BouncyCastle C# PublicKey different than GnuPG

Question

I am trying to get a public PGP key from a keyring created by GnuPG using the BouncyCastle C# library. I've gotten it to semi-work by using the following code. The problem is that the public key it outputs is about half the length of the real one and the last few bytes are also different. I'm just trying to get the real key.

UPDATE: Something interesting to note is that the keyring I generated only had one public key, yet I'm getting two out of bouncycastle. I also found that if you insert the second key into the first a few characters from the end, it produces almost the original key. Only a few chars at the end are different. So why are there two keys and why does this occur? What am I missing?

Is the GnuPG keyring not compatible?

Also note that the code shown here only gets the last key. I'm now adding each to a list.

Here is my code:

public static string ReadKey(string pubkeyFile)
{
    string theKey;
    Stream fs = File.OpenRead(pubkeyFile);

    //
    // Read the public key rings
    //
    PgpPublicKeyRingBundle pubRings = new PgpPublicKeyRingBundle(PgpUtilities.GetDecoderStream(fs));
    fs.Close();

    foreach (PgpPublicKeyRing pgpPub in pubRings.GetKeyRings())
    {
        pgpPub.GetPublicKey();

        foreach (PgpPublicKey pgpKey in pgpPub.GetPublicKeys())
        {
            //AsymmetricKeyParameter pubKey = pgpKey.GetKey();
            //SubjectPublicKeyInfo k = SubjectPublicKeyInfoFactory.CreateSubjectPublicKeyInfo(pubKey);
            //byte[] keyData = k.ToAsn1Object().GetDerEncoded();
            //byte[] keyData = k.GetEncoded();
            byte[] keyData = pgpKey.GetEncoded();
            theKey = Convert.ToBase64String(keyData);
        }
    }
    return theKey;
}

Here is the actual public key:

-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: GnuPG v2.0.20 (MingW32)
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=r3Qj
-----END PGP PUBLIC KEY BLOCK-----

Here is NEW KEY produced by BouncyCastle (sorry can't help formatting):

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

Still not the same. Put both keys in notepad and search the "tNCDnS", after that is where they change.

Thanks for sticking with me. I've gotten far enough with this that I don't want to scrap the whole code for some shitty encryption.

Answer 1

You may have been a victim of BouncyCastle's somewhat uncommon usage of the term "keyring". Here is BouncyCastle's usage of three related terms:

PgpPublicKey: This is the public part of a single mathematical key, in PGP format. It does not contain any subkeys.

PgpPublicKeyRing: This is a cryptographic key with its subkeys. Other programs usually refer to this as a PGP Key.

PgpPublicKeyRingBundle: This is any number of PgpPublicKeyRings (as defined in BouncyCastle). Other programs usually refer to this as a Public Key Ring (without bundle).

You iterated through the keyring to find all PgpPublicKey objects. You decoded them and return the last and only the last of them as a string. If you paste the input and output strings to pgpdump.net (you have to add the BEGIN and END headers to the output), you see that you lose the subkey in this procedure. Use the PgpPublicKeyRing's GetEncoded() method instead. This should retain all information and is also easier :-).

Additionally, PGP's Radix-encoding is a little bit more than just Base64-encoding. A lot of programs and libraries, including BC, ignores whether there are PGP headers and footers and also the CRC checksum that Radix-encoding includes as opposed to simple Base64. However, GPG is more strict and seems not to accept ASCII armors without CRC checksum. Therefore, you have to use the binary key (which is the byte[] keyData in your problem code) or create a proper PGP ASCII armor. I have edited the following code based on your code to implement the latter using BC's ArmoredOutputStream:

public static string ReadKey(string pubkeyFile)
{
    Stream fs = File.OpenRead(pubkeyFile);

    //
    // Read the public key rings
    //
    PgpPublicKeyRingBundle pubRings = new PgpPublicKeyRingBundle(PgpUtilities.GetDecoderStream(fs));
    fs.Close();

    foreach (PgpPublicKeyRing pgpPub in pubRings.GetKeyRings())
    {
            using (MemoryStream ms = new MemoryStream())
            {
                using (ArmoredOutputStream aos = new ArmoredOutputStream(ms))
                    pgpPub.Encode(aos);
                return System.Text.Encoding.ASCII.GetString(ms.ToArray());
            }
    }
    return null;
}

