12 MP_INT p,g; /* prime modulus and generator */
15 static string_t dh_makepublic(void *sst, uint8_t *secret, int32_t secretlen)
19 MP_INT a, b; /* a is secret key, b is public key */
24 read_mpbin(&a, secret, secretlen);
26 mpz_powm(&b, &st->g, &a, &st->p);
35 static dh_makeshared_fn dh_makeshared;
36 static void dh_makeshared(void *sst, uint8_t *secret, int32_t secretlen,
37 cstring_t rempublic, uint8_t *sharedsecret,
47 read_mpbin(&a, secret, secretlen);
48 mpz_set_str(&b, rempublic, 16);
50 mpz_powm(&c, &b, &a, &st->p);
52 write_mpbin(&c,sharedsecret,buflen);
59 static list_t *dh_apply(closure_t *self, struct cloc loc, dict_t *context,
66 st=safe_malloc(sizeof(*st),"dh_apply");
67 st->cl.description="dh";
70 st->cl.interface=&st->ops;
72 st->ops.makepublic=dh_makepublic;
73 st->ops.makeshared=dh_makeshared;
75 /* We have two string arguments: the first is the modulus, and the
76 second is the generator. Both are in hex. */
79 if (i->type!=t_string) {
80 cfgfatal(i->loc,"diffie-hellman","first argument must be a "
84 if (mpz_init_set_str(&st->p,p,16)!=0) {
85 cfgfatal(i->loc,"diffie-hellman","\"%s\" is not a hex number "
89 cfgfatal(loc,"diffie-hellman","you must provide a prime modulus\n");
94 if (i->type!=t_string) {
95 cfgfatal(i->loc,"diffie-hellman","second argument must be a "
99 if (mpz_init_set_str(&st->g,g,16)!=0) {
100 cfgfatal(i->loc,"diffie-hellman","\"%s\" is not a hex number "
104 cfgfatal(loc,"diffie-hellman","you must provide a generator\n");
108 if (i && i->type==t_bool && i->data.bool==False) {
109 Message(M_INFO,"diffie-hellman (%s:%d): skipping modulus "
110 "primality check\n",loc.file,loc.line);
112 /* Test that the modulus is really prime */
113 if (mpz_probab_prime_p(&st->p,5)==0) {
114 cfgfatal(loc,"diffie-hellman","modulus must be a prime\n");
118 size_t sz=mpz_sizeinbase(&st->p,2)/8;
120 cfgfatal(loc,"diffie-hellman","modulus far too large\n");
122 if (mpz_cmp(&st->g,&st->p) >= 0) {
123 cfgfatal(loc,"diffie-hellman","generator must be less than modulus\n");
128 st->ops.ceil_len=(mpz_sizeinbase(&st->p,2)+7)/8;
129 /* According to the docs, mpz_sizeinbase(,256) is allowed to return
130 * an answer which is 1 too large. But mpz_sizeinbase(,2) isn't. */
132 return new_closure(&st->cl);
135 void dh_module(dict_t *dict)
137 add_closure(dict,"diffie-hellman",dh_apply);