Method decrypt

lib/protocol/crypto.js:1134–1274

(data, p, dataLen)

  }
  free() {}
  decrypt(data, p, dataLen) {
    // `data` === encrypted data

    while (p < dataLen) {
      // Read first encrypted block
      if (this._blockPos < this._block.length) {
        const nb = Math.min(this._block.length - this._blockPos, dataLen - p);
        if (p !== 0 || nb !== dataLen || nb < data.length) {
          this._block.set(
            new Uint8Array(data.buffer, data.byteOffset + p, nb),
            this._blockPos
          );
        } else {
          this._block.set(data, this._blockPos);
        }

        p += nb;
        this._blockPos += nb;
        if (this._blockPos < this._block.length)
          return;

        let decrypted;
        let need;
        if (this._macETM) {
          this._len = need = readUInt32BE(this._block, 0);
        } else {
          // Decrypt first block to get packet length
          decrypted = this._decipherInstance.update(this._block);
          this._len = readUInt32BE(decrypted, 0);
          need = 4 + this._len - this._blockSize;
        }

        if (this._len > MAX_PACKET_SIZE
            || this._len < 5
            || (need & (this._blockSize - 1)) !== 0) {
          throw new Error('Bad packet length');
        }

        // Create MAC up front to calculate in parallel with decryption
        this._macInstance = createHmac(this._macSSLName, this._macKey);

        writeUInt32BE(BUF_INT, this.inSeqno, 0);
        this._macInstance.update(BUF_INT);
        if (this._macETM) {
          this._macInstance.update(this._block);
        } else {
          this._macInstance.update(new Uint8Array(decrypted.buffer,
                                                  decrypted.byteOffset,
                                                  4));
          this._pktLen = decrypted.length - 4;
          this._packetPos = this._pktLen;
          this._packet = Buffer.allocUnsafe(this._len);
          this._packet.set(
            new Uint8Array(decrypted.buffer,
                           decrypted.byteOffset + 4,
                           this._packetPos),
            0
          );