Crisis.Ionic.Zip.ZipEntry.SetupCryptoForExtract C# (CSharp) Method

        private void SetupCryptoForExtract(string password)
        {
            //if (password == null) return;
            if (_Encryption_FromZipFile == EncryptionAlgorithm.None) return;

            if (_Encryption_FromZipFile == EncryptionAlgorithm.PkzipWeak)
            {
                if (password == null)
                    throw new ZipException("Missing password.");

                this.ArchiveStream.Seek(this.FileDataPosition - 12, SeekOrigin.Begin);
                // workitem 10178
                Crisis.Ionic.Zip.SharedUtilities.Workaround_Ladybug318918(this.ArchiveStream);
                _zipCrypto_forExtract = ZipCrypto.ForRead(password, this);
            }

#if AESCRYPTO
            else if (_Encryption_FromZipFile == EncryptionAlgorithm.WinZipAes128 ||
                 _Encryption_FromZipFile == EncryptionAlgorithm.WinZipAes256)
            {
                if (password == null)
                    throw new ZipException("Missing password.");

                // If we already have a WinZipAesCrypto object in place, use it.
                // It can be set up in the ReadDirEntry(), or during a previous Extract.
                if (_aesCrypto_forExtract != null)
                {
                    _aesCrypto_forExtract.Password = password;
                }
                else
                {
                    int sizeOfSaltAndPv = GetLengthOfCryptoHeaderBytes(_Encryption_FromZipFile);
                    this.ArchiveStream.Seek(this.FileDataPosition - sizeOfSaltAndPv, SeekOrigin.Begin);
                    // workitem 10178
                    Ionic.Zip.SharedUtilities.Workaround_Ladybug318918(this.ArchiveStream);
                    int keystrength = GetKeyStrengthInBits(_Encryption_FromZipFile);
                    _aesCrypto_forExtract = WinZipAesCrypto.ReadFromStream(password, keystrength, this.ArchiveStream);
                }
            }
#endif
        }