1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
|
/* 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.
*/
/**
@file ocb3_init.c
OCB implementation, initialize state, by Tom St Denis
*/
#include "tomcrypt.h"
#ifdef LTC_OCB3_MODE
static void _ocb3_int_calc_offset_zero(ocb3_state *ocb, const unsigned char *nonce, unsigned long noncelen, unsigned long taglen)
{
int x, y, bottom;
int idx, shift;
unsigned char iNonce[MAXBLOCKSIZE];
unsigned char iKtop[MAXBLOCKSIZE];
unsigned char iStretch[MAXBLOCKSIZE+8];
/* Nonce = zeros(127-bitlen(N)) || 1 || N */
zeromem(iNonce, sizeof(iNonce));
for (x = ocb->block_len-1, y=0; y<(int)noncelen; x--, y++) {
iNonce[x] = nonce[noncelen-y-1];
}
iNonce[x] = 0x01;
iNonce[0] |= ((taglen*8) % 128) << 1;
/* bottom = str2num(Nonce[123..128]) */
bottom = iNonce[ocb->block_len-1] & 0x3F;
/* Ktop = ENCIPHER(K, Nonce[1..122] || zeros(6)) */
iNonce[ocb->block_len-1] = iNonce[ocb->block_len-1] & 0xC0;
if ((cipher_descriptor[ocb->cipher].ecb_encrypt(iNonce, iKtop, &ocb->key)) != CRYPT_OK) {
zeromem(ocb->Offset_current, ocb->block_len);
return;
}
/* Stretch = Ktop || (Ktop[1..64] xor Ktop[9..72]) */
for (x = 0; x < ocb->block_len; x++) {
iStretch[x] = iKtop[x];
}
for (y = 0; y < 8; y++) {
iStretch[x+y] = iKtop[y] ^ iKtop[y+1];
}
/* Offset_0 = Stretch[1+bottom..128+bottom] */
idx = bottom / 8;
shift = (bottom % 8);
for (x = 0; x < ocb->block_len; x++) {
ocb->Offset_current[x] = iStretch[idx+x] << shift;
if (shift > 0) {
ocb->Offset_current[x] |= iStretch[idx+x+1] >> (8-shift);
}
}
}
static const struct {
int len;
unsigned char poly_mul[MAXBLOCKSIZE];
} polys[] = {
{
8,
{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x1B }
}, {
16,
{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x87 }
}
};
/**
Initialize an OCB context
@param ocb [out] The destination of the OCB state
@param cipher The index of the desired cipher
@param key The secret key
@param keylen The length of the secret key (octets)
@param nonce The session nonce
@param noncelen The length of the session nonce (octets, up to 15)
@param taglen The length of the tag (octets, up to 16)
@return CRYPT_OK if successful
*/
int ocb3_init(ocb3_state *ocb, int cipher,
const unsigned char *key, unsigned long keylen,
const unsigned char *nonce, unsigned long noncelen,
unsigned long taglen)
{
int poly, x, y, m, err;
unsigned char *previous, *current;
LTC_ARGCHK(ocb != NULL);
LTC_ARGCHK(key != NULL);
LTC_ARGCHK(nonce != NULL);
/* valid cipher? */
if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
return err;
}
ocb->cipher = cipher;
/* Valid Nonce?
* As of RFC7253: "string of no more than 120 bits" */
if (noncelen > (120/8)) {
return CRYPT_INVALID_ARG;
}
/* The blockcipher must have a 128-bit blocksize */
if (cipher_descriptor[cipher].block_length != 16) {
return CRYPT_INVALID_ARG;
}
/* The TAGLEN may be any value up to 128 (bits) */
if (taglen > 16) {
return CRYPT_INVALID_ARG;
}
ocb->tag_len = taglen;
/* determine which polys to use */
ocb->block_len = cipher_descriptor[cipher].block_length;
x = (int)(sizeof(polys)/sizeof(polys[0]));
for (poly = 0; poly < x; poly++) {
if (polys[poly].len == ocb->block_len) {
break;
}
}
if (poly == x) {
return CRYPT_INVALID_ARG; /* block_len not found in polys */
}
if (polys[poly].len != ocb->block_len) {
return CRYPT_INVALID_ARG;
}
/* schedule the key */
if ((err = cipher_descriptor[cipher].setup(key, keylen, 0, &ocb->key)) != CRYPT_OK) {
return err;
}
/* L_* = ENCIPHER(K, zeros(128)) */
zeromem(ocb->L_star, ocb->block_len);
if ((err = cipher_descriptor[cipher].ecb_encrypt(ocb->L_star, ocb->L_star, &ocb->key)) != CRYPT_OK) {
return err;
}
/* compute L_$, L_0, L_1, ... */
for (x = -1; x < 32; x++) {
if (x == -1) { /* gonna compute: L_$ = double(L_*) */
current = ocb->L_dollar;
previous = ocb->L_star;
}
else if (x == 0) { /* gonna compute: L_0 = double(L_$) */
current = ocb->L_[0];
previous = ocb->L_dollar;
}
else { /* gonna compute: L_i = double(L_{i-1}) for every integer i > 0 */
current = ocb->L_[x];
previous = ocb->L_[x-1];
}
m = previous[0] >> 7;
for (y = 0; y < ocb->block_len-1; y++) {
current[y] = ((previous[y] << 1) | (previous[y+1] >> 7)) & 255;
}
current[ocb->block_len-1] = (previous[ocb->block_len-1] << 1) & 255;
if (m == 1) {
/* current[] = current[] XOR polys[poly].poly_mul[]*/
ocb3_int_xor_blocks(current, current, polys[poly].poly_mul, ocb->block_len);
}
}
/* initialize ocb->Offset_current = Offset_0 */
_ocb3_int_calc_offset_zero(ocb, nonce, noncelen, taglen);
/* initialize checksum to all zeros */
zeromem(ocb->checksum, ocb->block_len);
/* set block index */
ocb->block_index = 1;
/* initialize AAD related stuff */
ocb->ablock_index = 1;
ocb->adata_buffer_bytes = 0;
zeromem(ocb->aOffset_current, ocb->block_len);
zeromem(ocb->aSum_current, ocb->block_len);
return CRYPT_OK;
}
#endif
/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */
|
