diff --git a/docs/design/auth-framework.rst b/docs/design/auth-framework.rst
index 508a82f..597f955 100644
--- a/docs/design/auth-framework.rst
+++ b/docs/design/auth-framework.rst
@@ -256,7 +256,8 @@
                         _verify_signature,
                         _calc_hash,
                         _verify_hash,
-                        _auth_decrypt);
+                        _auth_decrypt,
+                        _convert_pk);
 
 ``_name`` must be a string containing the name of the CL. This name is used for
 debugging purposes.
@@ -266,6 +267,25 @@
 This function is mainly used in the ``MEASURED_BOOT`` and ``DRTM_SUPPORT``
 features to calculate the hashes of various images/data.
 
+Optionally, a platform function can be provided to convert public key
+(_convert_pk). It is only used if the platform saves a hash of the ROTPK.
+Most platforms save the hash of the ROTPK, but some may save slightly different
+information - e.g the hash of the ROTPK plus some related information.
+Defining this function allows to transform the ROTPK used to verify
+the signature to the buffer (a platform specific public key) which
+hash is saved in OTP.
+
+.. code:: c
+
+    int (*convert_pk)(void *full_pk_ptr, unsigned int full_pk_len,
+                      void **hashed_pk_ptr, unsigned int *hashed_pk_len);
+
+
+-  ``full_pk_ptr``: Pointer to Distinguished Encoding Rules (DER) ROTPK.
+-  ``full_pk_len``: DER ROTPK size.
+-  ``hashed_pk_ptr``: to return a pointer to a buffer, which hash should be the one saved in OTP.
+-  ``hashed_pk_len``: previous buffer size
+
 Image Parser Module (IPM)
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/docs/porting-guide.rst b/docs/porting-guide.rst
index bc9c00f..25b55e8 100644
--- a/docs/porting-guide.rst
+++ b/docs/porting-guide.rst
@@ -894,34 +894,6 @@
 either could not be updated or the authentication image descriptor indicates
 that it is not allowed to be updated.
 
-Function: plat_convert_pk()
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-::
-
-    Argument : void *, unsigned int, void **, unsigned int *
-    Return   : int
-
-This function is optional when Trusted Board Boot is enabled, and only
-used if the platform saves a hash of the ROTPK.
-First argument is the Distinguished Encoding Rules (DER) ROTPK.
-Second argument is its size.
-Third argument is used to return a pointer to a buffer, which hash should
-be the one saved in OTP.
-Fourth argument is a pointer to return its size.
-
-Most platforms save the hash of the ROTPK, but some may save slightly different
-information - e.g the hash of the ROTPK plus some related information.
-Defining this function allows to transform the ROTPK used to verify
-the signature to the buffer (a platform specific public key) which
-hash is saved in OTP.
-
-The default implementation copies the input key and length to the output without
-modification.
-
-The function returns 0 on success. Any other value means the expected
-public key buffer cannot be extracted.
-
 Dynamic Root of Trust for Measurement support (in BL31)
 -------------------------------------------------------