Was this page helpful?
Your feedback about this content is important. Let us know what you think.
Additional feedback?
1500 characters remaining
Collapse the table of content
Expand the table of content


Updated: May 2011

Computes a Hash-based Message Authentication Code (HMAC) using the RIPEMD160 hash function.

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

public class HMACRIPEMD160 : HMAC

HMACRIPEMD160 is a type of keyed hash algorithm that is constructed from the RIPEMD160 hash function and used as a Hash-based Message Authentication Code (HMAC). The HMAC process mixes a secret key with the message data, hashes the result with the hash function, mixes that hash value with the secret key again, and then applies the hash function a second time. The output hash is 160 bits in length.

An HMAC can be used to determine whether a message sent over an insecure channel has been tampered with, provided that the sender and receiver share a secret key. The sender computes the hash value for the original data and sends both the original data and hash value as a single message. The receiver recalculates the hash value on the received message and checks that the computed HMAC matches the transmitted HMAC.

Any change to the data or the hash value will result in a mismatch, because knowledge of the secret key is required to change the message and reproduce the correct hash value. Therefore, if the original and computed hash values match, the message is authenticated.

HMACRIPEMD160 accepts keys of any size, and produces a hash sequence that is 160 bits long.

The RIPEMD hash algorithm and its successors were developed by the European RIPE project. The original RIPEMD algorithm was designed to replace MD4 and MD5 and was later strengthened and renamed RIPEMD-160. The RIPEMD-160 hash algorithm produces a 160-bit hash value. The algorithm's designers have placed it in the public domain .

The following code example shows how to sign a file by using the HMACRIPEMD160 object and then how to verify the file.

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

public class HMACRIPEMD160example

    public static void Main(string[] Fileargs)
        string dataFile;
        string signedFile;
        //If no file names are specified, create them. 
        if (Fileargs.Length < 2)
            dataFile = @"text.txt";
            signedFile = "signedFile.enc";

            if (!File.Exists(dataFile))
                // Create a file to write to. 
                using (StreamWriter sw = File.CreateText(dataFile))
                    sw.WriteLine("Here is a message to sign");

            dataFile = Fileargs[0];
            signedFile = Fileargs[1];
            // Create a random key using a random number generator. This would be the 
            //  secret key shared by sender and receiver.
            byte[] secretkey = new Byte[64];
            //RNGCryptoServiceProvider is an implementation of a random number generator. 
            using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
                // The array is now filled with cryptographically strong random bytes.

                // Use the secret key to sign the message file.
                SignFile(secretkey, dataFile, signedFile);

                // Verify the signed file
                VerifyFile(secretkey, signedFile);
        catch (IOException e)
            Console.WriteLine("Error: File not found", e);

    }  //end main 
    // Computes a keyed hash for a source file and creates a target file with the keyed hash 
    // prepended to the contents of the source file.  
    public static void SignFile(byte[] key, String sourceFile, String destFile)
        // Initialize the keyed hash object. 
        using (HMACRIPEMD160 hmac = new HMACRIPEMD160(key))
            using (FileStream inStream = new FileStream(sourceFile, FileMode.Open))
                using (FileStream outStream = new FileStream(destFile, FileMode.Create))
                    // Compute the hash of the input file.
                    byte[] hashValue = hmac.ComputeHash(inStream);
                    // Reset inStream to the beginning of the file.
                    inStream.Position = 0;
                    // Write the computed hash value to the output file.
                    outStream.Write(hashValue, 0, hashValue.Length);
                    // Copy the contents of the sourceFile to the destFile. 
                    int bytesRead;
                    // read 1K at a time
                    byte[] buffer = new byte[1024];
                        // Read from the wrapping CryptoStream.
                        bytesRead = inStream.Read(buffer, 0, 1024);
                        outStream.Write(buffer, 0, bytesRead);
                    } while (bytesRead > 0);
    } // end SignFile 

    // Compares the key in the source file with a new key created for the data portion of the file. If the keys  
    // compare the data has not been tampered with. 
    public static bool VerifyFile(byte[] key, String sourceFile)
        bool err = false;
        // Initialize the keyed hash object.  
        using (HMACRIPEMD160 hmac = new HMACRIPEMD160(key))
            // Create an array to hold the keyed hash value read from the file.
            byte[] storedHash = new byte[hmac.HashSize / 8];
            // Create a FileStream for the source file. 
            using (FileStream inStream = new FileStream(sourceFile, FileMode.Open))
                // Read in the storedHash.
                inStream.Read(storedHash, 0, storedHash.Length);
                // Compute the hash of the remaining contents of the file. 
                // The stream is properly positioned at the beginning of the content,  
                // immediately after the stored hash value.
                byte[] computedHash = hmac.ComputeHash(inStream);
                // compare the computed hash with the stored value 

                for (int i = 0; i < storedHash.Length; i++)
                    if (computedHash[i] != storedHash[i])
                        err = true;
        if (err)
            Console.WriteLine("Hash values differ! Signed file has been tampered with!");
            return false;
            Console.WriteLine("Hash values agree -- no tampering occurred.");
            return true;

    } //end VerifyFile

} //end 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

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




May 2011

Updated the code example.

Information enhancement.

Community Additions

© 2015 Microsoft