(in-package :crypto) (defconstant +xtea-n-rounds+ 32) (defconstant +xtea-delta+ #x9e3779b9) (defclass xtea-context (cipher 8-byte-block-mixin)   ((key :accessor key))) (define-block-encryptor xtea 8   (with-words ((y z) plaintext plaintext-start)     (let ((key (key context))           (sum 0))       (declare (type (simple-array (unsigned-byte 32) (4)) key))       (declare (type (unsigned-byte 32) sum))       ;; could probably unroll this loop for reasonable performance gain      (dotimes (i +xtea-n-rounds+)         (setf y (mod32+ y (logxor (mod32+ z (logxor (mod32ash z 4)                                                     (mod32ash z -5)))                                   (mod32+ sum                                           (aref key (logand sum #x3))))))         (setf sum (mod32+ sum +xtea-delta+))         (setf z (mod32+ z (logxor (mod32+ y (logxor (mod32ash y 4)                                                     (mod32ash y -5)))                                   (mod32+ sum                                           (aref key (logand (mod32ash sum -11)                                                             #x3))))))         )       (store-words ciphertext ciphertext-start y z)))) (define-block-decryptor xtea 8   (with-words ((y z) ciphertext ciphertext-start)     (let ((key (key context))           (sum (mod32ash +xtea-delta+ 5)))       (declare (type (simple-array (unsigned-byte 32) (4)) key))       (declare (type (unsigned-byte 32) sum))       ;; could probably unroll this loop for reasonable performance gain      (dotimes (i +xtea-n-rounds+)         (setf z (mod32- z (logxor (mod32+ y (logxor (mod32ash y 4)                                                     (mod32ash y -5)))                                   (mod32+ sum                                           (aref key (logand (mod32ash sum -11)                                                             #x3))))))         (setf sum (mod32- sum +xtea-delta+))         (setf y (mod32- y (logxor (mod32+ z (logxor (mod32ash z 4)                                                     (mod32ash z -5)))                                   (mod32+ sum                                           (aref key (logand sum #x3)))))))       (store-words plaintext plaintext-start y z)))) (defmethod schedule-key ((cipher xtea-context) key)   (let ((ub32key (make-array 4 :element-type '(unsigned-byte 32))))     (with-words ((a b c d) key 0)       (setf (aref ub32key 0) a             (aref ub32key 1) b             (aref ub32key 2) c             (aref ub32key 3) d)       (setf (key cipher) ub32key)       cipher))) (defcipher xtea   (:encrypt-function xtea-encrypt-block)   (:decrypt-function xtea-decrypt-block)   (:block-length 8)   (:key-length (:fixed 16)))