Generating a SHA1 hash in Windows Phone outputs a different hash

Question

I'm currently using the built-in methods in Windows Phone and Silverlight to create a SHA1 hash of a string. This is the code:

private static string CalculateSHA1(string text)
    {
        SHA1Managed s = new SHA1Managed();
        UTF8Encoding enc = new UTF8Encoding();
        s.ComputeHash(enc.GetBytes(text.ToCharArray()));
        System.Diagnostics.Debug.WriteLine("Original Text {0}, Access {1}", text, Convert.ToBase64String(s.Hash));
        return Convert.ToBase64String(s.Hash);
    }

For example, I tried generating a hash for this string: "hello".

Silverlight Output: LPJNul+wow4m6DsqxbninhsWHlwfp0JecwQzYpOLmCQ=

Correct Output: aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d

What I am doing wrong in the code?

Answer 1

In your example, you are Base64 encoding the byte array. Your correct output is in hexadecimal format, which you can achieve using:

return BitConverter.ToString(s.Hash).Replace("-", "");

instead of:

return Convert.ToBase64String(s.Hash);

Answer 2

I've compared those two solutions:

Solution A:

// compatible Windows Phone 7.1, 8.0 and 8.1
public static string CalculateSHA1(string str)
{
    var bytes = Encoding.UTF8.GetBytes(str);
    byte[] sha1Bytes;
    using (var algorithm = new SHA1Managed())
        sha1Bytes = algorithm.ComputeHash(bytes);
    return BitConverter.ToString(sha1Bytes).Replace("-", "").ToLowerInvariant();
}

Solution B (based on D for Developer):

// compatible Windows Phone 8.1 only
public static string CalculateSHA1New(string str)
{
    var vector = CryptographicBuffer.ConvertStringToBinary(str, BinaryStringEncoding.Utf8);
    var digest = HashAlgorithmProvider.OpenAlgorithm("SHA1").HashData(vector);
    return CryptographicBuffer.EncodeToHexString(digest);
}

Well, solution A is like 40 times faster. So only use solution A. :)