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/xts/xts.cpp b/src/lib/modes/xts/xts.cpp
index b369fde29..1993bf15f 100644
--- a/src/lib/modes/xts/xts.cpp
+++ b/src/lib/modes/xts/xts.cpp
@@ -105,7 +105,7 @@ void XTS_Mode::key_schedule(const byte key[], size_t length)
    m_tweak_cipher->set_key(&key[key_half], key_half);
    }
 
-secure_vector<byte> XTS_Mode::start_raw(const byte nonce[], size_t nonce_len)
+void XTS_Mode::start_msg(const byte nonce[], size_t nonce_len)
    {
    if(!valid_nonce_length(nonce_len))
       throw Invalid_IV_Length(name(), nonce_len);
@@ -114,8 +114,6 @@ secure_vector<byte> XTS_Mode::start_raw(const byte nonce[], size_t nonce_len)
    m_tweak_cipher->encrypt(m_tweak.data());
 
    update_tweak(0);
-
-   return secure_vector<byte>();
    }
 
 void XTS_Mode::update_tweak(size_t which)
@@ -136,12 +134,8 @@ size_t XTS_Encryption::output_length(size_t input_length) const
    return input_length;
    }
 
-void XTS_Encryption::update(secure_vector<byte>& buffer, size_t offset)
+size_t XTS_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, "Input is full blocks");
@@ -163,6 +157,8 @@ void XTS_Encryption::update(secure_vector<byte>& buffer, size_t offset)
 
       update_tweak(to_proc);
       }
+
+   return sz;
    }
 
 void XTS_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
@@ -214,12 +210,8 @@ size_t XTS_Decryption::output_length(size_t input_length) const
    return input_length;
    }
 
-void XTS_Decryption::update(secure_vector<byte>& buffer, size_t offset)
+size_t XTS_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");
@@ -241,6 +233,8 @@ void XTS_Decryption::update(secure_vector<byte>& buffer, size_t offset)
 
       update_tweak(to_proc);
       }
+
+   return sz;
    }
 
 void XTS_Decryption::finish(secure_vector<byte>& buffer, size_t offset)
diff --git a/src/lib/modes/xts/xts.h b/src/lib/modes/xts/xts.h
index e751b1644..6c4ba8d99 100644
--- a/src/lib/modes/xts/xts.h
+++ b/src/lib/modes/xts/xts.h
@@ -42,7 +42,7 @@ class BOTAN_DLL XTS_Mode : public Cipher_Mode
       void update_tweak(size_t last_used);
 
    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;
 
       std::unique_ptr<BlockCipher> m_cipher, m_tweak_cipher;
@@ -57,7 +57,7 @@ class BOTAN_DLL XTS_Encryption final : public XTS_Mode
    public:
       explicit XTS_Encryption(BlockCipher* cipher) : XTS_Mode(cipher) {}
 
-      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;
 
@@ -72,7 +72,7 @@ class BOTAN_DLL XTS_Decryption final : public XTS_Mode
    public:
       explicit XTS_Decryption(BlockCipher* cipher) : XTS_Mode(cipher) {}
 
-      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;