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Asked: 2026-05-14T16:34:17+00:00

I want to implement a RSA algorithm to encrypt an image ( byte[] ).

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I want to implement a RSA algorithm to encrypt an image (byte[]). To generate my two keys I used this piece of code :

KeyPairGenerator keygen = KeyPairGenerator.getInstance("RSA");
keygen.initialize(512);
keyPair = keygen.generateKeyPair();

Once public and private key are generated, I would like to show them to the user so he can distribute the public key and use the private key to decode. How can I get back those key?

Using keygen.getPrivateKey() and keygen.getPublicKey() give me all the information of the RSA algorithm, not only the keys I need.

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1 Answer

  1. Editorial Team

    Via the Relevant KeySpec classes, you can call the getModulus() and getPublicExponent()/getPrivateExponent() methods to pull out the key components:

    KeyFactory fact = KeyFactory.getInstance("RSA");
RSAPublicKeySpec pub = fact.getKeySpec(kp.getPublic(),
  RSAPublicKeySpec.class);
RSAPrivateKeySpec priv = fact.getKeySpec(kp.getPrivate(),
  RSAPrivateKeySpec.class);

saveToFile("public.key", pub.getModulus(),
  pub.getPublicExponent());
saveToFile("private.key", priv.getModulus(),
  priv.getPrivateExponent());

    In case it’s useful, I wrote a few articles a while back dealing with some of the details of RSA encryption in Java (and Java-based cryptography generally.

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