Cryptography Reference
In-Depth Information
Alice
Bob
Figure 1.1. Simple communication scenario
For example, Alice might ask herself:
• Am I happy that anyone could read this email, or do I only want Bob to see it?
• How can I make sure that my email reaches Bob without being changed?
• Am I prepared (or allowed) to take any measures to protect my email before I
send it?
Bob might ask himself:
• How can I have confidence that this email actually came from Alice?
• Can I be sure that this is the email that Alice intended to send me?
• Is it possible that Alice could deny in the future that she sent me this email?
This simple communication scenario (or variations thereof) is one that we will
regularly return to when we consider different types of cryptographic mechanism.
However, it is important to realise that not all applications of cryptography
conform to this simple communication scenario. For example, we may need to
secure:
• a broadcast environment, where one sender is streaming data to a large number
of receivers;
• a data storage environment, which may not have an obvious recipient.
At this stage it suffices to appreciate that there are other basic scenarios that each
come with their own players and security risks.
1.2.3 Choosing security mechanisms
Alice and Bob's concerns in Section 1.2.2 may seem rather paranoid. Some people
regularly encrypt emails and so might regard these concerns as being important,
while other people rarely encrypt emails and might regard the questions raised
by Alice and Bob as being slightly absurd, or at least 'over the top' (for more
discussion of this particular issue, see Section 12.7.2).
 
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