Edit Question - KnowledgeHub

Title Body

I'm trying to understand what the Java java.security.Signature class does. If I compute an SHA1 message digest, and then encrypt that digest using RSA, I get a different result to asking the Signature class to sign the same thing: // Generate new key KeyPair keyPair = KeyPairGenerator.getInstance("RSA").generateKeyPair(); PrivateKey privateKey = keyPair.getPrivate(); String plaintext = "This is the message being signed"; // Compute signature Signature instance = Signature.getInstance("SHA1withRSA"); instance.initSign(privateKey); instance.update((plaintext).getBytes()); byte[] signature = instance.sign(); // Compute digest MessageDigest sha1 = MessageDigest.getInstance("SHA1"); byte[] digest = sha1.digest((plaintext).getBytes()); // Encrypt digest Cipher cipher = Cipher.getInstance("RSA"); cipher.init(Cipher.ENCRYPT_MODE, privateKey); byte[] cipherText = cipher.doFinal(digest); // Display results System.out.println("Input data: " + plaintext); System.out.println("Digest: " + bytes2String(digest)); System.out.println("Cipher text: " + bytes2String(cipherText)); System.out.println("Signature: " + bytes2String(signature)); Results in (for example): Input data: This is the message being signed Digest: 62b0a9ef15461c82766fb5bdaae9edbe4ac2e067 Cipher text: 057dc0d2f7f54acc95d3cf5cba9f944619394711003bdd12... Signature: 7177c74bbbb871cc0af92e30d2808ebae146f25d3fd8ba1622... I must have a fundamental misunderstanding of what Signature is doing - I've traced through it, and it appears to be calling update on a MessageDigest object, with the algorithm set to SHA1 as I would expect, then getting the digest, then doing the encryption. What's making the results differ? EDIT: Leonidas made me check whether the signature scheme is supposed to do what I think it does. There are two types of signature defined in th

Tags (comma-separated) Cancel