Sorry there was a minor typo in the last script, use this one instead!
rebol[
title: "String Encryption/Decryption Function (cipher)"
version: 0.1.0
author: "alan parman"
email: [EMAIL PROTECTED]
comment: {This encryption is only as good as your passphrase. Your passphrase may be upto 246 characters. The longer the passphrase, stronger the encryption}
]
cipher: func [{Candidate Function to encrypt/decrypt a string.
Uses CipherSaber (copyright Arnold Reinhold), a version of ARC4}
string [string!] "string to en-decrypt"
/decrypt "decrypt the string"
/pass "supply a passphrase without being prompted"
supplied-pass [string!] "pre-supplied passphrase"
/local passphrase initvector plaintextlength
][
; this function both encrypts and decrypts, for the purposes of this function what goes in is plaintext what comes out is ciphertext
;regardless if you are encrypting or decrypting
;series swap, define a swapping function, needed for encryption engine*******
s-swap: func ["swaps the elements of two series at the given index positions"
a [series!] {1st series}
index-a [integer!] {index position to swap in 1st series}
b [series!] {2nd series}
index-b [integer!] {index position to swap in 2nd series}
/local holder
] [
holder: pick a index-a
poke a index-a pick b index-b
poke b index-b holder
]
;***** begin true works of function here
either decrypt [
plaintext: decompress load string
] [
plaintext: string
]
;*****make or extract initvector, then set plaintext length
initvector: make block! 10
either decrypt [
for n 1 10 1 [
append initvector to-char (pick plaintext n)
]
remove/part plaintext 10
] [
random/seed to-integer checksum/secure form now ; reduces chances of deciphering the date from initvector
loop 10 [
append initvector to-char ((random 256) - 1) ;REBOL's random does 1 to N
]
]
plaintextlength: length? plaintext
;*****get passphrase
either pass [
passphrase: supplied-pass
][
passphrase: ""
]
while [any [
(length? passphrase) > 246
passphrase = ""
]
][
if (length? passphrase) > 246 [print "Passphrase must be 246 characters or less"]
passphrase: ask/hide "passphrase :>> "
]
;*****make key
key: make block! []
foreach letter passphrase [
append key letter
]
append key initvector
keylength: length? key
;*****make state, a block from 0 to 255, in order
state: make block! 256
for i 0 255 1 [append state i]
;*****mix state
;*******try a cs2 type addition, mixing 3 times
for number 1 3 1 [
j: 0 ; remember do 0 to 255, not 1 to 256
;i will index state i.e. each element is state(i)
;n is the index to cycle thru the key (i modulo keylength)
;j is the "randomly" choosen element of state
for i 0 255 1 [; must add + 1 to index i as the arrays are accessed 1 2 3 ... 256
;i.e. first element "0" is element 1 not element 0
n: i // keylength
state-i: to-integer pick state (i + 1)
key-n: to-integer pick key (n + 1)
j: (j + state-i + key-n) // 256
s-swap state (i + 1) state (j + 1)
] ;end of for
] ;***** end of 'for' of cs2 addition
;***** produce the ciphertext
i: j: n: 0
ciphertext: make block! [] ; contents of file going out
if (not decrypt) [
append ciphertext initvector
]
for count 0 (plaintextlength - 1) 1 [
i: ((count + 1) // 256) ; this "+1" is shown, but not clearly, on the instructions
; this is _not_ an indexing adjustment, it is an integral part of the ciphersaber process
state-i: pick state (i + 1)
j: ((j + state-i) // 256)
s-swap state (i + 1) state (j + 1)
n: (((pick state (i + 1)) + (pick state (j + 1))) // 256)
append ciphertext (xor (to-char pick state (n + 1)) (to-char pick plaintext (count + 1)))
] ;end of for
either decrypt [
ciphertext: to-string ciphertext
][
ciphertext: form compress to-string ciphertext
]
unset [plaintext]
return ciphertext
] ; end cipher
