Thursday, August 19, 2010

MD5 Checksum with Text mode in c#

I need to develop an MD5 checksum routine to check files that were being picked up from a Unix host. I found a number of blogs/code samples that showed the basics of using the MD5CryptoServiceProvider, so I quickly put together the code.

Unfortunately when I tested the results against the sample data, my checksums were different.

After some research I narrowed down the problem to the Unix MD5Sum using the file in TEXT mode. This is native for Unix, but not windows.

Ok, I can change my routine to use text mode as well? Not quite that simple.

I could not find a way to get .NET c# to read a file in text mode.

After some more research I found that the main difference when using text mode on a windows platform is that \r\n (carriage return, line feed) have the \r removed. In binary mode this is obviously not done.

So I did a quick test and did a string replace prior to doing the MD5 hash, and voila!!! I got the match.

So here is my class I created to allow for both modes when doing the MD5 checksum.

Hope this saves someone else some time!

class MD5FileCheckSum


public static string CalculateChecksum(Stream inputDataStream, bool textMode)


using (MD5 md5Computer = new MD5CryptoServiceProvider())


if (textMode)


//in text mode - for UNIX compatibility, we need to remove the \r characters from the \r\n end of lines

//this is also the same result as using the 'c' command fopen r

StreamReader sr = new StreamReader(inputDataStream);

string textdata1 = sr.ReadToEnd();

//remove the carriage returns

string textdata2 = textdata1.Replace("\r\n", "\n");

//convert back to a byte array

byte[] textbytes = Encoding.ASCII.GetBytes(textdata2);

//do the hash

byte[] retvaltext = md5Computer.ComputeHash(textbytes);

//return the result

return BitConverter.ToString(retvaltext).Replace("-", String.Empty);




//binary mode - just hash the whole data

byte[] retval = md5Computer.ComputeHash(inputDataStream);

return BitConverter.ToString(retval).Replace("-", String.Empty);





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