CODEWITHSUNDEEP
javacryptography
alessmar
alessmar

Reputation: 4727

How to programmatically generate a self signed certificate?

I have a RSA public key (2048 bit) generated by a HSM, that key has been saved in a file (with a size of 256 byte) and is encoded as DER.

Is it possibile to programmatically create a self-signed certificate using JDK API (without BouncyCastle) starting from that file?

I'm stuck with the first step, because I'm trying to load the key file to create a PublicKey object:

import java.io.FileInputStream;
import java.security.KeyFactory;
import java.security.PublicKey;
import java.security.spec.PKCS8EncodedKeySpec;

import org.apache.commons.io.IOUtils;

public class Crypto {
public static void main(String[] args) throws Exception {

    byte[] byteArray = IOUtils.toByteArray(new FileInputStream("/tmp/pub.key"));

    PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(byteArray);
    KeyFactory kf = KeyFactory.getInstance("RSA");
    PublicKey pub = kf.generatePublic(spec);
    ....
}
}

but I get this exception:

Exception in thread "main" java.security.spec.InvalidKeySpecException: Only RSAPublicKeySpec and X509EncodedKeySpec supported for RSA public keys
    at sun.security.rsa.RSAKeyFactory.generatePublic(RSAKeyFactory.java:289)
    at sun.security.rsa.RSAKeyFactory.engineGeneratePublic(RSAKeyFactory.java:184)
    at java.security.KeyFactory.generatePublic(KeyFactory.java:304)
    at org.alex.Crypto.main(Crypto.java:17)

Is there a way to do that?

Upvotes: 1

Views: 3413

Answers (2)

Maarten Bodewes
Maarten Bodewes

Reputation: 94058

Use X509EncodedKeySpec (which internally actually used PKCS#1 encoding for RSA keys) instead. Keep the rest of the code identical. PKCS#8 is for private keys, not public keys (because it uses the PKCS#8 internal structure required to wrap a key with another key, and wrapping public keys makes no sense).

Upvotes: 2

First Zero
First Zero

Reputation: 22376

The exception is telling you the issue! => Only RSAPublicKeySpec and X509EncodedKeySpec supported for RSA public keys

You are trying to use PKCS8EncodedKeySpec, which is not supported, create RSAPublicKeySpec or X509EncodedKeySpec class

Example

Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());

byte[] input = new byte[] { (byte) 0xbe, (byte) 0xef };
Cipher cipher = Cipher.getInstance("RSA/None/NoPadding", "BC");

KeyFactory keyFactory = KeyFactory.getInstance("RSA", "BC");
RSAPublicKeySpec pubKeySpec = new RSAPublicKeySpec(new BigInteger(
    "12345678", 16), new BigInteger("11", 16));
RSAPrivateKeySpec privKeySpec = new RSAPrivateKeySpec(new BigInteger(
    "12345678", 16), new BigInteger("12345678",
    16));

RSAPublicKey pubKey = (RSAPublicKey) keyFactory.generatePublic(pubKeySpec);
RSAPrivateKey privKey = (RSAPrivateKey) keyFactory.generatePrivate(privKeySpec);

cipher.init(Cipher.ENCRYPT_MODE, pubKey);

Upvotes: 0

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