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(Java) DSA Signature Create and VerifyShows how to create a DSA (DSS) signature for the contents of a file. The first step is to create an SHA-1 hash of the file contents. The hash is signed using the Digital Signature Algorithm and the signature bytes are retrieved as a hex-encoded string. The 2nd part of the example loads the signature and verifies it against the hash.
import com.chilkatsoft.*; public class ChilkatExample { static { try { System.loadLibrary("chilkat"); } catch (UnsatisfiedLinkError e) { System.err.println("Native code library failed to load.\n" + e); System.exit(1); } } public static void main(String argv[]) { // This example requires the Chilkat API to have been previously unlocked. // See Global Unlock Sample for sample code. CkCrypt2 crypt = new CkCrypt2(); crypt.put_EncodingMode("hex"); crypt.put_HashAlgorithm("sha-1"); // Return the SHA-1 hash of a file. The file may be any size. // The Chilkat Crypt component will stream the file when // computing the hash, keeping the memory usage constant // and reasonable. // The 20-byte SHA-1 hash is returned as a hex-encoded string. String hashStr = crypt.hashFileENC("hamlet.xml"); CkDsa dsa = new CkDsa(); // Load a DSA private key from a PEM file. Chilkat DSA // provides the ability to load and save DSA public and private // keys from encrypted or non-encrypted PEM or DER. // The LoadText method is for convenience only. You may // use any means to load the contents of a PEM file into // a string. String pemPrivateKey; pemPrivateKey = dsa.loadText("dsa_priv.pem"); boolean success = dsa.FromPem(pemPrivateKey); if (success != true) { System.out.println(dsa.lastErrorText()); return; } // You may optionally verify the key to ensure that it is a valid // DSA key. success = dsa.VerifyKey(); if (success != true) { System.out.println(dsa.lastErrorText()); return; } // Load the hash to be signed into the DSA object: success = dsa.SetEncodedHash("hex",hashStr); if (success != true) { System.out.println(dsa.lastErrorText()); return; } // Now that the DSA object contains both the private key and hash, // it is ready to create the signature: success = dsa.SignHash(); if (success != true) { System.out.println(dsa.lastErrorText()); return; } // If SignHash is successful, the DSA object contains the // signature. It may be accessed as a hex or base64 encoded // string. (It is also possible to access directly in byte array form via // the "Signature" property.) String hexSig = dsa.getEncodedSignature("hex"); System.out.println("Signature:"); System.out.println(hexSig); // ----------------------------------------------------------- // Step 2: Verify the DSA Signature // ----------------------------------------------------------- CkDsa dsa2 = new CkDsa(); // Load the DSA public key to be used for verification: String pemPublicKey; pemPublicKey = dsa2.loadText("dsa_pub.pem"); success = dsa2.FromPublicPem(pemPublicKey); if (success != true) { System.out.println(dsa2.lastErrorText()); return; } // Load the hash to be verified against the signature. success = dsa2.SetEncodedHash("hex",hashStr); if (success != true) { System.out.println(dsa2.lastErrorText()); return; } // Load the signature: success = dsa2.SetEncodedSignature("hex",hexSig); if (success != true) { System.out.println(dsa2.lastErrorText()); return; } // Verify: success = dsa2.Verify(); if (success != true) { System.out.println(dsa2.lastErrorText()); } else { System.out.println("DSA Signature Verified!"); } } } |
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