CODEWITHSUNDEEP
javabouncycastle
Pablo Fernandez
Pablo Fernandez

Reputation: 287820

Reconstructing private and public keys with Bouncy Castle?

If I get the actual key with getEncoded from a public or a private key in Bouncy Castle in Java (actual class seems to be BCECPublicKey and BCECPrivateKey). Is it possible to reconstruct the key objects to use them in code?

I found out here in Stack Overflow how to serialize the whole object to binary (and then to disk) and then back to binary and to an object of the appropriate class, but I believe that serialization contains implementation details and if I try to use those keys with anything else than Bouncy Castle, it'll fail. I'm not trying to do that now, but I want to future-proof my program.

This is how I'm creating the keys:

    KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("EC", "BC");
    keyPairGenerator.initialize(new ECGenParameterSpec("secp521r1"), new SecureRandom());
    java.security.KeyPair keyPair = keyPairGenerator.generateKeyPair();

    privateKey = keyPair.getPrivate();
    publicKey = keyPair.getPublic();

Upvotes: 3

Views: 6051

Answers (1)

President James K. Polk
President James K. Polk

Reputation: 42018

The KeyFactory is used to convert between encoded keys and the Java classes that represent them. However, the KeyFactory instance doesn't convert directly between a byte array and a Key class. Instead, you must already know what format the encoding uses, and then create a KeySpec object using the byte array in the constructor. The format can be determined by called the getFormat() method on the key. Here is an example illustrating some of these points.

import org.bouncycastle.jce.provider.BouncyCastleProvider;

import java.security.*;
import java.security.spec.ECGenParameterSpec;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

public class Main {

    public static void main(String[] args) throws Exception{
        Security.addProvider(new BouncyCastleProvider());
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("EC", "BC");
        keyPairGenerator.initialize(new ECGenParameterSpec("secp521r1"), new SecureRandom());
        java.security.KeyPair keyPair = keyPairGenerator.generateKeyPair();

        PrivateKey privateKey = keyPair.getPrivate();
        System.out.println(privateKey.getFormat());
        PublicKey publicKey = keyPair.getPublic();
        System.out.println(publicKey.getFormat());

        // A KeyFactory is used to convert encoded keys to their actual Java classes
        KeyFactory ecKeyFac = KeyFactory.getInstance("EC", "BC");

        // Now do a round-trip for a private key,
        byte [] encodedPriv = privateKey.getEncoded();
        // now take the encoded value and recreate the private key
        PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(encodedPriv);
        PrivateKey privateKey2 = ecKeyFac.generatePrivate(pkcs8EncodedKeySpec);

        // And a round trip for the public key as well.
        byte [] encodedPub = publicKey.getEncoded();
        X509EncodedKeySpec x509EncodedKeySpec = new X509EncodedKeySpec(encodedPub);
        PublicKey publicKey2 = ecKeyFac.generatePublic(x509EncodedKeySpec);
        System.out.println(publicKey2);

    }
}

Upvotes: 8

Related Questions