1/* LibTomCrypt, modular cryptographic library -- Tom St Denis
2 *
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
5 *
6 * The library is free for all purposes without any express
7 * guarantee it works.
8 *
9 * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
10 */
11
12/**
13   @file s_ocb_done.c
14   OCB implementation, internal helper, by Tom St Denis
15*/
16#include "tomcrypt.h"
17
18#ifdef OCB_MODE
19
20/* Since the last block is encrypted in CTR mode the same code can
21 * be used to finish a decrypt or encrypt stream.  The only difference
22 * is we XOR the final ciphertext into the checksum so we have to xor it
23 * before we CTR [decrypt] or after [encrypt]
24 *
25 * the names pt/ptlen/ct really just mean in/inlen/out but this is the way I wrote it...
26 */
27
28/**
29   Shared code to finish an OCB stream
30   @param ocb    The OCB state
31   @param pt     The remaining plaintext [or input]
32   @param ptlen  The length of the input (octets)
33   @param ct     [out] The output buffer
34   @param tag    [out] The destination for the authentication tag
35   @param taglen [in/out] The max size and resulting size of the authentication tag
36   @param mode   The mode we are terminating, 0==encrypt, 1==decrypt
37   @return       CRYPT_OK if successful
38*/
39int s_ocb_done(ocb_state *ocb, const unsigned char *pt, unsigned long ptlen,
40               unsigned char *ct, unsigned char *tag, unsigned long *taglen, int mode)
41
42{
43   unsigned char *Z, *Y, *X;
44   int err, x;
45
46   LTC_ARGCHK(ocb    != NULL);
47   LTC_ARGCHK(pt     != NULL);
48   LTC_ARGCHK(ct     != NULL);
49   LTC_ARGCHK(tag    != NULL);
50   LTC_ARGCHK(taglen != NULL);
51   if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
52      return err;
53   }
54   if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length ||
55       (int)ptlen > ocb->block_len || (int)ptlen < 0) {
56      return CRYPT_INVALID_ARG;
57   }
58
59   /* allocate ram */
60   Z = XMALLOC(MAXBLOCKSIZE);
61   Y = XMALLOC(MAXBLOCKSIZE);
62   X = XMALLOC(MAXBLOCKSIZE);
63   if (X == NULL || Y == NULL || Z == NULL) {
64      if (X != NULL) {
65         XFREE(X);
66      }
67      if (Y != NULL) {
68         XFREE(Y);
69      }
70      if (Z != NULL) {
71         XFREE(Z);
72      }
73      return CRYPT_MEM;
74   }
75
76   /* compute X[m] = len(pt[m]) XOR Lr XOR Z[m] */
77   ocb_shift_xor(ocb, X);
78   XMEMCPY(Z, X, ocb->block_len);
79
80   X[ocb->block_len-1] ^= (ptlen*8)&255;
81   X[ocb->block_len-2] ^= ((ptlen*8)>>8)&255;
82   for (x = 0; x < ocb->block_len; x++) {
83       X[x] ^= ocb->Lr[x];
84   }
85
86   /* Y[m] = E(X[m])) */
87   if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(X, Y, &ocb->key)) != CRYPT_OK) {
88      goto error;
89   }
90
91   if (mode == 1) {
92      /* decrypt mode, so let's xor it first */
93      /* xor C[m] into checksum */
94      for (x = 0; x < (int)ptlen; x++) {
95         ocb->checksum[x] ^= ct[x];
96      }
97   }
98
99   /* C[m] = P[m] xor Y[m] */
100   for (x = 0; x < (int)ptlen; x++) {
101       ct[x] = pt[x] ^ Y[x];
102   }
103
104   if (mode == 0) {
105      /* encrypt mode */
106      /* xor C[m] into checksum */
107      for (x = 0; x < (int)ptlen; x++) {
108          ocb->checksum[x] ^= ct[x];
109      }
110   }
111
112   /* xor Y[m] and Z[m] into checksum */
113   for (x = 0; x < ocb->block_len; x++) {
114       ocb->checksum[x] ^= Y[x] ^ Z[x];
115   }
116
117   /* encrypt checksum, er... tag!! */
118   if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(ocb->checksum, X, &ocb->key)) != CRYPT_OK) {
119      goto error;
120   }
121   cipher_descriptor[ocb->cipher].done(&ocb->key);
122
123   /* now store it */
124   for (x = 0; x < ocb->block_len && x < (int)*taglen; x++) {
125       tag[x] = X[x];
126   }
127   *taglen = x;
128
129#ifdef LTC_CLEAN_STACK
130   zeromem(X, MAXBLOCKSIZE);
131   zeromem(Y, MAXBLOCKSIZE);
132   zeromem(Z, MAXBLOCKSIZE);
133   zeromem(ocb, sizeof(*ocb));
134#endif
135error:
136   XFREE(X);
137   XFREE(Y);
138   XFREE(Z);
139
140   return err;
141}
142
143#endif
144
145
146/* $Source: /cvs/libtom/libtomcrypt/src/encauth/ocb/s_ocb_done.c,v $ */
147/* $Revision: 1.6 $ */
148/* $Date: 2006/03/31 14:15:35 $ */
149