编译后，这样运行：

$ java GenSig2 hello.txt

会生成签名文件sig。

VerSig2.java

import java.io.*;
import java.security.*;
import java.security.spec.*;

class VerSig2 {

    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 cert */
            FileInputStream certfis = new FileInputStream(args[0]);
            java.security.cert.CertificateFactory cf =
                java.security.cert.CertificateFactory.getInstance("X.509");
            java.security.cert.Certificate cert =  cf.generateCertificate(certfis);
            PublicKey pubKey = cert.getPublicKey();

            /* 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());
        };
    }
}

编译后，这样运行（StanSmith.cer 是利用 keytool 导出的公钥证书，见前文）：

$ java VerSig2 StanSmith.cer sig hello.txt
signature verifies: true

OpenSSL

虽然也研究了一下 OpenSSL，但发现与 Java 难以结合，难度也很大。例如它的教程中采用的是 RSA，而上面的 Java 使用的是 DSA。所以只是贴在这里备忘，可以忽略。

参考”An Introduction to the OpenSSL command line tool”

生成私钥

$ openssl genrsa -out key.pem 1024
$ cat key.pem
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

导出公钥