Add MAC::start_msg, update GMAC

GMAC needs a per-message nonce specified with `start`, and other
MACs are capable of using nonces (Skein-MAC, for instance) so move
this API up to MAC class.

Change GMAC::clone to clone the owned cipher.

4 files changed, 59 insertions, 47 deletions

diff --git a/src/lib/mac/gmac/gmac.cpp b/src/lib/mac/gmac/gmac.cpp
index 946e22cf0..4461cf370 100644
--- a/src/lib/mac/gmac/gmac.cpp
+++ b/src/lib/mac/gmac/gmac.cpp
@@ -64,17 +64,7 @@ void GMAC::key_schedule(const byte key[], size_t size)
    m_cipher->encrypt(m_H_ad.data(), m_H.data());
    }
 
-void GMAC::start(const std::vector<byte>& nonce)
-   {
-   start(nonce.data(), nonce.size());
-   }
-
-void GMAC::start(const secure_vector<byte>& nonce)
-   {
-   start(nonce.data(), nonce.size());
-   }
-
-void GMAC::start(const byte nonce[], size_t nonce_len)
+void GMAC::start_msg(const byte nonce[], size_t nonce_len)
    {
    secure_vector<byte> y0(GCM_BS);
 
@@ -118,6 +108,6 @@ void GMAC::final_result(byte mac[])
 
 MessageAuthenticationCode* GMAC::clone() const
    {
-   return new GMAC(BlockCipher::create(m_cipher->name()).release());
+   return new GMAC(m_cipher->clone());
    }
 }
diff --git a/src/lib/mac/gmac/gmac.h b/src/lib/mac/gmac/gmac.h
index b651c2e11..b05c5451f 100644
--- a/src/lib/mac/gmac/gmac.h
+++ b/src/lib/mac/gmac/gmac.h
@@ -53,7 +53,7 @@ class BOTAN_DLL GMAC : public MessageAuthenticationCode,
       */
       void start(const std::vector<byte>& nonce);
 
-      Key_Length_Specification key_spec() const
+      Key_Length_Specification key_spec() const override
          {
          return m_cipher->key_spec();
          }
@@ -71,7 +71,7 @@ class BOTAN_DLL GMAC : public MessageAuthenticationCode,
    private:
       void add_data(const byte[], size_t) override;
       void final_result(byte[]) override;
-      void start_msg(const byte nonce[], size_t nonce_len);
+      void start_msg(const byte nonce[], size_t nonce_len) override;
       void key_schedule(const byte key[], size_t size) override;
 
       static const size_t GCM_BS = 16;
diff --git a/src/lib/mac/mac.h b/src/lib/mac/mac.h
index 9c3614f33..d7808c1bf 100644
--- a/src/lib/mac/mac.h
+++ b/src/lib/mac/mac.h
@@ -51,6 +51,55 @@ class BOTAN_DLL MessageAuthenticationCode : public Buffered_Computation,
       virtual ~MessageAuthenticationCode() {}
 
       /**
+      * Prepare for processing a message under the specified nonce
+      *
+      * Most MACs neither require nor support a nonce; for these algorithms
+      * calling `start_msg` is optional and calling it with anything other than
+      * an empty string is an error. One MAC which *requires* a per-message
+      * nonce be specified is GMAC.
+      *
+      * @param nonce the message nonce bytes
+      * @param nonce_len the size of len in bytes
+      * Default implementation simply rejects all non-empty nonces
+      * since most hash/MAC algorithms do not support randomization
+      */
+      virtual void start_msg(const byte nonce[], size_t nonce_len)
+         {
+         BOTAN_UNUSED(nonce);
+         if(nonce_len > 0)
+            throw Invalid_IV_Length(name(), nonce_len);
+         }
+
+      /**
+      * Begin processing a message with a nonce
+      *
+      * @param nonce the per message nonce
+      */
+      template<typename Alloc>
+      void start(const std::vector<byte, Alloc>& nonce)
+         {
+         start_msg(nonce.data(), nonce.size());
+         }
+
+      /**
+      * Begin processing a message.
+      * @param nonce the per message nonce
+      * @param nonce_len length of nonce
+      */
+      void start(const byte nonce[], size_t nonce_len)
+         {
+         start_msg(nonce, nonce_len);
+         }
+
+      /**
+      * Begin processing a message.
+      */
+      void start()
+         {
+         return start_msg(nullptr, 0);
+         }
+
+      /**
       * Verify a MAC.
       * @param in the MAC to verify as a byte array
       * @param length the length of param in
diff --git a/src/tests/test_mac.cpp b/src/tests/test_mac.cpp
index 43b19b14e..33972fabc 100644
--- a/src/tests/test_mac.cpp
+++ b/src/tests/test_mac.cpp
@@ -11,10 +11,6 @@
   #include <botan/mac.h>
 #endif
 
-#if defined(BOTAN_HAS_GMAC)
-  #include <botan/gmac.h>
-#endif
-
 namespace Botan_Tests {
 
 namespace {
@@ -60,14 +56,7 @@ class Message_Auth_Tests : public Text_Based_Test
             result.test_eq(provider, mac->name(), algo);
 
             mac->set_key(key);
-
-#if defined(BOTAN_HAS_GMAC)
-            // GMAC needs to set an IV
-            if(Botan::GMAC* gmac = dynamic_cast<Botan::GMAC*>(mac.get()))
-               {
-               gmac->start(iv);
-               }
-#endif
+            mac->start(iv);
 
             mac->update(input);
 
@@ -80,13 +69,7 @@ class Message_Auth_Tests : public Text_Based_Test
 
             // do the same to test verify_mac()
             mac->set_key(key);
-#if defined(BOTAN_HAS_GMAC)
-            // GMAC needs to set an IV
-            if(Botan::GMAC* gmac = dynamic_cast<Botan::GMAC*>(mac.get()))
-               {
-               gmac->start(iv);
-               }
-#endif
+            mac->start(iv);
             mac->update(input);
 
             result.test_eq(provider + " correct mac", mac->verify_mac(expected.data(), expected.size()), true);
@@ -94,13 +77,8 @@ class Message_Auth_Tests : public Text_Based_Test
             if(input.size() > 2)
                {
                mac->set_key(key); // Poly1305 requires the re-key
-#if defined(BOTAN_HAS_GMAC)
-               // GMAC needs to set an IV
-               if(Botan::GMAC* gmac = dynamic_cast<Botan::GMAC*>(mac.get()))
-                  {
-                  gmac->start(iv);
-                  }
-#endif
+               mac->start(iv);
+
                mac->update(input[0]);
                mac->update(&input[1], input.size() - 2);
                mac->update(input[input.size()-1]);
@@ -109,13 +87,8 @@ class Message_Auth_Tests : public Text_Based_Test
 
                // do the same to test verify_mac()
                mac->set_key(key);
-#if defined(BOTAN_HAS_GMAC)
-               // GMAC needs to set an IV
-               if(Botan::GMAC* gmac = dynamic_cast<Botan::GMAC*>(mac.get()))
-                  {
-                  gmac->start(iv);
-                  }
-#endif
+               mac->start(iv);
+
                mac->update(input[ 0 ]);
                mac->update(&input[ 1 ], input.size() - 2);
                mac->update(input[ input.size() - 1 ]);