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#ifndef BU_MODE_OFB_H
#define BU_MODE_OFB_H
#include "bu/filter.h"
#include "bu/string.h"
namespace Bu
{
/**
* Output Feedback Mode. This cipher mode is one of the most resiliant.
* Instead of encrypting your data directly it encrypts a "key stream" using
* the initialization vector, and then XORs those blocks with your stream
* blocks. This means that an error in your stream will still produce an
* error in the output, but it will not propegate. Also, with most
* encryption schemes error correction codes on the source data will still
* work on the encrypted data or decrypted output.
*/
template<int iBlockSize, typename CipherType>
class CipherModeOfb : public CipherType
{
public:
CipherModeOfb(class Stream &rNext ) :
CipherType( rNext ),
bStart( true )
{
memset( aVector, 0, iBlockSize );
}
virtual ~CipherModeOfb()
{
}
void setIv( const Bu::String &sIv )
{
memcpy( aVector, sIv.getStr(), iBlockSize );
}
protected:
void decipher( void *pBuf )
{
CipherType::encipher( aVector );
uint8_t aTmp[iBlockSize];
memcpy( aTmp, aVector, iBlockSize );
for( int j = 0; j < iBlockSize; j++ )
((uint8_t *)pBuf)[j] ^= aVector[j];
memcpy( aVector, aTmp, iBlockSize );
}
void encipher( void *pBuf )
{
CipherType::encipher( aVector );
uint8_t aTmp[iBlockSize];
memcpy( aTmp, aVector, iBlockSize );
for( int j = 0; j < iBlockSize; j++ )
((uint8_t *)pBuf)[j] ^= aVector[j];
memcpy( aVector, aTmp, iBlockSize );
}
private:
bool bStart;
uint8_t aVector[iBlockSize];
};
};
#endif
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