cryptography-47-0-0 - SKILL.md Agent Skill

name: cryptography-47-0-0 description: Comprehensive toolkit for Python cryptographic operations using the cryptography library v47.0.0. Use when implementing encryption, decryption, hashing, digital signatures, key derivation, X.509 certificate handling, post-quantum cryptography (ML-KEM, ML-DSA), ASN.1 encoding/decoding, and other cryptographic primitives in Python applications.

cryptography 47.x

Overview

cryptography is a Python package that provides both high-level cryptographic recipes and low-level interfaces to common cryptographic algorithms including symmetric ciphers, message digests, key derivation functions, and asymmetric (public-key) cryptography. It is maintained by the Python Cryptographic Authority (PyCA).

The library is broadly divided into two layers:

Recipes layer — High-level, safe-to-use APIs that require minimal configuration. These are the recommended starting point for most use cases. Includes Fernet for symmetric encryption and x509 for certificate handling.
Hazardous Materials (hazmat) layer — Low-level cryptographic primitives in cryptography.hazmat. These are dangerous and can be used incorrectly, requiring deep knowledge of cryptographic concepts. Always prefer the recipes layer when possible.

The library is built on OpenSSL 3.0+ (or compatible backends like BoringSSL, LibreSSL 4.1+, AWS-LC) with a Rust-based build system. It requires Python 3.9+.

When to Use

Encrypting and decrypting data at rest or in transit
Generating and verifying digital signatures
Computing cryptographic hashes (SHA-2, SHA-3, BLAKE2)
Deriving cryptographic keys from passwords (PBKDF2, Argon2, HKDF, scrypt)
Creating, parsing, and verifying X.509 certificates and CSRs
Implementing two-factor authentication (HOTP/TOTP)
Performing asymmetric key operations (RSA, EC, Ed25519, X25519)
Post-quantum cryptography: ML-KEM key encapsulation, ML-DSA signing
Key wrapping (AES-KW)
HPKE (Hybrid Public Key Encryption) for post-quantum-ready encryption
Message authentication codes (HMAC, CMAC, Poly1305)
ASN.1 encoding and decoding of custom types

Core Concepts

Two-layer architecture: The library separates safe "recipes" from low-level "hazmat" primitives. Import paths starting with cryptography.hazmat signal that you are using dangerous building blocks.

Authenticated encryption: Plain encryption provides secrecy but not authenticity. Always use authenticated schemes (Fernet, AES-GCM, ChaCha20-Poly1305) to prevent tampering attacks.

Nonce uniqueness: For AEAD ciphers, never reuse a nonce with the same key — doing so compromises all messages encrypted with that key/nonce pair.

Secure random: Always use os.urandom() or the secrets module for cryptographic randomness. Never use the random module for security-sensitive values.

Key management: Keys should be randomly generated, kept secret, and rotated periodically. Use key derivation functions (KDFs) to derive keys from passwords.

Post-quantum readiness: ML-KEM (FIPS 203) and ML-DSA (FIPS 24) provide lattice-based post-quantum cryptography. Requires AWS-LC or BoringSSL backend — not available with standard OpenSSL wheels.

In-place operations: Since 47.0.0, many primitives support *_into() methods that write directly to pre-allocated buffers, reducing memory allocations in high-throughput scenarios.

Breaking Changes (46.x → 47.x)

Binary elliptic curves removed: SECT* classes are no longer available
OpenSSL 1.1.x support dropped: OpenSSL 3.0+ is now required
LibreSSL < 4.1: No longer supported
UnsupportedAlgorithm instead of ValueError: Key loading functions now raise UnsupportedAlgorithm for unsupported algorithms or explicit curve encodings
EC private key length validation: Keys with incorrectly encoded wrong-length private keys are now rejected

Deprecated (47.x, removed in future)

Python 3.8 support (removed in next release)
TripleDES with 64-bit or 128-bit keys (only 192-bit accepted in future)
CFB, OFB, CFB8 modes moved to decrepit module
Camellia cipher moved to decrepit module
macOS x86_64 wheels (switching to arm64 only)
32-bit Windows wheels

Installation / Setup

Install via pip or uv:

pip install cryptography
# or
uv add cryptography

Requires OpenSSL 3.0+ and a Rust compiler (MSRV 1.83.0). Pre-built wheels are available for most platforms. For post-quantum algorithms (ML-KEM, ML-DSA), you need AWS-LC or BoringSSL as the backend — standard OpenSSL wheels do not include these.

