michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifdef FREEBL_NO_DEPEND
michael@0: #include "stubs.h"
michael@0: #endif
michael@0: 
michael@0: #include "secport.h"
michael@0: #include "hasht.h"
michael@0: #include "blapit.h"
michael@0: #include "hmacct.h"
michael@0: #include "secerr.h"
michael@0: 
michael@0: /* MAX_HASH_BIT_COUNT_BYTES is the maximum number of bytes in the hash's length
michael@0:  * field. (SHA-384/512 have 128-bit length.) */
michael@0: #define MAX_HASH_BIT_COUNT_BYTES 16
michael@0: 
michael@0: /* Some utility functions are needed:
michael@0:  *
michael@0:  * These macros return the given value with the MSB copied to all the other
michael@0:  * bits. They use the fact that an arithmetic shift shifts-in the sign bit.
michael@0:  * However, this is not ensured by the C standard so you may need to replace
michael@0:  * them with something else on odd CPUs.
michael@0:  *
michael@0:  * Note: the argument to these macros must be an unsigned int.
michael@0:  * */
michael@0: #define DUPLICATE_MSB_TO_ALL(x) ( (unsigned int)( (int)(x) >> (sizeof(int)*8-1) ) )
michael@0: #define DUPLICATE_MSB_TO_ALL_8(x) ( (unsigned char)(DUPLICATE_MSB_TO_ALL(x)) )
michael@0: 
michael@0: /* constantTimeGE returns 0xff if a>=b and 0x00 otherwise, where a, b <
michael@0:  * MAX_UINT/2. */
michael@0: static unsigned char
michael@0: constantTimeGE(unsigned int a, unsigned int b)
michael@0: {
michael@0:     a -= b;
michael@0:     return DUPLICATE_MSB_TO_ALL(~a);
michael@0: }
michael@0: 
michael@0: /* constantTimeEQ8 returns 0xff if a==b and 0x00 otherwise. */
michael@0: static unsigned char
michael@0: constantTimeEQ8(unsigned char a, unsigned char b)
michael@0: {
michael@0:     unsigned int c = a ^ b;
michael@0:     c--;
michael@0:     return DUPLICATE_MSB_TO_ALL_8(c);
michael@0: }
michael@0: 
michael@0: /* MAC performs a constant time SSLv3/TLS MAC of |dataLen| bytes of |data|,
michael@0:  * where |dataLen| includes both the authenticated bytes and the MAC tag from
michael@0:  * the sender. |dataLen| must be >= the length of the MAC tag.
michael@0:  *
michael@0:  * |dataTotalLen| is >= |dataLen| and also accounts for any padding bytes
michael@0:  * that may follow the sender's MAC. (Only a single block of padding may
michael@0:  * follow in SSLv3, or up to 255 bytes in TLS.)
michael@0:  *
michael@0:  * Since the results of decryption are secret information (otherwise a
michael@0:  * padding-oracle is created), this function is constant-time with respect to
michael@0:  * |dataLen|.
michael@0:  *
michael@0:  * |header| contains either the 13-byte TLS header (containing the sequence
michael@0:  * number, record type etc), or it contains the SSLv3 header with the SSLv3
michael@0:  * padding bytes etc. */
michael@0: static SECStatus
michael@0: MAC(unsigned char *mdOut,
michael@0:     unsigned int *mdOutLen,
michael@0:     unsigned int mdOutMax,
michael@0:     const SECHashObject *hashObj,
michael@0:     const unsigned char *macSecret,
michael@0:     unsigned int macSecretLen,
michael@0:     const unsigned char *header,
michael@0:     unsigned int headerLen,
michael@0:     const unsigned char *data,
michael@0:     unsigned int dataLen,
michael@0:     unsigned int dataTotalLen,
michael@0:     unsigned char isSSLv3)
michael@0: {
michael@0:     void *mdState = hashObj->create();
michael@0:     const unsigned int mdSize = hashObj->length;
michael@0:     const unsigned int mdBlockSize = hashObj->blocklength;
michael@0:     /* mdLengthSize is the number of bytes in the length field that terminates
michael@0:      * the hash.
michael@0:      *
michael@0:      * This assumes that hash functions with a 64 byte block size use a 64-bit
michael@0:      * length, and otherwise they use a 128-bit length. This is true of {MD5,
michael@0:      * SHA*} (which are all of the hash functions specified for use with TLS
michael@0:      * today). */
michael@0:     const unsigned int mdLengthSize = mdBlockSize == 64 ? 8 : 16;
michael@0: 
michael@0:     const unsigned int sslv3PadLen = hashObj->type == HASH_AlgMD5 ? 48 : 40;
michael@0: 
michael@0:     /* varianceBlocks is the number of blocks of the hash that we have to
michael@0:      * calculate in constant time because they could be altered by the
michael@0:      * padding value.
