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, 5 Jan 2005
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How to compute the same hash as MD5SUM does (HEX).

Reason For This Howto

As you may know the MD5CryptoService, which the .NET Framework uses, doesn't create an md5 sum's string. So you only have the pure byte[] which isn't that useful if you want to use it in a database or on your Web Server to compare the sum with your file's sum! So, if many people have no idea how to get their sum into the right way, here's my howto to create the same sums like "md5sum" does:


This is the second version with the Hex-bug fixed.

using System.Security.Cryptography;
string MD5SUM(byte[] FileOrText) //Output: String<-> Input: Byte[] //
return BitConverter.ToString(new 

// Quite simple isn't it? I hope you enjoyed this tiny article and 
//I hope I could help ya! //

You can use this example of course for SHA1 as well, just change the MD5CryptoServiceProvider to SHA1CryptoServiceProvider.


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About the Author

Max Gattringer

Austria Austria
I am Max Gattringer an Austrian student - I've got a passion for programming C#, cryptograpy and nearly everything concerning PCs Big Grin | :-D

Comments and Discussions

GeneralThis is great! Pinmembermondokat3-Apr-07 11:27 
GeneralMD5 PinmemberARROLLO2-Jan-06 15:12 
GeneralPerformance Pinmemberaxelriet2-Feb-05 17:03 
GeneralYeah, you're right ;-) PinsussAnonymous7-Jan-05 13:36 
GeneralAnother suggestion PinmemberMrEyes6-Jan-05 0:09 
GeneralJust two suggestions PinmemberDennis C. Dietrich5-Jan-05 11:58 
GeneralRe: Just two suggestions PinmemberRobert Rohde5-Jan-05 21:09 
GeneralRe: Just two suggestions PinmemberDennis C. Dietrich6-Jan-05 2:08 
Robert Rohde wrote:
In general I agree that StringBuilder is faster. But in this case the calculation of the MD5 value will by far run longer than the string concatenation, so the change will not be significant.
First rule for optimizing: Only optimize what is relevant for optimization (90-10 rule).

I know what you mean and personally I would even apply another rule before it comes to the 90-10 rule you quoted (that would be the 'optimization last' rule of XP). However, I don't think that should be used in this case because this is about .NET best practices rather than general purpose rules. Consider the case that you want to calculate the MD5 hash not for one file (or a few big files) but for a bunch of small files. Calculating the MD5 hash for a few ten thousand files would lead to a few hundred thousand unnecessary memcopy operations during the string creation. And I'd say that is significant (although you might argue that it wouldn't matter on today's CPUs).
Best regards from Schöneberg
GeneralRe: Just two suggestions PinmemberJeffrey Sax6-Jan-05 14:52 
GeneralRe: Just two suggestions PinmemberMax Gattringer7-Jan-05 13:52 

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