re more technical details in article apr ulysses att com smb research att com steven bellovin writes here are some corrections and additions to hellman s note courtesy of dorothy denning again this is reposted with permission two requests first note the roles of s and s it appears to me and others that anyone who knows those values can construct the unit key and the nature of the generation process for k and k is such that neither can be produced alone thus the scheme cannot be implemented such that one repository generates the first half key and another generates the second that is ominous second these postings are not revealed scripture nor are they carefully crafted spook postings don t attempt to draw out hidden meanings as opposed to say the official announcements of clipper leave denning out of this given hellman s record of opposition to des which goes back before some folks on this newsgroup knew how to read i don t think you can impugn his integrity oh yeah the folks who invented clipper aren t stupid if you think something doesn t make sense it s almost certainly because you don t understand their goals this is an addition posted with permission to some tech details of cliper they enligthen the use of s and s for keygeneration date mon apr edt from denning cs cosc georgetown edu dorothy denning subject re clipper chip i just had another conversation with nsa to clarify some of the features of clipper please feel free to distribute this and my other messages on clipper the name of the encryption algorithm is skipjack martin hellman had written and the serial number of the unit added to produce a three part message which will then be encrypted under the system key sk producing e e m k e k uk serial number sk to which i responded my understanding is that e m k is not encrypted under sk called the family key and that the decrypt key corresponding to sk is held by law enforcement does anyone have first hand knowledge on this i was correct in that e m k is not encrypted under sk however skipjack being a single key system there is of course not a separate decrypt key for the family key sk the unit key also called the chip key is generated from the serial number n as follows let n n and n be bit blocks derived from n and let s and s be two bit seeds used as keys compute the bit block r e d e n s s s note that this is like using the des in triple encryption mode with two keys similarly compute blocks r and r starting with n and n i m unlear about whether the keys s and s change the fact that they re called seeds suggests they might then r r and r are concatenated together giving bits the first bits form k and the next bits form k the remaining bits are discarded the seeds s and s do not change the whole process is performed on a laptop computer and s and s are supplied by two independent people so that no one person knows both the same s and s are used during an entire programming session to generate keys for a stream of serial numbers everything is discarded at the end the computer could be thrown out if desired the serial number is bits and the values n n and n are formed by padding the serial number with fixed bit blocks separate padding for each value the resulting keys k and k are output onto separate floppy disks paired up with their serial number each pair is stored in a separate file the floppy disks are taken away by two separate people on behalf of the two escrow agencies dorothy denning denning cs georgetown edu i am sure more technical detail will be known when time goes by please remark that in posting this i do not automatically agree with it s contents and implications so don t swamp my mailbox i just think this is an valuable addition to the less than technical discussion that is rising here and no i don t mind if you call s and s backdoor as i could imagine the key generation process working without these seeds and the dependency of k k from the serial number friendly greetings germano caronni instruments register only through things they re designed to register space still contains infinite unknowns pgp key id germano caronni caronni nessie cs id ethz ch fd ccf f da ea c dd f
