Converting a string private key to PrivateKey type

Question

I am having below RSA private key in string format.

String privatekey = -----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

I am trying to convert this to PrivateKey type using below code snippet-

  public PrivateKey generatePrivateKey(String privateKey) throws Exception{

        privateKey = privateKey.replace("-----BEGIN RSA PRIVATE KEY-----", "");
        privateKey = privateKey.replace("-----END RSA PRIVATE KEY-----", "");
        privateKey = privateKey.replaceAll("\\s+", "");
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(privateKey.getBytes());
        KeyFactory kf = KeyFactory.getInstance("RSA");
        return kf.generatePrivate(keySpec);
    }

I am getting below error -

It is giving me an error on generatePrivate method.

Execution exception[[InvalidKeySpecException: java.security.InvalidKeyException: invalid key format]]

Tried using the answer here Java: Convert DKIM private key from RSA to DER for JavaMail

import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Base64;

public class pkcs1ToPkcs8 {

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

        String pkcs1 = //privatekey provided above

            // b64 now contains the base64 "body" of the PEM-PKCS#1 file
            byte[] oldder = Base64.getDecoder().decode(pkcs1.getBytes());

            // concatenate the mostly-fixed prefix plus the PKCS#1 data 
            final byte[] prefix = {0x30,(byte)0x82,0,0, 2,1,0, // SEQUENCE(lenTBD) and version INTEGER 
                    0x30,0x0d, 6,9,0x2a,(byte)0x86,0x48,(byte)0x86,(byte)0xf7,0x0d,1,1,1, 5,0, // AlgID for rsaEncryption,NULL
                    4,(byte)0x82,0,0 }; // OCTETSTRING(lenTBD) 
            byte[] newder = new byte [prefix.length + oldder.length];
            System.arraycopy (prefix,0, newder,0, prefix.length);
            System.arraycopy (oldder,0, newder,prefix.length, oldder.length);
            // and patch the (variable) lengths to be correct
            int len = oldder.length, loc = prefix.length-2; 
            newder[loc] = (byte)(len>>8); newder[loc+1] = (byte)len;
            len = newder.length-4; loc = 2;
            newder[loc] = (byte)(len>>8); newder[loc+1] = (byte)len;

            FileOutputStream fo = new FileOutputStream ("pkcs8_file");
            fo.write (newder); fo.close();
            System.out.println ("converted length " + newder.length);

    }

}

pedrofb pedrofb · Accepted Answer · 2019-04-14T14:47:49

BEGIN RSA PRIVATE KEY means your key is pkcs#1 format and not pkcs#8. Reading pkcs#1 keys is not natively supported by Java. You need to use bouncycastle library ( see Read RSA private key of format PKCS1 in JAVA )or use any of these solutions Getting RSA private key from PEM BASE64 Encoded private key file

if your key were pkcs#8, it would have the header BEGIN PRIVATE KEY. In that case, for your code to work correctly you would need additionally decode the key content from base64

To convert a pkcs#1 key to pkcs#8 you can use openssl

  openssl pkcs8 -topk8 -inform PEM -outform PEM -nocrypt -in pkcs1.key -out pkcs8.key

Converting a string private key to PrivateKey type

1 Answers