Computer World. Матросова Т.А. - 108 стр.

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• The ability to decrypt an entire encrypted message if you know the way that a

portion of it decrypts (called a known text attack).

• The properties of the plaintext and knowledge of those properties by an

attacker. (For example, a cryptographic system may be vulnerable to attack if

all messages encrypted with it begin or end with a known piece of plaintext.

These kinds of regularities were used by the Allies to crack the German

Enigma cipher during the Second World War.)

The goal in cryptographic design is to develop an algorithm that is so difficult to

reverse without the key that it is at least roughly equivalent to the effort required to

guess the key by trying possible solutions one at a time. We would like this property

to hold even when the attacker knows something about the contents of the messages

encrypted with the cipher. Some very sophisticated mathematics are involved in such

design.