Lohkosalaisuusjärjestelmien

Lohkosalaisuus, often translated as "block secrecy" or "block confidentiality," is a fundamental concept in the field of cryptography, particularly within the design of symmetric-key block ciphers. It refers to the property that the plaintext within a single block of data remains indistinguishable from any other plaintext block of the same size, given the same key, when encrypted by a secure block cipher. In essence, if you encrypt two identical blocks of plaintext with the same key, the resulting ciphertext blocks will also be identical. However, if the plaintext blocks are different, their corresponding ciphertext blocks should also be different and appear random.

This property is crucial for maintaining the security of encrypted data. Without lohkosalaisuus, an adversary might be able to infer information about the plaintext by observing patterns in the ciphertext. For example, if repeated plaintext blocks always resulted in repeated ciphertext blocks, an attacker could identify common patterns in the encrypted message, potentially revealing sensitive information. Secure block ciphers are designed to obscure such patterns, making the ciphertext appear as random noise to an unauthorized observer.

The achievement of lohkosalaisuus is typically a design goal for cryptographers when developing new block cipher algorithms. It is usually achieved through a combination of diffusion and confusion, principles introduced by Claude Shannon. Diffusion spreads the influence of a single plaintext bit over many ciphertext bits, while confusion obscures the relationship between the key and the ciphertext. Together, these mechanisms contribute to making it computationally infeasible to distinguish encrypted data from random data without the decryption key, thereby upholding the principle of lohkosalaisuus.