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AesManaged Class

Updated: June 2010

Provides a managed implementation of the Advanced Encryption Standard (AES) symmetric algorithm.

System.Object
  System.Security.Cryptography.SymmetricAlgorithm
    System.Security.Cryptography.Aes
      System.Security.Cryptography.AesManaged

Namespace:  System.Security.Cryptography
Assembly:  System.Core (in System.Core.dll)
public sealed class AesManaged : Aes

The AesManaged type exposes the following members.

  Name Description
Public method AesManaged Initializes a new instance of the AesManaged class.
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  Name Description
Public property BlockSize Gets or sets the block size, in bits, of the cryptographic operation. (Inherited from SymmetricAlgorithm.)
Public property FeedbackSize Gets or sets the number of bits to use as feedback. (Overrides SymmetricAlgorithm.FeedbackSize.)
Public property IV Gets or sets the initialization vector (IV) to use for the symmetric algorithm. (Overrides SymmetricAlgorithm.IV.)
Public property Key Gets or sets the secret key used for the symmetric algorithm. (Overrides SymmetricAlgorithm.Key.)
Public property KeySize Gets or sets the size, in bits, of the secret key used for the symmetric algorithm. (Overrides SymmetricAlgorithm.KeySize.)
Public property LegalBlockSizes Gets the block sizes, in bits, that are supported by the symmetric algorithm. (Inherited from SymmetricAlgorithm.)
Public property LegalKeySizes Gets the key sizes, in bits, that are supported by the symmetric algorithm. (Inherited from SymmetricAlgorithm.)
Public property Mode Gets or sets the mode for operation of the symmetric algorithm. (Overrides SymmetricAlgorithm.Mode.)
Public property Padding Gets or sets the padding mode used in the symmetric algorithm. (Overrides SymmetricAlgorithm.Padding.)
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  Name Description
Public method Clear Releases all resources used by the SymmetricAlgorithm class. (Inherited from SymmetricAlgorithm.)
Public method CreateDecryptor() Creates a symmetric decryptor object using the current key and initialization vector (IV). (Overrides SymmetricAlgorithm.CreateDecryptor().)
Public method CreateDecryptor(Byte[], Byte[]) Creates a symmetric decryptor object using the specified key and initialization vector (IV). (Overrides SymmetricAlgorithm.CreateDecryptor(Byte[], Byte[]).)
Public method CreateEncryptor() Creates a symmetric encryptor object using the current key and initialization vector (IV). (Overrides SymmetricAlgorithm.CreateEncryptor().)
Public method CreateEncryptor(Byte[], Byte[]) Creates a symmetric encryptor object using the specified key and initialization vector (IV). (Overrides SymmetricAlgorithm.CreateEncryptor(Byte[], Byte[]).)
Public method Dispose() Releases all resources used by the current instance of the SymmetricAlgorithm class. (Inherited from SymmetricAlgorithm.)
Protected method Dispose(Boolean) Releases the unmanaged resources used by the SymmetricAlgorithm and optionally releases the managed resources. (Inherited from SymmetricAlgorithm.)
Public method Equals(Object) Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected method Finalize Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public method GenerateIV Generates a random initialization vector (IV) to use for the symmetric algorithm. (Overrides SymmetricAlgorithm.GenerateIV().)
Public method GenerateKey Generates a random key to use for the symmetric algorithm. (Overrides SymmetricAlgorithm.GenerateKey().)
Public method GetHashCode Serves as a hash function for a particular type. (Inherited from Object.)
Public method GetType Gets the Type of the current instance. (Inherited from Object.)
Protected method MemberwiseClone Creates a shallow copy of the current Object. (Inherited from Object.)
Public method ToString Returns a string that represents the current object. (Inherited from Object.)
Public method ValidKeySize Determines whether the specified key size is valid for the current algorithm. (Inherited from SymmetricAlgorithm.)
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  Name Description
Protected field BlockSizeValue Represents the block size, in bits, of the cryptographic operation. (Inherited from SymmetricAlgorithm.)
Protected field FeedbackSizeValue Represents the feedback size, in bits, of the cryptographic operation. (Inherited from SymmetricAlgorithm.)
Protected field IVValue Represents the initialization vector (IV) for the symmetric algorithm. (Inherited from SymmetricAlgorithm.)
Protected field KeySizeValue Represents the size, in bits, of the secret key used by the symmetric algorithm. (Inherited from SymmetricAlgorithm.)
Protected field KeyValue Represents the secret key for the symmetric algorithm. (Inherited from SymmetricAlgorithm.)
Protected field LegalBlockSizesValue Specifies the block sizes, in bits, that are supported by the symmetric algorithm. (Inherited from SymmetricAlgorithm.)
Protected field LegalKeySizesValue Specifies the key sizes, in bits, that are supported by the symmetric algorithm. (Inherited from SymmetricAlgorithm.)
Protected field ModeValue Represents the cipher mode used in the symmetric algorithm. (Inherited from SymmetricAlgorithm.)
Protected field PaddingValue Represents the padding mode used in the symmetric algorithm. (Inherited from SymmetricAlgorithm.)
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The AES algorithm is essentially the Rijndael symmetric algorithm with a fixed block size and iteration count. This class functions the same way as the RijndaelManaged class but limits blocks to 128 bits and does not allow feedback modes.

Note Note

If the Windows security policy setting for Federal Information Processing Standards (FIPS)-compliant algorithms is enabled, using this algorithm throws a CryptographicException.

The following example demonstrates how to encrypt and decrypt sample data using the AesManaged class.


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

namespace Aes_Example
{
    class AesExample
    {
        public static void Main()
        {
            try
            {

                string original = "Here is some data to encrypt!";

                // Create a new instance of the AesManaged
                // class.  This generates a new key and initialization 
                // vector (IV).
                using (AesManaged myAes = new AesManaged())
                {

                    // Encrypt the string to an array of bytes.
                    byte[] encrypted = EncryptStringToBytes_Aes(original, myAes.Key, myAes.IV);

                    // Decrypt the bytes to a string.
                    string roundtrip = DecryptStringFromBytes_Aes(encrypted, myAes.Key, myAes.IV);

                    //Display the original data and the decrypted data.
                    Console.WriteLine("Original:   {0}", original);
                    Console.WriteLine("Round Trip: {0}", roundtrip);
                }

            }
            catch (Exception e)
            {
                Console.WriteLine("Error: {0}", e.Message);
            }
        }
        static byte[] EncryptStringToBytes_Aes(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("Key");
            byte[] encrypted;
            // Create an AesManaged object
            // with the specified key and IV.
            using (AesManaged aesAlg = new AesManaged())
            {
                aesAlg.Key = Key;
                aesAlg.IV = IV;

                // Create a decrytor to perform the stream transform.
                ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.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 the encrypted bytes from the memory stream.
            return encrypted;

        }

        static string DecryptStringFromBytes_Aes(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("Key");

            // Declare the string used to hold
            // the decrypted text.
            string plaintext = null;

            // Create an AesManaged object
            // with the specified key and IV.
            using (AesManaged aesAlg = new AesManaged())
            {
                aesAlg.Key = Key;
                aesAlg.IV = IV;

                // Create a decrytor to perform the stream transform.
                ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.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;

        }
    }
}


.NET Framework

Supported in: 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Date

History

Reason

June 2010

Added example.

Customer feedback.

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Managed versus CSP performance
For small byte arrays, AesManaged is around twice as fast as AesCryptoServiceProvider. For large arrays, it flips and AesCryptoServiceProvider is about twice as fast. Break-even is around 512 bytes.