Calculate hash when writing to stream

I am currently creating an encrypted file format that needs to be signed. For this I need to calculate the hash code of the content I have written to a stream.

In the .net framework there is numerous hash algorithms that can be used, and it works fine, but it requires me to process the stream three times.

byte[] content = new byte[] { 0, 1, 2, 3, 4, 5, 6 };

using (Stream fileStream = File.Open("myfile.bin", FileMode.Create))
{
    //Write content
    fileStream.Write(content, 0, content.Length);
}

byte[] hashValue = null;
using (Stream fileStream = File.Open("myfile.bin", FileMode.Open))
{
    HashAlgorithm hash = SHA256.Create();
    hashValue = hash.ComputeHash(fileStream);
}

using (Stream fileStream = File.Open("myfile.bin", FileMode.Append))
{
    fileStream.Write(hashValue, 0, hashValue.Length);
}

This is okay if it is encrypted to a file, but if it is encrypted to a network destination, the bytes are no longer available.

So basically I need to only process the data once. On CodeProject there is an article that has implemented CRC32 as a Stream that calculates the CRC32 code every time there is written data to it.

Something like:

byte[] content = new byte[] { 0, 1, 2, 3, 4, 5, 6 };

using (FileStream fileStream = File.Create("myfile.bin"))
using (Stream crcStream = new CRCStream(fileStream)) //Takes a base stream
{
    //Write content
    crcStream.Write(content, 0, content.Length); 

    //Write checksum
    fileStream.Write(crcStream.WriteCRC, 0, 4);
}

Obviously CRC32 is not a hash alogorithm, but it would be nice to have something like a HashStream that takes a HashAlgorithm. The HashStream would update the hash value every time write/read is called.

Something like:

byte[] content = new byte[] { 0, 1, 2, 3, 4, 5, 6 };

HashAlgorithm hashAlgo = SHA256.Create();

using (File