pycrypt-lib 0.9.0

A pure Python implementation of cryptographic primitives, written in a clean, Pythonic, and type-safe way.

🔐 pycrypt

A pure Python implementation of cryptographic primitives, written in a clean, Pythonic, and type-safe way.

⚠️ Disclaimer: pycrypt is an educational cryptography library. It is not safe for production use. Use only for learning how cryptographic algorithms work under the hood.

Do not roll your own crypto in production code. Use a safe, audited library that has been vetted by professionals.

📜 Overview

pycrypt implements major cryptographic primitives from scratch in pure and simple Python, using minimal external libraries.

Analysing the code may help in:

• Learning how encryption, hashing, and key exchange algorithms work.
• Exploring low level arithmetic operations.
• Teaching cryptography fundamentals to students familiar with intermediate-level Python.

📦 Features

Category	Algorithm	Description
Asymmetric	RSA	OAEP encryption/decryption, PSS signing/verification
	Diffie–Hellman (DH)	Modular exponentiation and HKDF-based key derivation
Symmetric	AES	ECB, CBC, CTR, and GCM modes
Hashing	SHA-1, SHA-256	HMAC and HKDF included

🗂️ Project Structure

pycrypt/
├── asymmetric/
│   ├── dh/
│   │   ├── core.py
│   │   └── groups.py
│   └── rsa/
│       ├── asn1.py
│       ├── core.py
│       └── utils.py
├── hash/
│   ├── sha/
│   │   ├── core.py
│   │   ├── hmac.py
│   │   └── variants.py
├── symmetric/
│   └── aes/
│       ├── core.py
│       ├── modes.py
│       └── utils.py
├── utils/
│   ├── padding.py
│   └── utils.py
└── main.py

🚀 Installation

pip install pycrypt-lib

🧩 Examples

🔸 Diffie–Hellman (DH) Key Exchange

from pycrypt.asymmetric import DH

params = DH.generate_parameters(2048)

alice_priv = params.generate_private_key()
bob_priv = params.generate_private_key()

alice_shared = alice_priv.exchange(bob_priv.public_key())
bob_shared = bob_priv.exchange(alice_priv.public_key())

assert alice_shared == bob_shared
print(f"Shared secret: {alice_shared.hex()}")

🔸 RSA Encryption and Signing

from pycrypt.asymmetric import RSAKey

key = RSAKey.generate(2048)
message = b"Hello RSA!"

cipher = key.oaep_encrypt(message)
plain = key.oaep_decrypt(cipher)

signature = key.pss_sign(message)
assert key.pss_verify(message, signature)

🔸 AES (GCM Mode)

from secrets import token_bytes
from pycrypt.symmetric import AES_GCM

key = token_bytes(16)
nonce = token_bytes(12)

aes = AES_GCM(key)
ciphertext, tag = aes.encrypt(b"Top Secret", nonce=nonce)
plaintext = aes.decrypt(ciphertext, nonce=nonce, tag=tag)

print(plaintext.decode())

🔸 SHA-256 Hash

from pycrypt.hash import SHA256

sha = SHA256()
sha.update(b"hello world")
print(sha.hexdigest())

🧠 Design Philosophy

• Pure Python - minimal external dependencies
• Readable and modular - each algorithm is split into core and implementation parts
• Type-safe - uses typing and ruff for static checks
• Educational focus - clarity > performance
• Standards-aligned - based on official cryptographic specs

Understanding how cryptography works is the first step toward using it safely.

🪪 License

MIT License

Copyright (c) 2025 Aravindaksha Balaji, Arnav Guntur

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

⚠️ Note: This library is not secure for production use. It is a learning and exploration tool only.

🌟 Cryptography Reference Standards

• FIPS PUB 197 – AES Standard
• FIPS PUB 180-4 – Secure Hash Standard (SHS)
• RFC 8017 – RSA Cryptography Standard (PKCS #1 v2.2)
• RFC 2631 - Diffie-Hellman Key Agreement Method