add curve25519.publickey and unittest for randomized multiply

extmod/modtrezorcrypto/modtrezorcrypto-curve25519.h

@@ -20,6 +20,23 @@ STATIC mp_obj_t mod_TrezorCrypto_Curve25519_make_new(const mp_obj_type_t *type,
     return MP_OBJ_FROM_PTR(o);
 }
 
+/// def trezor.crypto.curve.curve25519.publickey(secret_key: bytes) -> bytes:
+///     '''
+///     Computes public key from secret key.
+///     '''
+STATIC mp_obj_t mod_TrezorCrypto_Curve25519_publickey(mp_obj_t self, mp_obj_t secret_key) {
+    mp_buffer_info_t sk;
+    mp_get_buffer_raise(secret_key, &sk, MP_BUFFER_READ);
+    if (sk.len != 32) {
+        mp_raise_ValueError("Invalid length of secret key");
+    }
+    vstr_t vstr;
+    vstr_init_len(&vstr, 32);
+    curve25519_publickey((uint8_t *)vstr.buf, (const uint8_t *)sk.buf);
+    return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_TrezorCrypto_Curve25519_publickey_obj, mod_TrezorCrypto_Curve25519_publickey);
+
 /// def trezor.crypto.curve.curve25519.multiply(secret_key: bytes, public_key: bytes) -> bytes:
 ///     '''
 ///     Multiplies point defined by public_key with scalar defined by secret_key
@@ -43,6 +60,7 @@ STATIC mp_obj_t mod_TrezorCrypto_Curve25519_multiply(mp_obj_t self, mp_obj_t sec
 STATIC MP_DEFINE_CONST_FUN_OBJ_3(mod_TrezorCrypto_Curve25519_multiply_obj, mod_TrezorCrypto_Curve25519_multiply);
 
 STATIC const mp_rom_map_elem_t mod_TrezorCrypto_Curve25519_locals_dict_table[] = {
+    { MP_ROM_QSTR(MP_QSTR_publickey), MP_ROM_PTR(&mod_TrezorCrypto_Curve25519_publickey_obj) },
     { MP_ROM_QSTR(MP_QSTR_multiply), MP_ROM_PTR(&mod_TrezorCrypto_Curve25519_multiply_obj) },
 };
 STATIC MP_DEFINE_CONST_DICT(mod_TrezorCrypto_Curve25519_locals_dict, mod_TrezorCrypto_Curve25519_locals_dict_table);

src/tests/test_crypto_curve25519.py

@@ -5,6 +5,7 @@ import unittest
 from ubinascii import unhexlify
 
 from trezor.crypto.curve import curve25519
+from trezor.crypto import random
 
 class TestCryptoCurve25519(unittest.TestCase):
 
@@ -17,5 +18,18 @@ class TestCryptoCurve25519(unittest.TestCase):
             session2 = curve25519.multiply(unhexlify(sk), unhexlify(pk))
             self.assertEqual(session2, unhexlify(session))
 
+    def test_multiply_random(self):
+        for _ in range(100):
+            sk1 = bytearray(random.bytes(32))
+            sk2 = bytearray(random.bytes(32))
+            # taken from https://cr.yp.to/ecdh.html
+            sk1[0] &= 248 ; sk1[31] &= 127 ; sk1[31] |= 64
+            sk2[0] &= 248 ; sk2[31] &= 127 ; sk2[31] |= 64
+            pk1 = curve25519.publickey(sk1)
+            pk2 = curve25519.publickey(sk2)
+            session1 = curve25519.multiply(sk1, pk2)
+            session2 = curve25519.multiply(sk2, pk1)
+            self.assertEqual(session1, session2)
+
 if __name__ == '__main__':
     unittest.main()