创建公钥和私钥

Question

Im using the following code to create keys, but when i try to use KeyGeneration.getPublicKey() returns null .

public KeyGeneration() throws Exception,(more but cleared to make easier to read)
{
    KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
    kpg.initialize(1024);
    KeyPair kp = kpg.genKeyPair();
    PublicKey publicKey = kp.getPublic();
    PrivateKey privateKey = kp.getPrivate();

}

public static PublicKey getPublicKey() { return publicKey; }

Error message as below:

java.security.InvalidKeyException: No installed provider supports this key: (null)  
    at javax.crypto.Cipher.chooseProvider(Cipher.java:878)
    at javax.crypto.Cipher.init(Cipher.java:1213)
    at javax.crypto.Cipher.init(Cipher.java:1153)
    at RSAHashEncryption.RSAHashCipher(RSAHashEncryption.java:41)
    at RSAHashEncryption.exportEHash(RSAHashEncryption.java:21)
    at Main.main(Main.java:28)

If you would like to see the full code, i can post here.

Answer 1

If the code you supplied is a true reflection of your actual class, then the problem is that this:

    PublicKey publicKey = kp.getPublic();

is writing to a local variable, but this:

    public static PublicKey getPublicKey() { return publicKey; }

is returning the value of a different variable. In fact it has to be a static field of the enclosing class ... and I expect that it is null because you haven't initialized it!

I think the real problem here is that you don't really understand the difference between Java instance variables, static variables and local variables. Putting the pieces together, I suspect that your code should really look like this:

public class KeyGeneration {

    private PublicKey publicKey;
    private PrivateKey privateKey;

    public KeyGeneration() throws Exception /* replace with the actual list ... */ {
        KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
        kpg.initialize(1024);
        KeyPair kp = kpg.genKeyPair();
        publicKey = kp.getPublic();
        privateKey = kp.getPrivate();
    }

    public PublicKey getPublicKey() { return publicKey; }

    public PrivateKey getPrivateKey() { return privateKey; }

}