michael@0:      *
michael@0:      * In SSLv3, the padding must be minimal so the end of the plaintext
michael@0:      * varies by, at most, 15+20 = 35 bytes. (We conservatively assume that
michael@0:      * the MAC size varies from 0..20 bytes.) In case the 9 bytes of hash
michael@0:      * termination (0x80 + 64-bit length) don't fit in the final block, we
michael@0:      * say that the final two blocks can vary based on the padding.
michael@0:      *
michael@0:      * TLSv1 has MACs up to 48 bytes long (SHA-384) and the padding is not
michael@0:      * required to be minimal. Therefore we say that the final six blocks
michael@0:      * can vary based on the padding.
michael@0:      *
michael@0:      * Later in the function, if the message is short and there obviously
michael@0:      * cannot be this many blocks then varianceBlocks can be reduced. */
michael@0:     unsigned int varianceBlocks = isSSLv3 ? 2 : 6;
michael@0:     /* From now on we're dealing with the MAC, which conceptually has 13
michael@0:      * bytes of `header' before the start of the data (TLS) or 71/75 bytes
michael@0:      * (SSLv3) */
michael@0:     const unsigned int len = dataTotalLen + headerLen;
michael@0:     /* maxMACBytes contains the maximum bytes of bytes in the MAC, including
michael@0:      * |header|, assuming that there's no padding. */
michael@0:     const unsigned int maxMACBytes = len - mdSize - 1;
michael@0:     /* numBlocks is the maximum number of hash blocks. */
michael@0:     const unsigned int numBlocks =
michael@0: 	(maxMACBytes + 1 + mdLengthSize + mdBlockSize - 1) / mdBlockSize;
michael@0:     /* macEndOffset is the index just past the end of the data to be
michael@0:      * MACed. */
michael@0:     const unsigned int macEndOffset = dataLen + headerLen - mdSize;
michael@0:     /* c is the index of the 0x80 byte in the final hash block that
michael@0:      * contains application data. */
michael@0:     const unsigned int c = macEndOffset % mdBlockSize;
michael@0:     /* indexA is the hash block number that contains the 0x80 terminating
michael@0:      * value. */
michael@0:     const unsigned int indexA = macEndOffset / mdBlockSize;
michael@0:     /* indexB is the hash block number that contains the 64-bit hash
michael@0:      * length, in bits. */
michael@0:     const unsigned int indexB = (macEndOffset + mdLengthSize) / mdBlockSize;
michael@0:     /* bits is the hash-length in bits. It includes the additional hash
michael@0:      * block for the masked HMAC key, or whole of |header| in the case of
michael@0:      * SSLv3. */
michael@0:     unsigned int bits;
michael@0:     /* In order to calculate the MAC in constant time we have to handle
michael@0:      * the final blocks specially because the padding value could cause the
michael@0:      * end to appear somewhere in the final |varianceBlocks| blocks and we
michael@0:      * can't leak where. However, |numStartingBlocks| worth of data can
michael@0:      * be hashed right away because no padding value can affect whether
michael@0:      * they are plaintext. */
michael@0:     unsigned int numStartingBlocks = 0;
michael@0:     /* k is the starting byte offset into the conceptual header||data where
michael@0:      * we start processing. */
michael@0:     unsigned int k = 0;
michael@0:     unsigned char lengthBytes[MAX_HASH_BIT_COUNT_BYTES];
michael@0:     /* hmacPad is the masked HMAC key. */
michael@0:     unsigned char hmacPad[HASH_BLOCK_LENGTH_MAX];
michael@0:     unsigned char firstBlock[HASH_BLOCK_LENGTH_MAX];
michael@0:     unsigned char macOut[HASH_LENGTH_MAX];
michael@0:     unsigned i, j;
michael@0: 
michael@0:     /* For SSLv3, if we're going to have any starting blocks then we need
michael@0:      * at least two because the header is larger than a single block. */
michael@0:     if (numBlocks > varianceBlocks + (isSSLv3 ? 1 : 0)) {
