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5. Hashing algorithms
Other set of algorithms used in encryption is hashing algorithms. Hashing
algorithm takes clear text (for example you password) and creates almost unique
digest (another name is hash value) .
Hashing algorithms are specifically designed on such way that it is practically
impossible to recover clear text from its digest. Or in plain words words:
hashing is a one-way transformation of clear text.
Figure 4
Hash algorithms is used to validate the integrity of the message. For example,
clear text is a financial transaction. Digest of transaction would be calculated
by sender and receiver independently and then compared, using telephone call,
to verify that transaction has not been tempered with on the way from sender
to receiver.
6. Digital signatures
Digital signatures are used to protect authenticity and integrity of the
message. It means that Digital signature makes it possible to verify who created
signed document and even that this document is exactly as it was when signed.
The author only can digitally sign but all intended recipients can verify
both origin and integrity of signed document.
Digital signature uses a hash algorithm to create digest and then it uses
encryption algorithm to encrypt hash with with the encryption key
 Figure
5
Verification of Digital signature consists of three steps (see Figure 6).
First digital signature gets decrypted and digest of the original message
recovered, than digest of received message is calculated. Than two digests
compared. Difference in digests means that message is not the same that was
sent.
Figure 6
Some digital signatures are based on symmetric encryption algorithms and
others based on asymmetric algorithms. As you can see from the diagram everyone
who suppose to be able to verify signature has to have the decryption key.
It means that symmetric encryption base digital signature has a weakness.
Anyone who can verify signature can also generate one and not only the author.
Oops! So while integrity of signed document is ensured origin could be anyone
who can verify signature. Asymmetric encryption eliminate this weakness. Encryption
key would be known for author only and decryption key would be distributed
for intended audience.
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Energy Secretary fires nuclear security chief apparently for bad information security.
More here.
13 January 2006
No big virus out breaks for long time.
3 January 2006
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