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Introduction

The Crypto++ library is a freeware library of cryptographic schemes, written by Wei Dai. However the library also contains other useful classes which are not immediately apparent when you use the library. Two of these are the Gzip and Gunzip classes which can be used to compress and decompress (zip and unzip) data.

Compression

Compressing your data could not be simpler. Say you had data pData that was of size dwLen that you wished to compress.

#include <gzip.h>


Gzip zipper(1);    // 1 is fast, 9 is slow


  zipper.Put(pData,dwLen);
  zipper.Close();

  byte* pCompressed = new byte[zipper.MaxRetrieveable()];
  zipper.Get(pCompressed,zipper.MaxRetrieveable());

pCompressed now contains the compressed data.

Decompression

You may not be surprised to know that decompression is just as easy. (dwLen is now the length of our compressed data)

Gunzip unzipper;

  unzipper.Put(pCompressedData,dwLen);
  unzipper.Close();

  byte* pData = new byte[unzipper.MaxRetrieveable()];
  unzipper.Get(pData,unzipper.MaxRetrieveable());

pData now contains the uncompressed data.

Remarks

Thanks to Wei Dai for his permission to write this article in what is hoped to be a series of articles on the use of his Crypto++ library.

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password protected archive? Matthias Blum 14:23 15 Jan '09   Hey, does the gzip.h also support encrypted archives? Or how can I encrypt a big (~700MB) archive as fast as possible? Thanks, Matthias Sign In·View Thread·PermaLink Re: password protected archive? Shaun Wilde 1:06 16 Jan '09   It's been 8 years since I last had to use this 3rd party library, you will have to look up for yourself. I'll be more enthusiastic about encouraging thinking outside the box when there's evidence of any thinking going on inside it. - pTerry BizSquawk Sign In·View Thread·PermaLink Compressing and Decompressing Data using C++ jassshan 22:39 24 Nov '08   Halo,do someone have Compressing and Decompressing Data using C++ source code.IF u guys n girls have,can u all sent me the source code.my email at whocares1717@hotmail.com.thx Sign In·View Thread·PermaLink 1.00/5 Gzip a set of files sheyliger 4:21 7 Jul '08   Can this be used to gzip/gunzip a set of files? If so, does anyone have an example? Sign In·View Thread·PermaLink Re: Gzip a set of files Shaun Wilde 9:35 7 Jul '08   Try downloading the latest source code there may be sample source code there. The API is quite rich and you could probably do what you want by chaining various classes together. I'll be more enthusiastic about encouraging thinking outside the box when there's evidence of any thinking going on inside it. - pTerry www.many-monkeys.com Sign In·View Thread·PermaLink Well I've added header but it doesn't work Noagene 22:36 15 Aug '07   If i add only header file, it compiles well. But if i add 'Gzip zipper(1);' code, compiler puts error message why does this happen? I'm using Crypto++ 5.2.1 library.. Sign In·View Thread·PermaLink Re: Well I've added header but it doesn't work Shaun Wilde 0:28 19 Aug '07   What error message would that be? I'll be more enthusiastic about encouraging thinking outside the box when there's evidence of any thinking going on inside it. - pTerry www.many-monkeys.com Sign In·View Thread·PermaLink Re: Well I've added header but it doesn't work Noagene 14:38 19 Aug '07   It says Gzip is a undeclared identifier.. Even though I included the header. Sign In·View Thread·PermaLink Error code has been changed.. Noagene 19:55 19 Aug '07   'CryptoPP::Gzip::Gzip(CryptoPP::BufferedTransformation *,unsigned int,unsigned int,bool)' : cannot convert argument 1 'int' to 'CryptoPP::BufferedTransformation *' So it says Gzip zipper(1) is wrong.. how should i change it?? thx for your help. Sign In·View Thread·PermaLink Re: Error code has been changed.. butuzov_Ilya 23:27 6 Sep '07   Try Gzip zipper(NULL,1); Sign In·View Thread·PermaLink 3.00/5 Close() is No Longer Available... Jeffrey Walton 16:21 27 May '07   Which breaks Get() code for some unknown reason (to me at this point). The work around seems to be to use Gunzip as Wei demonstrates in test.cpp: void GunzipFile(const char *in, const char *out) { FileSource(in, true, new Gunzip(new FileSink(out))); } However, this means at times a double buffer space is required - one for the string, and the one for a BYTE[] if used. Sign In·View Thread·PermaLink Re: Close() is No Longer Available... Shaun Wilde 11:04 28 May '07   I assume Close from the Crypto++ library is not longer available? Well libraries/frameworks change I suppose. I'll be more enthusiastic about encouraging thinking outside the box when there's evidence of any thinking going on inside it. - pTerry www.many-monkeys.com Sign In·View Thread·PermaLink 5.00/5 Re: Close() is No Longer Available... Jeffrey Walton 12:03 28 May '07   Hi Shaun, It's nice to see you monitor your articles. BTW, I cited you in one of my articles: Tamper Aware and Self Healing Code[^] Jeff Sign In·View Thread·PermaLink Re: Close() is