Initial commit

BcAesCrypto.cs

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+using System;
+using System.Security.Cryptography;
+using System.Text;
+using Org.BouncyCastle.Crypto;
+using Org.BouncyCastle.Crypto.Digests;
+using Org.BouncyCastle.Crypto.Engines;
+using Org.BouncyCastle.Crypto.Generators;
+using Org.BouncyCastle.Crypto.Modes;
+using Org.BouncyCastle.Crypto.Parameters;
+
+public static class BcAesCrypto
+{
+    private const int KeySize = 32;        // 256-bit AES
+    private const int SaltSize = 16;       // 128-bit salt
+    private const int NonceSize = 12;      // GCM standard
+    private const int TagSize = 128;       // authentication tag (bits)
+    private const int Iterations = 150_000; // PBKDF2 cost factor
+
+    // -----------------------------
+    // PBKDF2 Key Derivation
+    // -----------------------------
+    private static byte[] DeriveKey(string password, byte[] salt)
+    {
+        var generator = new Pkcs5S2ParametersGenerator(new Sha256Digest());
+
+        generator.Init(
+            PbeParametersGenerator.Pkcs5PasswordToBytes(password.ToCharArray()),
+            salt,
+            Iterations
+        );
+
+        var keyParam = (KeyParameter)generator.GenerateDerivedMacParameters(KeySize * 8);
+        return keyParam.GetKey();
+    }
+
+    // -----------------------------
+    // Encrypt
+    // -----------------------------
+    public static string Encrypt(string plainText, string password)
+    {
+        byte[] salt = new byte[SaltSize];
+        RandomNumberGenerator.Fill(salt);
+
+        byte[] key = DeriveKey(password, salt);
+
+        byte[] nonce = new byte[NonceSize];
+        RandomNumberGenerator.Fill(nonce);
+
+        var cipher = new GcmBlockCipher(new AesEngine());
+
+        cipher.Init(true, new AeadParameters(
+            new KeyParameter(key),
+            TagSize,
+            nonce
+        ));
+
+        byte[] input = Encoding.UTF8.GetBytes(plainText);
+        byte[] output = new byte[cipher.GetOutputSize(input.Length)];
+
+        int len = cipher.ProcessBytes(input, 0, input.Length, output, 0);
+        cipher.DoFinal(output, len);
+
+        // Combine: salt + nonce + ciphertext
+        byte[] result = new byte[salt.Length + nonce.Length + output.Length];
+
+        Buffer.BlockCopy(salt, 0, result, 0, salt.Length);
+        Buffer.BlockCopy(nonce, 0, result, salt.Length, nonce.Length);
+        Buffer.BlockCopy(output, 0, result, salt.Length + nonce.Length, output.Length);
+
+        return Convert.ToBase64String(result);
+    }
+
+    // -----------------------------
+    // Decrypt
+    // -----------------------------
+    public static string Decrypt(string cipherText, string password)
+    {
+        byte[] data = Convert.FromBase64String(cipherText);
+
+        byte[] salt = new byte[SaltSize];
+        byte[] nonce = new byte[NonceSize];
+
+        Buffer.BlockCopy(data, 0, salt, 0, SaltSize);
+        Buffer.BlockCopy(data, SaltSize, nonce, 0, NonceSize);
+
+        int cipherLength = data.Length - SaltSize - NonceSize;
+        byte[] cipherBytes = new byte[cipherLength];
+
+        Buffer.BlockCopy(data, SaltSize + NonceSize, cipherBytes, 0, cipherLength);
+
+        byte[] key = DeriveKey(password, salt);
+
+        var cipher = new GcmBlockCipher(new AesEngine());
+
+        cipher.Init(false, new AeadParameters(
+            new KeyParameter(key),
+            TagSize,
+            nonce
+        ));
+
+        byte[] plain = new byte[cipher.GetOutputSize(cipherBytes.Length)];
+
+        int len = cipher.ProcessBytes(cipherBytes, 0, cipherBytes.Length, plain, 0);
+        cipher.DoFinal(plain, len);
+
+        return Encoding.UTF8.GetString(plain);
+    }
+}