@andybry/crypto-testing/test/shared/big-int.js

Utilities for expermenting with cryptography

const { assert } = require('chai')
const bigInt = require('../../shared/big-int')

const _855_2BYTES = [0, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1]
const _855_IN_BYTES = [3, 87]
const _855_IN_HEX = '0357'
const _000_1BYTE = [0, 0, 0, 0, 0, 0, 0, 0]

describe('shared/big-int', () => {
  describe('bigIntToBits', () => {
    it('should convert zero to 1 byte length', () => {
      assert.deepEqual(bigInt.bigIntToBits(0n), _000_1BYTE)
    })

    it('should convert a big integer to bits padded to a byte', () => {
      assert.deepEqual(bigInt.bigIntToBits(855n), _855_2BYTES)
    })
  })

  describe('bigIntToBytes', () => {
    it('should convert a big int to bytes', () => {
      assert.deepStrictEqual(
        bigInt.bigIntToBytes(855n),
        Uint8Array.from(_855_IN_BYTES)
      )
    })

    it('should left pad with zeros to min length', () => {
      assert.deepStrictEqual(
        bigInt.bigIntToBytes(855n, 4),
        Uint8Array.from([0, 0, ..._855_IN_BYTES])
      )
    })
  })

  describe('bigIntToBuffer', () => {
    it('should convert a big int to a buffer', () => {
      assert.instanceOf(bigInt.bigIntToBuffer(855n), Buffer)
    })
  })

  describe('bigIntToHex', () => {
    it('should convert a big int to its hex representation', () => {
      assert.equal(bigInt.bigIntToHex(855n), _855_IN_HEX)
    })
  })

  describe('eea', () => {
    it('should calculate the greatest common divisor', () => {
      const [primeA, primeB, gcd] = [59n, 101n, 12n]
      const [a, b] = [primeA * gcd, primeB * gcd]
      assert.strictEqual(bigInt.eea(a, b).gcd, gcd)
    })

    it('should calculate A and B such that A * a + B * b === gcd', () => {
      const [primeA, primeB, gcd] = [59n, 101n, 12n]
      const [a, b] = [primeA * gcd, primeB * gcd]
      const { coefA, coefB } = bigInt.eea(a, b)
      assert.strictEqual(coefA * a + coefB * b, gcd)
    })
  })
})