diff --git a/src/security/transform/base64-decode.hpp b/src/security/transform/base64-decode.hpp
index cfd5876..0ef0a46 100644
--- a/src/security/transform/base64-decode.hpp
+++ b/src/security/transform/base64-decode.hpp
@@ -49,7 +49,7 @@
   /**
    * @brief Read partial transformation results into output buffer and write them into next module.
    */
-  virtual void
+  void
   preTransform() final;
 
   /**
@@ -57,7 +57,7 @@
    *
    * @return number of bytes that have been accepted by the converter
    */
-  virtual size_t
+  size_t
   convert(const uint8_t* buf, size_t size) final;
 
   /**
@@ -65,7 +65,7 @@
    *
    * This method with read all decoding results from the converter and write them into next module.
    */
-  virtual void
+  void
   finalize() final;
 
   /**
diff --git a/src/security/transform/base64-encode.hpp b/src/security/transform/base64-encode.hpp
index ac9c664..7e9d99d 100644
--- a/src/security/transform/base64-encode.hpp
+++ b/src/security/transform/base64-encode.hpp
@@ -46,14 +46,14 @@
   /**
    * @brief Read partial transformation result (if exists) from BIO
    */
-  virtual void
+  void
   preTransform() final;
 
   /**
-   * @brief Encode @data into base64 format.
+   * @brief Encode @p data into base64 format.
    * @return The number of input bytes that have been accepted by the converter.
    */
-  virtual size_t
+  size_t
   convert(const uint8_t* data, size_t dataLen) final;
 
   /**
@@ -61,7 +61,7 @@
    *
    * This method with read all encoding results from the converter and write them into next module.
    */
-  virtual void
+  void
   finalize() final;
 
   /**
diff --git a/src/security/transform/block-cipher.hpp b/src/security/transform/block-cipher.hpp
index dd67858..885bd43 100644
--- a/src/security/transform/block-cipher.hpp
+++ b/src/security/transform/block-cipher.hpp
@@ -56,7 +56,7 @@
   /**
    * @brief Read partial transformation result (if exists) from BIO
    */
-  virtual void
+  void
   preTransform() final;
 
   /**
@@ -64,13 +64,13 @@
    *
    * @return number of bytes that are actually accepted
    */
-  virtual size_t
+  size_t
   convert(const uint8_t* data, size_t dataLen) final;
 
   /**
    * @brief Finalize the encryption
    */
-  virtual void
+  void
   finalize() final;
 
   /**
diff --git a/src/security/transform/bool-sink.hpp b/src/security/transform/bool-sink.hpp
index 12e62c9..d7d02e3 100644
--- a/src/security/transform/bool-sink.hpp
+++ b/src/security/transform/bool-sink.hpp
@@ -49,13 +49,13 @@
    *
    * @return the same value as @p size.
    */
-  virtual size_t
+  size_t
   doWrite(const uint8_t* buf, size_t size) final;
 
   /**
    * @brief Finalize sink processing
    */
-  virtual void
+  void
   doEnd() final;
 
 private:
diff --git a/src/security/transform/buffer-source.hpp b/src/security/transform/buffer-source.hpp
index 0833a0f..c091d98 100644
--- a/src/security/transform/buffer-source.hpp
+++ b/src/security/transform/buffer-source.hpp
@@ -62,7 +62,7 @@
   /**
    * @brief Write the whole buffer into the next module.
    */
-  virtual void
+  void
   doPump() final;
 
 private:
diff --git a/src/security/transform/digest-filter.hpp b/src/security/transform/digest-filter.hpp
index 935899f..952c4a7 100644
--- a/src/security/transform/digest-filter.hpp
+++ b/src/security/transform/digest-filter.hpp
@@ -47,13 +47,13 @@
    *
    * @return The number of bytes that have been accepted
    */
-  virtual size_t
+  size_t
   convert(const uint8_t* buf, size_t size) final;
 
   /**
    * @brief Finalize digest calculation and write the digest into next module.
    */
-  virtual void
+  void
   finalize() final;
 
 private:
diff --git a/src/security/transform/hex-decode.hpp b/src/security/transform/hex-decode.hpp
index 77d477d..5601ca4 100644
--- a/src/security/transform/hex-decode.hpp
+++ b/src/security/transform/hex-decode.hpp
@@ -50,13 +50,13 @@
    *
    * @return number of input bytes that are accepted
    */
-  virtual size_t
+  size_t
   convert(const uint8_t* buf, size_t size) final;
 
   /**
    * @throws Error if pending byte exists.
    */
-  virtual void
+  void
   finalize() final;
 
