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

using (FileStream fs = new FileStream(@"C:\file\location", FileMode.Open))
using (BufferedStream bs = new BufferedStream(fs))
{
    using (SHA1Managed sha1 = new SHA1Managed())
    {
        byte[] hash = sha1.ComputeHash(bs);
        StringBuilder formatted = new StringBuilder(2 * hash.Length);
        foreach (byte b in hash)
        {
            formatted.AppendFormat("{0:X2}", b);
        }
    }
}

formatted contains the string representation of the SHA-1 hash. Also, by using a FileStream instead of a byte buffer, ComputeHash computes the hash in chunks, so you don't have to load the entire file in one go, which is helpful for large files.

Answer 2

With the ComputeHash method. See here:

ComputeHash

Example snippet:

using(var cryptoProvider = new SHA1CryptoServiceProvider())
{
    string hash = BitConverter
            .ToString(cryptoProvider.ComputeHash(buffer));

    //do something with hash
}

Where buffer is the contents of your file.

Answer 3

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));
        }
    }

Answer 4

Also you can try:

FileStream fop = File.OpenRead(@"C:\test.bin");
string chksum = BitConverter.ToString(System.Security.Cryptography.SHA1.Create().ComputeHash(fop));