10-01-2012, 12:47 PM
Message Integrity and Message Authentication
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MESSAGE INTEGRITY
The cryptography systems that we have studied so far provide secrecy, or confidentiality, but not integrity. However, there are occasions where we may not even need secrecy but instead must have integrity.
Topics discussed in this section
11.1 Document and Fingerprint
11.2 Message and Message Digest
11.3 Difference
11.4 Checking Integrity
11.5 Cryptographic Hash Function Criteria
Document and Fingerprint
One way to preserve the integrity of a document is through the use of a fingerprint. If Alice needs to be sure that the contents of her document will not be changed, she can put her fingerprint at the bottom of the document
Message and Message Digest
The electronic equivalent of the document and fingerprint pair is the message and digest pair.
Difference
The two pairs (document / fingerprint) and (message / message digest) are similar, with some differences. The document and fingerprint are physically linked together. The message and message digest can be unlinked separately, and, most importantly, the message digest needs to be safe from change.
