>Hmmm. We must assume that generating the unit key U from the serial >number N rather than generating it from a randomly selected U1 and U2 >is an intentional way of assuring a "fail safe" for the government -- >U is completedly determined given S1, S2 and N. If S1 and S2 do not >change they constitute effective "master keys" (along with F), the >theft of which (or the possession of which by various authorities) >completely obviates the security of the system. However, more >interestingly, we know, for a fact that if S1 and S2 are fixed no >matter what the keyspace for U is no more than 2^30. Why not pick U1 >and U2 at random? Why this interesting restriction of they key space >if it NOT to provide an additional back door? > >I find it disturbing that at the very best my security is dependant on >approximately 30 bytes worth of information that could be written on >the back of a napkin. > >Even if S1 and S2 change periodically, the rationale behind this >restriction in the size of the keyspace seems strange if one is >assuming that the goal is security -- and makes perfect sense if the >goal is an illusion of security. > >If S1 and S2 do not change, even if they remain secret I wonder if >they can somehow be back-derived given enough unit key/serial number >pairs. We are assured that this cannot happen -- but no one >understands how Skipjack works outside of government officials and, >soon, foreign intelligence services that gain the information via >espionage. Presumably we will eventually have the information as well >-- reverse engineering gets more and more advanced every year -- but >by the time we know it may be too late.  Perhaps the trusted escrow agencies can be the ones who come up with S1 and S2, and if these agencies are really trusted (ACLU & NRA is an interesting example), we can hope that they'll use some physical process to come up with truly random numbers. If the NSA comes up with the numbers, that's a trap door you could drive a truck through.  >None of this makes me feel the least bit secure.  Me either.     It seems from the following that the CPSR is atleats starting to question this bogosity:      ---------------------------------------------------------------- April 16, 1993 Washington, DC                 COMPUTER PROFESSIONALS CALL FOR PUBLIC            DEBATE ON NEW GOVERNMENT ENCRYPTION INITIATIVE          Computer Professionals for Social Responsibility (CPSR) today called for the public disclosure of technical data underlying the government's newly-announced "Public Encryption Management" initiative.  The new cryptography scheme was announced today by the White House and the National Institute for Standards and Technology (NIST), which will implement the technical specifications of the plan.  A NIST spokesman acknowledged that the National Security Agency (NSA), the super- secret military intelligence agency, had actually developed the encryption technology around which the new initiative is built.          According to NIST, the technical specifications and the Presidential directive establishing the plan are classified.  To open the initiative to public review and debate, CPSR today filed a series of Freedom of Information Act (FOIA) requests with key agencies, including NSA, NIST, the National Security Council and the FBI for information relating to the encryption plan.  The CPSR requests are in keeping with the spirit of the Computer Security Act, which Congress passed in 1987 in order to open the development of non-military computer security standards to public scrutiny and to limit NSA's role in the creation of such standards.          CPSR previously has questioned the role of NSA in developing the so-called "digital signature standard" (DSS), a communications authentication technology that NIST proposed for government-wide use in 1991.  After CPSR sued NIST in a FOIA lawsuit last year, the civilian agency disclosed for the first time that NSA had, in fact, developed that security standard. NSA is due to file papers in federal court next week justifying the classification of records concerning its creation of the DSS.          David Sobel, CPSR Legal Counsel, called the administration's apparent commitment to the privacy of electronic communications, as reflected in today's official statement,  "a step in the right direction."  But he questioned the propriety of NSA's role in the process and the apparent secrecy that has thus far shielded the development process from public scrutiny.  "At a time when we are moving towards the development of a new information infrastructure, it is vital that standards designed to protect personal privacy be established openly and with full public participation.  It is not appropriate for NSA -- an agency with a long tradition of secrecy and opposition to effective civilian cryptography -- to play a leading role in the development process."          CPSR is a national public-interest alliance of computer industry professionals dedicated to examining the impact of technology on society.   CPSR has 21 chapters in the U.S. and maintains offices in Palo Alto, California, Cambridge, Massachusetts and Washington, DC.  For additional information on CPSR, call (415) 322-3778 or e-mail <cpsr@csli.stanford.edu>.