Cipher_Mode API improvements

The Cipher_Mode::update API is more general than needed to just
support ciphers (this is due to it previously being an API of
Transform which before 8b85b780515 was Cipher_Mode's base class)

Define a less general interface `process` which either processes the
blocks in-place, producing exactly as much output as there was input,
or (SIV/CCM case) saves the entire message for processing in `finish`.
These two uses cover all current or anticipated cipher modes.

Leaves `update` for compatability with existing callers; all that is
needed is an inline function forwarding to `process`.

Removes the return type from `start` - in all cipher implementations,
this always returned an empty vector.

Adds BOTAN_ARG_CHECK macro; right now BOTAN_ASSERT is being used
for argument checking in some places, which is not right at all.

2 files changed, 10 insertions, 16 deletions

diff --git a/src/lib/modes/cbc/cbc.cpp b/src/lib/modes/cbc/cbc.cpp
index fedeaf20d..8066dae12 100644
--- a/src/lib/modes/cbc/cbc.cpp
+++ b/src/lib/modes/cbc/cbc.cpp
@@ -61,7 +61,7 @@ void CBC_Mode::key_schedule(const byte key[], size_t length)
    m_cipher->set_key(key, length);
    }
 
-secure_vector<byte> CBC_Mode::start_raw(const byte nonce[], size_t nonce_len)
+void CBC_Mode::start_msg(const byte nonce[], size_t nonce_len)
    {
    if(!valid_nonce_length(nonce_len))
       throw Invalid_IV_Length(name(), nonce_len);
@@ -73,8 +73,6 @@ secure_vector<byte> CBC_Mode::start_raw(const byte nonce[], size_t nonce_len)
    */
    if(nonce_len)
       m_state.assign(nonce, nonce + nonce_len);
-
-   return secure_vector<byte>();
    }
 
 size_t CBC_Encryption::minimum_final_size() const
@@ -90,12 +88,8 @@ size_t CBC_Encryption::output_length(size_t input_length) const
       return round_up(input_length, cipher().block_size());
    }
 
-void CBC_Encryption::update(secure_vector<byte>& buffer, size_t offset)
+size_t CBC_Encryption::process(uint8_t buf[], size_t sz)
    {
-   BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
-   const size_t sz = buffer.size() - offset;
-   byte* buf = buffer.data() + offset;
-
    const size_t BS = cipher().block_size();
 
    BOTAN_ASSERT(sz % BS == 0, "CBC input is full blocks");
@@ -114,6 +108,8 @@ void CBC_Encryption::update(secure_vector<byte>& buffer, size_t offset)
 
       state().assign(&buf[BS*(blocks-1)], &buf[BS*blocks]);
       }
+
+   return sz;
    }
 
 void CBC_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
@@ -201,12 +197,8 @@ size_t CBC_Decryption::minimum_final_size() const
    return cipher().block_size();
    }
 
-void CBC_Decryption::update(secure_vector<byte>& buffer, size_t offset)
+size_t CBC_Decryption::process(uint8_t buf[], size_t sz)
    {
-   BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
-   const size_t sz = buffer.size() - offset;
-   byte* buf = buffer.data() + offset;
-
    const size_t BS = cipher().block_size();
 
    BOTAN_ASSERT(sz % BS == 0, "Input is full blocks");
@@ -227,6 +219,8 @@ void CBC_Decryption::update(secure_vector<byte>& buffer, size_t offset)
       buf += to_proc;
       blocks -= to_proc / BS;
       }
+
+   return sz;
    }
 
 void CBC_Decryption::finish(secure_vector<byte>& buffer, size_t offset)
diff --git a/src/lib/modes/cbc/cbc.h b/src/lib/modes/cbc/cbc.h
index 961991d4a..caad102d4 100644
--- a/src/lib/modes/cbc/cbc.h
+++ b/src/lib/modes/cbc/cbc.h
@@ -47,7 +47,7 @@ class BOTAN_DLL CBC_Mode : public Cipher_Mode
       byte* state_ptr() { return m_state.data(); }
 
    private:
-      secure_vector<byte> start_raw(const byte nonce[], size_t nonce_len) override;
+      void start_msg(const byte nonce[], size_t nonce_len) override;
 
       void key_schedule(const byte key[], size_t length) override;
 
@@ -65,7 +65,7 @@ class BOTAN_DLL CBC_Encryption : public CBC_Mode
       CBC_Encryption(BlockCipher* cipher, BlockCipherModePaddingMethod* padding) :
          CBC_Mode(cipher, padding) {}
 
-      void update(secure_vector<byte>& blocks, size_t offset = 0) override;
+      size_t process(uint8_t buf[], size_t size) override;
 
       void finish(secure_vector<byte>& final_block, size_t offset = 0) override;
 
@@ -100,7 +100,7 @@ class BOTAN_DLL CBC_Decryption : public CBC_Mode
       CBC_Decryption(BlockCipher* cipher, BlockCipherModePaddingMethod* padding) :
          CBC_Mode(cipher, padding), m_tempbuf(update_granularity()) {}
 
-      void update(secure_vector<byte>& blocks, size_t offset = 0) override;
+      size_t process(uint8_t buf[], size_t size) override;
 
       void finish(secure_vector<byte>& final_block, size_t offset = 0) override;