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Commit9929ab7

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add hillCipher at cryptography section (trekhleb#424)
* add hillCipher.js and its test case first commit* add README.md* update styleCo-authored-by: Oleksii Trekhleb <trehleb@gmail.com>
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#Hill Cipher
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* The Hill cipher is a polygraphic substitution cipher based on linear algebra.
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Each letter is represented by a number modulo 26.
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* Encryption: to encrypt a message, each block of n letters (considered as an n-component vector) is multiplied by an invertible n × n matrix, against modulus 26.
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Consider the message 'ACT', and the key below (or GYB/NQK/URP in letters):
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| 6 24 1|
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| 13 16 10|
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| 20 17 15|
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The message is the vector:
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| 0|
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| 2|
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| 19|
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Thus the enciphered vector is given by
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| 6 24 1|| 0|| 67|| 15|
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| 13 16 10| | 2 | = | 222 | ≡ | 14 | (mod 26)
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| 20 17 15|| 19|| 319|| 7|
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which corresponds to a ciphertext of 'POH'.
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* Decryption: to decrypt the message, each block is multiplied by the inverse of the matrix used for encryption.
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##Reference
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-[Wikipedia]https://en.wikipedia.org/wiki/Hill_cipher
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-[GeeksforGeeks]https://www.geeksforgeeks.org/hill-cipher/
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importhillCipherEncryptfrom'../hillCipher';
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describe('hillCipher',()=>{
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it('should throw an error when the length of the keyString does not equal to the power of length of the message ',()=>{
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constinvalidLenghOfkeyString=()=>{
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hillCipherEncrypt('hello','helloworld');
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};
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expect(invalidLenghOfkeyString).toThrowError();
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});
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it('should throw an error when message or keyString contains none letter character',()=>{
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constinvalidCharacterInMessage=()=>{
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hillCipherEncrypt('hell3','helloworld');
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};
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constinvalidCharacterInKeyString=()=>{
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hillCipherEncrypt('hello','hel12world');
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};
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expect(invalidCharacterInMessage).toThrowError();
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expect(invalidCharacterInKeyString).toThrowError();
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});
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it('should encrypt passed message using Hill Cipher',()=>{
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expect(hillCipherEncrypt('ACT','GYBNQKURP')).toBe('POH');
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expect(hillCipherEncrypt('GFG','HILLMAGIC')).toBe('SWK');
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});
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});
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/**
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* generate key matrix from given keyString
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*
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*@param {integer} length
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*@param {string} keyString
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*@return {Array[][]} keyMatrix
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*/
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constgenerateKeyMatrix=(length,keyString)=>{
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constkeyMatrix=[];
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letkeyStringIndex=0;
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for(leti=0;i<length;i+=1){
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constkeyMatrixRow=[];
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for(letj=0;j<length;j+=1){
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keyMatrixRow.push((keyString.codePointAt(keyStringIndex))%65);
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keyStringIndex+=1;
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}
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keyMatrix.push(keyMatrixRow);
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}
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returnkeyMatrix;
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};
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/**
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* generate message vector from given message
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*
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*@param {*} message
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*@return {Array} messageVector
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*/
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constgenerateMessageVector=(message)=>{
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constmessageVector=[];
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for(leti=0;i<message.length;i+=1){
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messageVector.push(message.codePointAt(i)%65);
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}
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returnmessageVector;
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};
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/**
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* validate data and encrypt message from given message and keyString
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*
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*@param {string} message plaintext
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*@param {string} keyString
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*@return {string} cipherString
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*
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*/
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exportdefaultfunctionhillCipherEncrypt(message,keyString){
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constlength=keyString.length**(0.5);
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// keyString.length must equal to square of message.length
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if(!Number.isInteger(length)&&length!==message.length){
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thrownewError('invalid key string length');
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}
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// keyString and messange can only contain letters
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if(!(/^[a-zA-Z]+$/.test(message))||!(/^[A-Za-z]+$/.test(keyString))){
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thrownewError('messange and key string can only contain letters');
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}
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constkeyMatrix=generateKeyMatrix(length,keyString);
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constmessageVector=generateMessageVector(message);
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letciperString='';
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for(letrow=0;row<length;row+=1){
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letitem=0;
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for(letcolumn=0;column<length;column+=1){
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item+=keyMatrix[row][column]*messageVector[column];
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}
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ciperString+=String.fromCharCode((item%26)+65);
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}
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returnciperString;
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}

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