1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis */
2 /* SPDX-License-Identifier: Unlicense */
3
4 /**
5 @file skipjack.c
6 Skipjack Implementation by Tom St Denis
7 */
8 #include "tomcrypt_private.h"
9
10 #ifdef LTC_SKIPJACK
11
12 const struct ltc_cipher_descriptor skipjack_desc =
13 {
14 "skipjack",
15 17,
16 10, 10, 8, 32,
17 &skipjack_setup,
18 &skipjack_ecb_encrypt,
19 &skipjack_ecb_decrypt,
20 &skipjack_test,
21 &skipjack_done,
22 &skipjack_keysize,
23 NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL
24 };
25
26 static const unsigned char sbox[256] = {
27 0xa3,0xd7,0x09,0x83,0xf8,0x48,0xf6,0xf4,0xb3,0x21,0x15,0x78,0x99,0xb1,0xaf,0xf9,
28 0xe7,0x2d,0x4d,0x8a,0xce,0x4c,0xca,0x2e,0x52,0x95,0xd9,0x1e,0x4e,0x38,0x44,0x28,
29 0x0a,0xdf,0x02,0xa0,0x17,0xf1,0x60,0x68,0x12,0xb7,0x7a,0xc3,0xe9,0xfa,0x3d,0x53,
30 0x96,0x84,0x6b,0xba,0xf2,0x63,0x9a,0x19,0x7c,0xae,0xe5,0xf5,0xf7,0x16,0x6a,0xa2,
31 0x39,0xb6,0x7b,0x0f,0xc1,0x93,0x81,0x1b,0xee,0xb4,0x1a,0xea,0xd0,0x91,0x2f,0xb8,
32 0x55,0xb9,0xda,0x85,0x3f,0x41,0xbf,0xe0,0x5a,0x58,0x80,0x5f,0x66,0x0b,0xd8,0x90,
33 0x35,0xd5,0xc0,0xa7,0x33,0x06,0x65,0x69,0x45,0x00,0x94,0x56,0x6d,0x98,0x9b,0x76,
34 0x97,0xfc,0xb2,0xc2,0xb0,0xfe,0xdb,0x20,0xe1,0xeb,0xd6,0xe4,0xdd,0x47,0x4a,0x1d,
35 0x42,0xed,0x9e,0x6e,0x49,0x3c,0xcd,0x43,0x27,0xd2,0x07,0xd4,0xde,0xc7,0x67,0x18,
36 0x89,0xcb,0x30,0x1f,0x8d,0xc6,0x8f,0xaa,0xc8,0x74,0xdc,0xc9,0x5d,0x5c,0x31,0xa4,
37 0x70,0x88,0x61,0x2c,0x9f,0x0d,0x2b,0x87,0x50,0x82,0x54,0x64,0x26,0x7d,0x03,0x40,
38 0x34,0x4b,0x1c,0x73,0xd1,0xc4,0xfd,0x3b,0xcc,0xfb,0x7f,0xab,0xe6,0x3e,0x5b,0xa5,
39 0xad,0x04,0x23,0x9c,0x14,0x51,0x22,0xf0,0x29,0x79,0x71,0x7e,0xff,0x8c,0x0e,0xe2,
40 0x0c,0xef,0xbc,0x72,0x75,0x6f,0x37,0xa1,0xec,0xd3,0x8e,0x62,0x8b,0x86,0x10,0xe8,
41 0x08,0x77,0x11,0xbe,0x92,0x4f,0x24,0xc5,0x32,0x36,0x9d,0xcf,0xf3,0xa6,0xbb,0xac,
42 0x5e,0x6c,0xa9,0x13,0x57,0x25,0xb5,0xe3,0xbd,0xa8,0x3a,0x01,0x05,0x59,0x2a,0x46
43 };
44
45 /* simple x + 1 (mod 10) in one step. */
46 static const int keystep[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
47
48 /* simple x - 1 (mod 10) in one step */
49 static const int ikeystep[] = { 9, 0, 1, 2, 3, 4, 5, 6, 7, 8 };
50
51 /**
52 Initialize the Skipjack block cipher
53 @param key The symmetric key you wish to pass
54 @param keylen The key length in bytes
55 @param num_rounds The number of rounds desired (0 for default)
56 @param skey The key in as scheduled by this function.
