+++ /dev/null
-/* LibTomCrypt, modular cryptographic library -- Tom St Denis
- *
- * LibTomCrypt is a library that provides various cryptographic
- * algorithms in a highly modular and flexible manner.
- *
- * The library is free for all purposes without any express
- * guarantee it works.
- */
-#include "tomcrypt.h"
-
-/**
- Source donated by Elliptic Semiconductor Inc (www.ellipticsemi.com) to the LibTom Projects
- */
-
-#ifdef LTC_XTS_MODE
-
-static int _tweak_uncrypt(const unsigned char *C, unsigned char *P, unsigned char *T, symmetric_xts *xts)
-{
- unsigned long x;
- int err;
-
- /* tweak encrypt block i */
-#ifdef LTC_FAST
- for (x = 0; x < 16; x += sizeof(LTC_FAST_TYPE)) {
- *(LTC_FAST_TYPE_PTR_CAST(&P[x])) = *(LTC_FAST_TYPE_PTR_CAST(&C[x])) ^ *(LTC_FAST_TYPE_PTR_CAST(&T[x]));
- }
-#else
- for (x = 0; x < 16; x++) {
- P[x] = C[x] ^ T[x];
- }
-#endif
-
- err = cipher_descriptor[xts->cipher].ecb_decrypt(P, P, &xts->key1);
-
-#ifdef LTC_FAST
- for (x = 0; x < 16; x += sizeof(LTC_FAST_TYPE)) {
- *(LTC_FAST_TYPE_PTR_CAST(&P[x])) ^= *(LTC_FAST_TYPE_PTR_CAST(&T[x]));
- }
-#else
- for (x = 0; x < 16; x++) {
- P[x] = P[x] ^ T[x];
- }
-#endif
-
- /* LFSR the tweak */
- xts_mult_x(T);
-
- return err;
-}
-
-/** XTS Decryption
- @param ct [in] Ciphertext
- @param ptlen Length of plaintext (and ciphertext)
- @param pt [out] Plaintext
- @param tweak [in] The 128--bit encryption tweak (e.g. sector number)
- @param xts The XTS structure
- Returns CRYPT_OK upon success
- */
-int xts_decrypt(const unsigned char *ct, unsigned long ptlen, unsigned char *pt, unsigned char *tweak,
- symmetric_xts *xts)
-{
- unsigned char PP[16], CC[16], T[16];
- unsigned long i, m, mo, lim;
- int err;
-
- /* check inputs */
- LTC_ARGCHK(pt != NULL);
- LTC_ARGCHK(ct != NULL);
- LTC_ARGCHK(tweak != NULL);
- LTC_ARGCHK(xts != NULL);
-
- /* check if valid */
- if ((err = cipher_is_valid(xts->cipher)) != CRYPT_OK) {
- return err;
- }
-
- /* get number of blocks */
- m = ptlen >> 4;
- mo = ptlen & 15;
-
- /* must have at least one full block */
- if (m == 0) {
- return CRYPT_INVALID_ARG;
- }
-
- if (mo == 0) {
- lim = m;
- } else {
- lim = m - 1;
- }
-
- if (cipher_descriptor[xts->cipher].accel_xts_decrypt && lim > 0) {
-
- /* use accelerated decryption for whole blocks */
- if ((err = cipher_descriptor[xts->cipher].accel_xts_decrypt(ct, pt, lim, tweak, &xts->key1, &xts->key2)) !=
- CRYPT_OK) {
- return err;
- }
- ct += lim * 16;
- pt += lim * 16;
-
- /* tweak is encrypted on output */
- XMEMCPY(T, tweak, sizeof(T));
- } else {
- /* encrypt the tweak */
- if ((err = cipher_descriptor[xts->cipher].ecb_encrypt(tweak, T, &xts->key2)) != CRYPT_OK) {
- return err;
- }
-
- for (i = 0; i < lim; i++) {
- if ((err = _tweak_uncrypt(ct, pt, T, xts)) != CRYPT_OK) {
- return err;
- }
- ct += 16;
- pt += 16;
- }
- }
-
- /* if ptlen not divide 16 then */
- if (mo > 0) {
- XMEMCPY(CC, T, 16);
- xts_mult_x(CC);
-
- /* PP = tweak decrypt block m-1 */
- if ((err = _tweak_uncrypt(ct, PP, CC, xts)) != CRYPT_OK) {
- return err;
- }
-
- /* Pm = first ptlen % 16 bytes of PP */
- for (i = 0; i < mo; i++) {
- CC[i] = ct[16 + i];
- pt[16 + i] = PP[i];
- }
- for (; i < 16; i++) {
- CC[i] = PP[i];
- }
-
- /* Pm-1 = Tweak uncrypt CC */
- if ((err = _tweak_uncrypt(CC, pt, T, xts)) != CRYPT_OK) {
- return err;
- }
- }
-
- /* Decrypt the tweak back */
- if ((err = cipher_descriptor[xts->cipher].ecb_decrypt(T, tweak, &xts->key2)) != CRYPT_OK) {
- return err;
- }
-
- return CRYPT_OK;
-}
-
-#endif
-
-/* ref: $Format:%D$ */
-/* git commit: $Format:%H$ */
-/* commit time: $Format:%ai$ */