Usage Examples

Simple symmetric encryption with Fernet (recommended starting point):

from cryptography.fernet import Fernet

key = Fernet.generate_key()
f = Fernet(key)
token = f.encrypt(b"a secret message")
plaintext = f.decrypt(token)

One-shot hashing (new in 47.0.0):

from cryptography.hazmat.primitives import hashes

result = hashes.Hash.hash(hashes.SHA256(), b"my data")

Signing with Ed25519:

from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey

private_key = Ed25519PrivateKey.generate()
signature = private_key.sign(b"message")
private_key.public_key().verify(signature, b"message")

ML-DSA post-quantum signing (requires AWS-LC/BoringSSL):

from cryptography.hazmat.primitives.asymmetric.mldsa import MLDSA65PrivateKey

private_key = MLDSA65PrivateKey.generate()
signature = private_key.sign(b"message")
private_key.public_key().verify(signature, b"message")

ML-KEM post-quantum key encapsulation (requires AWS-LC/BoringSSL):

from cryptography.hazmat.primitives.asymmetric.mlkem import MLKEM768PrivateKey

private_key = MLKEM768PrivateKey.generate()
shared_secret, ciphertext = private_key.public_key().encapsulate()
recovered_secret = private_key.decapsulate(ciphertext)

Advanced Topics

Fernet (Symmetric Encryption): High-level recipe for authenticated symmetric encryption with key rotation → Fernet

Authenticated Encryption (AEAD): ChaCha20-Poly1305, AES-GCM, AES-CCM, and other AEAD constructions with new encrypt_into/decrypt_into methods → AEAD

Asymmetric Cryptography: RSA, EC (no binary curves), Ed25519, X25519, Diffie-Hellman, DSA, and key serialization → Asymmetric

Post-Quantum ML-KEM: Module-Lattice Key Encapsulation Mechanism (FIPS 203) with MLKEM768/1038/512 → ML-KEM

Post-Quantum ML-DSA: Module-Lattice Digital Signature Algorithm (FIPS 204) with MLDSA65/87/44 and context-based signing → ML-DSA

Hashing: SHA-2, SHA-3, BLAKE2, SHAKE (XOF), and the new Hash.hash() one-shot API → Hashing

Key Derivation Functions: Argon2id/d/i, PBKDF2-HMAC, scrypt, HKDF (with new extract() and derive_into()), and KDF interfaces → KDFs

Message Authentication Codes: HMAC, CMAC, Poly1305 for integrity verification → MACs

X.509 Certificates: Creating CSRs, self-signed certificates, CA hierarchies, certificate verification, OCSP, and extensions → X.509

Symmetric Encryption (Cipher API): Low-level Cipher class with AES, ChaCha20, SM4 and modes CBC, CTR, GCM, OFB, CCM (CFB/OFB/CFB8 moved to decrepit) → Symmetric

Two-Factor Authentication: HOTP (RFC 4226) and TOTP (RFC 6238) for one-time passwords → 2FA

HPKE: Hybrid Public Key Encryption (RFC 9180) with post-quantum KEM support → HPKE

Key Wrapping: AES key wrap (RFC 3394) and padded key wrap (RFC 5649) → KeyWrap

ASN.1: Declarative ASN.1 type definitions with encoding/decoding (new in 47.0.0, API unstable) → ASN.1

Utilities: Random number generation, constant-time comparison, exceptions, padding, and decrepit algorithms → Utilities