Switched the key derivation to the PBKDF2 API of .NET 10 and pinned its results with tests

app/MindWork AI Studio/Tools/Encryption.cs

@@ -39,12 +39,11 @@ public sealed class Encryption(ILogger<Encryption> logger, byte[] secretPassword
         // Derive key and iv vector: the operations take several seconds. Thus, using a task:
         await Task.Run(() =>
         {
-            using var keyVectorObj = new Rfc2898DeriveBytes(secretPassword, secretKeySalt, ITERATIONS, HashAlgorithmName.SHA512);
-            var keyBytes = keyVectorObj.GetBytes(32); // the max valid key length = 256 bit = 32 bytes
-            var ivBytes = keyVectorObj.GetBytes(16); // the only valid block size = 128 bit = 16 bytes
-            
-            Array.Copy(keyBytes, this.key, this.key.Length);
-            Array.Copy(ivBytes, this.iv, this.iv.Length);
+            // The max valid key length = 256 bit = 32 bytes, and the only valid block size = 128 bit = 16 bytes:
+            var keyVectorBytes = Rfc2898DeriveBytes.Pbkdf2(secretPassword, secretKeySalt, ITERATIONS, HashAlgorithmName.SHA512, this.key.Length + this.iv.Length);
+
+            Array.Copy(keyVectorBytes, 0, this.key, 0, this.key.Length);
+            Array.Copy(keyVectorBytes, this.key.Length, this.iv, 0, this.iv.Length);
         });
 
         var initDuration = stopwatch.Elapsed;

app/MindWork AI Studio/Tools/EnterpriseEncryption.cs

@@ -292,11 +292,11 @@ public sealed class EnterpriseEncryption
     /// </summary>
     private Aes CreateAesV1(byte[] salt)
     {
-        // Derive key and IV using PBKDF2:
-        using var keyDerivation = new Rfc2898DeriveBytes(this.secretKey!, salt, V1_ITERATIONS, HashAlgorithmName.SHA512);
+        // Derive key and IV using PBKDF2, the first 32 bytes for AES-256 and the last 16 for its block size:
+        var keyAndIv = Rfc2898DeriveBytes.Pbkdf2(this.secretKey!, salt, V1_ITERATIONS, HashAlgorithmName.SHA512, 48);
         var aes = Aes.Create();
-        aes.Key = keyDerivation.GetBytes(32); // AES-256
-        aes.IV = keyDerivation.GetBytes(16);  // AES block size
+        aes.Key = keyAndIv[..32];
+        aes.IV = keyAndIv[32..];
         aes.Mode = CipherMode.CBC;
         aes.Padding = PaddingMode.PKCS7;
         return aes;

app/Tests/Tools/EncryptionTests.cs

@@ -0,0 +1,54 @@
+using AIStudio.Tools;
+
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace AIStudio.Tests.Tools;
+
+/// <summary>
+/// Checks the encryption which the app shares with the runtime, for the secrets which travel
+/// between both.
+/// </summary>
+/// <remarks>
+/// The runtime encrypts and decrypts the same values in Rust, with a password and a salt which it
+/// makes anew at every start. Both sides therefore have to derive exactly the same key and IV. The
+/// values here were built without AI Studio, the way the runtime builds them: PBKDF2 with SHA-512 and
+/// 100 iterations derives 48 bytes from the password and the salt, the first 32 being the AES-256 key
+/// and the last 16 the IV. openssl encrypted the text with AES-256-CBC, and the salt precedes the
+/// ciphertext.
+/// </remarks>
+[TestFixture]
+public sealed class EncryptionTests
+{
+    private static readonly byte[] SECRET_PASSWORD = Enumerable.Range(0, 512).Select(index => (byte)index).ToArray();
+
+    private static readonly byte[] SECRET_KEY_SALT = Enumerable.Range(0xA0, 16).Select(index => (byte)index).ToArray();
+
+    private static async Task<Encryption> CreateEncryptionAsync()
+    {
+        var encryption = new Encryption(NullLogger<Encryption>.Instance, SECRET_PASSWORD, SECRET_KEY_SALT);
+        await encryption.Initialize();
+        return encryption;
+    }
+
+    [TestCase("oKGio6SlpqeoqaqrrK2ur3lNRzNAfoSYKyC70CpjwS8=", "", TestName = "An empty text")]
+    [TestCase("oKGio6SlpqeoqaqrrK2urwUfAfn5LbbIjbOC9nSvtUU=", "sk-imported-key", TestName = "A text within one block")]
+    [TestCase("oKGio6SlpqeoqaqrrK2urwbjgbJCNk6Zw1Z9HyIiJdZJ+E7czzLYlM/undXUIsDr", "Schlüssel für Größe 🔑", TestName = "A text beyond ASCII")]
+    public async Task TheAppEncryptsLikeTheRuntime(string expectedEncryptedValue, string text)
+    {
+        var encryption = await CreateEncryptionAsync();
+
+        var encryptedText = await encryption.Encrypt(text);
+        Assert.That(encryptedText.EncryptedData, Is.EqualTo(expectedEncryptedValue));
+    }
+
+    [TestCase("oKGio6SlpqeoqaqrrK2ur3lNRzNAfoSYKyC70CpjwS8=", "", TestName = "An empty encrypted text")]
+    [TestCase("oKGio6SlpqeoqaqrrK2urwUfAfn5LbbIjbOC9nSvtUU=", "sk-imported-key", TestName = "An encrypted text within one block")]
+    [TestCase("oKGio6SlpqeoqaqrrK2urwbjgbJCNk6Zw1Z9HyIiJdZJ+E7czzLYlM/undXUIsDr", "Schlüssel für Größe 🔑", TestName = "An encrypted text beyond ASCII")]
+    public async Task TheAppDecryptsWhatTheRuntimeEncrypted(string encryptedValue, string expectedText)
+    {
+        var encryption = await CreateEncryptionAsync();
+
+        var text = await encryption.Decrypt(new EncryptedText(encryptedValue));
+        Assert.That(text, Is.EqualTo(expectedText));
+    }
+}