Creating public and private keys

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.

Which java version your are using ?

Suresh Atta
– Suresh Atta

2013-10-23 15:06:10 +00:00
Commented Oct 23, 2013 at 15:06 — Suresh Atta
– Suresh Atta, Commented Oct 23, 2013 at 15:06
We do not need the full code, just SSCCE =)

An SO User
– An SO User

2013-10-23 15:24:09 +00:00
Commented Oct 23, 2013 at 15:24 — An SO User
– An SO User, Commented Oct 23, 2013 at 15:24

Stephen C · Accepted Answer · 2013-10-23 15:45:01Z

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; } }

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