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_verify(ISha512 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] |= (byte)(signature[63] & 0x80);
Array.Copy(signature, 0, verifybuf, 0, 64);
verifybuf[63] &= 0x7F;
Array.Copy(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));
}
