Introduction to Cryptography with Open-Source Software

6 Cryptography with Open-Source Software

A vital principle for measuring the strength of a cryptosystem is provided

by Kerckhoff’s principle: that every aspect of the cryptosystem is known,

except the key. In particular, the encryption and decryption routines ar e

well known; the problem ge nerally is to determine the key. In practice this

is a very reasonable assumption. There are in fact o nly a small handful o f

cryptosystems strong enough to withstand modern attacks, and in almost

every use of a system, it will be clear which cryptosystem is being used. The

security of the system is then reliant on key management.

There are various classes of attacks aga ins t a cryptosystem:

Brute-force attack: The cryptanalyst simply tr ies every p ossible key ...