ICSharpCode.SharpZipLib.Zip.ZipFile.CreateAndInitDecryptionStream C# (CSharp) Method

        private Stream CreateAndInitDecryptionStream(Stream baseStream, ZipEntry entry) {
            CryptoStream result=null;

            if ((entry.Version<ZipConstants.VersionStrongEncryption)
                ||(entry.Flags&(int)GeneralBitFlags.StrongEncryption)==0) {
                var classicManaged=new PkzipClassicManaged();

                OnKeysRequired(entry.Name);
                if (HaveKeys==false) {
                    throw new ZipException("No password available for encrypted stream");
                }

                result=new CryptoStream(baseStream, classicManaged.CreateDecryptor(key, null), CryptoStreamMode.Read);
                CheckClassicPassword(result, entry);
            } else {
                if (entry.Version==ZipConstants.VERSION_AES) {
                    //
                    OnKeysRequired(entry.Name);
                    if (HaveKeys==false) {
                        throw new ZipException("No password available for AES encrypted stream");
                    }
                    int saltLen=entry.AESSaltLen;
                    var saltBytes=new byte[saltLen];
                    int saltIn=baseStream.Read(saltBytes, 0, saltLen);
                    if (saltIn!=saltLen)
                        throw new ZipException("AES Salt expected "+saltLen+" got "+saltIn);
                    //
                    var pwdVerifyRead=new byte[2];
                    baseStream.Read(pwdVerifyRead, 0, 2);
                    int blockSize=entry.AESKeySize/8; // bits to bytes

                    var decryptor=new ZipAESTransform(rawPassword_, saltBytes, blockSize, false);
                    byte[] pwdVerifyCalc=decryptor.PwdVerifier;
                    if (pwdVerifyCalc[0]!=pwdVerifyRead[0]||pwdVerifyCalc[1]!=pwdVerifyRead[1])
                        throw new Exception("Invalid password for AES");
                    result=new ZipAESStream(baseStream, decryptor, CryptoStreamMode.Read);
                } else{
                    throw new ZipException("Decryption method not supported");
                }
            }

            return result;
        }