Data Protection and Security

I

Introduction To Cryptography

I.II

Types of Cryptanalysis

As we have mentioned earlier, cryptanalysis is the branch of cryptology concerned with breaking the cryptographic systems used by others.

The earliest known cryptanalysis handbook is “Treatise on Cryptanalysis” by Al-Kindi, lived between 801 AD and 873 AD. The main topics of A l-Kindi's book are methods of cryptanalysis, cryptanalysis of ciphers and frequency analysis of Arabic.

Historically, frequency analysis was the main technique used to break simple ciphers. It uses statistics to measure the frequency of single letters and their combinations in natural languages. In modern cryptanalysis, since ciphers became more complex, frequency analysis loses its predominance over other mathematical techniques.

Cryptanalysis can be divided into subgroups depending on the amount of information the cryptanalyst can have access to. Types of cryptanalysis are as follows:

• Ciphertext-only attack: The cryptanalyst obtains examples of ciphertext and knows some statistical properties of typical plaintext.
• Known-plaintext attack: The cryptanalyst obtains examples of ciphertext/plaintext pairs.
• Chosen-plaintext attack: The cryptanalyst can generate a number of plaintexts and will obtain the corresponding ciphertexts.
• Adaptive chosen-plaintext attack: The cryptanalyst can perform several chosen-plaintext attacks and use knowledge gained from previous ones in the preparation of new plaintext.

Note that, the goal is not necessarily to be able to find the whole key or successfully decrypting the whole ciphertext. It is rather to obtain any information that helps in this respect.