57 @return CRYPT_OK if successful
58 */
skipjack_setup(const unsigned char * key,int keylen,int num_rounds,symmetric_key * skey)59 int skipjack_setup(const unsigned char *key, int keylen, int num_rounds, symmetric_key *skey)
60 {
61 int x;
62
63 LTC_ARGCHK(key != NULL);
64 LTC_ARGCHK(skey != NULL);
65
66 if (keylen != 10) {
67 return CRYPT_INVALID_KEYSIZE;
68 }
69
70 if (num_rounds != 32 && num_rounds != 0) {
71 return CRYPT_INVALID_ROUNDS;
72 }
73
74 /* make sure the key is in range for platforms where CHAR_BIT != 8 */
75 for (x = 0; x < 10; x++) {
76 skey->skipjack.key[x] = key[x] & 255;
77 }
78
79 return CRYPT_OK;
80 }
81
82 #define RULE_A \
83 tmp = g_func(w1, &kp, skey->skipjack.key); \
84 w1 = tmp ^ w4 ^ x; \
85 w4 = w3; w3 = w2; \
86 w2 = tmp;
87
88 #define RULE_B \
89 tmp = g_func(w1, &kp, skey->skipjack.key); \
90 tmp1 = w4; w4 = w3; \
91 w3 = w1 ^ w2 ^ x; \
92 w1 = tmp1; w2 = tmp;
93
94 #define RULE_A1 \
95 tmp = w1 ^ w2 ^ x; \
96 w1 = ig_func(w2, &kp, skey->skipjack.key); \
97 w2 = w3; w3 = w4; w4 = tmp;
98
99 #define RULE_B1 \
100 tmp = ig_func(w2, &kp, skey->skipjack.key); \
101 w2 = tmp ^ w3 ^ x; \
102 w3 = w4; w4 = w1; w1 = tmp;
103
g_func(unsigned w,int * kp,const unsigned char * key)104 static unsigned g_func(unsigned w, int *kp, const unsigned char *key)
105 {
106 unsigned char g1,g2;
107
108 g1 = (w >> 8) & 255; g2 = w & 255;
109 g1 ^= sbox[g2^key[*kp]]; *kp = keystep[*kp];
110 g2 ^= sbox[g1^key[*kp]]; *kp = keystep[*kp];
111 g1 ^= sbox[g2^key[*kp]]; *kp = keystep[*kp];
112 g2 ^= sbox[g1^key[*kp]]; *kp = keystep[*kp];
113 return ((unsigned)g1<<8)|(unsigned)g2;
114 }
115
ig_func(unsigned w,int * kp,const unsigned char * key)116 static unsigned ig_func(unsigned w, int *kp, const unsigned char *key)
117 {
118 unsigned char g1,g2;
119
120 g1 = (w >> 8) & 255; g2 = w & 255;
121 *kp = ikeystep[*kp]; g2 ^= sbox[g1^key[*kp]];
122 *kp = ikeystep[*kp]; g1 ^= sbox[g2^key[*kp]];
123 *kp = ikeystep[*kp]; g2 ^= sbox[g1^key[*kp]];
124 *kp = ikeystep[*kp]; g1 ^= sbox[g2^key[*kp]];
125 return ((unsigned)g1<<8)|(unsigned)g2;
126 }
127
128 /**
129 Encrypts a block of text with Skipjack
130 @param pt The input plaintext (8 bytes)
131 @param ct The output ciphertext (8 bytes)
132 @param skey The key as scheduled
133 @return CRYPT_OK if successful
134 */
135 #ifdef LTC_CLEAN_STACK
s_skipjack_ecb_encrypt(const unsigned char * pt,unsigned char * ct,const symmetric_key * skey)136 static int s_skipjack_ecb_encrypt(const unsigned char *pt, unsigned char *ct, const symmetric_key *skey)
137 #else
138 int skipjack_ecb_encrypt(const unsigned char *pt, unsigned char *ct, const symmetric_key *skey)
139 #endif
140 {
141 unsigned w1,w2,w3,w4,tmp,tmp1;
142 int x, kp;
