index.js

var asn = require('asn1.js')
var factor = require('./factor')
var one = new asn.bignum(1)

function urlize(base64) {
  return base64.replace(/\+/g, '-')
    .replace(/\//g, '_')
    .replace(/=/g, '')
}

function hex2b64url(str) {
  return urlize(Buffer.from(str, 'hex').toString('base64'))
}

function fromPEM(data) {
  var text = data.toString().split(/(\r\n|\r|\n)+/g);
  text = text.filter(function(line) {
    return line.trim().length !== 0;
  });
  text = text.slice(1, -1).join('');
  return Buffer.from(text.replace(/[^\w\d\+\/=]+/g, ''), 'base64');
}

var RSAPublicKey = asn.define('RSAPublicKey', function () {
  this.seq().obj(
    this.key('n').int(),
    this.key('e').int()
  )
})

var AlgorithmIdentifier = asn.define('AlgorithmIdentifier', function () {
  this.seq().obj(
    this.key('algorithm').objid(),
    this.key('parameters').optional().any()
  )
})

var PublicKeyInfo = asn.define('PublicKeyInfo', function () {
  this.seq().obj(
    this.key('algorithm').use(AlgorithmIdentifier),
    this.key('publicKey').bitstr()
  )
})

var Version = asn.define('Version', function () {
  this.int({
    0: 'two-prime',
    1: 'multi'
  })
})

var OtherPrimeInfos = asn.define('OtherPrimeInfos', function () {
  this.seq().obj(
    this.key('ri').int(),
    this.key('di').int(),
    this.key('ti').int()
  )
})

var RSAPrivateKey = asn.define('RSAPrivateKey', function () {
  this.seq().obj(
    this.key('version').use(Version),
    this.key('n').int(),
    this.key('e').int(),
    this.key('d').int(),
    this.key('p').int(),
    this.key('q').int(),
    this.key('dp').int(),
    this.key('dq').int(),
    this.key('qi').int(),
    this.key('other').optional().use(OtherPrimeInfos)
  )
})

var PrivateKeyInfo = asn.define('PrivateKeyInfo', function () {
  this.seq().obj(
    this.key('version').use(Version),
    this.key('algorithm').use(AlgorithmIdentifier),
    this.key('privateKey').bitstr()
  )
})

const RSA_OID = '1.2.840.113549.1.1.1'

function addExtras(obj, extras) {
  extras = extras || {}
  Object.keys(extras).forEach(
    function (key) {
      obj[key] = extras[key]
    }
  )
  return obj
}

function pad(hex) {
  return (hex.length % 2 === 1) ? '0' + hex : hex
}

function decodeRsaPublic(buffer, extras) {
  var key = RSAPublicKey.decode(buffer, 'der')
  var e = pad(key.e.toString(16))
  var jwk = {
    kty: 'RSA',
    n: bn2base64url(key.n),
    e: hex2b64url(e)
  }
  return addExtras(jwk, extras)
}

function decodeRsaPrivate(buffer, extras) {
  var key = RSAPrivateKey.decode(buffer, 'der')
  var e = pad(key.e.toString(16))
  var jwk = {
    kty: 'RSA',
    n: bn2base64url(key.n),
    e: hex2b64url(e),
    d: bn2base64url(key.d),
    p: bn2base64url(key.p),
    q: bn2base64url(key.q),
    dp: bn2base64url(key.dp),
    dq: bn2base64url(key.dq),
    qi: bn2base64url(key.qi)
  }
  return addExtras(jwk, extras)
}

function decodePublic(buffer, extras) {
  var info = PublicKeyInfo.decode(buffer, 'der')
  return decodeRsaPublic(info.publicKey.data, extras)
}

function decodePrivate(buffer, extras) {
  var info = PrivateKeyInfo.decode(buffer, 'der')
  return decodeRsaPrivate(info.privateKey.data, extras)
}

function getDecoder(header) {
  var match = /^-----BEGIN (RSA )?(PUBLIC|PRIVATE) KEY-----$/.exec(header)
  if (!match) { return null }
  var isRSA = !!(match[1])
  var isPrivate = (match[2] === 'PRIVATE')
  if (isPrivate) {
    return isRSA ? decodeRsaPrivate : decodePrivate
  }
  else {
    return isRSA ? decodeRsaPublic : decodePublic
  }
}

function pem2jwk(pem, extras) {
  var text = pem.toString().split(/(\r\n|\r|\n)+/g)
  text = text.filter(function(line) {
    return line.trim().length !== 0
  });
  var decoder = getDecoder(text[0])

  text = text.slice(1, -1).join('')
  return decoder(Buffer.from(text.replace(/[^\w\d\+\/=]+/g, ''), 'base64'), extras)
}

function recomputePrimes(jwk) {
  var pq = factor(jwk.e, jwk.d, jwk.n)
  var p = pq.p
  var q = pq.q
  var dp = jwk.d.mod(p.sub(one))
  var dq = jwk.d.mod(q.sub(one))
  var qi = q.invm(p)
  return {
    n: jwk.n,
    e: jwk.e,
    d: jwk.d,
    p: p,
    q: q,
    dp: dp,
    dq: dq,
    qi: qi
  }
}

function parse(jwk) {
  return {
    n: string2bn(jwk.n),
    e: string2bn(jwk.e),
    d: jwk.d && string2bn(jwk.d),
    p: jwk.p && string2bn(jwk.p),
    q: jwk.q && string2bn(jwk.q),
    dp: jwk.dp && string2bn(jwk.dp),
    dq: jwk.dq && string2bn(jwk.dq),
    qi: jwk.qi && string2bn(jwk.qi)
  }
}

function jwk2pem(json) {
  var jwk = parse(json)
  var isPrivate = !!(jwk.d)
  var t = isPrivate ? 'PRIVATE' : 'PUBLIC'
  var header = '-----BEGIN RSA ' + t + ' KEY-----\n'
  var footer = '\n-----END RSA ' + t + ' KEY-----\n'
  var data = null
  if (isPrivate) {
    if (!jwk.p) {
      jwk = recomputePrimes(jwk)
    }
    jwk.version = 'two-prime'
    data = RSAPrivateKey.encode(jwk, 'der')
  }
  else {
    data = RSAPublicKey.encode(jwk, 'der')
  }
  var body = data.toString('base64').match(/.{1,64}/g).join('\n')
  return header + body + footer
}

function bn2base64url(bn) {
  return hex2b64url(pad(bn.toString(16)))
}

function base64url2bn(str) {
  return new asn.bignum(Buffer.from(str, 'base64'))
}

function string2bn(str) {
  if (/^[0-9]+$/.test(str)) {
    return new asn.bignum(str, 10)
  }
  return base64url2bn(str)
}

module.exports = {
  pem2jwk: pem2jwk,
  jwk2pem: jwk2pem,
  BN: asn.bignum
}