Optimized Block Cipher Mode of Operation

As a based mode of operation,OFB has the character of stream cipher that it allows transmission units shorter than the block-cipher length to be encrypted.So it satisfies various data mode need.However,when the transmission unit is shorter than the block-cipher length,OFB is inefficient,since for every transmission unit,regardless how short,a call to the block cipher is needed.In this paper,in order to raise its efficiency,we introduce a shiftcount and a bumper and make all the outputs of block cipher be used.On the other hand,in order to enforce its security,we improve its feedback input mode and make it be provable security in the sense of strong secure notion of privacy.Finally we provide its security proof using the playing-game technique,the process of proof is natural and easy to understand.