No Longer Available... Shaun Wilde 20:55 29 May '07   Jeffrey Walton wrote: It's nice to see you monitor your articles I do try, but one is getting old and forgetful. I'll be more enthusiastic about encouraging thinking outside the box when there's evidence of any thinking going on inside it. - pTerry www.many-monkeys.com Sign In·View Thread·PermaLink Re: Close() is No Longer Available... Jeffrey Walton 12:08 28 May '07   Hi Shaun, I also forgot to mention that I saw you solution (after the post) in Close': is not a member of 'CryptoPP::Gzip[^]. I opted _not_ to maintain the past... Jeff Sign In·View Thread·PermaLink Re: Close() is No Longer Available... Shaun Wilde 20:56 29 May '07   I forgot I even posted a solution - even though if I actually looked at the rest of the messages it would have been apparent. Must check my glasses as well. I'll be more enthusiastic about encouraging thinking outside the box when there's evidence of any thinking going on inside it. - pTerry www.many-monkeys.com Sign In·View Thread·PermaLink 1.00/5 Crypto++ Integration Article Jeffrey Walton 19:28 8 Dec '06   Hi Shaun, I'm not trying to steal your thunder... http://www.codeproject.com/useritems/CryptoPPIntegration.asp[^] If you would be so kind as to add some of your hints, it would be very appreciated. Jeff Sign In·View Thread·PermaLink 2.00/5 Gzip work verry greatly! dungbkhn 18:50 28 Jun '05   Sign In·View Thread·PermaLink Got a wrong result! JerryCheng 23:44 11 Nov '03   In my thread, I have a Gzip instance. So, each time after I capture the desktop image, I use folowing code to compress the buffer just like the example: while(1) { ... //some code used to capture the desktop image zipper.Put((BYTE*)Buffer, Buflen) zipper.Close(); size = zipper.MaxRetrieveable(); //some other manipulate ... } BUT, when run the codes second time, I got a ZERO size ,that's to say ,the varible szie equal 0!!! Who can help me ??? Sign In·View Thread·PermaLink Re: Got a wrong result! Shaun Wilde 9:13 12 Nov '03   withou a full sample that exhibits the problem its hard to work out the problem. You might want to create a new zipper object in each loop so that it starts afresh each time. I don't use the crypto++ library at the mo as I am in a pure .NET environment. I am using VB on the current project www.many-monkeys.com Sign In·View Thread·PermaLink Re: Got a wrong result! JerryCheng 17:59 13 Nov '03   Yes, after I moved the codes in while loop to a function, it worked! But, there has a new problem. If I just only use the UNZIP instance to unzip a data buffer zipped by ZIP in another program, each time when I run unzipper.Close(); I got an exception said: Unhandle exception in **.zip(KERNAL32.DLL):0xE06D7363: Mirosoft C++ Exception. Why? Must I use ZIP and UNZIP together? Or I can't use UNZIP separetly? Thank you for your kind to answer my questions! Sign In·View Thread·PermaLink Re: Got a wrong result! Shaun Wilde 5:43 14 Nov '03   you should be able to - this is one for the crypto++ people. You could try stepping into the code and seeing where in the crypto++ code it fails exactly. I am using VB on the current project www.many-monkeys.com Sign In·View Thread·PermaLink encryption of file..help?? xxhimanshu 21:40 11 Nov '03   Hi, I have read many places and found that Crypto++ functions are very much compatible to php mcrypt library. I never knew how to use this in VC++ application. You have dobe such a wonderful work and its so easy to understand that i can compile and run your code easily. But i am having a small problem and hope that you can solve it out. I have to use the mcrypt library of php to encrypt a file at server and i have to decrypt the same file on client side using VC++. I am using Rijndael algorithm for encryption at server side through PHP. as the documentation says... mcrypt's MCRYPT_RIJNDAEL_128 is compatible with cryptopp-php's CRYPTOPP_CIPHER_AES/ CRYPTOPP_CIPHER_RIJNDAEL, which are just aliases for each other. and MCRYPT_MODE_CBC in mcrypt and CRYPTOPP_MODE_CBC in cryptopp-php. MCRYPT_MODE_ECB in mcrypt and CRYPTOPP_MODE_ECB in cryptopp-php. Can you tell me how to use crypto++ to do the same. or show me some piece of code to make it easy to understand..I need it urgently..Please help in doing the same. Any help or pointers are highly appreciated. Thanks a lot in advance.. Regards, Himanshu Sign In·View Thread·PermaLink Re: encryption of file..help?? Shaun Wilde 9:17 12 Nov '03   Your best bet is to post this to the crypto++ mailing list however as I remember there few samples in the library but the test harness they produce should give you pointers. I currently don't use crypto++, and I don't have the latest version onmy machine. I am using VB on the current project www.many-monkeys.com Sign In·View Thread·PermaLink zipping Anonymous 9:24 1 Jun '03   I want to know the algorithm of zipping the data and information. I want to bild up the application like winzip or winrar. Please tell me any logic for algorithm........ Sign In·View Thread·PermaLink

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