlockA = constantTimeEQ8(i, indexA);
 	unsigned char isBlockB = constantTimeEQ8(i, indexB);
 	for (j = 0; j < mdBlockSize; j++) {
 	    unsigned char isPastC = isBlockA & constantTimeGE(j, c);
 	    unsigned char isPastCPlus1 = isBlockA & constantTimeGE(j, c+1);
 	    unsigned char b = 0;
 	    if (k < headerLen) {
 		b = header[k];
 	    } else if (k < dataTotalLen + headerLen) {
 		b = data[k-headerLen];
 	    }
 	    k++;
 	    /* 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&~isPastC) | (0x80&isPastC);
 	    /* 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&~isPastCPlus1;
 	    /* If this is indexB (the final block), but not
 	     * indexA (the end of the data), then the 64-bit
 	     * length didn't fit into indexA and we're having to
 	     * add an extra block of zeros. */
 	    b &= ~isBlockB | isBlockA;
 	    /* The final bytes of one of the blocks contains the length. */
 	    if (j >= mdBlockSize - mdLengthSize) {
 		/* If this is indexB, write a length byte. */
 		b = (b&~isBlockB) |
 		    (isBlockB&lengthBytes[j-(mdBlockSize-mdLengthSize)]);
 	    }
 	    block[j] = b;
 	}
 	hashObj->update(mdState, block, mdBlockSize);
 	hashObj->end_raw(mdState, block, NULL, mdSize);
 	/* If this is indexB, copy the hash value to |macOut|. */
 	for (j = 0; j < mdSize; j++) {
 	    macOut[j] |= block[j]&isBlockB;
 	}
     }
     hashObj->begin(mdState);
     if (isSSLv3) {
 	/* We repurpose |hmacPad| to contain the SSLv3 pad2 block. */
 	for (i = 0; i < sslv3PadLen; i++)
 	    hmacPad[i] = 0x5c;
 	hashObj->update(mdState, macSecret, macSecretLen);
 	hashObj->update(mdState, hmacPad, sslv3PadLen);
 	hashObj->update(mdState, macOut, mdSize);
     } else {
 	/* Complete the HMAC in the standard manner. */
 	for (i = 0; i < mdBlockSize; i++)
 	    hmacPad[i] ^= 0x6a;
 	hashObj->update(mdState, hmacPad, mdBlockSize);
 	hashObj->update(mdState, macOut, mdSize);
     }
     hashObj->end(mdState, mdOut, mdOutLen, mdOutMax);
     hashObj->destroy(mdState, PR_TRUE);
     return SECSuccess;
 }
 SECStatus
 HMAC_ConstantTime(
     unsigned char *result,
     unsigned int *resultLen,
     unsigned int maxResultLen,
     const SECHashObject *hashObj,
     const unsigned char *secret,
     unsigned int secretLen,
     const unsigned char *header,
     unsigned int headerLen,
     const unsigned char *body,
     unsigned int bodyLen,
     unsigned int bodyTotalLen)
 {
     if (hashObj->end_raw == NULL)
 	return SECFailure;
     return MAC(result, resultLen, maxResultLen, hashObj, secret, secretLen,
 	       header, headerLen, body, bodyLen, bodyTotalLen,
 /* not SSLv3 */);
 }
 SECStatus
 SSLv3_MAC_ConstantTime(
     unsigned char *result,
     unsigned int *resultLen,
     unsigned int maxResultLen,
     const SECHashObject *hashObj,
     const unsigned char *secret,
     unsigned int secretLen,
     const unsigned char *header,
     unsigned int headerLen,
     const unsigned char *body,
     unsigned int bodyLen,
     unsigned int bodyTotalLen)
 {
     if (hashObj->end_raw == NULL)
 	return SECFailure;
     return MAC(result, resultLen, maxResultLen, hashObj, secret, secretLen,
 	       header, headerLen, body, bodyLen, bodyTotalLen,
 /* SSLv3 */);
 }

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security/nss/lib/freebl/hmacct.c@b8a032363ba2 (annotated)

security/nss/lib/freebl/hmacct.c