;;;; padding.lisp -- implementation of various padding algorithms (in-package :crypto) (defclass padding () ()) (defgeneric add-padding-bytes (padding text start block-offset block-size)   (:documentation "Add padding to the block in TEXT beginning at position START.  Padding is done according to PADDING and assumes that text prior to BLOCK-OFFSET is user-supplied. This function assumes that the portion of TEXT from START to  (+ START BLOCK-SIZE) is writable.")) (defgeneric count-padding-bytes (padding text start block-size)   (:documentation "Return the number of bytes of padding in the block in TEXT beginning at START.  The padding algorithm used for the block is PADDING."))  ;;; PKCS7 padding (defclass pkcs7-padding (padding) ()) (defmethod add-padding-bytes ((padding pkcs7-padding) text start                               block-offset block-size)   (declare (type simple-octet-vector text))   (declare (type index start block-offset))   (let* ((n-padding-bytes (- block-size block-offset))          (pad-byte (if (zerop n-padding-bytes) block-size n-padding-bytes)))     (declare (type (unsigned-byte 8) pad-byte))     (loop for i from (+ start block-offset)           for j from 0 below n-padding-bytes           do (setf (aref text i) pad-byte))     (values)))