summary how sensible is des towards bit errors hi i d like to thank you all for the fast responses special thanks go to those who replied lexical order marcus j ranum mjr tis com paul crowley pdc dcs ed ac uk pausch saaf se paul schlyter tarnold vnet ibm com todd w arnold wcs anchor ho att com bill stewart my question was how sensible is des encrypted data towards bit errors how much data per bit will be lost in average i assume you still have the correct key how much of the des encrypted data is affected depends on the used encryption mode according to marcus j ranum mjr tis com there is cfb cipher feedback mode ecb electronic code book mode cbc cipher block chaining mode ofb output feedback mode each mode does some stuff better than others ofb and cfb are designed for communications streams more than for files unfortunally people strongly disagree which mode will lead to destruction of all of the following data sure seems that some modes will resync quite fast others will never others will even only effect the very block summarized people said concerning this matter in cbc mode only the current block will be affected tarnold vnet ibm com todd w arnold if you use cbc cihper block chaining then the remainder of the data will be destroyed as well pausch saaf se paul schlyter in cfb mode des synchronizes quite fast probably within block according to maracus j ranum mjr tis com maybe someone definitely knows what happens in which mode nevertheless thank you all very much again axel dunkel i include the responses i got from tarnold vnet ibm com todd w arnold in ad cat axel dunkel writes how sensible is des encrypted data towards bit errors how much data per bit will be lost in average i assume you still have the correct key it depends on the mode you re using for a single bit input block a one bit error will have a percent chance of corrupting each of the output bits in other words it essentially turns the output block into a random number if you re encrypting data in cbc mode however only the one bit block will be affected the next block and all that follow it will be decrypted properly it s a good idea to have some kind of error correction in your system if corrupted bits are likely todd from pausch saaf se paul schlyter in article ad cat you write hello how sensible is des encrypted data towards bit errors how much data per bit will be lost in average i assume you still have the correct key at least bytes of data will be destroyed if one bit encrypted data is in error if you use cbc cihper block chaining then the remainder of the data will be destroyed as well des is very seisitive for single bit errors this is as it should be paul schlyter swedish amateur astronomer s society saaf nybrogatan a tr s stockholm sweden internet pausch saaf se from paul crowley pdc dcs ed ac uk how sensible is des encrypted data towards bit errors how much data per bit will be lost in average i assume you still have the correct key probably very bad you might lose the rest of the data stream if you want safety against dropped bits use an error correcting coder like the freeware gnu ecc o paul crowley pdc dcs ed ac uk trust me i know what i m doing x fold a fish for jesus from wcs anchor ho att com how sensible is des encrypted data towards bit errors how much data per bit will be lost in average i assume you still have the correct key it depends on the mode you re using des in electronic code book ecb takes a block of input bits and produces output bits so if any bits are changed the entire block of bits becomes bad i forget which feedback mode is which in all of them the results of encrypting one block affect later blocks with some modes the system self synchronizes so errors are repaired in a few blocks with other modes once one block is bad all later blocks will be bad too there s also the framing problem if you have a bit change the block that it s in changes and maybe later blocks also change but if you have bits lost or bits added bits in or bits out everything is confused after that from marcus j ranum mjr tis com depends on the mode you re using cfb for example synchronises pretty fast figure a bit error will destroy the current block and the next one mjr experience is what you get if you don t get what you want systemberatung axel dunkel koenigsberger strasse d kriftel germany e mail ad cat de voice fax
