SRP6-Verifier.js

const sha1 = require('js-sha1') /* Install Module js-sha1 */
const { BigInteger } = require('jsbn') /* Install Module jsbn */

const createVerifier = (username, password, salt) => {
    const N = new BigInteger("894B645E89E1535BBDAD5B8B290650530801B18EBFBF5E8FAB3C82872A3E9BB7", 16)
    const g = new BigInteger("7", 16)
    
    const h1 = Buffer.from(sha1.arrayBuffer(`${username}:${password}`.toUpperCase()))
    
    const h2 = Buffer.from(sha1.arrayBuffer(Buffer.concat([salt, h1]))).reverse()
    
    const h2bigint = new BigInteger(h2.toString("hex"), 16)
    
    const verifierBigint = g.modPow(h2bigint, N)
    
    let verifier = Buffer.from(verifierBigint.toByteArray()).reverse()
    
    verifier = verifier.slice(0, 32)
    if (verifier.length != 32) {
        verifier = Buffer.concat([verifier], 32)
    }
    
    return verifier
}

module.exports = { createVerifier }