33.6 Common Crypto Mistakes and Attacks
| 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 |
| Weak random numbers | Predictable tokens and keys | Use a cryptographic random generator (random_bytes() in PHP) |
| Treating encoding as encryption | Anyone can decode | Encrypt properly |
Common attack names you should recognise: brute force (try every key), dictionary/rainbow table (pre-computed hashes), man-in-the-middle (intercept and relay), downgrade (force weaker protocol), side-channel (leak through timing or power), and "harvest now, decrypt later" – the reason organisations are planning moves to post-quantum cryptography, which NIST began standardising in 2024.
Ravindra Bagale's Tip
Crypto madhe sarvat jast breaches algorithm tutlya mule nahi, tar key management chya chukamule hotat – key code madhe, key email madhe, key kadhich rotate nahi. Algorithm AES asla tari key sambhalli nahi tar sagla vyartha.
Practice task
Review the PHP code of your reels app (Chapter 16) and find: how passwords are stored, where the DB password lives, how session tokens are generated and which TLS versions your server allows. Write one fix for each weakness you find, using the table above.
Crypto quick reference
| Need | Use |
|---|---|
| Check a file did not change | SHA-256 (sha256sum) |
| Store user passwords | bcrypt / Argon2 (password_hash()) |
| Encrypt data at rest | AES-256-GCM, keys in KMS |
| Share a secret with someone new | Their public key (RSA/ECC) or ECDHE key exchange |
| Prove who sent it | Digital signature with a private key |
| Secure a website | TLS 1.2/1.3 with a CA-signed certificate |