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Found an example of how to implement Rijndael on http://www.obviex.com/samples/Encryption.aspx

Is this code secure enough for production systems?

using System;
using System.IO;
using System.Text;
using System.Security.Cryptography;

This class uses a symmetric key algorithm (Rijndael/AES) to encrypt and decrypt data. As long as encryption and decryption routines use the same parameters to generate the keys, the keys are guaranteed to be the same. The class uses static functions with duplicate code to make it easier to demonstrate encryption and decryption logic. In a real-life application, this may not be the most efficient way of handling encryption, so - as soon as you feel comfortable with it - you may want to redesign this class.

public class RijndaelSimple
{
    /// <summary>
    /// Encrypts specified plaintext using Rijndael symmetric key algorithm
    /// and returns a base64-encoded result.
    /// </summary>
    /// <param name="plainText">
    /// Plaintext value to be encrypted.
    /// </param>
    /// <param name="passPhrase">
    /// Passphrase from which a pseudo-random password will be derived. The
    /// derived password will be used to generate the encryption key.
    /// Passphrase can be any string. In this example we assume that this
    /// passphrase is an ASCII string.
    /// </param>
    /// <param name="saltValue">
    /// Salt value used along with passphrase to generate password. Salt can
    /// be any string. In this example we assume that salt is an ASCII string.
    /// </param>
    /// <param name="hashAlgorithm">
    /// Hash algorithm used to generate password. Allowed values are: "MD5" and
    /// "SHA1". SHA1 hashes are a bit slower, but more secure than MD5 hashes.
    /// </param>
    /// <param name="passwordIterations">
    /// Number of iterations used to generate password. One or two iterations
    /// should be enough.
    /// </param>
    /// <param name="initVector">
    /// Initialization vector (or IV). This value is required to encrypt the
    /// first block of plaintext data. For RijndaelManaged class IV must be 
    /// exactly 16 ASCII characters long.
    /// </param>
    /// <param name="keySize">
    /// Size of encryption key in bits. Allowed values are: 128, 192, and 256. 
    /// Longer keys are more secure than shorter keys.
    /// </param>
    /// <returns>
    /// Encrypted value formatted as a base64-encoded string.
    /// </returns>
    public static string Encrypt(string   plainText,
                                 string   passPhrase,
                                 string   saltValue,
                                 string   hashAlgorithm,
                                 int      passwordIterations,
                                 string   initVector,
                                 int      keySize)
    {
        // Convert strings into byte arrays.
        // Let us assume that strings only contain ASCII codes.
        // If strings include Unicode characters, use Unicode, UTF7, or UTF8 
        // encoding.
        byte[] initVectorBytes = Encoding.ASCII.GetBytes(initVector);
        byte[] saltValueBytes  = Encoding.ASCII.GetBytes(saltValue);

        // Convert our plaintext into a byte array.
        // Let us assume that plaintext contains UTF8-encoded characters.
        byte[] plainTextBytes  = Encoding.UTF8.GetBytes(plainText);

        // First, we must create a password, from which the key will be derived.
        // This password will be generated from the specified passphrase and 
        // salt value. The password will be created using the specified hash 
        // algorithm. Password creation can be done in several iterations.
        PasswordDeriveBytes password = new PasswordDeriveBytes(
                                                        passPhrase, 
                                                        saltValueBytes, 
                                                        hashAlgorithm, 
                                                        passwordIterations);

        // Use the password to generate pseudo-random bytes for the encryption
        // key. Specify the size of the key in bytes (instead of bits).
        byte[] keyBytes = password.GetBytes(keySize / 8);

        // Create uninitialized Rijndael encryption object.
        RijndaelManaged symmetricKey = new RijndaelManaged();

        // It is reasonable to set encryption mode to Cipher Block Chaining
        // (CBC). Use default options for other symmetric key parameters.
        symmetricKey.Mode = CipherMode.CBC;        

        // Generate encryptor from the existing key bytes and initialization 
        // vector. Key size will be defined based on the number of the key 
        // bytes.
        ICryptoTransform encryptor = symmetricKey.CreateEncryptor(
                                                         keyBytes, 
                                                         initVectorBytes);

        // Define memory stream which will be used to hold encrypted data.
        MemoryStream memoryStream = new MemoryStream();        

