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//= ===============================================================

// SHA1.js

//

// Module that replicates the SHA-1 Cryptographic Hash

// function in Javascript.

//= ===============================================================

// main variables

const CHAR_SIZE = 8

/**

* Adds padding to binary/hex string representation

*

* @param {string} str - string representation (binary/hex)

* @param {int} bits - total number of bits wanted

* @return {string} - string representation padding with empty (0) bits

*

* @example

* pad("10011", 8); // "00010011"

*/

function pad (str, bits) {

let res = str

while (res.length % bits !== 0) {

res = '0' + res

}

return res

}

/**

* Separates string into chunks of the same size

*

* @param {string} str - string to separate into chunks

* @param {int} size - number of characters wanted in each chunk

* @return {array} - array of original string split into chunks

*

* @example

* chunkify("this is a test", 2)

*/

function chunkify (str, size) {

const chunks = []

for (let i = 0; i < str.length; i += size) {

chunks.push(str.slice(i, i + size))

}

return chunks

}

/**

* Rotates string representation of bits to the left

*

* @param {string} bits - string representation of bits

* @param {int} turns - number of rotations to make

* @return {string} - string representation of bits after rotation

*

* @example

* rotateLeft("1011", 3); // "1101"

*/

function rotateLeft (bits, turns) {

return bits.substr(turns) + bits.substr(0, turns)

}

/**

* Pre-processes message to feed the algorithm loop

*

* @param {string} message - message to pre-process

* @return {string} - processed message

*/

function preProcess (message) {

// convert message to binary representation padded to

// 8 bits, and add 1

let m = message.split('')

.map(e => e.charCodeAt(0))

.map(e => e.toString(2))

.map(e => pad(e, 8))

.join('') + '1'

// extend message by adding empty bits (0)

while (m.length % 512 !== 448) {

m += '0'

}

// length of message in binary, padded, and extended

// to a 64 bit representation

let ml = (message.length * CHAR_SIZE).toString(2)

ml = pad(ml, 8)

ml = '0'.repeat(64 - ml.length) + ml

return m + ml

}

/**

* Hashes message using SHA-1 Cryptographic Hash Function

*

* @param {string} message - message to hash

* @return {string} - message digest (hash value)

*/

function SHA1 (message) {

// main variables

let H0 = 0x67452301

let H1 = 0xEFCDAB89

let H2 = 0x98BADCFE

let H3 = 0x10325476

let H4 = 0xC3D2E1F0

// pre-process message and split into 512 bit chunks

const bits = preProcess(message)

const chunks = chunkify(bits, 512)

chunks.forEach(function (chunk, i) {

// break each chunk into 16 32-bit words

const words = chunkify(chunk, 32)

// extend 16 32-bit words to 80 32-bit words

for (let i = 16; i < 80; i++) {

const val = [words[i - 3], words[i - 8], words[i - 14], words[i - 16]]

.map(e => parseInt(e, 2))

.reduce((acc, curr) => curr ^ acc, 0)

const bin = (val >>> 0).toString(2)

const paddedBin = pad(bin, 32)

const word = rotateLeft(paddedBin, 1)

words.push(word)

}

// initialize variables for this chunk

let [a, b, c, d, e] = [H0, H1, H2, H3, H4]

for (let i = 0; i < 80; i++) {

let f, k

if (i < 20) {

f = (b & c) | (~b & d)

k = 0x5A827999

} else if (i < 40) {

f = b ^ c ^ d

k = 0x6ED9EBA1

} else if (i < 60) {

f = (b & c) | (b & d) | (c & d)

k = 0x8F1BBCDC

} else {

f = b ^ c ^ d

k = 0xCA62C1D6

}

// make sure f is unsigned

f >>>= 0

const aRot = rotateLeft(pad(a.toString(2), 32), 5)

const aInt = parseInt(aRot, 2) >>> 0

const wordInt = parseInt(words[i], 2) >>> 0

const t = aInt + f + e + k + wordInt

e = d >>> 0

d = c >>> 0

const bRot = rotateLeft(pad(b.toString(2), 32), 30)

c = parseInt(bRot, 2) >>> 0

b = a >>> 0

a = t >>> 0

}

// add values for this chunk to main hash variables (unsigned)

H0 = (H0 + a) >>> 0

H1 = (H1 + b) >>> 0

H2 = (H2 + c) >>> 0

H3 = (H3 + d) >>> 0

H4 = (H4 + e) >>> 0

})

// combine hash values of main hash variables and return

const HH = [H0, H1, H2, H3, H4]

.map(e => e.toString(16))

.map(e => pad(e, 8))

.join('')

return HH

}

// export SHA1 function

export { SHA1 }