Modern cryptography and Kerckhoff’s Principle Jntuh notes NSC

Modern cryptography and Kerckhoff’s Principle

Modern cryptography

Modern cryptography is the pillar of computer and communications security. Its foundation is based on various concepts of mathematics such as number theory, computational-complexity theory, and probability theory.

Types of Cryptosystems

There are two types of cryptosystems based on which encryption-decryption is done in the system −

• Symmetric Key Encryption

• Asymmetric Key Encryption

Components of a cryptosystem :

Diff. between Classic and Modern Cryptography

Kerckhoff’s Principle for Cryptosystem

In the 19^th century, a Dutch cryptographer A. Kerckhoff stated the requirements of a best cryptosystem. He stated that a cryptographic system should be secure even if everything about the system is visible, except the key. The six design principles by Kerckhoff for good cryptosystem are –

• The system must be practically, if not mathematically, indecipherable.
• It must not be required to be secret, and it must be able to fall into the hands of the enemy without inconvenience.
• Its key must be communicable and can be retained without the help of written notes, and changeable or modifiable at the will of the correspondents.
• It must be applicable to telegraphic correspondence.
• Apparatus and documents must be portable, and its usage and function must not require the concourse of several people.
• Finally, it is necessary, given the circumstances that command its application, that the system be easy to use, requiring neither mental strain nor the knowledge of a long series of rules to observe.

What Is Kerckhoff’s Principle?

The second rule is currently known as Kerckhoff principle. It is applied in virtually all the contemporary encryption algorithms such as DES, AES, etc. These public algorithms are considered to be thoroughly secure. The security of the encrypted message depends solely on the security of the secret encryption key.

 “a cryptosystem should be secure even if everything about the system, except the key, is public knowledge.”

Keeping the algorithms secret may act as a significant barrier to cryptanalysis. However, keeping the algorithms secret is possible only when they are used in a strictly limited circle.