HP 635n - JetDirect IPv6/IPsec Print Server How To Use Manual page 11

A hash – also known as a message digest. A hash is the output of a one way function that
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attempts to ensure the integrity of the message (i.e., that the message has not been altered).
It is usually combined with authentication information to ensure that the message originator
can be authenticated and that the integrity of the message has not been disrupted. You can
think of a hash like an advanced checksum or an advanced cyclic redundancy check (CRC).
Let's cover hashes and digital signatures first. We'll assume that Jack wants to send John a message.
Jack wants to make sure that John knows the message came from him and that the message was not
altered in transit. However, Jack doesn't care about confidentiality – in other words, the actual
message can be sent "in the clear" – but does care about authentication and integrity. We can
accomplish this through hashes and digital signatures as shown in Figure 12.
In Figure 12, Jack has sent John a message with a digital signature. Let's see how John would
validate this message to make sure it came from Jack and was not altered. Refer to Figure 13.
Figure 12 – Digital Signature
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