Common Encryption Algorithms and Their Practical Characteristics

The author provides a concise reference of common cryptographic algorithms, indicating each algorithm's positioning, main characteristics, and whether it is still in active use.

Symmetric Encryption

Block ciphers :

DES – 56‑bit key, trivially broken by brute force, fully deprecated.

3DES – triple‑DES, slower and only marginally more secure; being phased out and prohibited by many compliance standards, though still found in legacy systems.

AES – supports 128/192/256‑bit keys (commonly referred to as AES‑256); fast, hardware‑accelerated, the de‑facto standard for disk encryption, HTTPS, and database encryption.

IDEA – once used in PGP email encryption; now essentially obsolete.

SM4 – Chinese national standard, 128‑bit key and 128‑bit block, positioned as a domestic counterpart to AES; mandatory in many Chinese financial, governmental, and compliance projects.

Stream ciphers :

RC4 – formerly popular for early HTTPS and WEP; severe vulnerabilities discovered, now deprecated.

ChaCha20 – modern stream cipher with excellent performance, especially on devices lacking AES hardware; typically combined with Poly1305 (ChaCha20‑Poly1305) and widely adopted in TLS 1.3.

Asymmetric Encryption

RSA – classic algorithm based on the difficulty of factoring large integers; used for encryption, digital signatures, and key exchange. Recommended key length ≥2048 bits (4096 bits for high‑security). Drawbacks: large keys and slow computation.

ECC (Elliptic Curve Cryptography) – provides RSA‑level security with much shorter keys (e.g., 256‑bit ECC ≈ 3072‑bit RSA), resulting in faster operations and lower resource consumption; popular in mobile, IoT, and blockchain applications.

ECDH – elliptic‑curve version of Diffie‑Hellman; same principle but more efficient, now heavily used in TLS handshakes.

DSA / ECDSA – dedicated digital‑signature algorithms; DSA is older, while ECDSA (the elliptic‑curve variant) is employed in Bitcoin transaction signing.

SM2 – Chinese national asymmetric algorithm based on ECC; supports encryption, signatures, and key exchange, and is often paired with SM4 in domestic compliance projects.

Hash / Digest Algorithms

MD5 – 128‑bit digest, cryptographically broken; should no longer be used for security, only occasional file‑integrity checks.

SHA‑1 – also broken and being phased out.

SHA‑2 family (SHA‑256, SHA‑512, etc.) – current mainstream, considered secure; used in HTTPS certificates, blockchain, and password storage.

SHA‑3 – new generation standard with a construction completely different from SHA‑2; currently a reserve to replace SHA‑2 if needed.

SM3 – Chinese national hash algorithm, 256‑bit digest, aligned with SHA‑256; required in domestic compliance scenarios.

Password‑Hashing Functions

bcrypt, scrypt, Argon2 – purpose‑built, deliberately slow, salted hash functions for storing user passwords; essential knowledge for system architects. Fast hashes such as MD5 or SHA should never be used for password storage.