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#lang typed/racket
;;; Copyright 2011, Matthias Andreas Benkard.
;;;
;;;-----------------------------------------------------------------------------
;;; This program is free software: you can redistribute it and/or modify
;;; it under the terms of the GNU Affero General Public License as published by
;;; the Free Software Foundation, either version 3 of the License, or
;;; (at your option) any later version.
;;;
;;; This program is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;;; GNU Affero General Public License for more details.
;;;
;;; You should have received a copy of the GNU Affero General Public License
;;; along with this program. If not, see <http://www.gnu.org/licenses/>.
;;;-----------------------------------------------------------------------------
;;;
(require "util.rkt")
(provide: [threefish (Bytes Bytes Bytes -> Bytes)])
(define-type Long Exact-Nonnegative-Integer)
(: l+ (Long Long -> Long))
(define (l+ a b)
(bitwise-and (+ a b) #xffffffffffffffff))
(: lxor (Long Long -> Long))
(define lxor bitwise-xor)
(: lrot (Long Exact-Nonnegative-Integer -> Long))
(define (lrot a e)
(let ([ash (arithmetic-shift a e)])
(bitwise-ior (bitwise-and ash #xffffffffffffffff)
(arithmetic-shift ash -64))))
(define (threefish key tweak plaintext)
(let*: ([size (bytes-length key)]
[words (quotient size 8)]
[rounds (case size
[(32 64) 72]
[(128) 80]
[else (error "Invalid key size")])]
[pbox : (Vectorof Long)
(case size
[(32) #(0 3 2 1)]
[(64) #(2 1 4 7 6 5 0 3)]
[(128) #(0 9 2 13 6 11 4 15 10 7 12 3 14 5 8 1)]
[else (error "Invalid key size")])]
[mixbox : (Vectorof (Vectorof Long))
(case size
[(32) #(#( 5 56)
#(36 28)
#(13 46)
#(58 44)
#(26 20)
#(53 35)
#(11 42)
#(59 50))]
[(64) #(#(38 30 50 53)
#(48 20 43 31)
#(34 14 15 27)
#(26 12 58 7)
#(33 49 8 42)
#(39 27 41 14)
#(29 26 11 9)
#(33 51 39 35))]
[(128) #(#(55 43 37 40 16 22 38 12)
#(25 25 46 13 14 13 52 57)
#(33 8 18 57 21 12 32 54)
#(34 43 25 60 44 9 59 34)
#(28 7 47 48 51 9 35 41)
#(17 6 18 25 43 42 40 15)
#(58 7 32 45 19 18 2 56)
#(47 49 27 58 37 48 53 56))]
[else (error "Invalid key size")])]
[mix
(λ: ([d : Integer] [j : Integer] [x0 : Long] [x1 : Long])
(let*: ([y0 : Long (l+ x0 x1)]
[y1 : Long
(lxor (lrot x1
(vector-ref (vector-ref mixbox (modulo d 8))
j))
y0)])
(values y0 y1)))]
[words->bytes
: ((Vectorof Long) -> Bytes)
(λ (v)
(bytes-append*
(reverse
(for/fold: ([blocks : (Listof Bytes) '()])
([i : Exact-Nonnegative-Integer (in-range words)])
(cons (integer->bytes/size (vector-ref v i) 'little-endian 8)
blocks)))))]
[bytes->word-list
: (Bytes -> (Listof Long))
(λ (b)
(for/fold: ([words : (Listof Long) '()])
([i : Exact-Nonnegative-Integer (in-range words)])
(cons (bytes->integer/le (subbytes b (* i 8) (* (add1 i) 8)))
words)))]
[bytes->words
: (Bytes -> (Vectorof Long))
(λ (b)
(list->vector (reverse (bytes->word-list b))))]
[key-words : (Vectorof Long)
(let ([ks (bytes->word-list key)])
(list->vector
(reverse
(cons
(foldl lxor (quotient (expt 2 64) 3) ks)
ks))))]
[tweak-words : (Vectorof Long)
(let ([t0 (bytes->integer/le (subbytes key 0 8))]
[t1 (bytes->integer/le (subbytes key 8 16))])
(vector t0 t1 (lxor t0 t1)))]
[key-schedule
: (Long Long -> Long)
;; XXX memoize?
(λ: ([s : Long] [i : Long])
(let ([k (vector-ref key-words (modulo (l+ s i) (l+ words 1)))])
(cond
[(= i (- words 1))
(l+ k s)]
[(= i (- words 2))
(l+ k (vector-ref tweak-words (modulo (l+ s 1) 3)))]
[(= i (- words 3))
(l+ k (vector-ref tweak-words (modulo s 3)))]
[else
k])))]
[make-subkey
: (Long -> (Vectorof Long))
(λ: ([s : Long])
(list->vector
(reverse
(for/fold: ([words : (Listof Long) '()])
([i : Exact-Nonnegative-Integer (in-range words)])
(cons (key-schedule s i) words)))))]
[state (bytes->words plaintext)])
(for: ([round : Exact-Nonnegative-Integer (in-range rounds)])
(let: ([e
: (Vectorof Long)
(if (zero? (modulo round 4))
(vector-map l+
state
(make-subkey (quotient round 4)))
(vector-copy state))])
(for: ([j : Exact-Nonnegative-Integer (in-range (quotient words 2))])
(let-values ([(f0 f1)
(mix round
j
(vector-ref e (* 2 j))
(vector-ref e (add1 (* 2 j))))])
(vector-set! e (* 2 j) f0)
(vector-set! e (add1 (* 2 j)) f1)))
(for: ([i : Exact-Nonnegative-Integer (in-range words)])
(vector-set! state i (vector-ref e (vector-ref pbox i))))))
(for: ([i : Exact-Nonnegative-Integer (in-range words)])
(vector-set! state
i
(l+ (vector-ref state i)
(key-schedule (quotient rounds 4) i))))
(words->bytes state)))
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