Java Secure Hash functions
A Secure Hash function would generate
a large number, called the hash value, when
given a document of some sort. This document can is of almost any type. We'll be using the simple strings in our examples.
The function is a
One-way hash function, which means that it was effectively impossible to recreate the document when given a hash value. When used
In conjunction with asymmetric keys, it allows the transmission of a document with the
Guarantee that the document had not been altered.
The sender of a document would use a secure hash function to
generate the hash value for a document. The sender would
Encrypt this hash value with their private key. The document and the key is then combined and sent to a receiver. The document is not encrypted.
Upon receiving the document, the receiver would
Use the sender's public key to decrypt the hash value. The receiver would then
Use the same secure hash function against the document to obtain a hash value. If This hash value matches the decrypted hash value and then the receiver was guaranteed that the document had not been Modifi Ed.
The intent is
Not to encrypt the document. While possible, this approach was useful when it was not important to hide the document from third parties De a guarantee that the document had not been modified.
Java supports the following hashing algorithms:
md5:the default size is bytes
Sha1:the default size is bytes
We will Use the SHA hash function for our Examples. This series is functions was developed by the
national Security Agency (
NSA ). There is three versions of this hash function:sha-0, SHA-1, and SHA-2. The SHA-2 is the more secure algorithm and Uses variable Digest sizes:sha-224, SHA-256, SHA-384, and SHA-512.
the
MessageDigest class works with arbitrary-sized data
producing a fixed size hash value . There is no public constructors for this class. The GetInstance method returns an instance of the class when given the name of the algorithm. Valid names is found At http://docs.oracle.com/javase/8/docs/technotes/ Guides/security/standardnames.html#messagedigest
In this example, we use SHA-256:
MessageDigest messagedigest = messagedigest.getinstance ("SHA-256");
Messagedigest.update (Message.getbytes ());
Package Com.doctor.ch08;import Java.nio.charset.standardcharsets;import Java.security.messagedigest;import Java.security.nosuchalgorithmexception;import javax.xml.bind.datatypeconverter;/** * Secure Hash functions * * @author Sdcuike * * Created on April 16, 2016 PM 8:22:01 */public class Securehashfunctions {public static void main (String [] args) throws nosuchalgorithmexception {String message = "This was a simple text message"; String HashValue = gethashvalue (message); System.out.println (HashValue); 83C660972991049C25E6CAD7A5600FC4D7C062C097B9A75C1C4F13238375C26C} static final String hash_algorithm = "SHA-256" ; static string Gethashvalue (String message) throws NoSuchAlgorithmException {MessageDigest digest = MESSAGEDIGEST.G Etinstance (Hash_algorithm); Byte[] B = digest.digest (Message.getbytes (standardcharsets.utf_8)); return datatypeconverter.printhexbinary (b); }}
Results:
83c660972991049c25e6cad7a5600fc4d7c062c097b9a75c1c4f13238375c26c
Reading notes: Learning Network programming with Java
Copyright? Packt Publishing
First Published:december 2015
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Published by Packt Publishing Ltd.
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Java Secure Hash functions
