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TripleDES Class

Updated: February 2009

Represents the base class for Triple Data Encryption Standard algorithms from which all TripleDES implementations must derive.

Namespace:  System.Security.Cryptography
Assembly:  mscorlib (in mscorlib.dll)

public abstract class TripleDES : SymmetricAlgorithm

TripleDES uses three successive iterations of the DES algorithm. It can use either two or three 56-bit keys.


TripleDES has been superseded by the Aes algorithm and its derived classes. Aes offers better security and performance than TripleDES. Use TripleDES only for compatibility with legacy applications and data.

This algorithm supports key lengths from 128 bits to 192 bits in increments of 64 bits.

The following code example method uses TripleDESCryptoServiceProvider with the specified key (Key) and initialization vector (IV) to encrypt a file specified by inName. It then outputs the encrypted result to the file specified by outName.

private static void EncryptData(String inName, String outName, byte[] tdesKey, byte[] tdesIV)
    //Create the file streams to handle the input and output files.
    FileStream fin = new FileStream(inName, FileMode.Open, FileAccess.Read);
    FileStream fout = new FileStream(outName, FileMode.OpenOrCreate, FileAccess.Write);

    //Create variables to help with read and write.
    byte[] bin = new byte[100]; //This is intermediate storage for the encryption.
    long rdlen = 0;              //This is the total number of bytes written.
    long totlen = fin.Length;    //This is the total length of the input file. 
    int len;                     //This is the number of bytes to be written at a time.

    TripleDESCryptoServiceProvider tdes = new TripleDESCryptoServiceProvider();          
    CryptoStream encStream = new CryptoStream(fout, tdes.CreateEncryptor(tdesKey, tdesIV), CryptoStreamMode.Write);


    //Read from the input file, then encrypt and write to the output file. 
    while(rdlen < totlen)
        len = fin.Read(bin, 0, 100);
        encStream.Write(bin, 0, len);
        rdlen = rdlen + len;
        Console.WriteLine("{0} bytes processed", rdlen);


Decryption can be handled in the same way; use CreateDecryptor instead of CreateEncryptor. The same key (Key) and initialization vector (IV) used to encrypt the file must be used to decrypt it.


A newer symmetric encryption algorithm, Advanced Encryption Standard (AES), is available. Consider using the Aes class instead of the TripleDES class.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0




February 2009

Added note about newer AES algorithm.

Information enhancement.