Understanding Cryptography: Symmetric, Asymmetric, and Hash Functions

Cryptography, the practice of secure communication, encompasses several distinct approaches. Symmetric algorithms rely on a single, shared secret key between parties for both encryption and decryption. Asymmetric (public key) algorithms use a pair of keys – one public for encryption, and one private for decryption. Hash functions produce unique "fingerprints" of data, ensuring integrity and enabling applications like password storage. Understanding these distinct algorithms is crucial for choosing the appropriate method to protect sensitive information in various digital contexts.

Key points emphasized:

• Distinct types of cryptographic algorithms exist.
• Symmetric: Shared secret key
• Asymmetric: Public/private key pairs
• Hash functions: Data integrity "fingerprints"

Cryptology is broken into two sections: Cryptography and Cryptanalysis. Cryptography, as described by Paar & Pelzl (2010), is the science of secret writing with the objective of hiding the meaning of the message. Cryptanalysis is the science of breaking cryptosystems. Researchers in academia typically do cryptanalysis. Cryptanalysis is vital to today's cryptosystems.  Without researchers breaking crypto methods, one will never know if they are secure. Cryptography can be split into three main branches. They are Symmetric Algorithms, Asymmetric Algorithms, and Cryptographic Protocols.

Symmetric algorithms are what people commonly think about when someone says cryptography. Symmetric algorithms allow two parties to have encryption and decryption methods, and they share the same secret key. Cryptography from early or ancient times until 1976 is exclusively based on symmetric methods. Symmetric ciphers are still used mainly for integrity checking and data encryption of messages.  There are other names for symmetric cryptography; some of them are a symmetric key, secret key, and single key schemes or algorithms.  Symmetric algorithms are best introduced with an easy-to-understand problem as described by Paar & Pelzl (2010). The example uses two users', Alice and Bob. They are interested in communicating over an insecure network.  The insecure network can be the Internet, mobile phones, or wireless networks.  The problem begins with the villain, Oscar, who has access to the network.  The unauthorized listening by Oscar is called eavesdropping. Alice encrypts the message using the symmetric algorithm or secret keys shared between them in this situation. Bob receives the ciphertext and decrypts the message using the same secret key as Alice. Encrypting the message with the key keeps Oscar from knowing what Alice and Bob communicate over the network.

Asymmetric algorithms, also called public keys, were introduced in 1976 by the creators Whitfield Diffie, Martin Hellman, and Ralph Merkle. Public-key cryptography works like a symmetric algorithm, but a user possesses a secret and a public key. The user keeps the secret or private key, and the public key is shared with others. With asymmetric algorithms or public key encryption, any person who has the user's public key can encrypt the message for the receiver; once received, the person who received the message then decrypts the message using their private key.

Hash functions are an essential cryptographic primitive widely used in protocols, as Paar & Pelzl (2010) point out. The hash function computes a digest of data to be sent, which is a short, fixed-length bit string. When a message is sent, the message digest, or hash value, is seen as the fingerprint of a message, which is a unique representation of a message.  Unlike all other crypto algorithms presented so far, hash functions do not have a public or private key. The hash function is a vital part of digital signature schemes and message authentication codes. Hash functions are also widely used in other cryptographic fields. Examples of where hash functions would be used are for storing of password hashes or key derivation.

Cryptology continues to be used generally in societies around the world, as Peltier (2013) points out. Activities such as streaming Netflix shows, banking, online shopping, and Skype communication are becoming digital. Everyday life and organization determine how nations are run. All depend on secure communication and transaction channels, as Peltier (2013) discusses.  Cryptology is universally used and continues to develop and evolve to adjust to technological improvements. Cryptology is no longer restricted to the defense and government it is now practically used by everyone.

References

Paar, C., & Pelzl, J. (2010). Understanding cryptography: A textbook for students and practitioners. Berlin, Heidelberg: Springer Berlin Heidelberg. https://link.springer.com/book/10.1007/978-3-642-04101-3

Peltier, T. R. (2013). Information Security Fundamentals, Second Edition, 2nd Edition https://www.routledge.com/Information-Security-Fundamentals/Peltier/p/book/9781439810620