package im.actor.keygen.curve25519;
// Disabling Bounds checks for speeding up calculations
/*-[
#define J2OBJC_DISABLE_ARRAY_BOUND_CHECKS 1
]-*/
public class curve_sigs {
public static void curve25519_keygen(byte[] curve25519_pubkey_out,
byte[] curve25519_privkey_in) {
ge_p3 ed = new ge_p3(); /* Ed25519 pubkey point */
int[] ed_y = new int[10];
int[] ed_y_plus_one = new int[10];
int[] one_minus_ed_y = new int[10];
int[] inv_one_minus_ed_y = new int[10];
int[] mont_x = new int[10];
/* 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)
NOTE: ed_y=1 is converted to mont_x=0 since fe_invert is mod-exp
*/
ge_scalarmult_base.ge_scalarmult_base(ed, curve25519_privkey_in);
fe_add.fe_add(ed_y_plus_one, ed.Y, ed.Z);
fe_sub.fe_sub(one_minus_ed_y, ed.Z, ed.Y);
fe_invert.fe_invert(inv_one_minus_ed_y, one_minus_ed_y);
fe_mul.fe_mul(mont_x, ed_y_plus_one, inv_one_minus_ed_y);
fe_tobytes.fe_tobytes(curve25519_pubkey_out, mont_x);
}
public static int curve25519_sign(Sha512 sha512provider, byte[] signature_out,
byte[] curve25519_privkey,
byte[] msg, int msg_len,
byte[] random) {
ge_p3 ed_pubkey_point = new ge_p3(); /* Ed25519 pubkey point */
byte[] ed_pubkey = new byte[32]; /* Ed25519 encoded pubkey */
byte[] sigbuf = new byte[msg_len + 128]; /* working buffer */
byte sign_bit = 0;
/* Convert the Curve25519 privkey to an Ed25519 public key */
ge_scalarmult_base.ge_scalarmult_base(ed_pubkey_point, curve25519_privkey);
ge_p3_tobytes.ge_p3_tobytes(ed_pubkey, ed_pubkey_point);
sign_bit = (byte) (ed_pubkey[31] & 0x80);
/* Perform an Ed25519 signature with explicit private key */
sign_modified.crypto_sign_modified(sha512provider, sigbuf, msg, msg_len, curve25519_privkey,
ed_pubkey, random);
System.arraycopy(sigbuf, 0, signature_out, 0, 64);
/* Encode the sign bit into signature (in unused high bit of S) */
signature_out[63] &= 0x7F; /* bit should be zero already, but just in case */
signature_out[63] |= sign_bit;
return 0;
}
public static int curve25519_verify(Sha512 sha512provider, byte[] signature,
byte[] curve25519_pubkey,
byte[] msg, int msg_len) {
int[] mont_x = new int[10];
int[] mont_x_minus_one = new int[10];
int[] mont_x_plus_one = new int[10];
int[] inv_mont_x_plus_one = new int[10];
int[] one = new int[10];
int[] ed_y = new int[10];
byte[] ed_pubkey = new byte[32];
long some_retval = 0;
byte[] verifybuf = new byte[msg_len + 64]; /* working buffer */
byte[] verifybuf2 = new byte[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)
NOTE: mont_x=-1 is converted to ed_y=0 since fe_invert is mod-exp
Then move the sign bit into the pubkey from the signature.
*/
fe_frombytes.fe_frombytes(mont_x, curve25519_pubkey);
fe_1.fe_1(one);
fe_sub.fe_sub(mont_x_minus_one, mont_x, one);
fe_add.fe_add(mont_x_plus_one, mont_x, one);
fe_invert.fe_invert(inv_mont_x_plus_one, mont_x_plus_one);
fe_mul.fe_mul(ed_y, mont_x_minus_one, inv_mont_x_plus_one);
fe_tobytes.fe_tobytes(ed_pubkey, ed_y);
/* Copy the sign bit, and remove it from signature */
ed_pubkey[31] &= 0x7F; /* bit should be zero already, but just in case */
ed_pubkey[31] |= (signature[63] & 0x80);
System.arraycopy(signature, 0, verifybuf, 0, 64);
verifybuf[63] &= 0x7F;
System.arraycopy(msg, 0, verifybuf, 64, (int) msg_len);
/* Then perform a normal Ed25519 verification, return 0 on success */
/* The below call has a strange API: */
/* verifybuf = R || S || message */
/* verifybuf2 = java to next call gets a copy of verifybuf, S gets
replaced with pubkey for hashing, then the whole thing gets zeroized
(if bad sig), or contains a copy of msg (good sig) */
return open.crypto_sign_open(sha512provider, verifybuf2, some_retval, verifybuf, 64 + msg_len, ed_pubkey);
}
}