Generate RSA key pair and encode public as string

Question

I want to generate 512 bit RSA keypair and then encode my public key as a string. How can I achieve this?

Warning: RSA 512 bit keys are completely insecure.

Maarten Bodewes
– Maarten Bodewes

2019-02-13 01:22:06 +00:00
Commented Feb 13, 2019 at 1:22 — Maarten Bodewes
– Maarten Bodewes, Commented Feb 13, 2019 at 1:22

Sir Wumpus IV · Accepted Answer · 2018-10-22 06:48:40Z

57

For output as Hex-String

import java.security.*;
public class Test {
    public static void main(String[] args) throws NoSuchAlgorithmException, NoSuchProviderException {
        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
        keyGen.initialize(512);
        byte[] publicKey = keyGen.genKeyPair().getPublic().getEncoded();
        StringBuffer retString = new StringBuffer();
        for (int i = 0; i < publicKey.length; ++i) {
            retString.append(Integer.toHexString(0x0100 + (publicKey[i] & 0x00FF)).substring(1));
        }
        System.out.println(retString);
    }
}

For output as byte values

import java.security.*;
public class Test {
    public static void main(String[] args) throws NoSuchAlgorithmException, NoSuchProviderException {
        KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
        keyGen.initialize(512);
        byte[] publicKey = keyGen.genKeyPair().getPublic().getEncoded();
        StringBuffer retString = new StringBuffer();
        retString.append("[");
        for (int i = 0; i < publicKey.length; ++i) {
            retString.append(publicKey[i]);
            retString.append(", ");
        }
        retString = retString.delete(retString.length()-2,retString.length());
        retString.append("]");
        System.out.println(retString); //e.g. [48, 92, 48, .... , 0, 1]
    }
}

edited Oct 22, 2018 at 6:48

Sir Wumpus IV

53 bronze badges

answered Nov 10, 2009 at 18:23

jitter

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4 Comments

Angela Over a year ago

Thank you very much! If i should get result like this [48, -137, -97, 49, 13, 6, 8, 42, -122, 72, -122, -9, 13, 2, 3, 15 4, 0, 3, -132, -115, 0, 48, -127] should i use just toString method instead retString.append(Integer.toHexString(0x0100 + (publicKey[i] & 0x00FF)).substring(1)); ??

Yatin Over a year ago

If I want the output in PEM format then how do I do it?

vsapiha Over a year ago

to output as HEX the simpler solution is to use javax.xml.bind.DatatypeConverter.printHexBinary(publicKey) @YatinGrover for PEM Base 64 you can use javax.xml.bind.DatatypeConverter.printBase64Binary(publicKey)

user2080225 Over a year ago

Also you can consider org.apache.commons.codec.binary.Hex#encodeHexString as a way to get a hex string from an array of bytes.

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