Cryptography Series

This blog introduces the notion of message recovery attacks, defines the corresponding security game, and proves that semantic security implies message recovery security via a black-box reduction. A semantic adversary is constructed by wrapping around a message recovery adversary, showing that any success in message recovery would contradict semantic security. This sets the stage for future reductions that interrelate various cryptographic security notions. [Read More]

This blog post explores the concept of Perfect Security in cryptography, which guarantees that observing a ciphertext provides no additional information about the original message. We establish a fundamental theorem stating that Perfect Security is equivalent to the statistical independence of ciphertexts and plaintexts. However, Shannon’s Theorem proves that achieving Perfect Security requires the secret key to be at least as long as the message, making practical implementations infeasible beyond small-scale use cases like the One-Time Pad. [Read More]