code: function decompressKey(key) {
    const format = key[0];
  
    assert(key.length === 33);
  
    switch (format) {
      case 0x02:
      case 0x03:
        return key;
      case 0x04:
        key[0] = 0x02;
        break;
      case 0x05:
        key[0] = 0x03;
        break;
      default:
        throw new Error('Bad point format.');
    }
  
    // Decompress the key.
    const out = secp256k1.publicKeyConvert(key, false);
  
    // Reset the first byte so as not to
    // mutate the original buffer.
    key[0] = format;
  
    return out;
  }
docs: Decompress a public key from the coins compression format.
  @param {Buffer} key
  @returns {Buffer}