Mouse-2 wrote:
>
>
>
>
> #include <iostream>
>
> #include <cryptopp/aes.h>
> #include <cryptopp/modes.h>
> #include <cryptopp/sha.h>
> #include <cryptopp/osrng.h>
> #include <cryptopp/files.h>
> #include <cryptopp/filters.h>
>
> USING_NAMESPACE(CryptoPP);
> USING_NAMESPACE(std);
>
> /**************************************************************/
> /* Code to illustrate usage of cryptographic primitives */
> /* provided by Crypto++ library v5.5.1 of Wei Dai. */
> /* */
> /* In particular, the program provides two functions: */
> /* */
> /* 1. Encrypt a file (key based on password) with random IV;*/
> /* */
> /* 2. Decrypt previously encrypted file. */
> /* */
> /* Issue with the original code: */
> /* - set IV in the encryptor but also used it as random */
> /* prefix, so garbage was the 1st encrypted block; */
> /* - did not "fast-forward" the encrypted file past the */
> /* first block (which was encrypted random garbage). */
> /* */
> /* Corrections performed: */
> /* - fixed encryptor by leaving random block prefixed, */
> /* but removing redundancy (having it in encryptor); */
> /* - fixed decryptor (see the source code). */
> /* */
> /*==========================================================*/
> /* Written by: */
> /* Rash <[email protected]> */
> /* */
> /* Modified by: */
> /* Mouse <[email protected]> */
> /* Sun Sep 2, 12:25:00 2007 */
> /* */
> /************************************************************/
> /* */
> /* Copyright (C) 2007 Rash <[email protected]> */
> /* Copyright (C) 2007 Mouse <[email protected]> */
> /* */
> /************************************************************/
>
> void encryptFile(const char* password, const char* inputFileName,
> const char* outputFileName)
> {
> byte pass[AES::BLOCKSIZE]; // digest of password
> byte iv[16]; // Initial Vector (IV), misused
> // by original author
> byte true_iv[16]; // real IV used - set to zero
>
> AutoSeededRandomPool rng;
>
> // digest password
> StringSource(password, true,
> new HashFilter(*(new SHA256),
> new ArraySink(pass, AES::BLOCKSIZE)));
>
> // random Initial Vector
> rng.GenerateBlock(iv, 16);
> memset(true_iv, 0, 16);
>
> // create object for encrypting
> AES::Encryption aesEncryption(pass,
> CryptoPP::AES::DEFAULT_KEYLENGTH);
> CBC_Mode_ExternalCipher::Encryption cbcEncryption(aesEncryption,
> true_iv);
>
> StreamTransformationFilter *encryptor;
> encryptor = new StreamTransformationFilter(cbcEncryption,
> new FileSink(outputFileName) );
>
> encryptor->Put(iv, 16); // this prefixes the file with random block (not
> IV)
> // Cryptographically it is equivalent to IV, so just as
> good
>
> // "bind" a file and encrypt one
> FileSource(inputFileName, true, encryptor);
> }
>
>
> void decryptFile(const char* password, const char*inputFileName,
> const char* outputFileName)
> {
> byte pass[AES::BLOCKSIZE];
> byte iv[16]; // here's 1st problem: AES IV is 16 bytes
> byte head_file[16]; // so must skip 16 bytes, not 8.
>
> memset(iv, 0, 16); // very correct - in fact the encryptor prefixes file
> // with a random block, so no need to pass the IV explicitly.
>
> try {
> StringSource(password, true, new HashFilter(*(new SHA256), new
>
> ArraySink(pass,AES::BLOCKSIZE)));
>
> CryptoPP::AES::Decryption aesDecryption(pass,
> CryptoPP::AES::DEFAULT_KEYLENGTH);
> CryptoPP::CBC_Mode_ExternalCipher::Decryption
> cbcDecryption(aesDecryption, iv);
>
> StreamTransformationFilter *decryptor;
> decryptor = new
> StreamTransformationFilter(cbcDecryption, new
> FileSink(outputFileName));
>
>
> // decryptor->Get(head_file, 16); // does not do anything useful,
> wrong here
> // We must somehow decrypt 1st block of the input file, without
> sending the
> // result into the output file.
> char garbage[16], iv_garbage[16]; // place for IV stuff
> ifstream inf;
> inf.open(inputFileName); inf.read(iv_garbage, 16); // absorb random
> prefix
>
> // Decrypt random prefix (with zero IV) to some dummy buffer to get
> // (a) decryptor state adjusted to IV, and
> // (b) file position pointer advanced to the past-IV spot.
> cbcDecryption.ProcessData((byte *)garbage, (const byte *)iv_garbage,
> 16);
>
> // NOW can run the decryption engine in "automatic" mode
> FileSource(inf, true, decryptor);
>
> inf.close(); // to be nice
> }
> catch(CryptoPP::Exception &e)
> {
> cerr << "Caught exception during decryption!" << endl;
> return;
> }
> }
>
> int main(int argc, char *argv[])
> {
> const char *pwd = "not-so-complicated parole";
> const char *pfn = "plain.txt";
> const char *cfn = "cipher.dat";
> const char *ofn = "plain2.txt";
>
> // Create test plaintext file "plain.txt"
> ofstream plain;
> plain.open(pfn);
> plain << "An excellent test of file encryption techniques.\n";
> plain << "This test will not demonstrate many tricks though.\n";
> plain.close();
>
> // Invoke encryptor to encrypt into "cipher.dat"
> encryptFile(pwd, pfn, cfn);
>
> // Invoke decryptor to decrypt into "plain2.txt"
> decryptFile(pwd, cfn, ofn);
>
> exit(0);
> }
>
>
your code is working on text but when i used a binary file like an image it
failed
please help
what changes should i make
please reply
thanks in advance
--
View this message in context:
http://old.nabble.com/Decrypt-file-using-AES%3A%3ACBC-tp12446523p29674413.html
Sent from the Crypto++ Users mailing list archive at Nabble.com.
--
You received this message because you are subscribed to the "Crypto++ Users"
Google Group.
To unsubscribe, send an email to [email protected].
More information about Crypto++ and this group is available at
http://www.cryptopp.com.
