Issue a private key and a public key?

I need to pass public key and private key in string format for encryption and decryption in pgp. I have created keys like this, but I cannot use them. So can anyone tell me how to get the public key and private key in string format. And also rsakeygenerator did not give a passphrase for the private key. So where do I get the passphrase for the private key?

private void button2_Click(object sender, EventArgs e)
{
    // keyPair = createASymRandomCipher();
    //CipherPublicKey publicKey = getCipherPublicKey(keyPair);
    AsymmetricCipherKeyPair keyPair = createASymRandomCipher();
    Org.BouncyCastle.Crypto.Parameters.RsaKeyParameters pubkey = (Org.BouncyCastle.Crypto.Parameters.RsaKeyParameters)keyPair.Public;
    Org.BouncyCastle.Crypto.Parameters.RsaPrivateCrtKeyParameters privkey = (Org.BouncyCastle.Crypto.Parameters.RsaPrivateCrtKeyParameters)keyPair.Private;
    CipherPublicKey pbkey = getCipherPublicKey(pubkey);
    CipherPrivateKey prvkey = getCipherPrivateKey(privkey);

}

private static AsymmetricCipherKeyPair createASymRandomCipher() 
{
    RsaKeyPairGenerator r = new RsaKeyPairGenerator();
    r.Init(new KeyGenerationParameters(new SecureRandom(),
          1024));
    AsymmetricCipherKeyPair keys = r.GenerateKeyPair();
    return keys;
}

[Serializable]
private struct CipherPrivateKey
{
    public byte[] modulus; 
    public byte[] publicExponent; 
    public byte[] privateExponent; 
    public byte[] p; 
    public byte[] q; 
    public byte[] dP; 
    public byte[] dQ; 
    public byte[] qInv;
}

[Serializable]
private struct CipherPublicKey 
{ 
    public bool isPrivate; 
    public byte[] modulus; 
    public byte[] exponent;
}

private static CipherPublicKey getCipherPublicKey(Org.BouncyCastle.Crypto.Parameters.RsaKeyParameters cPublic) 
{ 
    CipherPublicKey cpub = new CipherPublicKey(); cpub.modulus = cPublic.Modulus.ToByteArray(); 
    cpub.exponent = cPublic.Exponent.ToByteArray(); 
    return cpub; 
}

private static CipherPrivateKey getCipherPrivateKey(Org.BouncyCastle.Crypto.Parameters.RsaPrivateCrtKeyParameters cPrivate)
{
    CipherPrivateKey cpri = new CipherPrivateKey(); 
    cpri.dP = cPrivate.DP.ToByteArray(); 
    cpri.dQ = cPrivate.DQ.ToByteArray(); 
    cpri.modulus = cPrivate.Modulus.ToByteArray(); 
    cpri.p = cPrivate.P.ToByteArray(); 
    cpri.privateExponent = cPrivate.Exponent.ToByteArray(); 
    cpri.publicExponent = cPrivate.PublicExponent.ToByteArray(); 
    cpri.q = cPrivate.Q.ToByteArray(); 
    cpri.qInv = cPrivate.QInv.ToByteArray(); 
    return cpri;
}