signal-desktop/libtextsecure/crypto.js

/* global libsignal, crypto, textsecure, dcodeIO, window */

/* eslint-disable more/no-then, no-bitwise */

// eslint-disable-next-line func-names
(function() {
  const { encrypt, decrypt, calculateMAC, verifyMAC } = libsignal.crypto;

  const PROFILE_IV_LENGTH = 12; // bytes
  const PROFILE_KEY_LENGTH = 32; // bytes
  const PROFILE_TAG_LENGTH = 128; // bits
  const PROFILE_NAME_PADDED_LENGTH = 26; // bytes

  function verifyDigest(data, theirDigest) {
    return crypto.subtle.digest({ name: 'SHA-256' }, data).then(ourDigest => {
      const a = new Uint8Array(ourDigest);
      const b = new Uint8Array(theirDigest);
      let result = 0;
      for (let i = 0; i < theirDigest.byteLength; i += 1) {
        result |= a[i] ^ b[i];
      }
      if (result !== 0) {
        throw new Error('Bad digest');
      }
    });
  }
  function calculateDigest(data) {
    return crypto.subtle.digest({ name: 'SHA-256' }, data);
  }

  window.textsecure = window.textsecure || {};
  window.textsecure.crypto = {
    // Decrypts message into a raw string
    decryptWebsocketMessage(message, signalingKey) {
      const decodedMessage = message.toArrayBuffer();

      if (signalingKey.byteLength !== 52) {
        throw new Error('Got invalid length signalingKey');
      }
      if (decodedMessage.byteLength < 1 + 16 + 10) {
        throw new Error('Got invalid length message');
      }
      if (new Uint8Array(decodedMessage)[0] !== 1) {
        throw new Error(`Got bad version number: ${decodedMessage[0]}`);
      }

      const aesKey = signalingKey.slice(0, 32);
      const macKey = signalingKey.slice(32, 32 + 20);

      const iv = decodedMessage.slice(1, 1 + 16);
      const ciphertext = decodedMessage.slice(
        1 + 16,
        decodedMessage.byteLength - 10
      );
      const ivAndCiphertext = decodedMessage.slice(
        0,
        decodedMessage.byteLength - 10
      );
      const mac = decodedMessage.slice(
        decodedMessage.byteLength - 10,
        decodedMessage.byteLength
      );

      return verifyMAC(ivAndCiphertext, macKey, mac, 10).then(() =>
        decrypt(aesKey, ciphertext, iv)
      );
    },

    decryptAttachment(encryptedBin, keys, theirDigest) {
      if (keys.byteLength !== 64) {
        throw new Error('Got invalid length attachment keys');
      }
      if (encryptedBin.byteLength < 16 + 32) {
        throw new Error('Got invalid length attachment');
      }

      const aesKey = keys.slice(0, 32);
      const macKey = keys.slice(32, 64);

      const iv = encryptedBin.slice(0, 16);
      const ciphertext = encryptedBin.slice(16, encryptedBin.byteLength - 32);
      const ivAndCiphertext = encryptedBin.slice(
        0,
        encryptedBin.byteLength - 32
      );
      const mac = encryptedBin.slice(
        encryptedBin.byteLength - 32,
        encryptedBin.byteLength
      );

      return verifyMAC(ivAndCiphertext, macKey, mac, 32)
        .then(() => {
          if (!theirDigest) {
            throw new Error('Failure: Ask sender to update Signal and resend.');
          }
          return verifyDigest(encryptedBin, theirDigest);
        })
        .then(() => decrypt(aesKey, ciphertext, iv));
    },

    encryptAttachment(plaintext, keys, iv) {
      if (
        !(plaintext instanceof ArrayBuffer) &&
        !ArrayBuffer.isView(plaintext)
      ) {
        throw new TypeError(
          `\`plaintext\` must be an \`ArrayBuffer\` or \`ArrayBufferView\`; got: ${typeof plaintext}`
        );
      }

      if (keys.byteLength !== 64) {
        throw new Error('Got invalid length attachment keys');
      }
      if (iv.byteLength !== 16) {
        throw new Error('Got invalid length attachment iv');
      }
      const aesKey = keys.slice(0, 32);
      const macKey = keys.slice(32, 64);

