Merge branch 'fix/ccm_constant_time' into develop
This closes #73 and closes #76
This commit is contained in:
Steffen Jaeckel
commit
eb26b7efd4
@ -20,7 +20,7 @@
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/**
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CCM encrypt/decrypt and produce an authentication tag
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*1 'pt' and 'ct' can both be 'in' or 'out', depending on 'direction'
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*1 'pt', 'ct' and 'tag' can both be 'in' or 'out', depending on 'direction'
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@param cipher The index of the cipher desired
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@param key The secret key to use
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@ -33,8 +33,8 @@
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@param pt [*1] The plaintext
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@param ptlen The length of the plaintext (octets)
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@param ct [*1] The ciphertext
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@param tag [out] The destination tag
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@param taglen [in/out] The max size and resulting size of the authentication tag
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@param tag [*1] The destination tag
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@param taglen The max size and resulting size of the authentication tag
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@param direction Encrypt or Decrypt direction (0 or 1)
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@return CRYPT_OK if successful
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*/
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@ -48,10 +48,15 @@ int ccm_memory(int cipher,
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unsigned char *tag, unsigned long *taglen,
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int direction)
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{
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unsigned char PAD[16], ctr[16], CTRPAD[16], b;
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unsigned char PAD[16], ctr[16], CTRPAD[16], ptTag[16], b, *pt_real;
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unsigned char *pt_work = NULL;
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symmetric_key *skey;
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int err;
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unsigned long len, L, x, y, z, CTRlen;
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#ifdef LTC_FAST
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LTC_FAST_TYPE fastMask = -1; /* initialize fastMask at all zeroes */
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#endif
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unsigned char mask = 0xff; /* initialize mask at all zeroes */
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if (uskey == NULL) {
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LTC_ARGCHK(key != NULL);
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@ -65,6 +70,8 @@ int ccm_memory(int cipher,
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LTC_ARGCHK(tag != NULL);
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LTC_ARGCHK(taglen != NULL);
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pt_real = pt;
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#ifdef LTC_FAST
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if (16 % sizeof(LTC_FAST_TYPE)) {
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return CRYPT_INVALID_ARG;
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@ -140,6 +147,15 @@ int ccm_memory(int cipher,
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} else {
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skey = uskey;
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}
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/* initialize buffer for pt */
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if (direction == CCM_DECRYPT) {
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pt_work = XMALLOC(ptlen);
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if (pt_work == NULL) {
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goto error;
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}
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pt = pt_work;
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}
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/* form B_0 == flags | Nonce N | l(m) */
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x = 0;
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@ -203,11 +219,9 @@ int ccm_memory(int cipher,
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PAD[x++] ^= header[y];
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}
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/* remainder? */
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if (x != 0) {
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if ((err = cipher_descriptor[cipher].ecb_encrypt(PAD, PAD, skey)) != CRYPT_OK) {
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goto error;
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}
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/* remainder */
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if ((err = cipher_descriptor[cipher].ecb_encrypt(PAD, PAD, skey)) != CRYPT_OK) {
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goto error;
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}
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}
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@ -254,7 +268,7 @@ int ccm_memory(int cipher,
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goto error;
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}
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}
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} else {
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} else { /* direction == CCM_DECRYPT */
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for (; y < (ptlen & ~15); y += 16) {
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/* increment the ctr? */
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for (z = 15; z > 15-L; z--) {
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@ -328,18 +342,60 @@ int ccm_memory(int cipher,
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cipher_descriptor[cipher].done(skey);
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}
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/* store the TAG */
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for (x = 0; x < 16 && x < *taglen; x++) {
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tag[x] = PAD[x] ^ CTRPAD[x];
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if (direction == CCM_ENCRYPT) {
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/* store the TAG */
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for (x = 0; x < 16 && x < *taglen; x++) {
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tag[x] = PAD[x] ^ CTRPAD[x];
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}
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*taglen = x;
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} else { /* direction == CCM_DECRYPT */
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/* decrypt the tag */
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for (x = 0; x < 16 && x < *taglen; x++) {
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ptTag[x] = tag[x] ^ CTRPAD[x];
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}
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*taglen = x;
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/* check validity of the decrypted tag against the computed PAD (in constant time) */
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/* HACK: the boolean value of XMEM_NEQ becomes either 0 (CRYPT_OK) or 1 (CRYPT_ERR).
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* there should be a better way of setting the correct error code in constant
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* time.
