1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis */
2 /* SPDX-License-Identifier: Unlicense */
3
4 /* The implementation is based on:
5 * "Extending the Salsa20 nonce", https://cr.yp.to/snuffle/xsalsa-20081128.pdf
6 * "Salsa20 specification", http://cr.yp.to/snuffle/spec.pdf
7 * and salsa20-ref.c version 20051118
8 * Public domain from D. J. Bernstein
9 */
10
11 #include "tomcrypt.h"
12
13 #ifdef LTC_XSALSA20
14
15 static const char * const constants = "expand 32-byte k";
16
17 #define QUARTERROUND(a,b,c,d) \
18 x[b] ^= (ROL((x[a] + x[d]), 7)); \
19 x[c] ^= (ROL((x[b] + x[a]), 9)); \
20 x[d] ^= (ROL((x[c] + x[b]), 13)); \
21 x[a] ^= (ROL((x[d] + x[c]), 18));
22
23 /* use modified salsa20 doubleround (no final addition as in salsa20) */
s_xsalsa20_doubleround(ulong32 * x,int rounds)24 static void s_xsalsa20_doubleround(ulong32 *x, int rounds)
25 {
26 int i;
27
28 for (i = rounds; i > 0; i -= 2) {
29 /* columnround */
30 QUARTERROUND( 0, 4, 8,12)
31 QUARTERROUND( 5, 9,13, 1)
32 QUARTERROUND(10,14, 2, 6)
33 QUARTERROUND(15, 3, 7,11)
34 /* rowround */
35 QUARTERROUND( 0, 1, 2, 3)
36 QUARTERROUND( 5, 6, 7, 4)
37 QUARTERROUND(10,11, 8, 9)
38 QUARTERROUND(15,12,13,14)
39 }
40 }
41
42 #undef QUARTERROUND
43
44 /**
45 Initialize an XSalsa20 context
46 @param st [out] The destination of the XSalsa20 state
47 @param key The secret key
48 @param keylen The length of the secret key, must be 32 (octets)
49 @param nonce The nonce
50 @param noncelen The length of the nonce, must be 24 (octets)
51 @param rounds Number of rounds (must be evenly divisible by 2, default is 20)
52 @return CRYPT_OK if successful
53 */
xsalsa20_setup(salsa20_state * st,const unsigned char * key,unsigned long keylen,const unsigned char * nonce,unsigned long noncelen,int rounds)54 int xsalsa20_setup(salsa20_state *st, const unsigned char *key, unsigned long keylen,
55 const unsigned char *nonce, unsigned long noncelen,
56 int rounds)
57 {
58 const int sti[] = {0, 5, 10, 15, 6, 7, 8, 9}; /* indices used to build subkey fm x */
59 ulong32 x[64]; /* input to & output fm doubleround */
60 unsigned char subkey[32];
61 int i;
62
63 LTC_ARGCHK(st != NULL);
64 LTC_ARGCHK(key != NULL);
65 LTC_ARGCHK(keylen == 32);
66 LTC_ARGCHK(nonce != NULL);
67 LTC_ARGCHK(noncelen == 24);
68 if (rounds == 0) rounds = 20;
69 LTC_ARGCHK(rounds % 2 == 0); /* number of rounds must be evenly divisible by 2 */
70
71 /* load the state to "hash" the key */
72 LOAD32L(x[ 0], constants + 0);
73 LOAD32L(x[ 5], constants + 4);
74 LOAD32L(x[10], constants + 8);
75 LOAD32L(x[15], constants + 12);
76 LOAD32L(x[ 1], key + 0);
77 LOAD32L(x[ 2], key + 4);
78 LOAD32L(x[ 3], key + 8);
79 LOAD32L(x[ 4], key + 12);
80 LOAD32L(x[11], key + 16);
81 LOAD32L(x[12], key + 20);
82 LOAD32L(x[13], key + 24);
83 LOAD32L(x[14], key + 28);
84 LOAD32L(x[ 6], nonce + 0);
85 LOAD32L(x[ 7], nonce + 4);
86 LOAD32L(x[ 8], nonce + 8);
87 LOAD32L(x[ 9], nonce + 12);
88
89 /* use modified salsa20 doubleround (no final addition) */
90 s_xsalsa20_doubleround(x, rounds);
91
92 /* extract the subkey */
93 for (i = 0; i < 8; ++i) {
94 STORE32L(x[sti[i]], subkey + 4 * i);
95 }
96
97 /* load the final initial state */
98 LOAD32L(st->input[ 0], constants + 0);
99 LOAD32L(st->input[ 5], constants + 4);
100 LOAD32L(st->input[10], constants + 8);
101 LOAD32L(st->input[15], constants + 12);
102 LOAD32L(st->input[ 1], subkey + 0);
103 LOAD32L(st->input[ 2], subkey + 4);
104 LOAD32L(st->input[ 3], subkey + 8);
105 LOAD32L(st->input[ 4], subkey + 12);
106 LOAD32L(st->input[11], subkey + 16);
107 LOAD32L(st->input[12], subkey + 20);
108 LOAD32L(st->input[13], subkey + 24);
109 LOAD32L(st->input[14], subkey + 28);
110 LOAD32L(st->input[ 6], &(nonce[16]) + 0);
111 LOAD32L(st->input[ 7], &(nonce[16]) + 4);
112 st->input[ 8] = 0;
113 st->input[ 9] = 0;
114 st->rounds = rounds;
115 st->ksleft = 0;
116 st->ivlen = 24; /* set switch to say nonce/IV has been loaded */
117
118 #ifdef LTC_CLEAN_STACK
119 zeromem(x, sizeof(x));
120 zeromem(subkey, sizeof(subkey));
121 #endif
122
123 return CRYPT_OK;
124 }
125
126
127 #endif
128