genmac.html
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<TITLE>Generating a Message Authentication Code (MAC)
(Java Developers Almanac Example)
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<META CONTENT="Patrick Chan" NAME="AUTHOR">
<META CONTENT="Code Examples from The Java Developers Almanac 1.4" NAME="DESCRIPTION">
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<B><A HREF="../javax.crypto/pkg.html">javax.crypto</A></B><font color="#666666" SIZE="-2">
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<B><A HREF="../javax.crypto/pkg.html#MAC">MAC</A></B><font color="#666666" SIZE="-2">
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<h3>
e469.
Generating a Message Authentication Code (MAC)</h3>
A MAC is like hash code for a sequence of bytes. Unlike a hash code,
a MAC uses a secret key to generate the hash code, or more
specifically, the <font color="#0066ff"><i>message digest</i></font>. A MAC is generally used to
check the integrity or validity of information based on a secret key.
<pre>
try {
// Generate a key for the HMAC-MD5 keyed-hashing algorithm; see RFC 2104
// In practice, you would save this key.
KeyGenerator keyGen = KeyGenerator.getInstance(<font color="#0066ff"><i>"HmacMD5"</i></font>);
SecretKey key = keyGen.generateKey();
// Create a MAC object using HMAC-MD5 and initialize with key
Mac mac = Mac.getInstance(key.getAlgorithm());
mac.init(key);
String str = <font color="#0066ff"><i>"This message will be digested"</i></font>;
// Encode the string into bytes using utf-8 and digest it
byte[] utf8 = str.getBytes("UTF8");
byte[] digest = mac.doFinal(utf8);
// If desired, convert the digest into a string
String digestB64 = new sun.misc.BASE64Encoder().encode(digest);
} catch (InvalidKeyException e) {
} catch (NoSuchAlgorithmException e) {
} catch (UnsupportedEncodingException e) {
}
</pre>
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Related Examples
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e467. <a class="eglink" href="ListMac.html?l=rel">
Listing All Available Message Authentication Code (MAC) Key Generators
</a>
<br>
e468. <a class="eglink" href="GenMacKey.html?l=rel">
Generating a Message Authentication Code (MAC) Key
</a>
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See also:
<a class="eglink" href="/egs/javax.crypto/pkg.html?l=rel#Encrypting%20and%20Decrypting">
Encrypting and Decrypting
</a>
<a class="eglink" href="/egs/javax.crypto/pkg.html?l=rel#Key%20Agreement">
Key Agreement
</a>
<a class="eglink" href="/egs/javax.crypto/pkg.html?l=rel#Symmetric%20Keys">
Symmetric Keys
</a>
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