Encryption vs. Checksums: Which is Best?

TL;DR

For protecting data confidentiality (keeping it secret), use authenticated encryption. For verifying data integrity (making sure it hasn’t been changed) without secrecy, a checksum or hash is enough. Don’t try to build security yourself – use well-vetted libraries and protocols.

1. Understanding the Basics

Let’s break down what each approach does:

• Encryption: Transforms data into an unreadable format (ciphertext). Requires a key to decrypt it back to its original form (plaintext).
• Checksum/Hash: Creates a fixed-size “fingerprint” of the data. Any change to the data, no matter how small, will result in a different fingerprint.

2. Authenticated Encryption – The Gold Standard for Confidentiality

Authenticated encryption (AE) does two things at once:

• Confidentiality: Encrypts the data so only someone with the key can read it.
• Integrity & Authentication: Verifies that the data hasn’t been tampered with and confirms its source (if combined with appropriate key management).

Popular AE algorithms include:

• AES-GCM (Advanced Encryption Standard – Galois/Counter Mode)
• ChaCha20-Poly1305

Example using OpenSSL (command line):

openssl enc -aes-256-gcm -salt -in plaintext.txt -out ciphertext.enc -k password

3. Checksums/Hashes – For Integrity Only

Checksums and hashes are one-way functions. You can easily calculate the hash of a file, but you can’t get the original file back from the hash.

• Common Algorithms: MD5 (older, avoid for security), SHA-256, SHA-384, SHA-512
• Use Cases: File downloads (verify the downloaded file is complete and correct), data storage (detect accidental corruption).

Example using OpenSSL (command line):

openssl dgst -sha256 plaintext.txt

4. Why Not Just Encrypt & Add a Checksum?

This is where things get tricky. Adding a checksum to encrypted data doesn’t provide the same level of security as authenticated encryption for several reasons:

• Vulnerability to Padding Oracles: Attackers can sometimes manipulate the ciphertext and use the checksum verification process to learn information about the plaintext.
• Complexity: You need to carefully manage how the checksum is calculated and verified alongside the decryption process, which is prone to errors.
• No Authentication: A simple checksum doesn’t tell you who sent the data – just that it hasn’t been changed.

5. Contained & Encrypted Checksum/Hash – Still Not Enough

Encrypting a checksum or hash alongside the encrypted data is slightly better than adding an unencrypted one, but still doesn’t offer the same security as authenticated encryption.

• Still Vulnerable: While it prevents someone from trivially modifying the checksum, it doesn’t address the padding oracle vulnerabilities inherent in combining separate encryption and verification steps.
• Increased Complexity: You now have to manage two keys (one for encryption, one for the checksum).

6. Practical Recommendations

1. Prioritize Authenticated Encryption: If you need confidentiality, always use an authenticated encryption algorithm like AES-GCM or ChaCha20-Poly1305.
2. Use Established Libraries: Don’t try to implement encryption yourself! Use well-vetted cryptographic libraries in your programming language (e.g., OpenSSL, libsodium).
3. Checksums for Integrity Only: If you only need to verify data integrity and don’t care about secrecy, use a strong hash function like SHA-256 or SHA-384.
4. Key Management is Crucial: Securely store and manage your encryption keys. This is often the weakest link in any security system.

7. cyber security Summary

In short, authenticated encryption provides a robust solution for both confidentiality and integrity. Checksums/hashes are useful for verifying data hasn’t been altered but don’t offer secrecy. Avoid combining separate encryption and checksum steps unless you have very specific reasons and understand the risks involved.