Cryptography Abstraction: Developer’s Guide

TL;DR

Developers should generally avoid implementing cryptographic primitives directly. Use well-vetted libraries and APIs, focusing on how to use them securely rather than how they work internally. Understand the high-level concepts of cryptography relevant to your application (e.g., symmetric vs asymmetric encryption, hashing, digital signatures) but leave the complex math and implementation details to experts.

1. Why Not Implement Cryptography Yourself?

Cryptography is notoriously difficult to get right. Subtle errors can lead to devastating security vulnerabilities. Here’s why you shouldn’t roll your own:

• Complexity: Modern cryptographic algorithms are mathematically complex and require deep understanding of number theory, probability, and computer science.
• Side-Channel Attacks: Even a correct implementation can be vulnerable to side-channel attacks (timing attacks, power analysis, etc.) that exploit hardware characteristics.
• Constant Evolution: Cryptographic standards change as new vulnerabilities are discovered. Maintaining your own implementation is a continuous effort.
• Peer Review: Well-established libraries have been extensively reviewed by the cyber security community, increasing confidence in their correctness and robustness.

2. Levels of Abstraction

Think of cryptography abstraction as layers:

1. Lowest Level (Avoid): Implementing cryptographic primitives directly (e.g., AES, SHA-256). This is almost always a bad idea.
2. Mid-Level (Use with Caution): Using lower-level crypto libraries that provide building blocks but require you to manage key derivation, padding schemes, and other details. Requires significant expertise.
3. Highest Level (Recommended): Using high-level APIs and frameworks that abstract away the complexities of cryptography. This is the preferred approach for most developers.

3. Practical Steps: Choosing a Library

Select a well-respected library appropriate for your programming language and platform.

• Python: cryptography, PyNaCl
• Java: Bouncy Castle, Java Cryptography Extension (JCE)
• JavaScript: Web Crypto API (built-in to browsers), node-forge
• C/C++: OpenSSL (use with caution – complex!), libsodium

Important Considerations:

• Active Maintenance: Choose libraries that are actively maintained and receive regular security updates.
• Community Support: A large community means more resources, documentation, and help available if you encounter problems.
• Security Audits: Look for libraries that have undergone independent security audits.

4. Common Cryptographic Tasks & Abstraction Examples

1. Symmetric Encryption (e.g., AES): Use a library function to encrypt and decrypt data with a key.

   # Python example using cryptography
   from cryptography.fernet import Fernet
   key = Fernet.generate_key()
   f = Fernet(key)
   token = f.encrypt(b'my secret message')
   decrypted = f.decrypt(token).decode() # Decode bytes to string
   print(decrypted)

2. Hashing (e.g., SHA-256): Use a library function to generate a hash of data.

   # Python example using cryptography
   from cryptography.hashers import SHA256
   hash_object = SHA256(b'my password')
   digest = hash_object.hexdigest()
   print(digest)

3. Digital Signatures (e.g., RSA): Use a library function to sign and verify data.

   This often involves key generation, signing with a private key, and verification with a public key.

5. Focus on Secure Usage

Using the right library is only half the battle. You must use it correctly:

• Key Management: Protect your cryptographic keys! Store them securely (e.g., using a hardware security module or key management service).
• Random Number Generation: Use cryptographically secure random number generators for generating keys, initialization vectors (IVs), and nonces.
• Padding Schemes: Understand the implications of different padding schemes (e.g., PKCS#7) and use them correctly to avoid vulnerabilities like padding oracle attacks.
• Authentication: Ensure you are authenticating the source of cryptographic keys and data.

6. When to Consult an Expert

If your application requires:

• Custom cryptographic protocols
• High-assurance security (e.g., financial transactions, government applications)
• Integration with complex cyber security systems

Consult a cryptography expert to ensure the security of your implementation.