143
144 LTC_ARGCHK(pt != NULL);
145 LTC_ARGCHK(ct != NULL);
146 LTC_ARGCHK(skey != NULL);
147
148 /* load block */
149 w1 = ((unsigned)pt[0]<<8)|pt[1];
150 w2 = ((unsigned)pt[2]<<8)|pt[3];
151 w3 = ((unsigned)pt[4]<<8)|pt[5];
152 w4 = ((unsigned)pt[6]<<8)|pt[7];
153
154 /* 8 rounds of RULE A */
155 for (x = 1, kp = 0; x < 9; x++) {
156 RULE_A;
157 }
158
159 /* 8 rounds of RULE B */
160 for (; x < 17; x++) {
161 RULE_B;
162 }
163
164 /* 8 rounds of RULE A */
165 for (; x < 25; x++) {
166 RULE_A;
167 }
168
169 /* 8 rounds of RULE B */
170 for (; x < 33; x++) {
171 RULE_B;
172 }
173
174 /* store block */
175 ct[0] = (w1>>8)&255; ct[1] = w1&255;
176 ct[2] = (w2>>8)&255; ct[3] = w2&255;
177 ct[4] = (w3>>8)&255; ct[5] = w3&255;
178 ct[6] = (w4>>8)&255; ct[7] = w4&255;
179
180 return CRYPT_OK;
181 }
182
183 #ifdef LTC_CLEAN_STACK
skipjack_ecb_encrypt(const unsigned char * pt,unsigned char * ct,const symmetric_key * skey)184 int skipjack_ecb_encrypt(const unsigned char *pt, unsigned char *ct, const symmetric_key *skey)
185 {
186 int err = s_skipjack_ecb_encrypt(pt, ct, skey);
187 burn_stack(sizeof(unsigned) * 8 + sizeof(int) * 2);
188 return err;
189 }
190 #endif
191
192 /**
193 Decrypts a block of text with Skipjack
194 @param ct The input ciphertext (8 bytes)
195 @param pt The output plaintext (8 bytes)
196 @param skey The key as scheduled
197 @return CRYPT_OK if successful
198 */
199 #ifdef LTC_CLEAN_STACK
s_skipjack_ecb_decrypt(const unsigned char * ct,unsigned char * pt,const symmetric_key * skey)200 static int s_skipjack_ecb_decrypt(const unsigned char *ct, unsigned char *pt, const symmetric_key *skey)
201 #else
202 int skipjack_ecb_decrypt(const unsigned char *ct, unsigned char *pt, const symmetric_key *skey)
203 #endif
204 {
205 unsigned w1,w2,w3,w4,tmp;
206 int x, kp;
207
208 LTC_ARGCHK(pt != NULL);
209 LTC_ARGCHK(ct != NULL);
210 LTC_ARGCHK(skey != NULL);
211
212 /* load block */
213 w1 = ((unsigned)ct[0]<<8)|ct[1];
214 w2 = ((unsigned)ct[2]<<8)|ct[3];
215 w3 = ((unsigned)ct[4]<<8)|ct[5];
216 w4 = ((unsigned)ct[6]<<8)|ct[7];
217
218 /* 8 rounds of RULE B^-1
219
220 Note the value "kp = 8" comes from "kp = (32 * 4) mod 10" where 32*4 is 128 which mod 10 is 8
221 */
222 for (x = 32, kp = 8; x > 24; x--) {
223 RULE_B1;
224 }
225
226 /* 8 rounds of RULE A^-1 */
227 for (; x > 16; x--) {
228 RULE_A1;
229 }
230
231
232 /* 8 rounds of RULE B^-1 */
233 for (; x > 8; x--) {
234 RULE_B1;
235 }
236
237 /* 8 rounds of RULE A^-1 */
238 for (; x > 0; x--) {
239 RULE_A1;
240 }
241
242 /* store block */
243 pt[0] = (w1>>8)&255; pt[1] = w1&255;
244 pt[2] = (w2>>8)&255; pt[3] = w2&255;
245 pt[4] = (w3>>8)&255; pt[5] = w3&255;
246 pt[6] = (w4>>8)&255; pt[7] = w4&255;
