Verify a DSA signature
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import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.security.KeyFactory;
import java.security.PublicKey;
import java.security.Signature;
import java.security.spec.X509EncodedKeySpec;
public class VerSig {
public static void main(String[] args) {
/* Verify a DSA signature */
if (args.length != 3) {
System.out
.println("Usage: VerSig publickeyfile signaturefile datafile");
} else
try {
/* import encoded public key */
FileInputStream keyfis = new FileInputStream(args[0]);
byte[] encKey = new byte[keyfis.available()];
keyfis.read(encKey);
keyfis.close();
X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(encKey);
KeyFactory keyFactory = KeyFactory.getInstance("DSA", "SUN");
PublicKey pubKey = keyFactory.generatePublic(pubKeySpec);
/* input the signature bytes */
FileInputStream sigfis = new FileInputStream(args[1]);
byte[] sigToVerify = new byte[sigfis.available()];
sigfis.read(sigToVerify);
sigfis.close();
/*
* create a Signature object and initialize it with the public
* key
*/
Signature sig = Signature.getInstance("SHA1withDSA", "SUN");
sig.initVerify(pubKey);
/* Update and verify the data */
FileInputStream datafis = new FileInputStream(args[2]);
BufferedInputStream bufin = new BufferedInputStream(datafis);
byte[] buffer = new byte[1024];
int len;
while (bufin.available() != 0) {
len = bufin.read(buffer);
sig.update(buffer, 0, len);
}
;
bufin.close();
boolean verifies = sig.verify(sigToVerify);
System.out.println("signature verifies: " + verifies);
} catch (Exception e) {
System.err.println("Caught exception " + e.toString());
}
;
}
}
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