   /**
diff --git a/src/security/transform/hex-encode.hpp b/src/security/transform/hex-encode.hpp
index 95fc6e8..14a9b41 100644
--- a/src/security/transform/hex-encode.hpp
+++ b/src/security/transform/hex-encode.hpp
@@ -51,7 +51,7 @@
    *
    * @return The number of input bytes that have been accepted by the converter.
    */
-  virtual size_t
+  size_t
   convert(const uint8_t* data, size_t dataLen) final;
 
   /**
diff --git a/src/security/transform/hmac-filter.hpp b/src/security/transform/hmac-filter.hpp
index 5409952..0cec1fd 100644
--- a/src/security/transform/hmac-filter.hpp
+++ b/src/security/transform/hmac-filter.hpp
@@ -48,13 +48,13 @@
    *
    * @return The number of bytes that are actually accepted
    */
-  virtual size_t
+  size_t
   convert(const uint8_t* buf, size_t size) final;
 
   /**
    * @brief Finalize HMAC calculation and write the HMAC into next module.
    */
-  virtual void
+  void
   finalize() final;
 
 private:
diff --git a/src/security/transform/signer-filter.hpp b/src/security/transform/signer-filter.hpp
index 8db11f3..dc4ffff 100644
--- a/src/security/transform/signer-filter.hpp
+++ b/src/security/transform/signer-filter.hpp
@@ -47,13 +47,13 @@
    *
    * @return The number of bytes that are actually accepted
    */
-  virtual size_t
+  size_t
   convert(const uint8_t* buf, size_t size) final;
 
   /**
    * @brief Finalize signing and write the signature into next module.
    */
-  virtual void
+  void
   finalize() final;
 
 private:
diff --git a/src/security/transform/step-source.hpp b/src/security/transform/step-source.hpp
index 76388f7..a017fc6 100644
--- a/src/security/transform/step-source.hpp
+++ b/src/security/transform/step-source.hpp
@@ -68,9 +68,8 @@
    *
    * use write() and end() method explicitly to input data.
    */
-  virtual void
+  void
   doPump() final;
-
 };
 
 typedef StepSource stepSource;
diff --git a/src/security/transform/stream-sink.hpp b/src/security/transform/stream-sink.hpp
index ed41cbd..f384dc4 100644
--- a/src/security/transform/stream-sink.hpp
+++ b/src/security/transform/stream-sink.hpp
@@ -47,13 +47,13 @@
    *
    * @return number of bytes that have been written into the stream
    */
-  virtual size_t
+  size_t
   doWrite(const uint8_t* buf, size_t size) final;
 
   /**
    * @brief Finalize sink processing
    */
-  virtual void
+  void
   doEnd() final;
 
 private:
diff --git a/src/security/transform/stream-source.hpp b/src/security/transform/stream-source.hpp
index b818fe7..5dcefdd 100644
--- a/src/security/transform/stream-source.hpp
+++ b/src/security/transform/stream-source.hpp
@@ -49,7 +49,7 @@
   /**
    * @brief Read bytes from the input stream until EOF is reached and write them into the next module.
    */
-  virtual void
+  void
   doPump() final;
 
 public:
diff --git a/src/security/transform/strip-space.hpp b/src/security/transform/strip-space.hpp
index 7cc4dc8..d0e50aa 100644
--- a/src/security/transform/strip-space.hpp
+++ b/src/security/transform/strip-space.hpp
@@ -44,7 +44,7 @@
   StripSpace(const char* whitespaces = DEFAULT_WHITESPACES);
 
 private:
-  virtual size_t
+  size_t
   convert(const uint8_t* buf, size_t buflen) final;
 
 private:
diff --git a/src/security/transform/transform-base.hpp b/src/security/transform/transform-base.hpp
index 94fd43c..a06f0b1 100644
--- a/src/security/transform/transform-base.hpp
+++ b/src/security/transform/transform-base.hpp
@@ -222,7 +222,7 @@
   /**
    * @brief Abstraction of data processing in an intermediate module
    */
-  virtual size_t
+  size_t
   doWrite(const uint8_t* data, size_t dataLen) final;
 
   /**
@@ -230,7 +230,7 @@
    *
    * This method will not return until all transformation result is written into next module
    */
-  virtual void
+  void
   doEnd() final;
 
   /**
diff --git a/src/security/transform/verifier-filter.hpp b/src/security/transform/verifier-filter.hpp
index ee69f03..7fed9fc 100644
--- a/src/security/transform/verifier-filter.hpp
+++ b/src/security/transform/verifier-filter.hpp
@@ -49,13 +49,13 @@
    *
    * @return The number of bytes that are actually written
    */
-  virtual size_t
+  size_t
   convert(const uint8_t* buf, size_t size) final;
 
   /**
    * @brief Finalize verification and write the result (single byte) into next module.
    */
-  virtual void
+  void
   finalize() final;
 
 private: