diff options
Diffstat (limited to 'security/nss/lib/freebl/hmacct.c')
| -rw-r--r-- | security/nss/lib/freebl/hmacct.c | 335 |
1 files changed, 335 insertions, 0 deletions
diff --git a/security/nss/lib/freebl/hmacct.c b/security/nss/lib/freebl/hmacct.c new file mode 100644 index 000000000..c7815ac05 --- /dev/null +++ b/security/nss/lib/freebl/hmacct.c @@ -0,0 +1,335 @@ +/* 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, + 0 /* 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, + 1 /* SSLv3 */); +} |