crypto/encryption
transformation of plaintext into ciphertext using a key, rendering data unreadable without the corresponding decryption key.
symmetric encryption
one shared key for both encryption and decryption.
| cipher | type | key size | status |
|---|---|---|---|
| AES-128/256 | block cipher (SPN) | 128/256 bit | NIST standard, hardware-accelerated (AES-NI) |
| ChaCha20-Poly1305 | stream cipher + MAC | 256 bit | IETF standard, fast in software, used in TLS 1.3 and WireGuard |
| AES-256-GCM | authenticated encryption (AEAD) | 256 bit | most deployed AEAD mode |
AEAD (Authenticated Encryption with Associated Data) provides both confidentiality and integrity in a single operation. GCM and ChaCha20-Poly1305 are the two dominant AEAD modes.
asymmetric encryption
a public key encrypts, the corresponding private key decrypts.
| scheme | assumption | key size | status |
|---|---|---|---|
| RSA-OAEP | integer factorization | 2048-4096 bit | legacy, being phased out |
| ECIES (over Curve25519, secp256k1) | elliptic curve discrete log | 256 bit | current standard for hybrid encryption |
| ML-KEM (CRYSTALS-Kyber) | Module-LWE | 800-1568 bytes | NIST PQC standard (FIPS 203), post-quantum |
| CSIDH / dCTIDH | supersingular isogeny class group | ~64 bytes | non-interactive key exchange, conjectured post-quantum |
hybrid encryption: encrypt a symmetric key with an asymmetric scheme, then encrypt the payload with the symmetric key. virtually all real-world systems use this pattern (TLS, Signal, age, GPG).
homomorphic encryption
compute on ciphertext without decrypting. the result, when decrypted, equals the result of computing on the plaintext.
| scheme | operations | performance | use case |
|---|---|---|---|
| Paillier | addition only (partially homomorphic) | fast | voting, aggregation |
| BGV / BFV | addition + multiplication (somewhat homomorphic) | moderate | machine learning on encrypted data |
| TFHE | arbitrary boolean/arithmetic circuits (fully homomorphic) | ~10^6x slower than plaintext | general-purpose encrypted computation |
TFHE (Fully Homomorphic Encryption over the Torus) enables arbitrary computation on encrypted data. the performance gap is shrinking — hardware accelerators and algorithmic improvements reduce overhead by 100-1000x compared to early FHE schemes.