From 7c91ef340a40fc163cda1e1a86db6b044d96e165 Mon Sep 17 00:00:00 2001
From: Jack Lloyd <jack@randombit.net>
Date: Tue, 5 Sep 2017 17:49:25 -0400
Subject: Support arbitrary hashes for SM2 encryption

This is a contribution from Ribose Inc.
---
 src/lib/pubkey/sm2/sm2_enc.cpp | 29 +++++++++++++++++------------
 src/tests/test_sm2.cpp         |  6 +++---
 2 files changed, 20 insertions(+), 15 deletions(-)

(limited to 'src')

diff --git a/src/lib/pubkey/sm2/sm2_enc.cpp b/src/lib/pubkey/sm2/sm2_enc.cpp
index a832dd1ac..988db1ee9 100644
--- a/src/lib/pubkey/sm2/sm2_enc.cpp
+++ b/src/lib/pubkey/sm2/sm2_enc.cpp
@@ -43,11 +43,12 @@ namespace {
 class SM2_Encryption_Operation : public PK_Ops::Encryption
    {
    public:
-      SM2_Encryption_Operation(const SM2_Encryption_PublicKey& key) :
+      SM2_Encryption_Operation(const SM2_Encryption_PublicKey& key, const std::string& kdf_hash) :
          m_p_bytes(key.domain().get_curve().get_p().bytes()),
          m_order(key.domain().get_order()),
          m_base_point(key.domain().get_base_point(), m_order),
-         m_public_point(key.public_point(), m_order)
+         m_public_point(key.public_point(), m_order),
+         m_kdf_hash(kdf_hash)
          {}
 
       size_t max_input_bits() const override
@@ -60,8 +61,8 @@ class SM2_Encryption_Operation : public PK_Ops::Encryption
                                      size_t msg_len,
                                      RandomNumberGenerator& rng) override
          {
-         std::unique_ptr<HashFunction> hash = HashFunction::create("SM3");
-         std::unique_ptr<KDF> kdf = KDF::create("KDF2(SM3)");
+         std::unique_ptr<HashFunction> hash = HashFunction::create_or_throw(m_kdf_hash);
+         std::unique_ptr<KDF> kdf = KDF::create_or_throw("KDF2(" + m_kdf_hash + ")");
 
          secure_vector<uint8_t> ciphertext;
          ciphertext.reserve(1 + m_p_bytes*2 + msg_len + hash->output_length());
@@ -115,15 +116,18 @@ class SM2_Encryption_Operation : public PK_Ops::Encryption
       const BigInt& m_order;
       Blinded_Point_Multiply m_base_point;
       Blinded_Point_Multiply m_public_point;
+      const std::string m_kdf_hash;
    };
 
 class SM2_Decryption_Operation : public PK_Ops::Decryption
    {
    public:
       SM2_Decryption_Operation(const SM2_Encryption_PrivateKey& key,
-                               RandomNumberGenerator& rng) :
+                               RandomNumberGenerator& rng,
+                               const std::string& kdf_hash) :
          m_key(key),
-         m_rng(rng)
+         m_rng(rng),
+         m_kdf_hash(kdf_hash)
          {}
 
       secure_vector<uint8_t> decrypt(uint8_t& valid_mask,
@@ -135,7 +139,8 @@ class SM2_Decryption_Operation : public PK_Ops::Decryption
 
          valid_mask = 0;
 
-         std::unique_ptr<HashFunction> hash = HashFunction::create("SM3");
+         std::unique_ptr<HashFunction> hash = HashFunction::create_or_throw(m_kdf_hash);
+         std::unique_ptr<KDF> kdf = KDF::create_or_throw("KDF2(" + m_kdf_hash + ")");
 
          // Too short to be valid - no timing problem from early return
          if(ciphertext_len < 1 + p_bytes*2 + hash->output_length())
@@ -174,7 +179,6 @@ class SM2_Decryption_Operation : public PK_Ops::Decryption
 
          const size_t msg_len = ciphertext_len - (1 + p_bytes*2 + hash->output_length());
 
-         std::unique_ptr<KDF> kdf = KDF::create("KDF2(SM3)");
          const secure_vector<uint8_t> kdf_output =
             kdf->derive_key(msg_len, kdf_input.data(), kdf_input.size());
 
@@ -196,6 +200,7 @@ class SM2_Decryption_Operation : public PK_Ops::Decryption
       const SM2_Encryption_PrivateKey& m_key;
       RandomNumberGenerator& m_rng;
       const std::string m_ident;
+      const std::string m_kdf_hash;
    };
 
 }
@@ -207,8 +212,8 @@ SM2_Encryption_PublicKey::create_encryption_op(RandomNumberGenerator& /*rng*/,
    {
    if(provider == "base" || provider.empty())
       {
-      if(params == "")
-         return std::unique_ptr<PK_Ops::Encryption>(new SM2_Encryption_Operation(*this));
+      const std::string kdf_hash = (params.empty() ? "SM3" : params);
+      return std::unique_ptr<PK_Ops::Encryption>(new SM2_Encryption_Operation(*this, kdf_hash));
       }
 
    throw Provider_Not_Found(algo_name(), provider);
@@ -221,8 +226,8 @@ SM2_Encryption_PrivateKey::create_decryption_op(RandomNumberGenerator& rng,
    {
    if(provider == "base" || provider.empty())
       {
-      if(params == "")
-         return std::unique_ptr<PK_Ops::Decryption>(new SM2_Decryption_Operation(*this, rng));
+      const std::string kdf_hash = (params.empty() ? "SM3" : params);
+      return std::unique_ptr<PK_Ops::Decryption>(new SM2_Decryption_Operation(*this, rng, kdf_hash));
       }
 
    throw Provider_Not_Found(algo_name(), provider);
diff --git a/src/tests/test_sm2.cpp b/src/tests/test_sm2.cpp
index 88d872435..7172605bf 100644
--- a/src/tests/test_sm2.cpp
+++ b/src/tests/test_sm2.cpp
@@ -71,11 +71,11 @@ class SM2_Encryption_KAT_Tests : public PK_Encryption_Decryption_Test
             "SM2",
             "pubkey/sm2_enc.vec",
             "P,A,B,xG,yG,Order,Cofactor,Msg,x,Nonce,Ciphertext",
-            "") {}
+            "Hash") {}
 
-      virtual std::string default_padding(const VarMap&) const override
+      virtual std::string default_padding(const VarMap& vars) const override
          {
-         return "";
+         return get_opt_str(vars, "Hash", "SM3");
          }
 
       Botan::RandomNumberGenerator* test_rng(const std::vector<uint8_t>& nonce) const override
-- 
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