mirror of
https://github.com/oxen-io/session-android.git
synced 2024-12-24 16:57:50 +00:00
101 lines
3.6 KiB
C
101 lines
3.6 KiB
C
#include <string.h>
|
|
#include "ge.h"
|
|
#include "curve_sigs.h"
|
|
#include "crypto_sign.h"
|
|
|
|
void curve25519_keygen(unsigned char* curve25519_pubkey_out,
|
|
const unsigned char* curve25519_privkey_in)
|
|
{
|
|
ge_p3 ed; /* Ed25519 pubkey point */
|
|
fe ed_y, ed_y_plus_one, one_minus_ed_y, inv_one_minus_ed_y;
|
|
fe mont_x;
|
|
|
|
/* Perform a fixed-base multiplication of the Edwards base point,
|
|
(which is efficient due to precalculated tables), then convert
|
|
to the Curve25519 montgomery-format public key. In particular,
|
|
convert Curve25519's "montgomery" x-coordinate into an Ed25519
|
|
"edwards" y-coordinate:
|
|
|
|
mont_x = (ed_y + 1) / (1 - ed_y)
|
|
|
|
with projective coordinates:
|
|
|
|
mont_x = (ed_y + ed_z) / (ed_z - ed_y)
|
|
*/
|
|
|
|
ge_scalarmult_base(&ed, curve25519_privkey_in);
|
|
fe_add(ed_y_plus_one, ed.Y, ed.Z);
|
|
fe_sub(one_minus_ed_y, ed.Z, ed.Y);
|
|
fe_invert(inv_one_minus_ed_y, one_minus_ed_y);
|
|
fe_mul(mont_x, ed_y_plus_one, inv_one_minus_ed_y);
|
|
fe_tobytes(curve25519_pubkey_out, mont_x);
|
|
}
|
|
|
|
void curve25519_sign(unsigned char* signature_out,
|
|
const unsigned char* curve25519_privkey,
|
|
const unsigned char* msg, const unsigned long msg_len,
|
|
const unsigned char* random)
|
|
{
|
|
ge_p3 ed_pubkey_point; /* Ed25519 pubkey point */
|
|
unsigned char ed_pubkey[32]; /* Ed25519 encoded pubkey */
|
|
unsigned char sigbuf[msg_len + 64]; /* working buffer */
|
|
unsigned long long sigbuf_out_len = 0;
|
|
unsigned char sign_bit = 0;
|
|
|
|
/* Convert the Curve25519 privkey to an Ed25519 public key */
|
|
ge_scalarmult_base(&ed_pubkey_point, curve25519_privkey);
|
|
ge_p3_tobytes(ed_pubkey, &ed_pubkey_point);
|
|
sign_bit = ed_pubkey[31] & 0x80;
|
|
|
|
/* Perform an Ed25519 signature with explicit private key */
|
|
crypto_sign_modified(sigbuf, &sigbuf_out_len, msg, msg_len, curve25519_privkey,
|
|
ed_pubkey, random);
|
|
memmove(signature_out, sigbuf, 64);
|
|
|
|
/* Encode the sign bit into signature (in unused high bit of S) */
|
|
signature_out[63] |= sign_bit;
|
|
}
|
|
|
|
int curve25519_verify(const unsigned char* signature,
|
|
const unsigned char* curve25519_pubkey,
|
|
const unsigned char* msg, const unsigned long msg_len)
|
|
{
|
|
fe mont_x, mont_x_minus_one, mont_x_plus_one, inv_mont_x_plus_one;
|
|
fe one;
|
|
fe ed_y;
|
|
unsigned char ed_pubkey[32];
|
|
unsigned long long some_retval;
|
|
unsigned char verifybuf[msg_len + 64]; /* working buffer */
|
|
unsigned char verifybuf2[msg_len + 64]; /* working buffer #2 */
|
|
|
|
/* Convert the Curve25519 public key into an Ed25519 public key. In
|
|
particular, convert Curve25519's "montgomery" x-coordinate into an
|
|
Ed25519 "edwards" y-coordinate:
|
|
|
|
ed_y = (mont_x - 1) / (mont_x + 1)
|
|
|
|
Then move the sign bit into the pubkey from the signature.
|
|
*/
|
|
fe_frombytes(mont_x, curve25519_pubkey);
|
|
fe_1(one);
|
|
fe_sub(mont_x_minus_one, mont_x, one);
|
|
fe_add(mont_x_plus_one, mont_x, one);
|
|
fe_invert(inv_mont_x_plus_one, mont_x_plus_one);
|
|
fe_mul(ed_y, mont_x_minus_one, inv_mont_x_plus_one);
|
|
fe_tobytes(ed_pubkey, ed_y);
|
|
|
|
/* Copy the sign bit, and remove it from signature */
|
|
ed_pubkey[31] |= (signature[63] & 0x80);
|
|
memmove(verifybuf, signature, 64);
|
|
verifybuf[63] &= 0x7F;
|
|
|
|
memmove(verifybuf+64, msg, msg_len);
|
|
|
|
/* Then perform a normal Ed25519 verification, return 0 on success */
|
|
/* The below call has a strange API: */
|
|
/* verifybuf = R || S || message */
|
|
/* verifybuf2 = internal to next call gets a copy of verifybuf, S gets
|
|
replaced with pubkey for hashing, then the whole thing gets zeroized */
|
|
return crypto_sign_open(verifybuf2, &some_retval, verifybuf, 64 + msg_len, ed_pubkey);
|
|
}
|