JAVA RSA 256 Private Key JWT Creation - OpenSSL Key Pair

Steps to create RSA256 Keypair using OpenSSL

You need to convert your private key to PKCS8 format using following command: This will ensure your code to read the PEM openssl pkcs8 -topk8 -inform PEM -outform DER -in C:\certs\2021.key -nocrypt > pkcs8_key.key

Please note that the rsa key you have need to be converted to der format online 

can be done using below link

https://decoder.link/rsa_converter
 

       
       
import java.io.UnsupportedEncodingException;
import java.security.Key;
import java.security.KeyFactory;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.util.Base64;
import java.util.Date;

import io.jsonwebtoken.Claims;
import io.jsonwebtoken.Jws;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
import io.jsonwebtoken.impl.TextCodec;

public class JwtTokenUtilRSA {

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

		System.out.println(createAccessJwtToken());

	}

	public static String createAccessJwtToken() throws Exception {

		SignatureAlgorithm signatureAlgorithm = SignatureAlgorithm.RS256;
		Claims claims = Jwts.claims().setSubject("EXXXXXXXXciOSbWCwG");
		claims.put("aud", "XYZ.com");

		LocalDateTime currentTime = LocalDateTime.now();

		Key signingKey = getPrivateKey2();

		String token = Jwts.builder().setClaims(claims).setIssuer("issuer")
				.setIssuedAt(Date.from(currentTime.atZone(ZoneId.systemDefault()).toInstant()))
				.signWith(SignatureAlgorithm.RS256, signingKey).compact();

		return token;
	}
    
    	private static PrivateKey getPrivateKey2() throws NoSuchAlgorithmException, InvalidKeySpecException {
	    String rsaPrivateKey = "-----BEGIN PRIVATE KEY-----" +
	            "MIIEvgIBADANBgkqhkiG9w0BAQEFAASCBKgwggSkAgEAAoIBAQDJPwCTr8LDSi/7" +
	            "f0PXtiGZHcT/7B2AAIlATC178lp1mI42Exmw2X/yOiNU6mkiYQxxkv1vr8blViga" +
	            "mfhwCjahzI9ix0PzyEjVxfFWYlnfoorNGOwWgAqD3kzgnnUVPQXFmYRjtVD43sM4" +
	            "54h9Q1nFfPnVe9vgyckKI/p2nVUyZZlMo36/PRZdAV15vVvuvBJLW3gW3Xb2OuLy" +
	            "sF7/NEQe2zi5A87j4pbeRpBmGWzmloF3dNjwtCZAiSmX01nLe0bZYJIHgDgmPDKt" +
	            "qond8Pe1+zEDDf6fyq9mfT/naSOL1mQbLK2VQdGUGWmNgIpTgPEpolv3AdwbOtMx" +
	            "47GiOBPdAgMBAAECggEAeimjiQNNoEzdmbakkUJ/XLpEhvJm6ffpWT2k8rOok/Aa" +
	            "i9rGYqN1Vq5SGk79qR/udNc8v1qdy0Okrpk+xYx9o3RQqi66Ijc3d4VkPgMP+YBq" +
	            "75usXPA28du1ITkva8gSQ+QwCHLdh2V6boWmRhvnV8nIwv4f+HGld2FlvjE9sYwF" +
	            "Zwuo51G5TBkMnLaklHzMB18sTrcC4EmFvFfEsH6lzY3XaZXbMiwV802VbTasiXGi" +
	            "+HDMfUrxza1AVUz4zqlZhWvJL2c9RinLnSsS1eZ/FGbRrjZbfyE/IMFiMapP9LGi" +
	            "Cw1Gdt9NAwWtx78lgOrrW1+YYLVJEUlXZmPcPBkCZQKBgQDrP9tl10I8wlp6XyRY" +
	            "1Ge2xqAaSuHSwIMdSw9eRyO9K/CCV7hmzNOUvVe7U3Q5knxD5aoIul2Behn6BzDA" +
	            "hovtQALmFn0lmwsb7IKa/zM1o3BM5qrSwCTXSiBfKyi207jCK35wJPAJeemCl1JQ" +
	            "NY0Fug31/+SPLcGyO0HIcxaZrwKBgQDa/1HEHQ6yn2Eb3H/KtNrh5CQYu004LBaz" +
	            "ISsR7JwfyHscrE34Fx1eyEuJDVehGC30U61zh5h/dibr9M4wJqUTvJuhJh3X/w7r" +
	            "w1vWSE9rOJsOFenjWVv+2VO6TkaayWPDC79mCR/UBIXULOdMwi6NhDd8eqVraZzg" +
	            "b5TTHntqMwKBgB6KP7VM6LBymsRgLZvKl1xHFOnU5tQxYdQftnMK0Tzxw1tof+v4" +
	            "k08v9X/AKcp/ldpKqnRPnWv9qfmnjVCxJuE5+iZcrQqAwkRxw9LTZpaEDUQufea2" +
	            "QxIf8WvpcnOpsMakVtnAMdlJFmN5uZnoGdKwgLd67PUZf5ff0X5wUnLJAoGBAM60" +
	            "Itc6nf7XFG+ZxjzsS5TfI3r8fzw/0QUuj1qRvCL7tcgwkj9SgfROlY08vLNfATEW" +
	            "MidTmwrj2ITqQhuMvk9MvJB0S8LuCYValbpB8kQ/34qCAIsIcx6uvqqg6196KuGU" +
	            "mwmSHyqdQjwsTf1TY2FLpJunn68stlfYud4zbUWlAoGBAMCxCk2QabirfKSpKeXY" +
	            "On52j23o/8g2OfDPtd1cS30mTtDUStv3Sqr5Tegz+/7IwugORQujae4b20qgBSds" +
	            "NP9gb8RGmxLryZsEfwV1qppx0d1gEcyYcySYBhz+9qKyByeD8lotbZ0WGMu/UAg/" +
	            "ftaiqVv/CKA/h256T/5uThS3" +
	            "-----END PRIVATE KEY-----";

	    rsaPrivateKey = rsaPrivateKey.replace("-----BEGIN PRIVATE KEY-----", "");
	    rsaPrivateKey = rsaPrivateKey.replace("-----END PRIVATE KEY-----", "");

	    PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(Base64.getDecoder().decode(rsaPrivateKey));
	    KeyFactory kf = KeyFactory.getInstance("RSA");
	    PrivateKey privKey = kf.generatePrivate(keySpec);
	    return privKey;
	
	}

}