Merge pull request #2 from iotanbo/bugfix-issue#1

Fixed issue #1

Author: DavyLandman

src/compact_x25519.c

@@ -21,7 +21,14 @@ void compact_x25519_shared(
     const uint8_t my_private_key[X25519_KEY_SIZE], 
     const uint8_t their_public_key[X25519_KEY_SIZE]
 ) {
-    c25519_smult(shared_secret, their_public_key, my_private_key);
+    // Ensure that supplied private key is clamped (fix issue #1).
+    // Calling `c25519_prepare` multiple times for the same private key
+    // is OK because it won't modify already clamped key.
+    uint8_t clamped_private_key[X25519_KEY_SIZE];
+    memcpy(clamped_private_key, my_private_key, X25519_KEY_SIZE);
+    c25519_prepare(clamped_private_key);
+    c25519_smult(shared_secret, their_public_key, clamped_private_key);
+    compact_wipe(clamped_private_key, X25519_KEY_SIZE);
 }
 
 #ifndef COMPACT_DISABLE_X25519_DERIVE

test/run-all.c

@@ -61,6 +61,64 @@ static int testX25519(pcg32_random_t* rng) {
         return -1;
     }
 }
+
+int testX25519WithRfc7748Vectors(void) {
+    printf("Testing X25519 using rfc7748 test vectors: ");
+    int r = 0;
+    uint8_t alice_sec[X25519_KEY_SIZE] = {
+        0x77, 0x07, 0x6d, 0x0a, 0x73, 0x18, 0xa5, 0x7d,
+        0x3c, 0x16, 0xc1, 0x72, 0x51, 0xb2, 0x66, 0x45,
+        0xdf, 0x4c, 0x2f, 0x87, 0xeb, 0xc0, 0x99, 0x2a,
+        0xb1, 0x77, 0xfb, 0xa5, 0x1d, 0xb9, 0x2c, 0x2a
+    };
+
+    uint8_t alice_pub[X25519_KEY_SIZE] = {
+        0x85, 0x20, 0xf0, 0x09, 0x89, 0x30, 0xa7, 0x54,
+        0x74, 0x8b, 0x7d, 0xdc, 0xb4, 0x3e, 0xf7, 0x5a,
+        0x0d, 0xbf, 0x3a, 0x0d, 0x26, 0x38, 0x1a, 0xf4,
+        0xeb, 0xa4, 0xa9, 0x8e, 0xaa, 0x9b, 0x4e, 0x6a
+    };
+
+    uint8_t bob_sec[X25519_KEY_SIZE] = {
+        0x5d, 0xab, 0x08, 0x7e, 0x62, 0x4a, 0x8a, 0x4b,
+        0x79, 0xe1, 0x7f, 0x8b, 0x83, 0x80, 0x0e, 0xe6,
+        0x6f, 0x3b, 0xb1, 0x29, 0x26, 0x18, 0xb6, 0xfd,
+        0x1c, 0x2f, 0x8b, 0x27, 0xff, 0x88, 0xe0, 0xeb
+    };
+
+    uint8_t bob_pub[X25519_KEY_SIZE] = {
+        0xde, 0x9e, 0xdb, 0x7d, 0x7b, 0x7d, 0xc1, 0xb4,
+        0xd3, 0x5b, 0x61, 0xc2, 0xec, 0xe4, 0x35, 0x37,
+        0x3f, 0x83, 0x43, 0xc8, 0x5b, 0x78, 0x67, 0x4d,
+        0xad, 0xfc, 0x7e, 0x14, 0x6f, 0x88, 0x2b, 0x4f
+    };
+
+    uint8_t expected_shared[X25519_KEY_SIZE] = {
+        0x4a, 0x5d, 0x9d, 0x5b, 0xa4, 0xce, 0x2d, 0xe1,
+        0x72, 0x8e, 0x3b, 0xf4, 0x80, 0x35, 0x0f, 0x25,
+        0xe0, 0x7e, 0x21, 0xc9, 0x47, 0xd1, 0x9e, 0x33,
+        0x76, 0xf0, 0x9b, 0x3c, 0x1e, 0x16, 0x17, 0x42
+    };
+
+
+    uint8_t shared1[X25519_SHARED_SIZE];
+    uint8_t shared2[X25519_SHARED_SIZE];
+
+    compact_x25519_shared(shared1, alice_sec, bob_pub);
+    compact_x25519_shared(shared2, bob_sec, alice_pub);
+
+    if (memcmp(shared1, shared2, X25519_SHARED_SIZE) != 0) {
+        printf("Fail\n");
+        r--;
+    }
+
+    if (memcmp(shared1, expected_shared, X25519_KEY_SIZE) != 0) {
+        printf("Fail\n");
+        r--;
+    }
+    if (r == 0) printf("Success\n");
+    return r;
+}
 #endif
 
 #ifndef COMPACT_DISABLE_ED25519
@@ -105,6 +163,7 @@ int main(void) {
 
     int result = 0;
 #ifndef COMPACT_DISABLE_X25519
+    testX25519WithRfc7748Vectors();
     for (int i = 0; i < 5; i++) {
         result += testX25519(&rng);
     }