Add KEM scheme for McEliece

3 files changed, 111 insertions, 0 deletions

diff --git a/src/lib/pubkey/mce/info.txt b/src/lib/pubkey/mce/info.txt
index 6c0da2199..bc4249422 100644
--- a/src/lib/pubkey/mce/info.txt
+++ b/src/lib/pubkey/mce/info.txt
@@ -6,6 +6,7 @@ gf2m_rootfind_dcmp.h
 gf2m_small_m.h
 goppa_code.h
 mce_overbeck_cca2.h
+mce_kem.h
 mceliece.h
 mceliece_key.h
 polyn_gf2m.h
diff --git a/src/lib/pubkey/mce/mce_kem.cpp b/src/lib/pubkey/mce/mce_kem.cpp
new file mode 100644
index 000000000..31dc2cfe2
--- /dev/null
+++ b/src/lib/pubkey/mce/mce_kem.cpp
@@ -0,0 +1,65 @@
+/**
+ * (C) 2014 cryptosource GmbH
+ * (C) 2014 Falko Strenzke [email protected]
+ *
+ * Distributed under the terms of the Botan license
+ *
+ */
+
+#include <botan/mce_kem.h>
+#include <botan/sha2_64.h>
+
+namespace Botan {
+
+McEliece_KEM_Encryptor::McEliece_KEM_Encryptor(const McEliece_PublicKey& public_key) :
+   m_raw_pub_op(public_key, public_key.get_code_length())
+   {
+   }
+
+std::pair<secure_vector<byte>, secure_vector<byte>>
+McEliece_KEM_Encryptor::encrypt(RandomNumberGenerator& rng)
+   {
+   const McEliece_PublicKey& key = m_raw_pub_op.get_key();
+   secure_vector<Botan::byte> plaintext((key.get_message_word_bit_length()+7)/8);
+   rng.randomize(&plaintext[0], plaintext.size() );
+
+   // unset unused bits in the last plaintext byte
+   u32bit used = key.get_message_word_bit_length() % 8;
+   if(used)
+      {
+      byte mask = (1 << used) - 1;
+      plaintext[plaintext.size() - 1] &= mask;
+      }
+
+   secure_vector<gf2m> err_pos = create_random_error_positions(key.get_code_length(), key.get_t(), rng);
+
+   mceliece_message_parts parts(err_pos, plaintext, key.get_code_length());
+   secure_vector<Botan::byte> message_and_error_input = parts.get_concat();
+
+   SHA_512 hash;
+   hash.update(message_and_error_input);
+   secure_vector<byte> sym_key = hash.final();
+   secure_vector<byte> ciphertext = m_raw_pub_op.encrypt(&message_and_error_input[0],
+                                                         message_and_error_input.size(), rng);
+
+   return std::make_pair(ciphertext, sym_key);
+   }
+
+
+McEliece_KEM_Decryptor::McEliece_KEM_Decryptor(const McEliece_PrivateKey& mce_key) :
+   m_raw_priv_op(mce_key)
+   {
+   }
+
+secure_vector<Botan::byte> McEliece_KEM_Decryptor::decrypt(const byte msg[], size_t msg_len)
+   {
+   secure_vector<Botan::byte> message_and_error = m_raw_priv_op.decrypt(&msg[0], msg_len );
+
+   SHA_512 hash;
+   hash.update(message_and_error);
+
+   secure_vector<byte> sym_key = hash.final();
+   return sym_key;
+   }
+
+}
diff --git a/src/lib/pubkey/mce/mce_kem.h b/src/lib/pubkey/mce/mce_kem.h
new file mode 100644
index 000000000..4e46a0fab
--- /dev/null
+++ b/src/lib/pubkey/mce/mce_kem.h
@@ -0,0 +1,45 @@
+/**
+ * (C) 2014 cryptosource GmbH
+ * (C) 2014 Falko Strenzke [email protected]
+ *
+ * Distributed under the terms of the Botan license
+ *
+ */
+
+#ifndef BOTAN_MCE_KEM_H__
+#define BOTAN_MCE_KEM_H__
+
+#include <botan/mceliece.h>
+#include <utility>
+
+namespace Botan {
+
+class BOTAN_DLL McEliece_KEM_Encryptor
+   {
+   public:
+      McEliece_KEM_Encryptor(const McEliece_PublicKey& public_key);
+
+      /**
+      * returns the pair (mceliece ciphertext, symmetric key)
+      */
+      std::pair<secure_vector<byte>, secure_vector<byte>> encrypt(RandomNumberGenerator& rng);
+
+   private:
+      McEliece_Public_Operation m_raw_pub_op;
+   };
+
+class BOTAN_DLL McEliece_KEM_Decryptor
+   {
+    public:
+      McEliece_KEM_Decryptor(const McEliece_PrivateKey& mce_key);
+
+      /**
+      * returns the derived 512-bit symmetric key
+      */
+      secure_vector<Botan::byte> decrypt(const byte msg[], size_t msg_len);
+   private:
+      McEliece_Private_Operation m_raw_priv_op;
+  };
+}
+
+#endif /* h-guard */