Comment en Vérifier Données Integrity avec Hashes

问题

You besoin en confirm ce données a non changed puisque un known-good state, utilisant un previously recorded hachage.

Prérequis

• Understanding of hash functions
• Ability to store and retrieve a hash value

Étapes

1. 1. Record the baseline hash

   Compute a hash (SHA-256 recommended) of the data in its known-good state. Store this hash in a secure, separate location. The hash serves as a compact fingerprint of the original data.

   entrée

   original file

   输出

   SHA-256: a1b2c3...

2. 2. Re-hash the current data

   At a later time, compute the hash of the data again using the same algorithm and encoding. Any change — even a single bit — will produce a completely different hash due to the avalanche effect.

   entrée

   current file

   输出

   SHA-256: d4e5f6...

3. 3. Compare and interpret

   If the hashes match, the data is unchanged. If they differ, the data has been modified. For accidental corruption (e.g., disk errors), this detects the problem. For intentional tampering, the hash must be stored somewhere the attacker cannot modify.

   entrée

   a1b2c3... == d4e5f6...?

   输出

   DIFFERENT — data changed

Résultat attendu

Un definitive yes/aucun answer sur whether le données a changed puisque le baseline hachage was recorded.

Erreurs courantes

Using a weak hash like CRC32 for security

CRC32 detects accidental corruption but is trivial to collide. Use SHA-256 for tamper detection.

Storing the hash next to the data

If an attacker can modify the data, they can also recompute and replace the hash. Store the hash in a separate, trusted location.

Dépannage指引

• If hashes differ unexpectedly, check for encoding or line-ending changes before assuming corruption.
• Use a hash comparison tool that shows both values for easy inspection.

Limites de sécurité

• Hash comparison detects changes but cannot identify what changed. For that, use a diff tool.
• All hashing is local.