michael@0: 	numStartingBlocks = numBlocks - varianceBlocks;
michael@0: 	k = mdBlockSize*numStartingBlocks;
michael@0:     }
michael@0: 
michael@0:     bits = 8*macEndOffset;
michael@0:     hashObj->begin(mdState);
michael@0:     if (!isSSLv3) {
michael@0: 	/* Compute the initial HMAC block. For SSLv3, the padding and
michael@0: 	 * secret bytes are included in |header| because they take more
michael@0: 	 * than a single block. */
michael@0: 	bits += 8*mdBlockSize;
michael@0: 	memset(hmacPad, 0, mdBlockSize);
michael@0: 	PORT_Assert(macSecretLen <= sizeof(hmacPad));
michael@0: 	memcpy(hmacPad, macSecret, macSecretLen);
michael@0: 	for (i = 0; i < mdBlockSize; i++)
michael@0: 	    hmacPad[i] ^= 0x36;
michael@0: 	hashObj->update(mdState, hmacPad, mdBlockSize);
michael@0:     }
michael@0: 
michael@0:     j = 0;
michael@0:     memset(lengthBytes, 0, sizeof(lengthBytes));
michael@0:     if (mdLengthSize == 16) {
michael@0: 	j = 8;
michael@0:     }
michael@0:     if (hashObj->type == HASH_AlgMD5) {
michael@0: 	/* MD5 appends a little-endian length. */
michael@0: 	for (i = 0; i < 4; i++) {
michael@0: 	    lengthBytes[i+j] = bits >> (8*i);
michael@0: 	}
michael@0:     } else {
michael@0: 	/* All other TLS hash functions use a big-endian length. */
michael@0: 	for (i = 0; i < 4; i++) {
michael@0: 	    lengthBytes[4+i+j] = bits >> (8*(3-i));
michael@0: 	}
michael@0:     }
michael@0: 
michael@0:     if (k > 0) {
michael@0: 	if (isSSLv3) {
michael@0: 	    /* The SSLv3 header is larger than a single block.
michael@0: 	     * overhang is the number of bytes beyond a single
michael@0: 	     * block that the header consumes: either 7 bytes
michael@0: 	     * (SHA1) or 11 bytes (MD5). */
michael@0: 	    const unsigned int overhang = headerLen-mdBlockSize;
michael@0: 	    hashObj->update(mdState, header, mdBlockSize);
michael@0: 	    memcpy(firstBlock, header + mdBlockSize, overhang);
michael@0: 	    memcpy(firstBlock + overhang, data, mdBlockSize-overhang);
michael@0: 	    hashObj->update(mdState, firstBlock, mdBlockSize);
michael@0: 	    for (i = 1; i < k/mdBlockSize - 1; i++) {
michael@0: 		hashObj->update(mdState, data + mdBlockSize*i - overhang,
michael@0: 				mdBlockSize);
michael@0: 	    }
michael@0: 	} else {
michael@0: 	    /* k is a multiple of mdBlockSize. */
michael@0: 	    memcpy(firstBlock, header, 13);
michael@0: 	    memcpy(firstBlock+13, data, mdBlockSize-13);
michael@0: 	    hashObj->update(mdState, firstBlock, mdBlockSize);
michael@0: 	    for (i = 1; i < k/mdBlockSize; i++) {
michael@0: 		hashObj->update(mdState, data + mdBlockSize*i - 13,
michael@0: 				mdBlockSize);
michael@0: 	    }
michael@0: 	}
michael@0:     }
michael@0: 
michael@0:     memset(macOut, 0, sizeof(macOut));
michael@0: 
michael@0:     /* We now process the final hash blocks. For each block, we construct
michael@0:      * it in constant time. If i == indexA then we'll include the 0x80
michael@0:      * bytes and zero pad etc. For each block we selectively copy it, in
michael@0:      * constant time, to |macOut|. */
michael@0:     for (i = numStartingBlocks; i <= numStartingBlocks+varianceBlocks; i++) {
michael@0: 	unsigned char block[HASH_BLOCK_LENGTH_MAX];
michael@0: 	unsigned char isBlockA = constantTimeEQ8(i, indexA);
michael@0: 	unsigned char isBlockB = constantTimeEQ8(i, indexB);
michael@0: 	for (j = 0; j < mdBlockSize; j++) {
michael@0: 	    unsigned char isPastC = isBlockA & constantTimeGE(j, c);
michael@0: 	    unsigned char isPastCPlus1 = isBlockA & constantTimeGE(j, c+1);
michael@0: 	    unsigned char b = 0;
michael@0: 	    if (k < headerLen) {
michael@0: 		b = header[k];
michael@0: 	    } else if (k < dataTotalLen + headerLen) {
michael@0: 		b = data[k-headerLen];
michael@0: 	    }
michael@0: 	    k++;
michael@0: 
michael@0: 	    /* If this is the block containing the end of the
michael@0: 	     * application data, and we are at the offset for the
