Information is transformed into a form which obscures the
content so that the attacker has difficulty understanding it. Examples
include:
DES encryption for protecting transmitted information,
RSA cryptosystem for exchanging session keys over an open channel, and
the one-time-pad which provides perfect secrecy if properly implemented.
Complexity: Shannon's 1949 paper
[Shannon49] on
cryptanalysis asserted that, with the exception of the perfect protection
provided by the on-time-pad, cryptography is based on driving up the
workload for the attacker to break the code. The goal is to create
computational leverage so that the encryption and decryption process are
relatively easy for those in possession of the key(s) while the same process
for those without the key(s) is relatively hard. Proper use of cryptography
requires proper key management, which in many cases is the far harder
problem. Encryptions algorithms which provide the proper leverage are now
quite common.
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