Java: How can I generate PrivateKey from a string?

Question

I am trying to encode a message with SH1 RSA , but I have no experience with a security object, except for some basic information about RSA . I was given the private key as a String . I managed to write the following block of code to do this job, but I'm not sure if I am doing the job reliably and correctly.

I am not an expert, but I have placed my private key, since the line in the code is unsafe, I think. Can anyone guide me?

 String privateKeyString = "mykeyhere..."; byte[] privateKeyBytes = privateKeyString.getBytes(); String encodedPrivateKey = Base64.encodeToString(privateKeyBytes, Base64.URL_SAFE); KeyFactory factory = KeyFactory.getInstance(RSA); PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(encodedPrivateKey.getBytes()); RSAPrivateKey privateKey = (RSAPrivateKey) factory.generatePrivate(keySpec); Signature instance = Signature.getInstance(ALGORITHM); instance.initSign(privateKey); instance.update(content.getBytes()); return new String(instance.sign()); 

My private key has the form:

 "-----BEGIN PRIVATE KEY-----\n"+ "MIIE...\n"+ "cH0iRj...\n"+ "O0Hhj...\n"+ . . . "fG6...\n"+ "B6/hF...\n"+ "3Mq38...\n"+ "-----END PRIVATE KEY-----\n" 

Answer 1

The format of your key is an unencrypted PKCS8 encoded private key with base64. Here is an example of how to decode it into a private key. (Don't worry about the security of the private key in this example, this is just an example for an example).

 import java.io.*; import java.security.KeyFactory; import java.security.PrivateKey; import java.security.spec.PKCS8EncodedKeySpec; import android.util.Base64; public class ReadPKCS8Pem { private final static String PRIVATE_KEY = "-----BEGIN PRIVATE KEY-----\n" + "MIICdQIBADANBgkqhkiG9w0BAQEFAASCAl8wggJbAgEAAoGBAM7t8Ub1DP+B91NJ\n" + "nC45zqIvd1QXkQ5Ac1EJl8mUglWFzUyFbhjSuF4mEjrcecwERfRummASbLoyeMXl\n" + "eiPg7jvSaz2szpuV+afoUo9c1T+ORNUzq31NvM7IW6+4KhtttwbMq4wbbPpBfVXA\n" + "IAhvnLnCp/VyY/npkkjAid4c7RoVAgMBAAECgYBcCuy6kj+g20+G5YQp756g95oN\n" + "dpoYC8T/c9PnXz6GCgkik2tAcWJ+xlJviihG/lObgSL7vtZMEC02YXdtxBxTBNmd\n" + "upkruOkL0ElIu4S8CUwD6It8oNnHFGcIhwXUbdpSCr1cx62A0jDcMVgneQ8vv6vB\n" + "/YKlj2dD2SBq3aaCYQJBAOvc5NDyfrdMYYTY+jJBaj82JLtQ/6K1vFIwdxM0siRF\n" + "UYqSRA7G8A4ga+GobTewgeN6URFwWKvWY8EGb3HTwFkCQQDgmKtjjJlX3BotgnGD\n" + "gdxVgvfYG39BL2GnotSwUbjjce/yZBtrbcClfqrrOWWw7lPcX1d0v8o3hJfLF5dT\n" + "6NAdAkA8qAQYUCSSUwxJM9u0DOqb8vqjSYNUftQ9dsVIpSai+UitEEx8WGDn4SKd\n" + "V8kupy/gJlau22uSVYI148fJSCGRAkBz+GEHFiJX657YwPI8JWHQBcBUJl6fGggi\n" + "t0F7ibceOkbbsjU2U4WV7sHyk8Cei3Fh6RkPf7i60gxPIe9RtHVBAkAnPQD+BmND\n" + "By8q5f0Kwtxgo2+YkxGDP5bxDV6P1vd2C7U5/XxaN53Kc0G8zu9UlcwhZcQ5BljH\n" + "N24cUWZOo+60\n" + "-----END PRIVATE KEY-----"; public static void main(String[] args) throws Exception { // Read in the key into a String StringBuilder pkcs8Lines = new StringBuilder(); BufferedReader rdr = new BufferedReader(new StringReader(PRIVATE_KEY)); String line; while ((line = rdr.readLine()) != null) { pkcs8Lines.append(line); } // Remove the "BEGIN" and "END" lines, as well as any whitespace String pkcs8Pem = pkcs8Lines.toString(); pkcs8Pem = pkcs8Pem.replace("-----BEGIN PRIVATE KEY-----", ""); pkcs8Pem = pkcs8Pem.replace("-----END PRIVATE KEY-----", ""); pkcs8Pem = pkcs8Pem.replaceAll("\\s+",""); // Base64 decode the result byte [] pkcs8EncodedBytes = Base64.decode(pkcs8Pem, Base64.DEFAULT); // extract the private key PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(pkcs8EncodedBytes); KeyFactory kf = KeyFactory.getInstance("RSA"); PrivateKey privKey = kf.generatePrivate(keySpec); System.out.println(privKey); } }