bluecrypt-keypairs.js/lib/rsa.js

/*global Promise*/
(function (exports) {
'use strict';

var RSA = exports.Rasha = {};
if ('undefined' !== typeof module) { module.exports = RSA; }
var Enc = {};
var textEncoder = new TextEncoder();

RSA._stance = "We take the stance that if you're knowledgeable enough to"
  + " properly and securely use non-standard crypto then you shouldn't need Bluecrypt anyway.";
RSA._universal = "Bluecrypt only supports crypto with standard cross-browser and cross-platform support.";
RSA.generate = function (opts) {
  var wcOpts = {};
  if (!opts) { opts = {}; }
  if (!opts.kty) { opts.kty = 'RSA'; }

  // Support PSS? I don't think it's used for Let's Encrypt
  wcOpts.name = 'RSASSA-PKCS1-v1_5';
  if (!opts.modulusLength) {
    opts.modulusLength = 2048;
  }
  wcOpts.modulusLength = opts.modulusLength;
  if (wcOpts.modulusLength >= 2048 && wcOpts.modulusLength < 3072) {
    // erring on the small side... for no good reason
    wcOpts.hash = { name: "SHA-256" };
  } else if (wcOpts.modulusLength >= 3072 && wcOpts.modulusLength < 4096) {
    wcOpts.hash = { name: "SHA-384" };
  } else if (wcOpts.modulusLength < 4097) {
    wcOpts.hash = { name: "SHA-512" };
  } else {
    // Public key thumbprints should be paired with a hash of similar length,
    // so anything above SHA-512's keyspace would be left under-represented anyway.
    return Promise.Reject(new Error("'" + wcOpts.modulusLength + "' is not within the safe and universally"
      + " acceptable range of 2048-4096. Typically you should pick 2048, 3072, or 4096, though other values"
      + " divisible by 8 are allowed. " + RSA._stance));
  }
  // TODO maybe allow this to be set to any of the standard values?
  wcOpts.publicExponent = new Uint8Array([0x01, 0x00, 0x01]);

  var extractable = true;
  return window.crypto.subtle.generateKey(
    wcOpts
  , extractable
  , [ 'sign', 'verify' ]
  ).then(function (result) {
    return window.crypto.subtle.exportKey(
      "jwk"
    , result.privateKey
    ).then(function (privJwk) {
      return {
        private: privJwk
      , public: RSA.neuter({ jwk: privJwk })
      };
    });
  });
};

// Chopping off the private parts is now part of the public API.
// I thought it sounded a little too crude at first, but it really is the best name in every possible way.
RSA.neuter = function (opts) {
  // trying to find the best balance of an immutable copy with custom attributes
  var jwk = {};
  Object.keys(opts.jwk).forEach(function (k) {
    if ('undefined' === typeof opts.jwk[k]) { return; }
    // ignore RSA private parts
    if (-1 !== ['d', 'p', 'q', 'dp', 'dq', 'qi'].indexOf(k)) { return; }
    jwk[k] = JSON.parse(JSON.stringify(opts.jwk[k]));
  });
  return jwk;
};

// https://stackoverflow.com/questions/42588786/how-to-fingerprint-a-jwk
RSA.__thumbprint = function (jwk) {
  // Use the same entropy for SHA as for key
  var len = Math.floor(jwk.n.length * 0.75);
  var alg = 'SHA-256';
  // TODO this may be a bug
  // need to confirm that the padding is no more or less than 1 byte
  if (len >= 511) {
    alg = 'SHA-512';
  } else if (len >= 383) {
    alg = 'SHA-384';
  }
  return window.crypto.subtle.digest(
    { name: alg }
  , textEncoder.encode('{"e":"' + jwk.e + '","kty":"RSA","n":"' + jwk.n + '"}')
  ).then(function (hash) {
    return Enc.bufToUrlBase64(new Uint8Array(hash));
  });
};

RSA.thumbprint = function (opts) {
  return Promise.resolve().then(function () {
    var jwk;
    if ('EC' === opts.kty) {
      jwk = opts;
    } else if (opts.jwk) {
      jwk = opts.jwk;
    } else {
      return RSA.import(opts).then(function (jwk) {
        return RSA.__thumbprint(jwk);
      });
    }
    return RSA.__thumbprint(jwk);
  });
};

Enc.bufToUrlBase64 = function (u8) {
  return Enc.bufToBase64(u8)
    .replace(/\+/g, '-').replace(/\//g, '_').replace(/=/g, '');
};

Enc.bufToBase64 = function (u8) {
  var bin = '';
  u8.forEach(function (i) {
    bin += String.fromCharCode(i);
  });
  return btoa(bin);
};

}('undefined' !== typeof module ? module.exports : window));