diff options
Diffstat (limited to 'libtomcrypt/src/encauth/ocb/s_ocb_done.c')
| -rw-r--r-- | libtomcrypt/src/encauth/ocb/s_ocb_done.c | 144 |
1 files changed, 144 insertions, 0 deletions
diff --git a/libtomcrypt/src/encauth/ocb/s_ocb_done.c b/libtomcrypt/src/encauth/ocb/s_ocb_done.c new file mode 100644 index 0000000..7399b54 --- /dev/null +++ b/libtomcrypt/src/encauth/ocb/s_ocb_done.c @@ -0,0 +1,144 @@ +/* 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. + * + * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.org + */ + +/** + @file s_ocb_done.c + OCB implementation, internal helper, by Tom St Denis +*/ +#include "tomcrypt.h" + +#ifdef OCB_MODE + +/* Since the last block is encrypted in CTR mode the same code can + * be used to finish a decrypt or encrypt stream. The only difference + * is we XOR the final ciphertext into the checksum so we have to xor it + * before we CTR [decrypt] or after [encrypt] + * + * the names pt/ptlen/ct really just mean in/inlen/out but this is the way I wrote it... + */ + +/** + Shared code to finish an OCB stream + @param ocb The OCB state + @param pt The remaining plaintext [or input] + @param ptlen The length of the input (octets) + @param ct [out] The output buffer + @param tag [out] The destination for the authentication tag + @param taglen [in/out] The max size and resulting size of the authentication tag + @param mode The mode we are terminating, 0==encrypt, 1==decrypt + @return CRYPT_OK if successful +*/ +int s_ocb_done(ocb_state *ocb, const unsigned char *pt, unsigned long ptlen, + unsigned char *ct, unsigned char *tag, unsigned long *taglen, int mode) + +{ + unsigned char *Z, *Y, *X; + int err, x; + + LTC_ARGCHK(ocb != NULL); + LTC_ARGCHK(pt != NULL); + LTC_ARGCHK(ct != NULL); + LTC_ARGCHK(tag != NULL); + LTC_ARGCHK(taglen != NULL); + if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) { + return err; + } + if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length || + (int)ptlen > ocb->block_len || (int)ptlen < 0) { + return CRYPT_INVALID_ARG; + } + + /* allocate ram */ + Z = XMALLOC(MAXBLOCKSIZE); + Y = XMALLOC(MAXBLOCKSIZE); + X = XMALLOC(MAXBLOCKSIZE); + if (X == NULL || Y == NULL || Z == NULL) { + if (X != NULL) { + XFREE(X); + } + if (Y != NULL) { + XFREE(Y); + } + if (Z != NULL) { + XFREE(Z); + } + return CRYPT_MEM; + } + + /* compute X[m] = len(pt[m]) XOR Lr XOR Z[m] */ + ocb_shift_xor(ocb, X); + XMEMCPY(Z, X, ocb->block_len); + + X[ocb->block_len-1] ^= (ptlen*8)&255; + X[ocb->block_len-2] ^= ((ptlen*8)>>8)&255; + for (x = 0; x < ocb->block_len; x++) { + X[x] ^= ocb->Lr[x]; + } + + /* Y[m] = E(X[m])) */ + cipher_descriptor[ocb->cipher].ecb_encrypt(X, Y, &ocb->key); + + if (mode == 1) { + /* decrypt mode, so let's xor it first */ + /* xor C[m] into checksum */ + for (x = 0; x < (int)ptlen; x++) { + ocb->checksum[x] ^= ct[x]; + } + } + + /* C[m] = P[m] xor Y[m] */ + for (x = 0; x < (int)ptlen; x++) { + ct[x] = pt[x] ^ Y[x]; + } + + if (mode == 0) { + /* encrypt mode */ + /* xor C[m] into checksum */ + for (x = 0; x < (int)ptlen; x++) { + ocb->checksum[x] ^= ct[x]; + } + } + + /* xor Y[m] and Z[m] into checksum */ + for (x = 0; x < ocb->block_len; x++) { + ocb->checksum[x] ^= Y[x] ^ Z[x]; + } + + /* encrypt checksum, er... tag!! */ + cipher_descriptor[ocb->cipher].ecb_encrypt(ocb->checksum, X, &ocb->key); + cipher_descriptor[ocb->cipher].done(&ocb->key); + + /* now store it */ + for (x = 0; x < ocb->block_len && x < (int)*taglen; x++) { + tag[x] = X[x]; + } + *taglen = x; + +#ifdef LTC_CLEAN_STACK + zeromem(X, MAXBLOCKSIZE); + zeromem(Y, MAXBLOCKSIZE); + zeromem(Z, MAXBLOCKSIZE); + zeromem(ocb, sizeof(*ocb)); +#endif + + XFREE(X); + XFREE(Y); + XFREE(Z); + + return CRYPT_OK; +} + +#endif + + +/* $Source: /cvs/libtom/libtomcrypt/src/encauth/ocb/s_ocb_done.c,v $ */ +/* $Revision: 1.4 $ */ +/* $Date: 2005/05/05 14:35:58 $ */ |