Calling GnuPG in Java via a Runtime Process to encrypt and decrypt files - Decrypt always hangs

Question

NOTE: Coming back to this later as I've been unable to find a working solution. Draining the input streams manually instead of using BufferedReaders doesn't seem to help as the inputStream.read() method permanently blocks the program. I placed the gpg call in a batch file, and called the batch file from Java to only get the same result. Once gpg is called with the decrypt option, the input stream seems to become inaccessible, blocking the entire program. I'll have to come back to this when I have more time to focus on the task. In the mean time, I'll have to get decryption working by some other means (probably BouncyCastle).

The last option to probably try is to call cmd.exe, and write the command through the input stream generated by that process...

I appreciate the assistance on this issue.

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I've been working on this problem for a couple days and haven't made any progress, so I thought I'd turn to the exeprtise here for some help.

I am creating a simple program that will call GnuPG via a Java runtime process. It needs to be able to encrypt and decrypt files. Encryption works, but I'm having some problems decrypting files. Whenever I try to decrypt a file, the process hangs.exitValue() always throws it's IllegalThreadStateException and the program chugs along as if it's still waiting. The code for these methods is attached below. The ultimate goal of the program is to decrypt the file, and parse it's contents in Java.

I've tried three approaches to getting the gpgDecrypt method to work. The first approach involved removing the passphrase-fd option and writing the passphrase to gpg via the gpgOutput stream in the catch block, assuming it was prompting for the passphrase like it would via the command line. This didn't work, so I put the passphrase in a file and added the -passphrase-fd option. In this case, the program repeats infinitely. If I write anything via the gpgOutput stream the program will complete. The Exit value printed will have a value of 2, and the result variable will be blank.

The third option is BouncyCastle, but I'm having problems getting it to recognize my private key (which is probably a separate post all together).

The keys I'm using to encrypt and decrypt are 4096-bit RSA keys, generated by GnuPG. In both cases using the passphrase and the passphrase file, I've tried piping the output to a file via > myFile.txt, but it doesn't seem to make any difference.

Here are the gpgEncrypt, gpgDecrypt and getStreamText methods. I posted both since the encrypt works, and I can't see any glaring differences between how I'm executing and handling the process between the encrypt and decrypt methods. getStreamText just reads the contents of the streams and returns a string.

EDIT: Quick note, Windows environment. If I copy the decrypt command output, it works via the console just fine. So I know the command is valid.

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public boolean gpgEncrypt(String file, String recipient, String outputFile){
    boolean success = true;
    StringBuilder gpgCommand = new StringBuilder("gpg --recipient \"");
    gpgCommand.append(recipient).append("\" --output \"").append(outputFile).append("\" --yes --encrypt \"");
    gpgCommand.append(file).append("\"");

    System.out.println("ENCRYPT COMMAND: " + gpgCommand);
    try {
        Process gpgProcess = Runtime.getRuntime().exec(gpgCommand.toString());

        BufferedReader gpgOutput = new BufferedReader(new InputStreamReader(gpgProcess.getInputStream()));
        BufferedWriter gpgInput = new BufferedWriter(new OutputStreamWriter(gpgProcess.getOutputStream()));
        BufferedReader gpgErrorOutput = new BufferedReader(new InputStreamReader(gpgProcess.getErrorStream()));

        boolean executing = true;

        while(executing){
            try{
                int exitValue = gpgProcess.exitValue();

                if(gpgErrorOutput.ready()){
                    String error = getStreamText(gpgErrorOutput);
                    System.err.println(error);
                    success = false;
                    break;
                }else if(gpgOutput.ready()){
                    System.out.println(getStreamText(gpgOutput));
                }

                executing = false;
            }catch(Exception e){
                //The process is not yet ready to exit.  Take a break and try again.
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e1) {
                    System.err.println("This thread has insomnia: " + e1.getMessage());
                }
            }
        }
    } catch (IOException e) {
        System.err.println("Error running GPG via runtime: " + e.getMessage());
        success = false;
    }

    return success;
}

public String gpgDecrypt(String file, String passphraseFile){
    String result = null;
    StringBuilder command = new StringBuilder("gpg --passphrase-fd 0 --decrypt \"");
    command.append(file).append("\" 0<\"").append(passphraseFile).append("\"");             
    System.out.println("DECRYPT COMMAND: " + command.toString());
    try {

        Process gpgProcess = Runtime.getRuntime().exec(command.toString());

        BufferedReader gpgOutput = new BufferedReader(new InputStreamReader(gpgProcess.getInputStream()));
        BufferedReader gpgErrorOutput = new BufferedReader(new InputStreamReader(gpgProcess.getErrorStream()));
        BufferedWriter gpgInput = new BufferedWriter(new OutputStreamWriter(gpgProcess.getOutputStream()));

        boolean executing = true;

        while(executing){
            try{
                if(gpgErrorOutput.ready()){
                    result = getStreamText(gpgErrorOutput);
                    System.err.println(result);
                    break;
                }else if(gpgOutput.ready()){
                    result = getStreamText(gpgOutput);
                }

                int exitValue = gpgProcess.exitValue();
                System.out.println("EXIT: " + exitValue);

                executing = false;
            }catch(IllegalThreadStateException e){
                System.out.println("Not yet ready.  Stream status: " + gpgOutput.ready() + ", error: " + gpgErrorOutput.ready());

                try {
                    Thread.sleep(100);
                } catch (InterruptedException e1) {
                    System.err.println("This thread has insomnia: " + e1.getMessage());
                }
            }
        }
    } catch (IOException e) {
        System.err.println("Unable to execute GPG decrypt command via command line: " + e.getMessage());
    }

    return result;
}

private String getStreamText(BufferedReader reader) throws IOException{
    StringBuilder result = new StringBuilder();
    try{
        while(reader.ready()){
            result.append(reader.readLine());
            if(reader.ready()){
                result.append("\n");
            }
        }
    }catch(IOException ioe){
        System.err.println("Error while reading the stream: " + ioe.getMessage());
        throw ioe;
    }
    return result.toString();
}

Answer 1

I forget how you handle it in Java, there are 100 methods for that. But I was stuck with decrypt command itself, it was very helpful, though you didn't need all those quotes and if you wish to decrypt a large file, it goes like this:

gpg --passphrase-fd 0 --output yourfile.txt --decrypt /encryptedfile.txt.gpg/ 0</passwrdfile.txt