[program-l] Re: Text file checksum code
- From: "Jacob Kruger" <jacobk@xxxxxxxxxxxx>
- To: <program-l@xxxxxxxxxxxxx>
- Date: Wed, 25 Mar 2009 11:04:03 +0200
Ok, from the second one, this seems the simplest:
public string GetMD5Hash(string input)
{
System.Security.Cryptography.MD5CryptoServiceProvider x = new
System.Security.Cryptography.MD5CryptoServiceProvider();
byte[] bs = System.Text.Encoding.UTF8.GetBytes(input);
bs = x.ComputeHash(bs);
System.Text.StringBuilder s = new System.Text.StringBuilder();
foreach (byte b in bs)
{
s.Append(b.ToString("x2").ToLower());
}
string password = s.ToString();
return password;
}
Apart from that one, how would you then decode the info to get it back to
normal text/XML?
TIA
Jacob Kruger
Blind Biker
Skype: BlindZA
'...fate had broken his body, but not his spirit...'
----- Original Message -----
From: "Mark Long" <markalong64@xxxxxxxxxxx>
To: "Program-l" <program-l@xxxxxxxxxxxxx>
Sent: Wednesday, March 25, 2009 10:43 AM
Subject: [program-l] Re: Text file checksum code
If the file is of arbitrary length then it can be padded to have the same
checksum. This is called a forced collision.
If you hashed it using two algorithms then it would be very much harder to
do. I suggest that a sha1 and an MD5 would defeat most attackers.
Sample code:
http://dotnetpulse.blogspot.com/2007/12/sha1-hash-calculation-in-c.html
http://blog.brezovsky.net/en-text-2.html
Hope that helps
Mark
--------------------------------------------------
From: "Jacob Kruger" <jacobk@xxxxxxxxxxxx>
Sent: Wednesday, March 25, 2009 7:53 AM
To: "Program-l" <program-l@xxxxxxxxxxxxx>
Subject: [program-l] Text file checksum code
Hi there
Currently looking into implementing a form of custom licensing system for
some apps for work, and the one thing we might need to do is to use some
form of checksum to make sure that the text/XML file to be used for
storing licensing information hasn't been modified as such, so am
currently looking for some sample code/examples related to doing this
with text files since it doesn't as such seem to be naturally supported
within the CLR framework/C#/VB.Net.
Any ideas?
Apart from that, here's a link to MS's own updated C# code samples file
download page:
http://code.msdn.microsoft.com/Release/ProjectReleases.aspx?ProjectName=csharpsamples&ReleaseId=8
Stay well
Jacob Kruger
Blind Biker
Skype: BlindZA
'...fate had broken his body, but not his spirit...'
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