Source

`stdlib/tests/x25519_test.cpp`

2// Original work; see ACKNOWLEDGMENTS.md for the open-source ideas we build upon.

3// Unit tests for the `x25519` module against the RFC 7748 test vectors (§5.2, §6.1) — the

4// from-scratch field arithmetic and Montgomery ladder must match the spec bit for bit.

5#include <gtest/gtest.h>

7#include "x25519.hpp"

9namespace x = cheatah::x25519;

11// RFC 7748 §5.2 vector 1: scalar * point -> known output.

12TEST(CheatahX25519, Rfc7748Vector1) {

13 EXPECT_EQ(x::x25519("a546e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449ac4",

14 "e6db6867583030db3594c1a424b15f7c726624ec26b3353b10a903a6d0ab1c4c"),

15 "c3da55379de9c6908e94ea4df28d084f32eccf03491c71f754b4075577a28552");

16}

18// RFC 7748 §5.2 vector 2 (different scalar/point pair).

19TEST(CheatahX25519, Rfc7748Vector2) {

20 EXPECT_EQ(x::x25519("4b66e9d4d1b4673c5ad22691957d6af5c11b6421e0ea01d42ca4169e7918ba0d",

21 "e5210f12786811d3f4b7959d0538ae2c31dbe7106fc03c3efc4cd549c715a493"),

22 "95cbde9476e8907d7aade45cb4b873f88b595a68799fa152e6f8f7647aac7957");

23}

25// RFC 7748 §5.2: one iteration of the iterated test (scalar applied to the base point form).

26TEST(CheatahX25519, IteratedOnce) {

27 EXPECT_EQ(x::x25519("0900000000000000000000000000000000000000000000000000000000000000",

28 "0900000000000000000000000000000000000000000000000000000000000000"),

29 "422c8e7a6227d7bca1350b3e2bb7279f7897b87bb6854b783c60e80311ae3079");

30}

32// RFC 7748 §6.1: the full Diffie-Hellman exchange — both public keys and the shared secret.

33TEST(CheatahX25519, DiffieHellman) {

34 const std::string alice_priv =

35 "77076d0a7318a57d3c16c17251b26645df4c2f87ebc0992ab177fba51db92c2a";

36 const std::string bob_priv =

37 "5dab087e624a8a4b79e17f8b83800ee66f3bb1292618b6fd1c2f8b27ff88e0eb";

38 const std::string alice_pub = x::x25519_base(alice_priv);

39 const std::string bob_pub = x::x25519_base(bob_priv);

40 EXPECT_EQ(alice_pub, "8520f0098930a754748b7ddcb43ef75a0dbf3a0d26381af4eba4a98eaa9b4e6a");

41 EXPECT_EQ(bob_pub, "de9edb7d7b7dc1b4d35b61c2ece435373f8343c85b78674dadfc7e146f882b4f");

42 const std::string shared = "4a5d9d5ba4ce2de1728e3bf480350f25e07e21c947d19e3376f09b3c1e161742";

43 EXPECT_EQ(x::x25519(alice_priv, bob_pub), shared);

44 EXPECT_EQ(x::x25519(bob_priv, alice_pub), shared); // both sides agree

45}

47// Malformed input (wrong length, non-hex) and the all-zero contributory check return "".

48TEST(CheatahX25519, RejectsMalformed) {

49 EXPECT_EQ(x::x25519("abc", "abc"), "");

50 EXPECT_EQ(x::x25519_base("zz46e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449ac4"),

51 "");

52 // a zero point yields a zero shared secret -> rejected (small-subgroup degeneracy)

53 EXPECT_EQ(x::x25519("a546e36bf0527c9d3b16154b82465edd62144c0ac1fc5a18506a2244ba449ac4",

54 "0000000000000000000000000000000000000000000000000000000000000000"),

55 "");

56}