        // Define cryptographic stream (always use Write mode for encryption).
        CryptoStream cryptoStream = new CryptoStream(memoryStream, 
                                                     encryptor,
                                                     CryptoStreamMode.Write);
        // Start encrypting.
        cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);

        // Finish encrypting.
        cryptoStream.FlushFinalBlock();

        // Convert our encrypted data from a memory stream into a byte array.
        byte[] cipherTextBytes = memoryStream.ToArray();

        // Close both streams.
        memoryStream.Close();
        cryptoStream.Close();

        // Convert encrypted data into a base64-encoded string.
        string cipherText = Convert.ToBase64String(cipherTextBytes);

        // Return encrypted string.
        return cipherText;
    }

    /// <summary>
    /// Decrypts specified ciphertext using Rijndael symmetric key algorithm.
    /// </summary>
    /// <param name="cipherText">
    /// Base64-formatted ciphertext value.
    /// </param>
    /// <param name="passPhrase">
    /// Passphrase from which a pseudo-random password will be derived. The
    /// derived password will be used to generate the encryption key.
    /// Passphrase can be any string. In this example we assume that this
    /// passphrase is an ASCII string.
    /// </param>
    /// <param name="saltValue">
    /// Salt value used along with passphrase to generate password. Salt can
    /// be any string. In this example we assume that salt is an ASCII string.
    /// </param>
    /// <param name="hashAlgorithm">
    /// Hash algorithm used to generate password. Allowed values are: "MD5" and
    /// "SHA1". SHA1 hashes are a bit slower, but more secure than MD5 hashes.
    /// </param>
    /// <param name="passwordIterations">
    /// Number of iterations used to generate password. One or two iterations
    /// should be enough.
    /// </param>
    /// <param name="initVector">
    /// Initialization vector (or IV). This value is required to encrypt the
    /// first block of plaintext data. For RijndaelManaged class IV must be
    /// exactly 16 ASCII characters long.
    /// </param>
    /// <param name="keySize">
    /// Size of encryption key in bits. Allowed values are: 128, 192, and 256.
    /// Longer keys are more secure than shorter keys.
    /// </param>
    /// <returns>
    /// Decrypted string value.
    /// </returns>
    /// <remarks>
    /// Most of the logic in this function is similar to the Encrypt
    /// logic. In order for decryption to work, all parameters of this function
    /// - except cipherText value - must match the corresponding parameters of
    /// the Encrypt function which was called to generate the
    /// ciphertext.
    /// </remarks>
    public static string Decrypt(string   cipherText,
                                 string   passPhrase,
                                 string   saltValue,
                                 string   hashAlgorithm,
                                 int      passwordIterations,
                                 string   initVector,
                                 int      keySize)
    {
        // Convert strings defining encryption key characteristics into byte
        // arrays. Let us assume that strings only contain ASCII codes.
        // If strings include Unicode characters, use Unicode, UTF7, or UTF8
        // encoding.
        byte[] initVectorBytes = Encoding.ASCII.GetBytes(initVector);
        byte[] saltValueBytes  = Encoding.ASCII.GetBytes(saltValue);

        // Convert our ciphertext into a byte array.
        byte[] cipherTextBytes = Convert.FromBase64String(cipherText);

        // First, we must create a password, from which the key will be 
        // derived. This password will be generated from the specified 
        // passphrase and salt value. The password will be created using
        // the specified hash algorithm. Password creation can be done in
        // several iterations.
        PasswordDeriveBytes password = new PasswordDeriveBytes(
                                                        passPhrase, 
                                                        saltValueBytes, 
                                                        hashAlgorithm, 
                                                        passwordIterations);

        // Use the password to generate pseudo-random bytes for the encryption
        // key. Specify the size of the key in bytes (instead of bits).
        byte[] keyBytes = password.GetBytes(keySize / 8);

        // Create uninitialized Rijndael encryption object.
        RijndaelManaged    symmetricKey = new RijndaelManaged();

        // It is reasonable to set encryption mode to Cipher Block Chaining
        // (CBC). Use default options for other symmetric key parameters.
        symmetricKey.Mode = CipherMode.CBC;

        // Generate decryptor from the existing key bytes and initialization 
        // vector. Key size will be defined based on the number of the key 
        // bytes.
        ICryptoTransform decryptor = symmetricKey.CreateDecryptor(
                                                         keyBytes, 
                                                         initVectorBytes);