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*/
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err = XMEM_NEQ(ptTag, PAD, *taglen);
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/* Zero the plaintext if the tag was invalid (in constant time) */
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if (ptlen > 0) {
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y = 0;
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mask *= 1 - err; /* mask = ( err ? 0 : 0xff ) */
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#ifdef LTC_FAST
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fastMask *= 1 - err;
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if (ptlen & ~15) {
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for (; y < (ptlen & ~15); y += 16) {
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for (z = 0; z < 16; z += sizeof(LTC_FAST_TYPE)) {
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*((LTC_FAST_TYPE*)(&pt_real[y+z])) = *((LTC_FAST_TYPE*)(&pt[y+z])) & fastMask;
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}
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}
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}
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#endif
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for (; y < ptlen; y++) {
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pt_real[y] = pt[y] & mask;
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}
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}
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}
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*taglen = x;
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#ifdef LTC_CLEAN_STACK
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fastMask = 0;
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mask = 0;
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zeromem(skey, sizeof(*skey));
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zeromem(PAD, sizeof(PAD));
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zeromem(CTRPAD, sizeof(CTRPAD));
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if (pt_work != NULL) {
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zeromem(pt_work, ptlen);
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}
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#endif
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error:
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if (pt_work) {
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XFREE(pt_work);
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}
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if (skey != uskey) {
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XFREE(skey);
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}
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@ -114,10 +114,12 @@ int ccm_test(void)
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};
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unsigned long taglen, x, y;
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unsigned char buf[64], buf2[64], tag2[16], tag[16];
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unsigned char buf[64], buf2[64], tag[16], tag2[16], tag3[16], zero[64];
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int err, idx;
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symmetric_key skey;
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ccm_state ccm;
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zeromem(zero, 64);
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idx = find_cipher("aes");
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if (idx == -1) {
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@ -166,8 +168,8 @@ int ccm_test(void)
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if (XMEMCMP(buf, tests[x].ct, tests[x].ptlen)) {
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#if defined(LTC_TEST_DBG)
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printf("\n%d: x=%lu y=%lu\n", __LINE__, x, y);
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print_hex("ct is ", tag, taglen);
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print_hex("ct should", tests[x].tag, taglen);
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print_hex("ct is ", buf, tests[x].ptlen);
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print_hex("ct should", tests[x].ct, tests[x].ptlen);
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#endif
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return CRYPT_FAIL_TESTVECTOR;
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}
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@ -188,14 +190,16 @@ int ccm_test(void)
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}
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if (y == 0) {
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if ((err = ccm_memory(idx,
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XMEMCPY(tag3, tests[x].tag, tests[x].taglen);
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taglen = tests[x].taglen;
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if ((err = ccm_memory(idx,
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tests[x].key, 16,
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NULL,
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tests[x].nonce, tests[x].noncelen,
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tests[x].header, tests[x].headerlen,
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buf2, tests[x].ptlen,
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buf,
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tag2, &taglen, 1 )) != CRYPT_OK) {
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tag3, &taglen, 1 )) != CRYPT_OK) {
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return err;
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}
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} else {
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@ -219,24 +223,56 @@ int ccm_test(void)
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if (XMEMCMP(buf2, tests[x].pt, tests[x].ptlen)) {
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#if defined(LTC_TEST_DBG)
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printf("\n%d: x=%lu y=%lu\n", __LINE__, x, y);
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print_hex("pt is ", tag, taglen);
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print_hex("pt should", tests[x].tag, taglen);
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print_hex("pt is ", buf2, tests[x].ptlen);
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print_hex("pt should", tests[x].pt, tests[x].ptlen);
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#endif
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return CRYPT_FAIL_TESTVECTOR;
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}
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if (XMEMCMP(tag2, tests[x].tag, tests[x].taglen)) {
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if (y == 0) {
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/* check if decryption with the wrong tag does not reveal the plaintext */
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XMEMCPY(tag3, tests[x].tag, tests[x].taglen);
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tag3[0] ^= 0xff; /* set the tag to the wrong value */
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taglen = tests[x].taglen;
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if ((err = ccm_memory(idx,
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tests[x].key, 16,
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NULL,
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tests[x].nonce, tests[x].noncelen,
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tests[x].header, tests[x].headerlen,
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buf2, tests[x].ptlen,
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buf,
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tag3, &taglen, 1 )) != CRYPT_ERROR) {
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return CRYPT_FAIL_TESTVECTOR;
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}
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if (XMEMCMP(buf2, zero, tests[x].ptlen)) {
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#if defined(LTC_CCM_TEST_DBG)
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printf("\n%d: x=%lu y=%lu\n", __LINE__, x, y);
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print_hex("pt is ", buf2, tests[x].ptlen);
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print_hex("pt should", zero, tests[x].ptlen);
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#endif
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return CRYPT_FAIL_TESTVECTOR;
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}
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} else {
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/* FIXME: Only check the tag if ccm_memory was not called: ccm_memory already
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validates the tag. ccm_process and ccm_done should somehow do the same,
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although with current setup it is impossible to keep the plaintext hidden
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if the tag is incorrect.
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*/
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if (XMEMCMP(tag2, tests[x].tag, tests[x].taglen)) {
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#if defined(LTC_TEST_DBG)
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printf("\n%d: x=%lu y=%lu\n", __LINE__, x, y);
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print_hex("tag is ", tag, tests[x].taglen);
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print_hex("tag should", tests[x].tag, tests[x].taglen);
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printf("\n%d: x=%lu y=%lu\n", __LINE__, x, y);
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print_hex("tag is ", tag2, tests[x].taglen);
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print_hex("tag should", tests[x].tag, tests[x].taglen);
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#endif
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return CRYPT_FAIL_TESTVECTOR;
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return CRYPT_FAIL_TESTVECTOR;
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}
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}
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if (y == 0) {
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cipher_descriptor[idx].done(&skey);
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}
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}
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}
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return CRYPT_OK;
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#endif
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}
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