      return encrypt(aesKey, plaintext, iv).then(ciphertext => {
        const ivAndCiphertext = new Uint8Array(16 + ciphertext.byteLength);
        ivAndCiphertext.set(new Uint8Array(iv));
        ivAndCiphertext.set(new Uint8Array(ciphertext), 16);

        return calculateMAC(macKey, ivAndCiphertext.buffer).then(mac => {
          const encryptedBin = new Uint8Array(16 + ciphertext.byteLength + 32);
          encryptedBin.set(ivAndCiphertext);
          encryptedBin.set(new Uint8Array(mac), 16 + ciphertext.byteLength);
          return calculateDigest(encryptedBin.buffer).then(digest => ({
            ciphertext: encryptedBin.buffer,
            digest,
          }));
        });
      });
    },
    encryptProfile(data, key) {
      const iv = libsignal.crypto.getRandomBytes(PROFILE_IV_LENGTH);
      if (key.byteLength !== PROFILE_KEY_LENGTH) {
        throw new Error('Got invalid length profile key');
      }
      if (iv.byteLength !== PROFILE_IV_LENGTH) {
        throw new Error('Got invalid length profile iv');
      }
      return crypto.subtle
        .importKey('raw', key, { name: 'AES-GCM' }, false, ['encrypt'])
        .then(keyForEncryption =>
          crypto.subtle
            .encrypt(
              { name: 'AES-GCM', iv, tagLength: PROFILE_TAG_LENGTH },
              keyForEncryption,
              data
            )
            .then(ciphertext => {
              const ivAndCiphertext = new Uint8Array(
                PROFILE_IV_LENGTH + ciphertext.byteLength
              );
              ivAndCiphertext.set(new Uint8Array(iv));
              ivAndCiphertext.set(
                new Uint8Array(ciphertext),
                PROFILE_IV_LENGTH
              );
              return ivAndCiphertext.buffer;
            })
        );
    },
    decryptProfile(data, key) {
      if (data.byteLength < 12 + 16 + 1) {
        throw new Error(`Got too short input: ${data.byteLength}`);
      }
      const iv = data.slice(0, PROFILE_IV_LENGTH);
      const ciphertext = data.slice(PROFILE_IV_LENGTH, data.byteLength);
      if (key.byteLength !== PROFILE_KEY_LENGTH) {
        throw new Error('Got invalid length profile key');
      }
      if (iv.byteLength !== PROFILE_IV_LENGTH) {
        throw new Error('Got invalid length profile iv');
      }
      const error = new Error(); // save stack
      return crypto.subtle
        .importKey('raw', key, { name: 'AES-GCM' }, false, ['decrypt'])
        .then(keyForEncryption =>
          crypto.subtle
            .decrypt(
              { name: 'AES-GCM', iv, tagLength: PROFILE_TAG_LENGTH },
              keyForEncryption,
              ciphertext
            )
            .catch(e => {
              if (e.name === 'OperationError') {
                // bad mac, basically.
                error.message =
                  'Failed to decrypt profile data. Most likely the profile key has changed.';
                error.name = 'ProfileDecryptError';
                throw error;
              }
            })
        );
    },
    encryptProfileName(name, key) {
      const padded = new Uint8Array(PROFILE_NAME_PADDED_LENGTH);
      padded.set(new Uint8Array(name));
      return textsecure.crypto.encryptProfile(padded.buffer, key);
    },
    decryptProfileName(encryptedProfileName, key) {
      const data = dcodeIO.ByteBuffer.wrap(
        encryptedProfileName,
        'base64'
      ).toArrayBuffer();
      return textsecure.crypto.decryptProfile(data, key).then(decrypted => {
        // unpad
        const padded = new Uint8Array(decrypted);
        let i;
        for (i = padded.length; i > 0; i -= 1) {
          if (padded[i - 1] !== 0x00) {
            break;
          }
        }

        return dcodeIO.ByteBuffer.wrap(padded)
          .slice(0, i)
          .toArrayBuffer();
      });
    },

    getRandomBytes(size) {
      return libsignal.crypto.getRandomBytes(size);
    },
  };
})();