Update to NSS 3.14.3 Beta 1 for the TLS CBC constant-time

mozilla/security/nss/lib/freebl/hmacct.c

+/* 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 */);
+}
+