how to generate public and private key in PEM format

dsa, java, pem, public-key, rsa

Solution

Instead of manually generating the PEM String, you can use the bouncy castle to do it for you: since it's a tested library you can be sure about the output. The following code is in Kotlin but can easily be used with Java syntax:

        val gen = KeyPairGenerator.getInstance("RSA")
        gen.initialize(2048)
        val pair = gen.generateKeyPair()
        val privateKey: PrivateKey = pair.private
       
  
        val pemObject = PemObject("RSA PRIVATE KEY", privateKey.encoded)
        
        val byteStream = ByteArrayOutputStream()
        val pemWriter = PemWriter(OutputStreamWriter(byteStream))
        pemWriter.writeObject(pemObject)
        pemWriter.close();
        println(String(byteStream.toByteArray()))

Problem

I need to generating a RSA and DSA key pair (public and private key) in PEM format using java. I want the public and private key files to be opened with this format: -----BEGIN PUBLIC KEY----- MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAryQICCl6NZ5gDKrnSztO 3Hy8PEUcuyvg/ikC+VcIo2SFFSf18a3IMYldIugqqqZCs4/4uVW3sbdLs/6PfgdX 7O9D22ZiFWHPYA2k2N744MNiCD1UE+tJyllUhSblK48bn+v1oZHCM0nYQ2NqUkvS j+hwUU3RiWl7x3D2s9wSdNt7XUtW05a/FXehsPSiJfKvHJJnGOX0BgTvkLnkAOTd OrUZ/wK69Dzu4IvrN4vs9Nes8vbwPa/ddZEzGR0cQMt0JBkhk9kU/qwqUseP1QRJ 5I1jR4g8aYPL/ke9K35PxZWuDp3U0UPAZ3PjFAh+5T+fc7gzCs9dPzSHloruU+gl FQIDAQAB -----END PUBLIC KEY----- My public key is already generated before with this format that i do not want it: 0Ÿ0 *†H†÷ 0Ÿ0 *†H†÷ ok, this is my code of key generation: ``` private static void createKey() throws Exception { Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider()); BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); System.out.print("Password to encrypt the private key: "); String password = in.readLine(); System.out.println("Generating an RSA keypair..."); // Create an RSA key KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA"); keyPairGenerator.initialize(1024); KeyPair keyPair = keyPairGenerator.genKeyPair(); System.out.println("Done generating the keypair.\n"); // Now we need to write the public key out to a file System.out.print("Public key filename: "); String publicKeyFilename = "C:/Users/Joe/Desktop/" + in.readLine(); // Get the encoded form of the public key so we can // use it again in the future. This is X.509 by default. byte[] publicKeyBytes = keyPair.getPublic().getEncoded(); // Write the encoded public key out to the filesystem FileOutputStream fos = new FileOutputStream(publicKeyFilename); fos.write(publicKeyBytes); fos.close(); // Now we need to do the same thing with the private key, // but we need to password encrypt it as well. System.out.print("Private key filename: "); String privateKeyFilename = "C:/Users/Joe/Desktop/" + in.readLine(); // Get the encoded form. This is PKCS#8 by default. byte[] privateKeyBytes = keyPair.getPrivate().getEncoded(); // Here we actually encrypt the private key byte[] encryptedPrivateKeyBytes = passwordEncrypt(password.toCharArray(),privateKeyBytes); fos = new FileOutputStream(privateKeyFilename); fos.write(encryptedPrivateKeyBytes); fos.close(); } ``` thank you for your help..

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