Introduce Block::Decryptor<> CRTP base class.

Inherit DesDecryptor from it.

Chaos/Cipher/Block/Decryptor.hpp

@@ -0,0 +1,40 @@
+#ifndef CHAOS_CIPHER_BLOCK_DECRYPTOR_HPP
+#define CHAOS_CIPHER_BLOCK_DECRYPTOR_HPP
+
+namespace Chaos::Cipher::Block
+{
+
+template<typename T>
+class Decryptor
+{
+public:
+    template<typename OutputIt, typename InputIt>
+    void DecryptBlock(OutputIt out, InputIt inBegin, InputIt inEnd)
+    {
+        Impl().DecryptBlock(out, inBegin, inEnd);
+    }
+
+    template<typename Block>
+    auto DecryptBlock(Block block)
+    {
+        return Impl().DecryptBlock(block);
+    }
+
+protected:
+    Decryptor() = default;
+
+private:
+    const T & Impl() const
+    {
+        return static_cast<const T &>(*this);
+    }
+
+    T & Impl()
+    {
+        return static_cast<T &>(*this);
+    }
+};
+
+} // namespace Chaos::Cipher::Block
+
+#endif // CHAOS_CIPHER_BLOCK_DECRYPTOR_HPP