        // Define memory stream which will be used to hold encrypted data.
        MemoryStream  memoryStream = new MemoryStream(cipherTextBytes);

        // Define cryptographic stream (always use Read mode for encryption).
        CryptoStream  cryptoStream = new CryptoStream(memoryStream, 
                                                      decryptor,
                                                      CryptoStreamMode.Read);

        // Since at this point we don't know what the size of decrypted data
        // will be, allocate the buffer long enough to hold ciphertext;
        // plaintext is never longer than ciphertext.
        byte[] plainTextBytes = new byte[cipherTextBytes.Length];

        // Start decrypting.
        int decryptedByteCount = cryptoStream.Read(plainTextBytes, 
                                                   0, 
                                                   plainTextBytes.Length);

        // Close both streams.
        memoryStream.Close();
        cryptoStream.Close();

        // Convert decrypted data into a string. 
        // Let us assume that the original plaintext string was UTF8-encoded.
        string plainText = Encoding.UTF8.GetString(plainTextBytes, 
                                                   0, 
                                                   decryptedByteCount);

        // Return decrypted string.   
        return plainText;
    }
}

/// <summary>
/// Illustrates the use of RijndaelSimple class to encrypt and decrypt data.
/// </summary>
public class RijndaelSimpleTest
{
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main(string[] args)
    {
        string   plainText          = "Hello, World!";    // original plaintext

        string   passPhrase         = "Pas5pr@se";        // can be any string
        string   saltValue          = "s@1tValue";        // can be any string
        string   hashAlgorithm      = "SHA1";             // can be "MD5"
        int      passwordIterations = 2;                  // can be any number
        string   initVector         = "@1B2c3D4e5F6g7H8"; // must be 16 bytes
        int      keySize            = 256;                // can be 192 or 128

        Console.WriteLine(String.Format("Plaintext : {0}", plainText));

        string  cipherText = RijndaelSimple.Encrypt(plainText,
                                                    passPhrase,
                                                    saltValue,
                                                    hashAlgorithm,
                                                    passwordIterations,
                                                    initVector,
                                                    keySize);

        Console.WriteLine(String.Format("Encrypted : {0}", cipherText));

        plainText          = RijndaelSimple.Decrypt(cipherText,
                                                    passPhrase,
                                                    saltValue,
                                                    hashAlgorithm,
                                                    passwordIterations,
                                                    initVector,
                                                    keySize);

        Console.WriteLine(String.Format("Decrypted : {0}", plainText));
    }
}
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1 Answer 1

up vote 1 down vote accepted

This code uses obsolete PasswordDeriveBytes class, use Rfc2898DeriveBytes class instead (Thanks @tom for highlighting this issue):

Rfc2898DeriveBytes password = new Rfc2898DeriveBytes(
    passPhrase,
    saltValueBytes,
    passwordIterations);

Also, even though IV (initVectorBytes) may be publicly stored it should not be reused for different encryptions. You can derive it from pseudo-random bytes:

byte[] initVectorBytes = password.GetBytes(symmetricKey.BlockSize / 8);

Other than that encryption/decryption looks properly implemented, and I completely agree with original code writer that initialization/duplicate steps should be taken to constructor. It will reduce the number of parameters in Encrypt/Decrypt methods to one - actual payload.

Depending on your specifics you can also expose methods accepting and returning encrypting/decrypting streams for large encryption volumes if necessary.

share|improve this answer
    
what about the obselete GetBytes method? and the constant IV? –  tom Jan 17 '13 at 16:39
    
Oops, missed this part. Will update the answer, thanks –  almaz Jan 17 '13 at 16:45
    
In order to properly decrypt previously encrypted string you need to pass the same IV that was used during encryption. In addition different encryptions should use different IVs. You can store IV the same way you store salt, but since it functions similarly to salt I would rather derive it from password+salt dependent random bytes. –  almaz Jan 17 '13 at 17:26
    
Deleted my previous comment. Question should have been - if I am going to use a unique IV for every string that I encrypt, how do get that back when I decrypt? –  tom Jan 17 '13 at 17:46
    
You should store the salt along with encrypted text in order to decrypt it. Same stands for IV - you should have it at the time of decryption, but since it's redundant to store 2 "salting" fields I suggested to build it from password+salt. –  almaz Jan 17 '13 at 19:18
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