michael@0: 	     * 0x80 value, then overwrite b with 0x80. */
michael@0: 	    b = (b&~isPastC) | (0x80&isPastC);
michael@0: 	    /* If this the the block containing the end of the
michael@0: 	     * application data and we're past the 0x80 value then
michael@0: 	     * just write zero. */
michael@0: 	    b = b&~isPastCPlus1;
michael@0: 	    /* If this is indexB (the final block), but not
michael@0: 	     * indexA (the end of the data), then the 64-bit
michael@0: 	     * length didn't fit into indexA and we're having to
michael@0: 	     * add an extra block of zeros. */
michael@0: 	    b &= ~isBlockB | isBlockA;
michael@0: 
michael@0: 	    /* The final bytes of one of the blocks contains the length. */
michael@0: 	    if (j >= mdBlockSize - mdLengthSize) {
michael@0: 		/* If this is indexB, write a length byte. */
michael@0: 		b = (b&~isBlockB) |
michael@0: 		    (isBlockB&lengthBytes[j-(mdBlockSize-mdLengthSize)]);
michael@0: 	    }
michael@0: 	    block[j] = b;
michael@0: 	}
michael@0: 
michael@0: 	hashObj->update(mdState, block, mdBlockSize);
michael@0: 	hashObj->end_raw(mdState, block, NULL, mdSize);
michael@0: 	/* If this is indexB, copy the hash value to |macOut|. */
michael@0: 	for (j = 0; j < mdSize; j++) {
michael@0: 	    macOut[j] |= block[j]&isBlockB;
michael@0: 	}
michael@0:     }
michael@0: 
michael@0:     hashObj->begin(mdState);
michael@0: 
michael@0:     if (isSSLv3) {
michael@0: 	/* We repurpose |hmacPad| to contain the SSLv3 pad2 block. */
michael@0: 	for (i = 0; i < sslv3PadLen; i++)
michael@0: 	    hmacPad[i] = 0x5c;
michael@0: 
michael@0: 	hashObj->update(mdState, macSecret, macSecretLen);
michael@0: 	hashObj->update(mdState, hmacPad, sslv3PadLen);
michael@0: 	hashObj->update(mdState, macOut, mdSize);
michael@0:     } else {
michael@0: 	/* Complete the HMAC in the standard manner. */
michael@0: 	for (i = 0; i < mdBlockSize; i++)
michael@0: 	    hmacPad[i] ^= 0x6a;
michael@0: 
michael@0: 	hashObj->update(mdState, hmacPad, mdBlockSize);
michael@0: 	hashObj->update(mdState, macOut, mdSize);
michael@0:     }
michael@0: 
michael@0:     hashObj->end(mdState, mdOut, mdOutLen, mdOutMax);
michael@0:     hashObj->destroy(mdState, PR_TRUE);
michael@0: 
michael@0:     return SECSuccess;
michael@0: }
michael@0: 
michael@0: SECStatus
michael@0: HMAC_ConstantTime(
michael@0:     unsigned char *result,
michael@0:     unsigned int *resultLen,
michael@0:     unsigned int maxResultLen,
michael@0:     const SECHashObject *hashObj,
michael@0:     const unsigned char *secret,
michael@0:     unsigned int secretLen,
michael@0:     const unsigned char *header,
michael@0:     unsigned int headerLen,
michael@0:     const unsigned char *body,
michael@0:     unsigned int bodyLen,
michael@0:     unsigned int bodyTotalLen)
michael@0: {
michael@0:     if (hashObj->end_raw == NULL)
michael@0: 	return SECFailure;
michael@0:     return MAC(result, resultLen, maxResultLen, hashObj, secret, secretLen,
michael@0: 	       header, headerLen, body, bodyLen, bodyTotalLen,
michael@0: 	       0 /* not SSLv3 */);
michael@0: }
michael@0: 
michael@0: SECStatus
michael@0: SSLv3_MAC_ConstantTime(
michael@0:     unsigned char *result,
michael@0:     unsigned int *resultLen,
michael@0:     unsigned int maxResultLen,
michael@0:     const SECHashObject *hashObj,
michael@0:     const unsigned char *secret,
michael@0:     unsigned int secretLen,
michael@0:     const unsigned char *header,
michael@0:     unsigned int headerLen,
michael@0:     const unsigned char *body,
michael@0:     unsigned int bodyLen,
michael@0:     unsigned int bodyTotalLen)
michael@0: {
michael@0:     if (hashObj->end_raw == NULL)
michael@0: 	return SECFailure;
michael@0:     return MAC(result, resultLen, maxResultLen, hashObj, secret, secretLen,
michael@0: 	       header, headerLen, body, bodyLen, bodyTotalLen,
michael@0: 	       1 /* SSLv3 */);
michael@0: }
michael@0: