This rule is flagging correct and necessary usage of a non-random IV. This is an example made from the one in the MSFT docs.
using System;
using System.IO;
using System.Security.Cryptography;
namespace RijndaelManaged_Example
{
class RijndaelExample
{
public static void Main()
{
try
{
string original = "Here is some data to encrypt!";
byte[] encrypted;
byte[] key;
byte[] iv;
// Create a new instance of the Rijndael
// class. This generates a new key and initialization
// vector (IV).
using (Rijndael encryptingRijndael = Rijndael.Create())
{
key = encryptingRijndael.Key;
iv = encryptingRijndael.IV;
encrypted = EncryptStringToBytes(original, key, iv);
}
using (Rijndael decryptingRijndael = Rijndael.Create())
{
string sharedKeyNotIv = DecryptStringFromBytes(encrypted, key, decryptingRijndael.IV);
string sharedKeyAndIv = DecryptStringFromBytes(encrypted, key, iv);
Console.WriteLine("Original: \t\t\t\t\t{0}", original);
Console.WriteLine("Round Trip (sharedKeyNotIv):\t{0}", sharedKeyNotIv);
Console.WriteLine("Round Trip (sharedKeyAndIv):\t{0}", sharedKeyAndIv);
}
}
catch (Exception e)
{
Console.WriteLine("Error: {0}", e.Message);
}
}
static byte[] EncryptStringToBytes(string plainText, byte[] Key, byte[] IV)
{
// Check arguments.
if (plainText == null || plainText.Length <= 0)
throw new ArgumentNullException("plainText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
if (IV == null || IV.Length <= 0)
throw new ArgumentNullException("IV");
byte[] encrypted;
// Create an Rijndael object
// with the specified key and IV.
using (Rijndael rijAlg = Rijndael.Create())
{
rijAlg.Key = Key;
rijAlg.IV = IV;
// Create an encryptor to perform the stream transform.
ICryptoTransform encryptor = rijAlg.CreateEncryptor(rijAlg.Key, rijAlg.IV);
// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
{
//Write all data to the stream.
swEncrypt.Write(plainText);
}
encrypted = msEncrypt.ToArray();
}
}
}
return encrypted;
}
static string DecryptStringFromBytes(byte[] cipherText, byte[] Key, byte[] IV)
{
// Check arguments.
if (cipherText == null || cipherText.Length <= 0)
throw new ArgumentNullException("cipherText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
if (IV == null || IV.Length <= 0)
throw new ArgumentNullException("IV");
// Declare the string used to hold
// the decrypted text.
string plaintext = null;
// Create an Rijndael object
// with the specified key and IV.
using (Rijndael rijAlg = Rijndael.Create())
{
rijAlg.Key = Key;
rijAlg.IV = IV;
ICryptoTransform decryptor = rijAlg.CreateDecryptor(rijAlg.Key, rijAlg.IV);
// Create the streams used for decryption.
using (MemoryStream msDecrypt = new MemoryStream(cipherText))
{
using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
{
using (StreamReader srDecrypt = new StreamReader(csDecrypt))
{
// Read the decrypted bytes from the decrypting stream
// and place them in a string.
plaintext = srDecrypt.ReadToEnd();
}
}
}
}
return plaintext;
}
}
}
output
Original: Here is some data to encrypt!
Round Trip (sharedKeyNotIv): ���_S|�
[�bn��a to encrypt!
Round Trip (sharedKeyAndIv): Here is some data to encrypt!
The IV needs to be reused in order to decrypt the whole value correctly.
