Improve error message for deprecated hash-to-curve strategy (#592)

Author: changtong9

yacl/crypto/ecc/openssl/openssl_group.cc

@@ -297,7 +297,13 @@ EcPoint OpensslGroup::HashToCurve(HashToCurveStrategy strategy,
   HashAlgorithm hash_algorithm;
   switch (strategy) {
     case HashToCurveStrategy::TryAndRehash_SHA2:
-      YACL_THROW("HashToCurveStrategy::TryAndRehash_SHA2 has been deprecated.");
+      YACL_THROW(
+          "HashToCurveStrategy::TryAndRehash_SHA2 has been deprecated.\n"
+          "It is recommended to use curve-specific, standard-compliant "
+          "strategies for better security and interoperability.\n\n"
+          "For example:\n"
+          "  - For NIST curves like P-256: Use SHA256_SSWU_RO_.\n"
+          "  - For the SM2 curve: Use TryAndRehash_SM.");
       break;
     case HashToCurveStrategy::TryAndRehash_SHA3:
       if (bits <= 256) {

yacl/crypto/ecc/openssl/openssl_test.cc

@@ -84,14 +84,8 @@ TEST(OpensslTest, HashToCurveWorks) {
   };
 
   for (int i = 0; i < 1000; ++i) {
-    // is_unique(curve->HashToCurve(HashToCurveStrategy::TryAndRehash_SHA2,
-    //                              fmt::format("id{}", i)));
     is_unique(curve->HashToCurve(HashToCurveStrategy::TryAndRehash_SM,
                                  fmt::format("id{}", i)));
-    // is_unique(curve->HashToCurve(HashToCurveStrategy::TryAndRehash_BLAKE3,
-    //                              fmt::format("id{}", i)));
-    // Same strategy as above TryAndRehash_BLAKE3
-    // is_unique(curve->HashToCurve(fmt::format("id{}", i)));
   }
 }