I have this bit of t-sql code
set @UrlHash = convert(bigint, hashbytes('MD5', @Url))
I wonder if I can write a function in C# which returns me the exact same hash as the line above without going to SQL.
Is it possible?
Requirement is that C# MUST created exact same hash.
The select
SELECT CONVERT(BIGINT, HASHBYTES('MD5', 'http://stackoverflow.com'))
will yield the following result:
-3354682182756996262
If you now try to create a MD5 hash in C#
MD5 md5 = MD5.Create();
byte[] textToHash = Encoding.UTF8.GetBytes("http://stackoverflow.com");
byte[] result = md5.ComputeHash(textToHash);
long numeric = BitConverter.ToInt64(result, 0);
numeric will be 8957512937738269783.
So what's the issue (besides the fact that a MD5 hash is 128-bit and BIGINT/long is just 64-bit)?
It's an endian issue (the bytes are in the wrong order). Let's fix it using the BitConverter class and reverse the bytes as needed:
MD5 md5 = MD5.Create();
byte[] textToHash = Encoding.UTF8.GetBytes("http://stackoverflow.com");
byte[] result = md5.ComputeHash(textToHash);
if (BitConverter.IsLittleEndian)
Array.Reverse(result);
long numeric = BitConverter.ToInt64(result, 0);
numeric is now -3354682182756996262 as you want.
You should use MD5 class, here is the example from http://blogs.msdn.com/b/csharpfaq/archive/2006/10/09/how-do-i-calculate-a-md5-hash-from-a-string_3f00_.aspx, with output as int 64 :
public int64 CalculateMD5Hash(string input)
{
// step 1, calculate MD5 hash from input
MD5 md5 = System.Security.Cryptography.MD5.Create();
byte[] inputBytes = System.Text.Encoding.ASCII.GetBytes(input);
byte[] hash = md5.ComputeHash(inputBytes);
return BitConverter.ToInt64(hash, 0);
}
Isn't an MD5 hash standard? Can't you use a standard MD5 C# implementation? What about using the code in here?
