# Chaocipher

(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Chaocipher is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Description

The Chaocipher was invented by J.F.Byrne in 1918 and, although simple by modern cryptographic standards, does not appear to have been broken until the algorithm was finally disclosed by his family in 2010.

The algorithm is described in this paper by R.Moshe in 2010 and there is a C# implementation here.

The task is to code the algorithm in your language and to test that it works with the plaintext 'WELLDONEISBETTERTHANWELLSAID' used in the paper itself.

## Kotlin

This is based on the C# implementation referred to in the task description. <lang scala>// Version 1.2.40

object Chao {

```   private val lAlphabet = "HXUCZVAMDSLKPEFJRIGTWOBNYQ"
private val rAlphabet = "PTLNBQDEOYSFAVZKGJRIHWXUMC"
```
```   fun encrypt(plainText: String, showSteps: Boolean = false): String {
var left  = lAlphabet
var right = rAlphabet
val cText = CharArray(plainText.length)
val temp  = CharArray(26)
```
```       for (i in 0 until plainText.length) {
if (showSteps) println("\$left  \$right")
val index = right.indexOf(plainText[i])
cText[i] = left[index]
if (i == plainText.length - 1) break
```
```           // permute left
```
```           for (j in index..25) temp[j - index] = left[j]
for (j in 0 until index) temp[26 - index + j] = left[j]
var store = temp[1]
for (j in 2..13) temp[j - 1] = temp[j]
temp[13] = store
left = String(temp)
```
```           // permute right
```
```           for (j in index..25) temp[j - index] = right[j]
for (j in 0 until index) temp[26 - index + j] = right[j]
store = temp[0]
for (j in 1..25) temp[j - 1] = temp[j]
temp[25] = store
store = temp[2]
for (j in 3..13) temp[j - 1] = temp[j]
temp[13] = store
right = String(temp)
}
```
```       return String(cText)
}
```
```   fun decrypt(cipherText: String, showSteps: Boolean = false): String {
var left  = lAlphabet
var right = rAlphabet
val pText = CharArray(cipherText.length)
val temp  = CharArray(26)
```
```       for (i in 0 until cipherText.length) {
if (showSteps) println("\$left  \$right")
val index = left.indexOf(cipherText[i])
pText[i] = right[index]
if (i == cipherText.length - 1) break
```
```           // permute left
```
```           for (j in index..25) temp[j - index] = left[j]
for (j in 0 until index) temp[26 - index + j] = left[j]
var store = temp[1]
for (j in 2..13) temp[j - 1] = temp[j]
temp[13] = store
left = String(temp)
```
```           // permute right
```
```           for (j in index..25) temp[j - index] = right[j]
for (j in 0 until index) temp[26 - index + j] = right[j]
store = temp[0]
for (j in 1..25) temp[j - 1] = temp[j]
temp[25] = store
store = temp[2]
for (j in 3..13) temp[j - 1] = temp[j]
temp[13] = store
right = String(temp)
}
```
```       return String(pText)
}
```

}

fun main(args: Array<String>) {

```   val plainText = "WELLDONEISBETTERTHANWELLSAID"
println("The original plaintext is : \$plainText")
println("\nThe left and right alphabets after each permutation" +
" during encryption are :\n")
val cipherText = Chao.encrypt(plainText, true)
println("\nThe ciphertext is : \$cipherText")
val plainText2 = Chao.decrypt(cipherText)
println("\nThe recovered plaintext is : \$plainText2")
```

}</lang>

Output:
```The original plaintext is : WELLDONEISBETTERTHANWELLSAID

The left and right alphabets after each permutation during encryption are :

HXUCZVAMDSLKPEFJRIGTWOBNYQ  PTLNBQDEOYSFAVZKGJRIHWXUMC
ONYQHXUCZVAMDBSLKPEFJRIGTW  XUCPTLNBQDEOYMSFAVZKGJRIHW
ZILGMTONQXCVARDBSKWPEYHUFJ  LNBIMSAVKGQDJOERYHFWZXUCPT
JILGMTONQXCVAZRDBSKWPEYHUF  LNIMSAVKGQDJOBERYHFWZXUCPT
RBSKWPEYHUFJIDLGMTONQXCVAZ  RYFWZXUCPTLNIHMSAVKGQDJOBE
RSKWPEYHUFJIDBLGMTONQXCVAZ  YFZXUCPTLNIHMWSAVKGQDJOBER
HFJIDBLGMTONQUXCVAZRSKWPEY  LNHMWSAVKGQDJIOBERYFZXUCPT
JDBLGMTONQUXCIVAZRSKWPEYHF  MWAVKGQDJIOBESRYFZXUCPTLNH
BGMTONQUXCIVALZRSKWPEYHFJD  VKQDJIOBESRYFGZXUCPTLNHMWA
YFJDBGMTONQUXHCIVALZRSKWPE  HMAVKQDJIOBESWRYFGZXUCPTLN
HIVALZRSKWPEYCFJDBGMTONQUX  RYGZXUCPTLNHMFAVKQDJIOBESW
QXHIVALZRSKWPUEYCFJDBGMTON  SWYGZXUCPTLNHRMFAVKQDJIOBE
KPUEYCFJDBGMTWONQXHIVALZRS  NHMFAVKQDJIOBRESWYGZXUCPTL
SPUEYCFJDBGMTKWONQXHIVALZR  NHFAVKQDJIOBRMESWYGZXUCPTL
OQXHIVALZRSPUNEYCFJDBGMTKW  WYZXUCPTLNHFAGVKQDJIOBRMES
UEYCFJDBGMTKWNOQXHIVALZRSP  GVQDJIOBRMESWKYZXUCPTLNHFA
JBGMTKWNOQXHIDVALZRSPUEYCF  OBMESWKYZXUCPRTLNHFAGVQDJI

The ciphertext is : OAHQHCNYNXTSZJRRHJBYHQKSOUJY

The recovered plaintext is : WELLDONEISBETTERTHANWELLSAID
```