// Compute the hash for a ContosoKeyedHash that has transformed a
// file stream.
private static void EncodeStream()
{
//<Snippet4>
byte[] keyData = new byte[24];
RandomNumberGenerator.Create().GetBytes(keyData);
ContosoKeyedHash localCrypto = new ContosoKeyedHash(keyData);
//</Snippet4>
string filePath = (System.IO.Directory.GetCurrentDirectory() +
"\\members.txt");
try
{
//<Snippet14>
FileStream fileStream =
new FileStream(filePath, FileMode.Open, FileAccess.Read);
localCrypto.ComputeHash(fileStream);
//</Snippet14>
SummarizeMAC(localCrypto,
"ContosoKeyedHash after encoding a file stream.");
}
catch (FileNotFoundException)
{
Console.WriteLine("The specified path was not found: " +
filePath);
}
}
// Compute the hash for a ContosoKeyedHash that has transformed
// a byte array.
private static void EncodeMessage()
{
byte[] keyData = new byte[24];
RandomNumberGenerator.Create().GetBytes(keyData);
ContosoKeyedHash localCrypto = new ContosoKeyedHash(keyData);
//<Snippet13>
string message = "Hello World.";
byte[] encodedMessage =
EncodeBytes(Encoding.ASCII.GetBytes(message));
localCrypto.ComputeHash(encodedMessage);
//</Snippet13>
SummarizeMAC(localCrypto,
"ContosoKeyedHash after encoding a message.");
}
// Write a summary of the specified ContosoKeyedHash to the
// console window.
private static void SummarizeMAC(
ContosoKeyedHash localCrypto,
string description)
{
//<Snippet20>
string classDescription = localCrypto.ToString();
//</Snippet20>
//<Snippet7>
byte[] computedHash = localCrypto.Hash;
//</Snippet7>
//<Snippet8>
int hashSize = localCrypto.HashSize;
//</Snippet8>
//<Snippet11>
int outputBlockSize = localCrypto.OutputBlockSize;
//</Snippet11>
// Retrieve the key used in the hash algorithm.
//<Snippet10>
byte[] key = localCrypto.Key;
//</Snippet10>
Console.WriteLine("\n**********************************");
Console.WriteLine(classDescription);
Console.WriteLine(description);
Console.WriteLine("----------------------------------");
Console.WriteLine("The size of the computed hash : " + hashSize);
Console.WriteLine("The key used in the hash algorithm : " +
Encoding.ASCII.GetString(key));
Console.WriteLine("The value of the computed hash : " +
Encoding.ASCII.GetString(computedHash));
}
// Transform the byte array using ContosoKeyedHash,
// then summarize its properties.
private static byte[] EncodeBytes(byte[] sourceBytes)
{
int currentPosition = 0;
byte[] targetBytes = new byte[1024];
int sourceByteLength = sourceBytes.Length;
// Create an encryptor with a random key and the
// KeyedHashAlgorithm class name.
byte[] key = new byte[24];
RandomNumberGenerator.Create().GetBytes(key);
string keyedHashName =
"System.Security.Cryptography.KeyedHashAlgorithm";
ContosoKeyedHash localCrypto =
new ContosoKeyedHash(keyedHashName, key);
// Retrieve the block size to read the bytes.
//<Snippet9>
int inputBlockSize = localCrypto.InputBlockSize;
//</Snippet9>
try
{
// Determine if multiple blocks can be transformed.
//<Snippet6>
if (localCrypto.CanTransformMultipleBlocks)
//</Snippet6>
{
int numBytesRead = 0;
while (sourceByteLength - currentPosition >=
inputBlockSize)
{
// Transform the bytes from the currentposition in the
// sourceBytes array, writing the bytes to the
// targetBytes array.
//<Snippet18>
numBytesRead = localCrypto.TransformBlock(
sourceBytes,
currentPosition,
inputBlockSize,
targetBytes,
currentPosition);
//</Snippet18>
// Advance the current position in the source array.
currentPosition += numBytesRead;
}
// Transform the final block of bytes.
//<Snippet19>
byte[] finalBytes = localCrypto.TransformFinalBlock(
sourceBytes,
currentPosition,
sourceByteLength - currentPosition);
//</Snippet19>
// Copy the contents of the finalBytes array to the
// targetBytes array.
finalBytes.CopyTo(targetBytes, currentPosition);
}
}
catch (Exception ex)
{
Console.WriteLine("Caught unexpected exception:" +
ex.ToString());
}
// Find the length of valid bytes (those without zeros).
//<Snippet15>
IEnumerator enum1 = targetBytes.GetEnumerator();
int i = 0;
while (enum1.MoveNext())
{
if (enum1.Current.ToString().Equals("0"))
{
break;
}
i++;
}
// Compute the hash based on the valid bytes in the array.
localCrypto.ComputeHash(targetBytes, 0, i);
//</Snippet15>
SummarizeMAC(localCrypto, "ContosoKeyedHash after computing " +
"hash for specified region of byte array");
//<Snippet5>
// Determine if the current transform can be reused.
if (!localCrypto.CanReuseTransform)
//</Snippet5>
{
// Free up any used resources.
//<Snippet12>
localCrypto.Clear();
//</Snippet12>
//<Snippet16>
localCrypto.Initialize();
//</Snippet16>
}
// Create a new array with the number of valid bytes.
byte[] returnedArray = new byte[i];
for (int j = 0; j < i; j++)
{
returnedArray[j] = targetBytes[j];
}
return(returnedArray);
}
