static int
crypto_scalarmult_curve25519_ref10(unsigned char *q,
const unsigned char *n,
const unsigned char *p)
{
unsigned char e[32];
unsigned int i;
fe x1;
fe x2;
fe z2;
fe x3;
fe z3;
fe tmp0;
fe tmp1;
int pos;
unsigned int swap;
unsigned int b;
for (i = 0;i < 32;++i) e[i] = n[i];
e[0] &= 248;
e[31] &= 127;
e[31] |= 64;
fe_frombytes(x1,p);
fe_1(x2);
fe_0(z2);
fe_copy(x3,x1);
fe_1(z3);
swap = 0;
for (pos = 254;pos >= 0;--pos) {
b = e[pos / 8] >> (pos & 7);
b &= 1;
swap ^= b;
fe_cswap(x2,x3,swap);
fe_cswap(z2,z3,swap);
swap = b;
fe_sub(tmp0,x3,z3);
fe_sub(tmp1,x2,z2);
fe_add(x2,x2,z2);
fe_add(z2,x3,z3);
fe_mul(z3,tmp0,x2);
fe_mul(z2,z2,tmp1);
fe_sq(tmp0,tmp1);
fe_sq(tmp1,x2);
fe_add(x3,z3,z2);
fe_sub(z2,z3,z2);
fe_mul(x2,tmp1,tmp0);
fe_sub(tmp1,tmp1,tmp0);
fe_sq(z2,z2);
fe_mul121666(z3,tmp1);
fe_sq(x3,x3);
fe_add(tmp0,tmp0,z3);
fe_mul(z3,x1,z2);
fe_mul(z2,tmp1,tmp0);
}
fe_cswap(x2,x3,swap);
fe_cswap(z2,z3,swap);
fe_invert(z2,z2);
fe_mul(x2,x2,z2);
fe_tobytes(q,x2);
return 0;
}
void ed25519_key_exchange(unsigned char *shared_secret, const unsigned char *public_key, const unsigned char *private_key) {
unsigned char e[32];
unsigned int i;
fe x1;
fe x2;
fe z2;
fe x3;
fe z3;
fe tmp0;
fe tmp1;
int pos;
unsigned int swap;
unsigned int b;
/* copy the private key and make sure it's valid */
for (i = 0; i < 32; ++i) {
e[i] = private_key[i];
}
e[0] &= 248;
e[31] &= 63;
e[31] |= 64;
/* unpack the public key and convert edwards to montgomery */
/* due to CodesInChaos: montgomeryX = (edwardsY + 1)*inverse(1 - edwardsY) mod p */
fe_frombytes(x1, public_key);
fe_1(tmp1);
fe_add(tmp0, x1, tmp1);
fe_sub(tmp1, tmp1, x1);
fe_invert(tmp1, tmp1);
fe_mul(x1, tmp0, tmp1);
fe_1(x2);
fe_0(z2);
fe_copy(x3, x1);
fe_1(z3);
swap = 0;
for (pos = 254; pos >= 0; --pos) {
b = e[pos / 8] >> (pos & 7);
b &= 1;
swap ^= b;
fe_cswap(x2, x3, swap);
fe_cswap(z2, z3, swap);
swap = b;
/* from montgomery.h */
fe_sub(tmp0, x3, z3);
fe_sub(tmp1, x2, z2);
fe_add(x2, x2, z2);
fe_add(z2, x3, z3);
fe_mul(z3, tmp0, x2);
fe_mul(z2, z2, tmp1);
fe_sq(tmp0, tmp1);
fe_sq(tmp1, x2);
fe_add(x3, z3, z2);
fe_sub(z2, z3, z2);
fe_mul(x2, tmp1, tmp0);
fe_sub(tmp1, tmp1, tmp0);
fe_sq(z2, z2);
fe_mul121666(z3, tmp1);
fe_sq(x3, x3);
fe_add(tmp0, tmp0, z3);
fe_mul(z3, x1, z2);
fe_mul(z2, tmp1, tmp0);
}
fe_cswap(x2, x3, swap);
fe_cswap(z2, z3, swap);
fe_invert(z2, z2);
fe_mul(x2, x2, z2);
fe_tobytes(shared_secret, x2);
}
