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Common Crypto Mistakes and Attacks
Common Crypto Mistakes and Attacks The usual crypto mistakes and attack names. Inventing your own crypto. Using old algorithms (MD5, DES). Hard-coding keys. Reusing a nonce. Brute force (try every key), rainbow table (pre-computed hashes), man-in-the-middle , downgrade (force a weaker protocol), and
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What it is
The usual crypto mistakes and attack names.
Mistakes
Inventing your own crypto. Using old algorithms (MD5, DES). Hard-coding keys. Reusing a nonce.
Attack names
Brute force (try every key), rainbow table (pre-computed hashes), man-in-the-middle, downgrade (force a weaker protocol), and “harvest now, decrypt later”.
| Mistake | Why it is dangerous | Fix |
|---|---|---|
| Storing passwords with MD5/SHA-1 or no salt | Cracked quickly with Hashcat and rainbow tables | bcrypt/Argon2 via password_hash() |
| Hard-coded keys in source code | Anyone with the code has the key | KMS, Secrets Manager, environment variables |
| Using ECB mode or old ciphers (DES, RC4) | Patterns leak, known breaks | AES-GCM or ChaCha20-Poly1305 |
| Rolling your own crypto | Subtle bugs you cannot see | Use well-known libraries (OpenSSL, libsodium) |
| Old TLS versions, expired certificates | Downgrade and MITM attacks | TLS 1.2/1.3 only, auto-renew certificates |
Learn more in the lesson: 33.6 Common Crypto Mistakes and Attacks