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 security subject except some base information about RSA. I have been given a private key as String. I have managed to write following code block to do the job but I am not sure if I am doing the job securely and correctly.

I am not an expert but putting my private key as String in code is not secure I guess. 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 is in form as:

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

Answer 1

Your key format is an unencrypted base64-encoded PKCS8-encoded private key. 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, it is just a throwaway for the 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);     }  }