Comments on: Calculating CRC-32 in C# and .NET http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net?utm_source=rss&utm_medium=rss&utm_campaign=calculating_crc32_in_c_and_net A .NET developer in silicon valley Wed, 11 Apr 2012 18:41:57 +0000 hourly 1 http://wordpress.org/?v=3.3.2 By: Damien Guard http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net#comment-46848 Damien Guard Wed, 02 Nov 2011 19:50:03 +0000 http://damieng.com/blog/archive/2006/08/08/calculating_crc32_in_c_and_net.aspx#comment-46848 If you want to ensure file integrity, sure, SHA256 is a great choice, but some people need to calculate a CRC32 for backwards compatibility with things like ZIP. [)amien If you want to ensure file integrity, sure, SHA256 is a great choice, but some people need to calculate a CRC32 for backwards compatibility with things like ZIP.

[)amien

]]> By: John Doe http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net#comment-46845 John Doe Wed, 02 Nov 2011 17:05:03 +0000 http://damieng.com/blog/archive/2006/08/08/calculating_crc32_in_c_and_net.aspx#comment-46845 I may be missing something, but why not use System.Security.Cryptography.SHA256 instead if all you need is to verify file integrity? I may be missing something, but why not use System.Security.Cryptography.SHA256 instead if all you need is to verify file integrity?

]]> By: Damien Guard http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net#comment-44913 Damien Guard Tue, 29 Mar 2011 14:49:19 +0000 http://damieng.com/blog/archive/2006/08/08/calculating_crc32_in_c_and_net.aspx#comment-44913 It produces a 32-bit CRC (hence the name). If you display this as hexadecimal then each pair of two hex letters is 8 bits. Four of these pairs gives 32-bits. [)amien It produces a 32-bit CRC (hence the name). If you display this as hexadecimal then each pair of two hex letters is 8 bits. Four of these pairs gives 32-bits.

[)amien

]]> By: ibram http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net#comment-44911 ibram Tue, 29 Mar 2011 13:05:46 +0000 http://damieng.com/blog/archive/2006/08/08/calculating_crc32_in_c_and_net.aspx#comment-44911 Thank you for the code. I made some performance tests, that could be interesting. For a 55MB text file: System.Security.Cryptography.SHA256 needs 779 ms. System.Security.Cryptography.MD5 needs 144 ms. CRC32 needs 660 ms. Is it correct that the crc is just a 8 character string? I tried to use the Create() method, but than realized that this creates the SHA1Managed object. Crc32.Create().ComputeHash( fs ) Than I put this in your code: public new static Crc32 Create() { return new Crc32(); } Thank you for the code.
I made some performance tests, that could be interesting.
For a 55MB text file:
System.Security.Cryptography.SHA256 needs 779 ms.
System.Security.Cryptography.MD5 needs 144 ms.
CRC32 needs 660 ms.

Is it correct that the crc is just a 8 character string?

I tried to use the Create() method, but than realized that this creates the SHA1Managed object.
Crc32.Create().ComputeHash( fs )

Than I put this in your code:
public new static Crc32 Create()
{
return new Crc32();
}

]]> By: Damien Guard http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net#comment-41815 Damien Guard Fri, 14 May 2010 21:02:41 +0000 http://damieng.com/blog/archive/2006/08/08/calculating_crc32_in_c_and_net.aspx#comment-41815 You'll see it inherits from the HashAlgorithm class which has a ComputeHash method that takes a Stream object, reads 4K blocks at a time and calls through to HashCore for each block. [)amien You’ll see it inherits from the HashAlgorithm class which has a ComputeHash method that takes a Stream object, reads 4K blocks at a time and calls through to HashCore for each block.

[)amien

]]> By: Chizl http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net#comment-41814 Chizl Fri, 14 May 2010 20:44:21 +0000 http://damieng.com/blog/archive/2006/08/08/calculating_crc32_in_c_and_net.aspx#comment-41814 In your example you have: using (FileStream fs = File.Open("c:\\myfile.txt", FileMode.Open))       foreach (byte b in crc32.Compute(fs)) hash += b.ToString("x2").ToLower(); However the only Compute mehtods I see are static and none of them take a FileStream object. In your example you have:
using (FileStream fs = File.Open(“c:\\myfile.txt”, FileMode.Open))
      foreach (byte b in crc32.Compute(fs)) hash += b.ToString(“x2″).ToLower();

However the only Compute mehtods I see are static and none of them take a FileStream object.

]]> By: Phooey http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net#comment-39546 Phooey Thu, 08 Apr 2010 08:20:20 +0000 http://damieng.com/blog/archive/2006/08/08/calculating_crc32_in_c_and_net.aspx#comment-39546 If you interpret size as being the size of the array, yes, but the array already has a length, why would you need to pass it in again? When passing the array, an offset and size, size refers to the size of the data, see the parameter definition for the HashCore function of the HashAlgorithm: cbSize: The number of bytes in the byte array to use as data Cheers, Phooey. If you interpret size as being the size of the array, yes, but the array already has a length, why would you need to pass it in again?

When passing the array, an offset and size, size refers to the size of the data, see the parameter definition for the HashCore function of the HashAlgorithm:

cbSize:
The number of bytes in the byte array to use as data

Cheers,
Phooey.

]]> By: Damien Guard http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net#comment-39472 Damien Guard Wed, 07 Apr 2010 15:54:30 +0000 http://damieng.com/blog/archive/2006/08/08/calculating_crc32_in_c_and_net.aspx#comment-39472 That is intentional - start is an index into the buffer to start populating at. If you change the loop as you describe it will go out of bounds with a non-zero value of start. [)amien That is intentional – start is an index into the buffer to start populating at. If you change the loop as you describe it will go out of bounds with a non-zero value of start.

[)amien

]]> By: Phooey http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net#comment-39464 Phooey Wed, 07 Apr 2010 14:53:24 +0000 http://damieng.com/blog/archive/2006/08/08/calculating_crc32_in_c_and_net.aspx#comment-39464 Thanks for the code, there's a little bug in the CalculateHash function: for(int i = start; i < size; i++) needs to be: for(int i = start; i < size+start; i++) else you wont hash the whole buffer for non-zero values of start. Cheers, Phooey. Thanks for the code, there’s a little bug in the CalculateHash function:

for(int i = start; i < size; i++)

needs to be:

for(int i = start; i < size+start; i++)

else you wont hash the whole buffer for non-zero values of start.

Cheers,
Phooey.

]]> By: ASP.NET Performance - Part 3 - Cache Busting - Karl Seguin - CodeBetter.Com - Stuff you need to Code Better! http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net#comment-34252 ASP.NET Performance - Part 3 - Cache Busting - Karl Seguin - CodeBetter.Com - Stuff you need to Code Better! Mon, 11 Jan 2010 13:53:45 +0000 http://damieng.com/blog/archive/2006/08/08/calculating_crc32_in_c_and_net.aspx#comment-34252 [...] of our asset folder) and hash values. For my "hash" I'm using a CRC32, specifically Damien Guard's C# implementation. The nice thing about CRC32 is that we end up with pretty small values. The downside is that [...] [...] of our asset folder) and hash values. For my "hash" I'm using a CRC32, specifically Damien Guard's C# implementation. The nice thing about CRC32 is that we end up with pretty small values. The downside is that [...]

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