EDIT: The following is a complete program with no external dependencies. It works for me, i.e. outputs "Same!". Please run that exact program and check whether it outputs "Same!" or "Difference!". If it outputs "Same!", then you can use it to correct your own program code:

using System;
using System.IO;
using Org.BouncyCastle.Bcpg.OpenPgp;

class Program
{
    private const string PGP_OVERFLOW_KEYBODY =
    "mQENBFP2z94BCADKfQT9DGHm4y/VEAYGL7XiUavbv+aE7D2OZ2jCbwnx7BYzQBu8\r\n" +
    "63v5qYe7oH0oBOiw67VaQSjS58fSBAE8vlTkKjvRAscHJNUX9qZrQoRtpMSnrK7N\r\n" +
    "Ca9N2ptvof7ykF1TAgbxDSSnhwysVznYc7mx76BO6Qx8KChqEd0Yp3w2U89YkUqN\r\n" +
    "qdzjB7ZIhj5hDM9f4eyHwsz0uZgyqLKK5VgNj6dHVmOHZt6+RIydRC2lGfocWKM8\r\n" +
    "loPkk6GiSX9sdEm6GXxi7gV/Q3Jr0G099AFg57cWyj1eO6NC8YHLgBHwrB1IkFwi\r\n" +
    "J0x5IHZssy/XleQ1i1izc3ntWiiH24powuAhABEBAAG0H3N5bmFwczMgPHN5bmFw\r\n" +
    "czNAc2FmZS1tYWlsLm5ldD6JATkEEwECACMFAlP2z94CGwMHCwkIBwMCAQYVCAIJ\r\n" +
    "CgsEFgIDAQIeAQIXgAAKCRD944Hz1MHUYP+AB/4roauazFR5lDrJBFB0YoH4VFKM\r\n" +
    "28IJtuy6OThg3cxhqI/N74sZoxtB90QQk4lcshdpwD7CIe9TCKrnhWokIdm4N91m\r\n" +
    "TGDmW7iIeM3kcPp3mj9/7hGOetESuz9JxhBQ0aHAXYk5LdHeDKyRg1KL3JvWrJ27\r\n" +
    "fioDoLLpxxdudSd2nJLhi0hAaHKnkLVl98r37AwxTigGj+J2rN47D+UepJraf8je\r\n" +
    "eZrY/RfwKJVleF1KYPIgduwX3jdiABrI4EsZP/CdbEWTvmmkFFtD4clSMsmqaXPT\r\n" +
    "a3VeaL/saScBPL93tDsjqCddcgW28hsnhzoJ7TM78j2zNcTXZjK8/tNCDnShuQEN\r\n" +
    "BFP2z94BCADmCAMIpOp518ywUlG5Pze5HdpgGiQF26XzwxUt3mPAMXBUQ7vqRMD/\r\n" +
    "zNagPXKthp/p4t0jRoFwFwF+7CqRrxkv2Rrj5OqDD7JqETY5nfRZ0Hvfi4cPkf2g\r\n" +
    "S17SVI4LSFQ/v/sISNNiI3Bo/xvpOeK+Af087j4BEe8vjFuyzf08HCglKoL6WAp8\r\n" +
    "5+Wc2vj+7EbH61YloKKNugq34AyuNh1QYml6LI04b2KR0b/qXTW8UqLvrh4YGaOp\r\n" +
    "k80l7DpBmKgGtXn8JFfU9V3sGCscSnfzDvKjqpmtKXiJFxO2pyPCN5jRKfGMOSyA\r\n" +
    "fZ21NIrBJER/WvuIAls8Tikk+wKRKXrpABEBAAGJAR8EGAECAAkFAlP2z94CGwwA\r\n" +
    "CgkQ/eOB89TB1GDDEAf+OA9hgb3FLbEtcNvkUl9wTtLaxr9nAsBowofNEITH96hV\r\n" +
    "w4i6em9Rjg29/+4JrnDhibuhsFr/F8uKoj+iZGFw2NpXHYI6yS+BLbuVj8jOkYAy\r\n" +
    "Gq34HMNWXuS1Nr4VHOxKbKmmLu8YhdYRk2KF9fPI2Qj376C69W90R/LHByCrcCg7\r\n" +
    "xmqAvO9a8Eac7Rk+Fc+5NKVw9D1rP7MqZGgIQQoh8jLiI2MblvEEahwNxA9AYs8U\r\n" +
    "PpMD0pdo93wxXIYuKc40MF4yFL9LfpPxDnf373dbYQjk3pNThQ5RagIgLNEhRow4\r\n" +
    "5x/1wcO6FMx5a/irQXnJ2o1XYRvznBeCsoyOAYbikA==";

    static void Main(string[] args)
    {
        string parsedKey = ReadKeyDirectly(PGP_OVERFLOW_KEYBODY);
        if (parsedKey != PGP_OVERFLOW_KEYBODY.Replace("\r\n",""))
            Console.WriteLine("Difference!");
        else
            Console.WriteLine("Same!");
    }

    public static string ReadKeyDirectly(string stringKeyData)
    {
        Stream fs = new MemoryStream(System.Text.Encoding.ASCII.GetBytes(stringKeyData));
        fs.Seek(0, SeekOrigin.Begin);

        PgpPublicKeyRingBundle pubRings = new PgpPublicKeyRingBundle(PgpUtilities.GetDecoderStream(fs));

        foreach (PgpPublicKeyRing pubRing in pubRings.GetKeyRings())
            return Convert.ToBase64String(pubRing.GetEncoded());
        return null;
    }
}