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            <td class="blob-line-code"><div class="code-body highlight"><pre><div class='line' id='LC1'>SHA implements secure hash functions that can be used for cryptography, data integrity and security purposes.</div><div class='line' id='LC2'><br/></div><div class='line' id='LC3'>Sha covers the following standards:</div><div class='line' id='LC4'>	SHA-1 (FIPS 180-2)</div><div class='line' id='LC5'>	SHA-256 (FIPS 180-2)</div><div class='line' id='LC6'>	HMAC-SHA-1 (FIPS 198a)</div><div class='line' id='LC7'>	HMAC-SHA-256 (FIPS 198a)</div><div class='line' id='LC8'><br/></div><div class='line' id='LC9'>What is a hash function?</div><div class='line' id='LC10'>	A hash function takes a message, and generates a number.</div><div class='line' id='LC11'>	A good hash function has the following properties:</div><div class='line' id='LC12'>		The number is large enough that you will never find two messages with the same number (a &#39;collision&#39;)</div><div class='line' id='LC13'>		It is computationally unfeasible to extract message information from its hash (without trying every possible combination)</div><div class='line' id='LC14'>		A small (1 bit) change in the message will produce a huge (approximately half of all bits) change in the hash.</div><div class='line' id='LC15'>		Fast to calculate</div><div class='line' id='LC16'><br/></div><div class='line' id='LC17'>	SHA is slower than simple hashes (eg. parity), but has very high security - high enough to be used in currency transactions and confidential documents.</div><div class='line' id='LC18'>	SHA-1 is currently secure, but there is some suggestion it may not be for much longer.</div><div class='line' id='LC19'>	SHA-256 is slightly slower, but has higher security.</div><div class='line' id='LC20'><br/></div><div class='line' id='LC21'>What is an HMAC?</div><div class='line' id='LC22'>	HMACs are Hashed Message Authentication Codes. Using them, it is possible to prove that you have a secret key without actually disclosing it.</div></pre></div></td>
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