fix: migrate PIN hashing from SHA-256 to Argon2id (#54)

Replace SHA-256 with Argon2id (m=64MiB, t=3, p=1) for PIN hashing.
Existing SHA-256 hashes are verified transparently via format detection
(argon2id: prefix). New PINs are always hashed with Argon2id.

Addresses CWE-916: Use of Password Hash With Insufficient Computational Effort.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CHANGELOG.fr.md

@@ -2,6 +2,9 @@
 
 ## [Non publié]
 
+### Modifié
+- Hachage du PIN migré de SHA-256 vers Argon2id pour résistance au brute-force (CWE-916). Les PINs SHA-256 existants sont vérifiés de façon transparente ; les nouveaux PINs utilisent Argon2id (#54)
+
 ## [0.6.7] - 2026-03-29
 
 ### Modifié

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## [Unreleased]
 
+### Changed
+- PIN hashing migrated from SHA-256 to Argon2id for brute-force resistance (CWE-916). Existing SHA-256 PINs are verified transparently; new PINs use Argon2id (#54)
+
 ## [0.6.7] - 2026-03-29
 
 ### Changed

docs/architecture.md

@@ -171,8 +171,8 @@ Chaque hook encapsule la logique d'état via `useReducer` :
 - `save_profiles` — Sauvegarde de la configuration
 - `delete_profile_db` — Suppression du fichier de base de données
 - `get_new_profile_init_sql` — Récupération du schéma consolidé
-- `hash_pin` — Hachage Argon2 du PIN
-- `verify_pin` — Vérification du PIN
+- `hash_pin` — Hachage Argon2id du PIN (format `argon2id:salt:hash`)
+- `verify_pin` — Vérification du PIN (supporte Argon2id et legacy SHA-256 pour rétrocompatibilité)
 - `repair_migrations` — Réparation des checksums de migration (rusqlite)
 
 ## Pages et routing

src-tauri/src/commands/profile_commands.rs

@@ -1,3 +1,4 @@
+use argon2::{Algorithm, Argon2, Params, Version};
 use rand::RngCore;
 use serde::{Deserialize, Serialize};
 use sha2::{Digest, Sha256, Sha384};
@@ -118,24 +119,55 @@ pub fn get_new_profile_init_sql() -> Result<Vec<String>, String> {
     ])
 }
 
+// Argon2id parameters for PIN hashing (same as export_import_commands.rs)
+const ARGON2_M_COST: u32 = 65536; // 64 MiB
+const ARGON2_T_COST: u32 = 3;
+const ARGON2_P_COST: u32 = 1;
+const ARGON2_OUTPUT_LEN: usize = 32;
+const ARGON2_SALT_LEN: usize = 16;
+
+fn argon2_hash(pin: &str, salt: &[u8]) -> Result<Vec<u8>, String> {
+    let params = Params::new(ARGON2_M_COST, ARGON2_T_COST, ARGON2_P_COST, Some(ARGON2_OUTPUT_LEN))
+        .map_err(|e| format!("Argon2 params error: {}", e))?;
+    let argon2 = Argon2::new(Algorithm::Argon2id, Version::V0x13, params);
+    let mut hash = vec![0u8; ARGON2_OUTPUT_LEN];
+    argon2
+        .hash_password_into(pin.as_bytes(), salt, &mut hash)
+        .map_err(|e| format!("Argon2 hash error: {}", e))?;
+    Ok(hash)
+}
+
 #[tauri::command]
 pub fn hash_pin(pin: String) -> Result<String, String> {
-    let mut salt = [0u8; 16];
+    let mut salt = [0u8; ARGON2_SALT_LEN];
     rand::rngs::OsRng.fill_bytes(&mut salt);
     let salt_hex = hex_encode(&salt);
 
-    let mut hasher = Sha256::new();
-    hasher.update(salt_hex.as_bytes());
-    hasher.update(pin.as_bytes());
-    let result = hasher.finalize();
-    let hash_hex = hex_encode(&result);
+    let hash = argon2_hash(&pin, &salt)?;
+    let hash_hex = hex_encode(&hash);
 
-    // Store as "salt:hash"
-    Ok(format!("{}:{}", salt_hex, hash_hex))
+    // Store as "argon2id:salt:hash" to distinguish from legacy SHA-256 "salt:hash"
+    Ok(format!("argon2id:{}:{}", salt_hex, hash_hex))
 }
 
 #[tauri::command]
 pub fn verify_pin(pin: String, stored_hash: String) -> Result<bool, String> {
+    // Argon2id format: "argon2id:salt_hex:hash_hex"
+    if let Some(rest) = stored_hash.strip_prefix("argon2id:") {
+        let parts: Vec<&str> = rest.split(':').collect();
+        if parts.len() != 2 {
+            return Err("Invalid Argon2id hash format".to_string());
+        }
+        let salt = hex_decode(parts[0])?;
+        let expected_hash = parts[1];
+
+        let computed = argon2_hash(&pin, &salt)?;
+        let computed_hex = hex_encode(&computed);
+
+        return Ok(computed_hex == expected_hash);
+    }
+
+    // Legacy SHA-256 format: "salt_hex:hash_hex"
     let parts: Vec<&str> = stored_hash.split(':').collect();
     if parts.len() != 2 {
         return Err("Invalid stored hash format".to_string());
@@ -156,6 +188,19 @@ fn hex_encode(bytes: &[u8]) -> String {
     bytes.iter().map(|b| format!("{:02x}", b)).collect()
 }
 
+fn hex_decode(hex: &str) -> Result<Vec<u8>, String> {
+    if hex.len() % 2 != 0 {
+        return Err("Invalid hex string length".to_string());
+    }
+    (0..hex.len())
+        .step_by(2)
+        .map(|i| {
+            u8::from_str_radix(&hex[i..i + 2], 16)
+                .map_err(|e| format!("Invalid hex character: {}", e))
+        })
+        .collect()
+}
+
 /// Repair migration checksums for a profile database.
 /// Updates stored checksums to match current migration SQL, avoiding re-application
 /// of destructive migrations (e.g., migration 2 which DELETEs categories/keywords).