Understanding Cryptography: From Basics to Symmetric & Asymmetric Ciphers

Passwords are ubiquitous in both wartime and peacetime, and with the rise of big data, information security has become essential for everyone. Understanding what cryptography can and cannot do is crucial for developing security awareness.

1. What Is a Password?

A password is a set of symbols generated according to agreed rules to hide the original message. In everyday life we use passwords (or more accurately, passphrases) to log into computers, WeChat, email, etc.

2. Encryption Schemes

Cryptography studies secure communication in insecure environments by transforming information into a secret form before transmission.

Symmetric encryption : Encryption and decryption use the same key. Symmetric ciphers are divided into block ciphers and stream ciphers.

Asymmetric encryption : Encryption and decryption use different keys; the public key can be shared openly while the private key must remain secret, and deriving the private key from the public key is computationally infeasible.

Typical symmetric algorithms include DES, Triple DES, GDES, IDEA, FEAL, RC5, etc.

3. Message Authentication

Hash (or digest) algorithms map an arbitrary‑length bit string to a fixed‑length output. Message authentication codes (MACs) use cryptographic algorithms to provide data integrity verification.

4. Stream Cipher

Also called a stream cipher, it is a type of symmetric algorithm characterized by simple implementation, fast encryption/decryption, and limited error propagation. It is widely used in wireless communication and secure channels.

Example: RC4, once popular in WAP, SSL, and TLS, is now prohibited in current TLS versions.

5. Block Cipher

Block ciphers process plaintext in fixed‑size blocks, transforming each block into ciphertext under the control of a key.

6. Symmetric Encryption Model

In symmetric systems, the same key encrypts and decrypts data, requiring both parties to securely share and protect the key, thereby ensuring confidentiality and integrity.

7. Block Cipher Modes

Block ciphers can operate in various modes (e.g., ECB, CBC, CFB, OFB, CTR) to enhance security and adapt to different application requirements.