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 gcm_process.c
14   GCM implementation, process message data, by Tom St Denis
15*/
16#include "tomcrypt.h"
17
18#ifdef GCM_MODE
19
20/**
21  Process plaintext/ciphertext through GCM
22  @param gcm       The GCM state
23  @param pt        The plaintext
24  @param ptlen     The plaintext length (ciphertext length is the same)
25  @param ct        The ciphertext
26  @param direction Encrypt or Decrypt mode (GCM_ENCRYPT or GCM_DECRYPT)
27  @return CRYPT_OK on success
28 */
29int gcm_process(gcm_state *gcm,
30                     unsigned char *pt,     unsigned long ptlen,
31                     unsigned char *ct,
32                     int direction)
33{
34   unsigned long x;
35   int           y, err;
36   unsigned char b;
37
38   LTC_ARGCHK(gcm != NULL);
39   if (ptlen > 0) {
40      LTC_ARGCHK(pt  != NULL);
41      LTC_ARGCHK(ct  != NULL);
42   }
43
44   if (gcm->buflen > 16 || gcm->buflen < 0) {
45      return CRYPT_INVALID_ARG;
46   }
47
48   if ((err = cipher_is_valid(gcm->cipher)) != CRYPT_OK) {
49      return err;
50   }
51
52   /* in AAD mode? */
53   if (gcm->mode == GCM_MODE_AAD) {
54      /* let's process the AAD */
55      if (gcm->buflen) {
56         gcm->totlen += gcm->buflen * CONST64(8);
57         gcm_mult_h(gcm, gcm->X);
58      }
59
60      /* increment counter */
61      for (y = 15; y >= 12; y--) {
62          if (++gcm->Y[y] & 255) { break; }
63      }
64      /* encrypt the counter */
65      if ((err = cipher_descriptor[gcm->cipher].ecb_encrypt(gcm->Y, gcm->buf, &gcm->K)) != CRYPT_OK) {
66         return err;
67      }
68
69      gcm->buflen = 0;
70      gcm->mode   = GCM_MODE_TEXT;
71   }
72
73   if (gcm->mode != GCM_MODE_TEXT) {
74      return CRYPT_INVALID_ARG;
75   }
76
77   x = 0;
78#ifdef LTC_FAST
79   if (gcm->buflen == 0) {
80      if (direction == GCM_ENCRYPT) {
81         for (x = 0; x < (ptlen & ~15); x += 16) {
82             /* ctr encrypt */
83             for (y = 0; y < 16; y += sizeof(LTC_FAST_TYPE)) {
84                 *((LTC_FAST_TYPE*)(&ct[x + y])) = *((LTC_FAST_TYPE*)(&pt[x+y])) ^ *((LTC_FAST_TYPE*)(&gcm->buf[y]));
85                 *((LTC_FAST_TYPE*)(&gcm->X[y])) ^= *((LTC_FAST_TYPE*)(&ct[x+y]));
86             }
87             /* GMAC it */
88             gcm->pttotlen += 128;
89             gcm_mult_h(gcm, gcm->X);
90             /* increment counter */
91             for (y = 15; y >= 12; y--) {
92                 if (++gcm->Y[y] & 255) { break; }
93             }
94             if ((err = cipher_descriptor[gcm->cipher].ecb_encrypt(gcm->Y, gcm->buf, &gcm->K)) != CRYPT_OK) {
95                return err;
96             }
97         }
98      } else {
99         for (x = 0; x < (ptlen & ~15); x += 16) {
100             /* ctr encrypt */
101             for (y = 0; y < 16; y += sizeof(LTC_FAST_TYPE)) {
102                 *((LTC_FAST_TYPE*)(&gcm->X[y])) ^= *((LTC_FAST_TYPE*)(&ct[x+y]));
103                 *((LTC_FAST_TYPE*)(&pt[x + y])) = *((LTC_FAST_TYPE*)(&ct[x+y])) ^ *((LTC_FAST_TYPE*)(&gcm->buf[y]));
104             }
105             /* GMAC it */
106             gcm->pttotlen += 128;
107             gcm_mult_h(gcm, gcm->X);
108             /* increment counter */
109             for (y = 15; y >= 12; y--) {
110                 if (++gcm->Y[y] & 255) { break; }
111             }
112             if ((err = cipher_descriptor[gcm->cipher].ecb_encrypt(gcm->Y, gcm->buf, &gcm->K)) != CRYPT_OK) {
113                return err;
114             }
115         }
116     }
117   }
118#endif
119
120   /* process text */
121   for (; x < ptlen; x++) {
122       if (gcm->buflen == 16) {
123          gcm->pttotlen += 128;
124          gcm_mult_h(gcm, gcm->X);
125
126          /* increment counter */
127          for (y = 15; y >= 12; y--) {
128              if (++gcm->Y[y] & 255) { break; }
129          }
130          if ((err = cipher_descriptor[gcm->cipher].ecb_encrypt(gcm->Y, gcm->buf, &gcm->K)) != CRYPT_OK) {
131             return err;
132          }
133          gcm->buflen = 0;
134       }
135
136       if (direction == GCM_ENCRYPT) {
137          b = ct[x] = pt[x] ^ gcm->buf[gcm->buflen];
138       } else {
139          b = ct[x];
140          pt[x] = ct[x] ^ gcm->buf[gcm->buflen];
141       }
142       gcm->X[gcm->buflen++] ^= b;
143   }
144
145   return CRYPT_OK;
146}
147
148#endif
149
150/* $Source: /cvs/libtom/libtomcrypt/src/encauth/gcm/gcm_process.c,v $ */
151/* $Revision: 1.14 $ */
152/* $Date: 2006/11/19 19:33:36 $ */
153