Java Cryptography - Retrieving keys

In this chapter, we will learn how to retrieve a key from the keystore using Java Cryptography.
To retrieve a key from the keystore, follow the steps given below.
The getInstance() method of the KeyStore class of the java.security package accepts a string value representing the type of the keystore and returns a KeyStore object.
Create an object of the KeyStore class using this method as shown below.
//Creating the KeyStore object
KeyStore keyStore = KeyStore.getInstance("JCEKS");

The load() method of the KeyStore class accepts a FileInputStream object representing the keystore file and a String parameter specifying the password of the KeyStore.
In general, the KeyStore is stored in the file named cacerts, in the location C:/Program Files/Java/jre1.8.0_101/lib/security/ and its default password is changeit, load it using the load() method as shown below.
//Loading the KeyStore object
char[] password = "changeit".toCharArray();
String path = "C:/Program Files/Java/jre1.8.0_101/lib/security/cacerts";
java.io.FileInputStream fis = new FileInputStream(path);
keyStore.load(fis, password);

Instantiate the KeyStore.ProtectionParameter as shown below.
//Creating the KeyStore.ProtectionParameter object
KeyStore.ProtectionParameter protectionParam = new KeyStore.PasswordProtection(password);

Create the SecretKey (interface) object by instantiating its Sub class SecretKeySpec. While instantiating you need to pass password and algorithm as parameters to its constructor as shown below.
//Creating SecretKey object
SecretKey mySecretKey = new SecretKeySpec(new String(keyPassword).getBytes(), "DSA");

Create an object of the SecretKeyEntry class by passing the SecretKey object created in the above step as shown below.
//Creating SecretKeyEntry object
KeyStore.SecretKeyEntry secretKeyEntry = new KeyStore.SecretKeyEntry(mySecretKey);

The setEntry() method of the KeyStore class accepts a String parameter representing the keystore entry alias, a SecretKeyEntry object, a ProtectionParameter object and, stores the entry under the given alias.
Set the entry to the keystore using the setEntry() method as shown below.
//Set the entry to the keystore
keyStore.setEntry("secretKeyAlias", secretKeyEntry, protectionParam);

The getEntry() method of the KeyStore class accepts an alias (String parameter) and, an object of the ProtectionParameter class as parameters and returns a KeyStoreEntry object then you can cast this it into KeyStore.SecretKeyEntry object.
Create an object of the KeyStore.SecretKeyEntry class by passing the alias for required key and the protection parameter object created in the previous steps, to the getEntry() method as shown below.
//Creating the KeyStore.SecretKeyEntry object
KeyStore.SecretKeyEntry secretKeyEnt = (KeyStore.SecretKeyEntry)keyStore.getEntry("secretKeyAlias", protectionParam);

The getSecretKey() method of the SecretKeyEntry class returns a SecretKey object. Using this method create a SecretKey object as shown below.
//Creating SecretKey object
SecretKey mysecretKey = secretKeyEnt.getSecretKey();      
System.out.println(mysecretKey);

Following example shows how to retrieve keys from a key store. Here, we store a key in a keystore, which is in the “cacerts” file (windows 10 operating system), retrieve it, and display some of the properties of it such as the algorithm used to generate the key and, the format of the retrieved key.
import java.io.FileInputStream;
import java.security.KeyStore;
import java.security.KeyStore.ProtectionParameter;
import java.security.KeyStore.SecretKeyEntry;

import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

public class RetrievingFromKeyStore{
   public static void main(String args[]) throws Exception{
      //Creating the KeyStore object
      KeyStore keyStore = KeyStore.getInstance("JCEKS");

      //Loading the the KeyStore object
      char[] password = "changeit".toCharArray();
      java.io.FileInputStream fis = new FileInputStream(
         "C:/Program Files/Java/jre1.8.0_101/lib/security/cacerts");
      
      keyStore.load(fis, password);
      
      //Creating the KeyStore.ProtectionParameter object
      ProtectionParameter protectionParam = new KeyStore.PasswordProtection(password);

      //Creating SecretKey object
      SecretKey mySecretKey = new SecretKeySpec("myPassword".getBytes(), "DSA");
      
      //Creating SecretKeyEntry object
      SecretKeyEntry secretKeyEntry = new SecretKeyEntry(mySecretKey);
      keyStore.setEntry("secretKeyAlias", secretKeyEntry, protectionParam);

      //Storing the KeyStore object
      java.io.FileOutputStream fos = null;
      fos = new java.io.FileOutputStream("newKeyStoreName");
      keyStore.store(fos, password);
      
      //Creating the KeyStore.SecretKeyEntry object
      SecretKeyEntry secretKeyEnt = (SecretKeyEntry)keyStore.getEntry("secretKeyAlias", protectionParam);

      //Creating SecretKey object
      SecretKey mysecretKey = secretKeyEnt.getSecretKey();      
      System.out.println("Algorithm used to generate key : "+mysecretKey.getAlgorithm());   
      System.out.println("Format used for the key: "+mysecretKey.getFormat());
   }
}
The above program generates the following output −
Algorithm used to generate key: DSA
Format of the key: RAW


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