tests: Add Wycheproof ECDH vectors

Adds a test for the ECDH module using the Wycheproof vectors.
We use a python script to convert the JSON-formatted vectors
into C code, in the same spirit as https://github.com/bitcoin-core/secp256k1/pull/1245

Co-authored-by: Sean Andersen <6730974+andozw@users.noreply.github.com>

src/modules/ecdh/Makefile.am.include

@@ -2,3 +2,4 @@ include_HEADERS += include/secp256k1_ecdh.h
 noinst_HEADERS += src/modules/ecdh/main_impl.h
 noinst_HEADERS += src/modules/ecdh/tests_impl.h
 noinst_HEADERS += src/modules/ecdh/bench_impl.h
+noinst_HEADERS += src/wycheproof/ecdh_secp256k1_test.h

src/modules/ecdh/tests_impl.h

@@ -7,6 +7,13 @@
 #ifndef SECP256K1_MODULE_ECDH_TESTS_H
 #define SECP256K1_MODULE_ECDH_TESTS_H
 
+static int ecdh_hash_function_test_xpassthru(unsigned char *output, const unsigned char *x, const unsigned char *y, void *data) {
+    (void)y;
+    (void)data;
+    memcpy(output, x, 32);
+    return 1;
+}
+
 static int ecdh_hash_function_test_fail(unsigned char *output, const unsigned char *x, const unsigned char *y, void *data) {
     (void)output;
     (void)x;
@@ -142,11 +149,45 @@ static void test_result_basepoint(void) {
     }
 }
 
+static void test_ecdh_wycheproof(void) {
+#include "../../wycheproof/ecdh_secp256k1_test.h"
+    int t;
+    for (t = 0; t < SECP256K1_ECDH_WYCHEPROOF_NUMBER_TESTVECTORS; t++) {
+        int parsed_ok;
+        secp256k1_pubkey point;
+        const unsigned char *pk;
+        const unsigned char *sk;
+        const unsigned char *expected_shared_secret;
+        unsigned char output_ecdh[65] = { 0 };
+
+        int expected_result;
+
+        memset(&point, 0, sizeof(point));
+        pk = &wycheproof_ecdh_public_keys[testvectors[t].pk_offset];
+        parsed_ok = secp256k1_ec_pubkey_parse(CTX, &point, pk, testvectors[t].pk_len);
+
+        expected_result = testvectors[t].expected_result;
+        CHECK(parsed_ok == expected_result);
+        if (!parsed_ok) {
+            continue;
+        }
+
+        sk = &wycheproof_ecdh_private_keys[testvectors[t].sk_offset];
+        CHECK(testvectors[t].sk_len == 32);
+
+        CHECK(secp256k1_ecdh(CTX, output_ecdh, &point, sk, ecdh_hash_function_test_xpassthru, NULL) == 1);
+        expected_shared_secret = &wycheproof_ecdh_shared_secrets[testvectors[t].shared_offset];
+
+        CHECK(secp256k1_memcmp_var(output_ecdh, expected_shared_secret, testvectors[t].shared_len) == 0);
+    }
+}
+
 static void run_ecdh_tests(void) {
     test_ecdh_api();
     test_ecdh_generator_basepoint();
     test_bad_scalar();
     test_result_basepoint();
+    test_ecdh_wycheproof();
 }
 
 #endif /* SECP256K1_MODULE_ECDH_TESTS_H */

src/wycheproof/WYCHEPROOF_COPYING

@@ -3,9 +3,18 @@
   `b063b4aedae951c69df014cd25fa6d69ae9e8cb9`, see
   https://github.com/google/wycheproof/blob/b063b4aedae951c69df014cd25fa6d69ae9e8cb9/testvectors_v1/ecdsa_secp256k1_sha256_bitcoin_test.json
 
+* The file `ecdh_secp256k1_test.json` in this directory
+  comes from Google's project Wycheproof with git commit
+  `d9f6ec7d8bd8c96da05368999094e4a75ba5cb3d`, see
+  https://github.com/google/wycheproof/blob/d9f6ec7d8bd8c96da05368999094e4a75ba5cb3d/testvectors_v1/ecdh_secp256k1_test.json
+
 * The file `ecdsa_secp256k1_sha256_bitcoin_test.h` is generated from
   `ecdsa_secp256k1_sha256_bitcoin_test.json` using the script
-  `tests_wycheproof_generate.py`.
+  `tests_wycheproof_generate_ecdsa.py`.
+
+* The file `ecdh_secp256k1_test.h` is generated from
+  `ecdh_secp256k1_test.json` using the script
+  `tests_wycheproof_generate_ecdh.py`.
 
 -------------------------------------------------------------------------------
 

src/wycheproof/ecdsa_secp256k1_sha256_bitcoin_test.h

@@ -1,4 +1,4 @@
-/* Note: this file was autogenerated using tests_wycheproof_generate.py. Do not edit. */
+/* Note: this file was autogenerated using tests_wycheproof_generate_ecdsa.py. Do not edit. */
 #define SECP256K1_ECDSA_WYCHEPROOF_NUMBER_TESTVECTORS (463)
 
 typedef struct {