How do I do a SHA1 File Checksum in C#?

Question

How do I use the SHA1CryptoServiceProvider() on a file to create a SHA1 Checksum of the file?

Answer 1

If you are already reading the file as a stream, then the following technique calculates the hash as you read it. The only caveat is that you need to consume the whole stream.

class Program
    {
        static void Main(string[] args)
        {
            String sourceFileName = "C:\\test.txt";
            Byte[] shaHash;

            //Use Sha1Managed if you really want sha1
            using (var shaForStream = new SHA256Managed())
            using (Stream sourceFileStream = File.Open(sourceFileName, FileMode.Open))
            using (Stream sourceStream = new CryptoStream(sourceFileStream, shaForStream, CryptoStreamMode.Read))
            {
                //Do something with the sourceStream 
                //NOTE You need to read all the bytes, otherwise you'll get an exception ({"Hash must be finalized before the hash value is retrieved."}) 
                while(sourceStream.ReadByte() != -1);                
                shaHash = shaForStream.Hash;
            }

            Console.WriteLine(Convert.ToBase64String(shaHash));
        }
    }