1/* $OpenBSD: mod_ed25519.c,v 1.1 2014/01/08 05:00:01 tedu Exp $ */
2
3/*
4 * Public Domain, Authors: Daniel J. Bernstein, Niels Duif, Tanja Lange,
5 * Peter Schwabe, Bo-Yin Yang.
6 * Copied from supercop-20130419/crypto_sign/ed25519/ref/ed25519.c
7 */
8
9#include "crypto_api.h"
10
11#include "ge25519.h"
12
13static void get_hram(unsigned char *hram, const unsigned char *sm, const unsigned char *pk, unsigned char *playground, unsigned long long smlen)
14{
15  unsigned long long i;
16
17  for (i =  0;i < 32;++i)    playground[i] = sm[i];
18  for (i = 32;i < 64;++i)    playground[i] = pk[i-32];
19  for (i = 64;i < smlen;++i) playground[i] = sm[i];
20
21  crypto_hash_sha512(hram,playground,smlen);
22}
23
24#ifndef VERIFYONLY
25int crypto_sign_ed25519_keypair(
26    unsigned char *pk,
27    unsigned char *sk
28    )
29{
30  sc25519 scsk;
31  ge25519 gepk;
32  unsigned char extsk[64];
33  int i;
34
35  randombytes(sk, 32);
36  crypto_hash_sha512(extsk, sk, 32);
37  extsk[0] &= 248;
38  extsk[31] &= 127;
39  extsk[31] |= 64;
40
41  sc25519_from32bytes(&scsk,extsk);
42
43  ge25519_scalarmult_base(&gepk, &scsk);
44  ge25519_pack(pk, &gepk);
45  for(i=0;i<32;i++)
46    sk[32 + i] = pk[i];
47  return 0;
48}
49
50int crypto_sign_ed25519(
51    unsigned char *sm,unsigned long long *smlen,
52    const unsigned char *m,unsigned long long mlen,
53    const unsigned char *sk
54    )
55{
56  sc25519 sck, scs, scsk;
57  ge25519 ger;
58  unsigned char r[32];
59  unsigned char s[32];
60  unsigned char extsk[64];
61  unsigned long long i;
62  unsigned char hmg[crypto_hash_sha512_BYTES];
63  unsigned char hram[crypto_hash_sha512_BYTES];
64
65  crypto_hash_sha512(extsk, sk, 32);
66  extsk[0] &= 248;
67  extsk[31] &= 127;
68  extsk[31] |= 64;
69
70  *smlen = mlen+64;
71  for(i=0;i<mlen;i++)
72    sm[64 + i] = m[i];
73  for(i=0;i<32;i++)
74    sm[32 + i] = extsk[32+i];
75
76  crypto_hash_sha512(hmg, sm+32, mlen+32); /* Generate k as h(extsk[32],...,extsk[63],m) */
77
78  /* Computation of R */
79  sc25519_from64bytes(&sck, hmg);
80  ge25519_scalarmult_base(&ger, &sck);
81  ge25519_pack(r, &ger);
82
83  /* Computation of s */
84  for(i=0;i<32;i++)
85    sm[i] = r[i];
86
87  get_hram(hram, sm, sk+32, sm, mlen+64);
88
89  sc25519_from64bytes(&scs, hram);
90  sc25519_from32bytes(&scsk, extsk);
91  sc25519_mul(&scs, &scs, &scsk);
92
93  sc25519_add(&scs, &scs, &sck);
94
95  sc25519_to32bytes(s,&scs); /* cat s */
96  for(i=0;i<32;i++)
97    sm[32 + i] = s[i];
98
99  return 0;
100}
101#endif
102int crypto_sign_ed25519_open(
103    unsigned char *m,unsigned long long *mlen,
104    const unsigned char *sm,unsigned long long smlen,
105    const unsigned char *pk
106    )
107{
108  unsigned int i;
109  int ret;
110  unsigned char t2[32];
111  ge25519 get1, get2;
112  sc25519 schram, scs;
113  unsigned char hram[crypto_hash_sha512_BYTES];
114
115  *mlen = (unsigned long long) -1;
116  if (smlen < 64) return -1;
117
118  if (ge25519_unpackneg_vartime(&get1, pk)) return -1;
119
120  get_hram(hram,sm,pk,m,smlen);
121
122  sc25519_from64bytes(&schram, hram);
123
124  sc25519_from32bytes(&scs, sm+32);
125
126  ge25519_double_scalarmult_vartime(&get2, &get1, &schram, &ge25519_base, &scs);
127  ge25519_pack(t2, &get2);
128
129  ret = crypto_verify_32(sm, t2);
130
131  if (!ret)
132  {
133    for(i=0;i<smlen-64;i++)
134      m[i] = sm[i + 64];
135    *mlen = smlen-64;
136  }
137  else
138  {
139    for(i=0;i<smlen-64;i++)
140      m[i] = 0;
141  }
142  return ret;
143}
144