How to resolve the algorithm Chaocipher step by step in the XPL0 programming language

Published on 12 May 2024 09:40 PM
#Xpl0

How to resolve the algorithm Chaocipher step by step in the XPL0 programming language

Table of Contents

Problem Statement

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 M.Rubin in 2010 and there is a C# implementation here.

Code the algorithm in your language and test that it works with the plaintext 'WELLDONEISBETTERTHANWELLSAID' used in the paper itself.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Chaocipher step by step in the XPL0 programming language

Source code in the xpl0 programming language

include xpllib; \For StrLen, StrCopy, Print

func StrChar(Str, C);
char Str, C;
[loop   [if Str(0) = 0 then return 0;
        if Str(0) = C then return Str;
        Str:= Str+1;
        ];
];

def \CMode\ ENCRYPT, DECRYPT;
char L_alphabet, R_alphabet;

proc Chao(In, Out, Mode, Show_steps);
char In, Out, Mode, Show_steps;
int Len, I, J, Index;
char Store, Left(27), Right(27), Temp(27);
[Len:= StrLen(In);
StrCopy(Left, L_alphabet);
StrCopy(Right, R_alphabet);
Temp(26):= 0;

for I:= 0 to Len-1 do
        [if Show_steps then Print("%s  %s\n", Left, Right);
        if Mode = ENCRYPT then
                [Index:= StrChar(Right, In(I)) - Right;
                Out(I):= Left(Index);
                ]
        else    [Index:= StrChar(Left, In(I)) - Left;
                Out(I):= Right(Index);
                ];
        if I = Len-1 then return;

        \Permute Left
        for J:= Index to 26-1 do Temp(J-Index):= Left(J);
        for J:= 0 to Index-1 do Temp(26-Index+J):= Left(J);
        Store:= Temp(1);
        for J:= 2 to 14-1 do Temp(J-1):= Temp(J);
        Temp(13):= Store;
        StrCopy(Left, Temp);

        \Permute Right
        for J:= Index to 26-1 do Temp(J-Index):= Right(J);
        for J:= 0 to Index-1 do Temp(26-Index+J):= Right(J);
        Store:= Temp(0);
        for J:= 1 to 26-1 do Temp(J-1):= Temp(J);
        Temp(25):= Store;
        Store:= Temp(2);
        for J:= 3 to 14-1 do Temp(J-1):= Temp(J);
        Temp(13):= Store;
        StrCopy(Right, Temp);
        ];
];

char Plain_text, Cipher_text, Plain_text2;
[L_alphabet:= "HXUCZVAMDSLKPEFJRIGTWOBNYQ";
 R_alphabet:= "PTLNBQDEOYSFAVZKGJRIHWXUMC";
 Plain_text:= "WELLDONEISBETTERTHANWELLSAID";
Cipher_text:= MAlloc(StrLen(Plain_text) + 1);
Plain_text2:= MAlloc(StrLen(Plain_text) + 1);
Print("The original plaintext is : %s\n", Plain_text);
Print("\nThe left and right alphabets after each permutation during encryption are :\n\n");
Chao(Plain_text, Cipher_text, ENCRYPT, true);
Print("\nThe ciphertext is : %s\n", Cipher_text);
Chao(Cipher_text, Plain_text2, DECRYPT, false);
Print("\nThe recovered plaintext is : %s\n", Plain_text2);
Release(Cipher_text);
Release(Plain_text2);
]

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