Symmetric Cryptography

Summary

Cryptography is the science that studies secure communication in adversarial environments. Symmetric Cryptography deals with two cases:

• either sender and receiver share the same secret key, as for encryption and message authentication;
• or neither sender nor receiver use any key at all, as, e.g., in the case of cryptographic hash functions.

Specifically, Symmetric Cryptography deals with symmetric primitives (block and stream ciphers, message authentication codes and hash functions), and complex cryptosystems and cryptographic protocols employing these primitives.

Since symmetric cryptosystems are one to two orders of magnitude more efficient than asymmetric systems, most security applications use symmetric cryptography to ensure the privacy, the authenticity and the integrity of sensitive data. Even most applications of public-key cryptography are actually working in a hybrid way, separating an asymmetric protocol layer for key transmission or key agreement from secure payload transmission by symmetric techniques.