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Java安全－－密码

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<a name="navskip"></a><td height="25" colspan="4"><img alt="6.无纸签名" src="imagemaster/titlebar6.jpg" border="0" height="25" width="562"></td>
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<td bgcolor="ffffff" width="15">&nbsp;</td><td bgcolor="ffffff" width="12">&nbsp;</td><td valign="top" align="left" bgcolor="ffffff" width="*">
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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>数字签名代码示例：简单的方法</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 6 页（共7 页）</nobr></font></td>
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<p>
<code>Signature</code> 类使用由 <code>KeyPairGenerator</code> 类产生的密钥来操作数字签名。下面的示例中使用了下列方法：</p>
<ul>
<li>
<code>KeyPairGenerator.getInstance("RSA")</code>、<code>.initialize(1024)</code> 和 <code>.generateKeyPair()</code>：生成密钥。<br>
<br>
</li>
<li>
<code>Cipher.getInstance("MD5WithRSA")</code>：创建 <code>Signature</code> 对象。<br>
<br>
</li>
<li>
<code>.initSign(key.getPrivate())</code>：初始化 <code>Signature</code> 对象。<br>
<br>
</li>
<li>
<code>.update(plainText)</code> 和 <code>.sign()</code>：用明文字符串计算签名。<br>
<br>
</li>
<li>
<code>.initVerify(key.getPublic())</code> 和 <code>.verify(signature)</code>：验证签名。</li>
</ul>
<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12"> 
import java.security.*;
import javax.crypto.*;
//
// This example uses the digital signature features to generate and
// verify a signature much more easily than the previous example
public class DigitalSignature2Example {

  public static void main (String[] args) throws Exception {
    //
    // check args and get plaintext
    if (args.length !=1) {
      System.err.println("Usage: java DigitalSignature1Example text");
      System.exit(1);
    }
    byte[] plainText = args[0].getBytes("UTF8");
    //
    // generate an RSA keypair
    System.out.println( "\nStart generating RSA key" );
    KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
    keyGen.initialize(1024);

    KeyPair key = keyGen.generateKeyPair();
    System.out.println( "Finish generating RSA key" );
    //
    // get a signature object using the MD5 and RSA combo
    // and sign the plaintext with the private key,
    // listing the provider along the way

    Signature sig = Signature.getInstance("MD5WithRSA");
    sig.initSign(key.getPrivate());
    sig.update(plainText);
    byte[] signature = sig.sign();
    System.out.println( sig.getProvider().getInfo() );
    System.out.println( "\nSignature:" );
    System.out.println( new String(signature, "UTF8") );
    //
    // verify the signature with the public key
    System.out.println( "\nStart signature verification" );
    sig.initVerify(key.getPublic());
    sig.update(plainText);
    try {
      if (sig.verify(signature)) {
        System.out.println( "Signature verified" );
      } else System.out.println( "Signature failed" );
    } catch (SignatureException se) {
      System.out.println( "Signature failed" );
    }
  }
}
</code>
</pre>
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