session-desktop/libtextsecure/ProvisioningCipher.js

(function() {
  'use strict';

  function ProvisioningCipher() {}

  ProvisioningCipher.prototype = {
    decrypt: function(provisionEnvelope) {
      var masterEphemeral = provisionEnvelope.publicKey.toArrayBuffer();
      var message = provisionEnvelope.body.toArrayBuffer();
      if (new Uint8Array(message)[0] != 1) {
        throw new Error('Bad version number on ProvisioningMessage');
      }

      var iv = message.slice(1, 16 + 1);
      var mac = message.slice(message.byteLength - 32, message.byteLength);
      var ivAndCiphertext = message.slice(0, message.byteLength - 32);
      var ciphertext = message.slice(16 + 1, message.byteLength - 32);

      return libsignal.Curve.async
        .calculateAgreement(masterEphemeral, this.keyPair.privKey)
        .then(function(ecRes) {
          return libsignal.HKDF.deriveSecrets(
            ecRes,
            new ArrayBuffer(32),
            'TextSecure Provisioning Message'
          );
        })
        .then(function(keys) {
          return libsignal.crypto
            .verifyMAC(ivAndCiphertext, keys[1], mac, 32)
            .then(function() {
              return libsignal.crypto.decrypt(keys[0], ciphertext, iv);
            });
        })
        .then(function(plaintext) {
          var provisionMessage = textsecure.protobuf.ProvisionMessage.decode(
            plaintext
          );
          var privKey = provisionMessage.identityKeyPrivate.toArrayBuffer();

          return libsignal.Curve.async
            .createKeyPair(privKey)
            .then(function(keyPair) {
              var ret = {
                identityKeyPair: keyPair,
                number: provisionMessage.number,
                provisioningCode: provisionMessage.provisioningCode,
                userAgent: provisionMessage.userAgent,
                readReceipts: provisionMessage.readReceipts,
              };
              if (provisionMessage.profileKey) {
                ret.profileKey = provisionMessage.profileKey.toArrayBuffer();
              }
              return ret;
            });
        });
    },
    getPublicKey: function() {
      return Promise.resolve()
        .then(
          function() {
            if (!this.keyPair) {
              return libsignal.Curve.async.generateKeyPair().then(
                function(keyPair) {
                  this.keyPair = keyPair;
                }.bind(this)
              );
            }
          }.bind(this)
        )
        .then(
          function() {
            return this.keyPair.pubKey;
          }.bind(this)
        );
    },
  };

  libsignal.ProvisioningCipher = function() {
    var cipher = new ProvisioningCipher();

    this.decrypt = cipher.decrypt.bind(cipher);
    this.getPublicKey = cipher.getPublicKey.bind(cipher);
  };
})();