247
248 return CRYPT_OK;
249 }
250
251 #ifdef LTC_CLEAN_STACK
skipjack_ecb_decrypt(const unsigned char * ct,unsigned char * pt,const symmetric_key * skey)252 int skipjack_ecb_decrypt(const unsigned char *ct, unsigned char *pt, const symmetric_key *skey)
253 {
254 int err = s_skipjack_ecb_decrypt(ct, pt, skey);
255 burn_stack(sizeof(unsigned) * 7 + sizeof(int) * 2);
256 return err;
257 }
258 #endif
259
260 /**
261 Performs a self-test of the Skipjack block cipher
262 @return CRYPT_OK if functional, CRYPT_NOP if self-test has been disabled
263 */
skipjack_test(void)264 int skipjack_test(void)
265 {
266 #ifndef LTC_TEST
267 return CRYPT_NOP;
268 #else
269 static const struct {
270 unsigned char key[10], pt[8], ct[8];
271 } tests[] = {
272 {
273 { 0x00, 0x99, 0x88, 0x77, 0x66, 0x55, 0x44, 0x33, 0x22, 0x11 },
274 { 0x33, 0x22, 0x11, 0x00, 0xdd, 0xcc, 0xbb, 0xaa },
275 { 0x25, 0x87, 0xca, 0xe2, 0x7a, 0x12, 0xd3, 0x00 }
276 }
277 };
278 unsigned char buf[2][8];
279 int x, y, err;
280 symmetric_key key;
281
282 for (x = 0; x < (int)(sizeof(tests) / sizeof(tests[0])); x++) {
283 /* setup key */
284 if ((err = skipjack_setup(tests[x].key, 10, 0, &key)) != CRYPT_OK) {
285 return err;
286 }
287
288 /* encrypt and decrypt */
289 skipjack_ecb_encrypt(tests[x].pt, buf[0], &key);
290 skipjack_ecb_decrypt(buf[0], buf[1], &key);
291
292 /* compare */
293 if (compare_testvector(buf[0], 8, tests[x].ct, 8, "Skipjack Encrypt", x) != 0 ||
294 compare_testvector(buf[1], 8, tests[x].pt, 8, "Skipjack Decrypt", x) != 0) {
295 return CRYPT_FAIL_TESTVECTOR;
296 }
297
298 /* now see if we can encrypt all zero bytes 1000 times, decrypt and come back where we started */
299 for (y = 0; y < 8; y++) buf[0][y] = 0;
300 for (y = 0; y < 1000; y++) skipjack_ecb_encrypt(buf[0], buf[0], &key);
301 for (y = 0; y < 1000; y++) skipjack_ecb_decrypt(buf[0], buf[0], &key);
302 for (y = 0; y < 8; y++) if (buf[0][y] != 0) return CRYPT_FAIL_TESTVECTOR;
303 }
304
305 return CRYPT_OK;
306 #endif
307 }
308
309 /** Terminate the context
310 @param skey The scheduled key
311 */
skipjack_done(symmetric_key * skey)312 void skipjack_done(symmetric_key *skey)
313 {
314 LTC_UNUSED_PARAM(skey);
315 }
316
317 /**
318 Gets suitable key size
319 @param keysize [in/out] The length of the recommended key (in bytes). This function will store the suitable size back in this variable.
320 @return CRYPT_OK if the input key size is acceptable.
321 */
skipjack_keysize(int * keysize)322 int skipjack_keysize(int *keysize)
323 {
324 LTC_ARGCHK(keysize != NULL);
325 if (*keysize < 10) {
326 return CRYPT_INVALID_KEYSIZE;
327 }
328 if (*keysize > 10) {
329 *keysize = 10;
330 }
331 return CRYPT_OK;
332 }
333
334 #endif
335