Reputation: 79
How do I unwrap a key using RSA private key in Bouncy castle? I receive the already wrapped key which was wrapped using the RSA public key. I have the RSA key pair. I just cannot find the api in the C# Bouncy Castle that I can use to unwrap it.
This code in the C# source code (https://github.com/bcgit/bc-csharp) is currently commented out. The commented out lines for the RSA is exactly what I need, but when I try to use them it seems that its been removed or never implemented
Key key = cipher.unwrap(wrappedKey, "RSA", IBufferedCipher.PRIVATE_KEY);
The line above is exactly what I need. Why has it been commented out? The full function in WrapTest.cs is given below:
public ITestResult Perform()
{
try
{
// IBufferedCipher cipher = CipherUtilities.GetCipher("DES/ECB/PKCS5Padding");
IWrapper cipher = WrapperUtilities.GetWrapper("DES/ECB/PKCS5Padding");
IAsymmetricCipherKeyPairGenerator fact = GeneratorUtilities.GetKeyPairGenerator("RSA");
fact.Init(
new RsaKeyGenerationParameters(
BigInteger.ValueOf(0x10001),
new SecureRandom(),
512,
25));
AsymmetricCipherKeyPair keyPair = fact.GenerateKeyPair();
AsymmetricKeyParameter priKey = keyPair.Private;
AsymmetricKeyParameter pubKey = keyPair.Public;
byte[] priKeyBytes = PrivateKeyInfoFactory.CreatePrivateKeyInfo(priKey).GetDerEncoded();
CipherKeyGenerator keyGen = GeneratorUtilities.GetKeyGenerator("DES");
// Key wrapKey = keyGen.generateKey();
byte[] wrapKeyBytes = keyGen.GenerateKey();
KeyParameter wrapKey = new DesParameters(wrapKeyBytes);
// cipher.Init(IBufferedCipher.WRAP_MODE, wrapKey);
cipher.Init(true, wrapKey);
// byte[] wrappedKey = cipher.Wrap(priKey);
byte[] wrappedKey = cipher.Wrap(priKeyBytes, 0, priKeyBytes.Length);
// cipher.Init(IBufferedCipher.UNWRAP_MODE, wrapKey);
cipher.Init(false, wrapKey);
// Key key = cipher.unwrap(wrappedKey, "RSA", IBufferedCipher.PRIVATE_KEY);
byte[] unwrapped = cipher.Unwrap(wrappedKey, 0, wrappedKey.Length);
//if (!Arrays.AreEqual(priKey.getEncoded(), key.getEncoded()))
if (!Arrays.AreEqual(priKeyBytes, unwrapped))
{
return new SimpleTestResult(false, "Unwrapped key does not match");
}
return new SimpleTestResult(true, Name + ": Okay");
}
catch (Exception e)
{
return new SimpleTestResult(false, Name + ": exception - " + e.ToString());
}
}
Upvotes: 0
Views: 2570
Reputation: 42009
I'm not entirely clear on what you need, but you can use RSA keys to wrap and unwrap AES keys in Bouncycastle. Here is a Java example that creates an RSA keypair, saves the private key to a file, and then saves an AES key that has been wrapped in the public key.
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.SecureRandom;
public class Main {
private static final SecureRandom rand = new SecureRandom();
public static void main(String[] args) throws Exception {
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(1024, rand);
KeyPair kp = kpg.generateKeyPair();
// Write out private key to file, PKCS8-encoded DER
Files.write(Paths.get("privkey.der"), kp.getPrivate().getEncoded());
KeyGenerator kg = KeyGenerator.getInstance("AES");
kg.init(256, rand);
SecretKey aesKey = kg.generateKey();
Cipher c = Cipher.getInstance("RSA/ECB/PKCS1PADDING");
c.init(Cipher.WRAP_MODE, kp.getPublic(), rand);
byte[] wrappedKey = c.wrap(aesKey);
// Write out wrapped key
Files.write(Paths.get("wrappedkey"), wrappedKey);
}
}
And here is a C# example that consumes the output from the Java example and unwraps the AES key.
using System.IO;
using Org.BouncyCastle.Asn1;
using Org.BouncyCastle.Asn1.Pkcs;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Security;
namespace RSADecryptWithBouncy
{
class MainClass
{
private static KeyParameter Unwrap(byte [] key, AsymmetricKeyParameter privKeyParam) {
var wrapper = WrapperUtilities.GetWrapper("RSA/NONE/PKCS1PADDING");
wrapper.Init(false, privKeyParam);
var aesKeyBytes = wrapper.Unwrap(key, 0, key.Length);
return new KeyParameter(aesKeyBytes);
}
public static void Main(string[] args)
{
var privKeyBytes = File.ReadAllBytes("../../privkey.der");
var seq = Asn1Sequence.GetInstance(privKeyBytes);
var rsaKeyParams = PrivateKeyFactory.CreateKey(PrivateKeyInfo.GetInstance(seq));
var wrappedKey = File.ReadAllBytes("../../wrappedKey");
var aesKey2 = Unwrap(wrappedKey, rsaKeyParams);
}
}
}
You will have to adapt this to your needs.
Upvotes: 2