session-desktop/libloki/crypto.js

/* global window, libsignal, textsecure, StringView */

// eslint-disable-next-line func-names
(function() {
  window.libloki = window.libloki || {};

  class FallBackDecryptionError extends Error {}

  const IV_LENGTH = 16;

  class FallBackSessionCipher {
    constructor(address) {
      this.identityKeyString = address.getName();
      this.pubKey = StringView.hexToArrayBuffer(address.getName());
    }

    async encrypt(plaintext) {
      const myKeyPair = await textsecure.storage.protocol.getIdentityKeyPair();
      const myPrivateKey = myKeyPair.privKey;
      const symmetricKey = libsignal.Curve.calculateAgreement(
        this.pubKey,
        myPrivateKey
      );
      const iv = libsignal.crypto.getRandomBytes(IV_LENGTH);
      const ciphertext = await libsignal.crypto.encrypt(
        symmetricKey,
        plaintext,
        iv
      );
      const ivAndCiphertext = new Uint8Array(
        iv.byteLength + ciphertext.byteLength
      );
      ivAndCiphertext.set(new Uint8Array(iv));
      ivAndCiphertext.set(new Uint8Array(ciphertext), iv.byteLength);
      return {
        type: textsecure.protobuf.Envelope.Type.FRIEND_REQUEST,
        body: ivAndCiphertext,
        registrationId: null,
      };
    }

    async decrypt(ivAndCiphertext) {
      const iv = ivAndCiphertext.slice(0, IV_LENGTH);
      const cipherText = ivAndCiphertext.slice(IV_LENGTH);
      const myKeyPair = await textsecure.storage.protocol.getIdentityKeyPair();
      const myPrivateKey = myKeyPair.privKey;
      const symmetricKey = libsignal.Curve.calculateAgreement(
        this.pubKey,
        myPrivateKey
      );
      try {
        return await libsignal.crypto.decrypt(symmetricKey, cipherText, iv);
      } catch (e) {
        throw new FallBackDecryptionError(
          `Could not decrypt message from ${
            this.identityKeyString
          } using FallBack encryption.`
        );
      }
    }
  }

  window.libloki.crypto = {
    FallBackSessionCipher,
    FallBackDecryptionError,
  };
})();