Page 123 - CISSO_Prep_ Guide
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The problem with a simple hash operation like this is that the
message and the digest of the message can still be altered by a
malicious person in the middle of the transmission path.
Therefore the solution is to combine two functions to protect
both the message digest and to provide proof of the origin of the
message.
Digital Signatures
A digital signature combines a hash function with asymmetric
encryption. The hash function provides proof of integrity,
whereas the process of encrypting the hash of the message with
a private key does two things - it protects the hash from
alteration and provides proof of origin of the message.
