C# AES asymmetric encryption and decryption example

aes-example.cs

string ivAsBase64;
string encryptedTextAsBase64;
string keyAsBase64;

using (AesCryptoServiceProvider aes = new AesCryptoServiceProvider())
{
	// Store the IV (they can be stored if you don't re-use a key)
	aes.GenerateIV();
	byte[] iv = aes.IV;
	ivAsBase64 = Convert.ToBase64String(iv);
	Console.WriteLine("IV base64: {0}", ivAsBase64);

	// See how long the default key length is
	aes.GenerateKey();
	Console.WriteLine("Algorithm key length should be: {0}", aes.Key.Length);

	// Set a key
	string key = "a very long sentence for a key that should exceed the max length of a key for AES therefore we're going to need to substring it based on the GenerateKey length we're given";
	Console.WriteLine("Key length: {0}", key.Length);

	byte[] keyBytes = Encoding.UTF8.GetBytes(key.Substring(0, aes.Key.Length));
	aes.Key = keyBytes;
	Console.WriteLine("Key length is now: {0}", aes.Key.Length);

	// Base64 the key for storage
	keyAsBase64 = Convert.ToBase64String(aes.Key);
	Console.WriteLine("Key base64: {0}", keyAsBase64);

	// Encrypt the text
	byte[] textBytes = Encoding.UTF8.GetBytes("chris áááéééééé óóóó 💩");
	var cryptor = aes.CreateEncryptor();
	byte[] encryptedBytes = cryptor.TransformFinalBlock(textBytes, 0, textBytes.Length);
	encryptedTextAsBase64 = Convert.ToBase64String(encryptedBytes);
	Console.WriteLine("Encrypted (base64'd): {0}", encryptedTextAsBase64);
}

Console.WriteLine("==================================================");

using (AesCryptoServiceProvider aes = new AesCryptoServiceProvider())
{
	// Decrypt the text
	byte[] iv = Convert.FromBase64String(ivAsBase64);
	byte[] keyBytes = Convert.FromBase64String(keyAsBase64);
	byte[] fromBase64ToBytes = Convert.FromBase64String(encryptedTextAsBase64);
	var decryptor = aes.CreateDecryptor(keyBytes, iv);
	byte[] decryptedBytes = decryptor.TransformFinalBlock(fromBase64ToBytes, 0, fromBase64ToBytes.Length);

	Console.WriteLine("Decrypted: {0}", Encoding.UTF8.GetString(decryptedBytes));
}

Good code when run in the same function. But what about making 2 separate functions ? I don't understand how handle iv & key ? :(

Good code when run in the same function. But what about making 2 separate functions ? I don't understand how handle iv & key ? :(

You'll have to pass the key into the second function. Just prepend the IV bytes to the cipher text byte array (you'll need an array of the right size) and split them apart in the decrypt function.