Add support for computing SM2 ZA field to FFI

This is a contribution from Ribose Inc.

3 files changed, 50 insertions, 0 deletions

diff --git a/src/lib/ffi/ffi.h b/src/lib/ffi/ffi.h
index 565d5ce7b..005d32eee 100644
--- a/src/lib/ffi/ffi.h
+++ b/src/lib/ffi/ffi.h
@@ -961,6 +961,12 @@ BOTAN_DLL int botan_privkey_load_sm2_enc(botan_privkey_t* key,
                                          const botan_mp_t scalar,
                                          const char* curve_name);
 
+BOTAN_DLL int botan_pubkey_sm2_compute_za(uint8_t out[],
+                                          size_t* out_len,
+                                          const char* ident,
+                                          const char* hash_algo,
+                                          const botan_pubkey_t key);
+
 /*
 * Public Key Encryption
 */
diff --git a/src/lib/ffi/ffi_pkey_algs.cpp b/src/lib/ffi/ffi_pkey_algs.cpp
index b06fd113c..83ee51768 100644
--- a/src/lib/ffi/ffi_pkey_algs.cpp
+++ b/src/lib/ffi/ffi_pkey_algs.cpp
@@ -6,6 +6,7 @@
 */
 
 #include <botan/ffi.h>
+#include <botan/hash.h>
 #include <botan/internal/ffi_util.h>
 #include <botan/internal/ffi_pkey.h>
 #include <botan/internal/ffi_rng.h>
@@ -570,6 +571,41 @@ int botan_privkey_load_ecdh(botan_privkey_t* key,
 
 /* SM2 specific operations */
 
+int botan_pubkey_sm2_compute_za(uint8_t out[],
+                                size_t* out_len,
+                                const char* ident,
+                                const char* hash_algo,
+                                const botan_pubkey_t key)
+   {
+   if(out == nullptr || out_len == nullptr)
+      return BOTAN_FFI_ERROR_NULL_POINTER;
+   if(ident == nullptr || hash_algo == nullptr || key == nullptr)
+      return BOTAN_FFI_ERROR_NULL_POINTER;
+
+#if defined(BOTAN_HAS_SM2)
+   return ffi_guard_thunk(BOTAN_CURRENT_FUNCTION, [=]() {
+      const Botan::Public_Key& pub_key = safe_get(key);
+      const Botan::EC_PublicKey* ec_key = dynamic_cast<const Botan::EC_PublicKey*>(&pub_key);
+      if(key == nullptr)
+         return BOTAN_FFI_ERROR_BAD_PARAMETER;
+
+      if(ec_key->algo_name() != "SM2_Sig" && ec_key->algo_name() != "SM2_Enc")
+         return BOTAN_FFI_ERROR_BAD_PARAMETER;
+
+      const std::string ident_str(ident);
+      std::unique_ptr<Botan::HashFunction> hash =
+         Botan::HashFunction::create_or_throw(hash_algo);
+
+      const std::vector<uint8_t> za =
+         Botan::sm2_compute_za(*hash, ident_str, ec_key->domain(), ec_key->public_point());
+
+      return write_vec_output(out, out_len, za);
+      });
+#else
+   return BOTAN_FFI_ERROR_NOT_IMPLEMENTED;
+#endif
+   }
+
 int botan_pubkey_load_sm2(botan_pubkey_t* key,
                           const botan_mp_t public_x,
                           const botan_mp_t public_y,
diff --git a/src/tests/test_ffi.cpp b/src/tests/test_ffi.cpp
index 41fa3a044..4a8e7b317 100644
--- a/src/tests/test_ffi.cpp
+++ b/src/tests/test_ffi.cpp
@@ -1408,6 +1408,10 @@ class FFI_Unit_Tests : public Test
          TEST_FFI_OK(botan_privkey_export_pubkey, (&pub, priv));
          ffi_test_pubkey_export(result, pub, priv, rng);
 
+         uint8_t za[32];
+         size_t sizeof_za = sizeof(za);
+         TEST_FFI_OK(botan_pubkey_sm2_compute_za, (za, &sizeof_za, "Ident", "SM3", pub));
+
          // Check key load functions
          botan_mp_t private_scalar, public_x, public_y;
          botan_mp_init(&private_scalar);
@@ -1495,6 +1499,10 @@ class FFI_Unit_Tests : public Test
          TEST_FFI_OK(botan_privkey_export_pubkey, (&pub, priv));
          ffi_test_pubkey_export(result, pub, priv, rng);
 
+         uint8_t za[32];
+         size_t sizeof_za = sizeof(za);
+         TEST_FFI_OK(botan_pubkey_sm2_compute_za, (za, &sizeof_za, "Ident", "SM3", pub));
+
          // Check key load functions
          botan_mp_t private_scalar, public_x, public_y;
          botan_mp_init(&private_scalar);