remain secret. For example, a military battle plan might have no value after a certain
period of time, or a financial transaction request might have no significance after the
transaction has been completed. For these purposes, less security is required than for
long-term needs, since an attacker would be required to break the code in a limited
period of time and a weaker system might be sufficient.
this is an important consideration. Some systems are more efficient or computationally
economical than others.
computational effort may be the deciding factor in choosing one system over the others.
be exchanged without prior security. Strangers can freely exchange encryption keys,
since they are public and need not be kept secret. When using symmetric keys, on the
other hand, any exchange must be done secretly, since someone overhearing or
intercepting the exchange will be able to decrypt subsequent traffic.
convenient to use one of these methods.
worst part is that the user may have a false sense of security, which encourages him to
take unwarranted risks in using the system.
implemented correctly. Microsoft, for example, has released erroneous implementations
of encryption algorithms.
implementation is trustworthy is the availability of the source code. If the source code
has been released, then public scrutiny will presumably find errors that might exist in
the code.