The Risks Digest

The RISKS Digest

Forum on Risks to the Public in Computers and Related Systems

ACM Committee on Computers and Public Policy, Peter G. Neumann, moderator

Volume 15 Issue 48

Weds 9 February 1994


o Notes on key escrow meeting with NSA
Matt Blaze
o Re: Campaign and Petition Against Clipper
Dorothy Denning
o Information on RISKS
o Info on RISKS (comp.risks)

Notes on key escrow meeting with NSA

Matt Blaze <>
Tue, 08 Feb 94 16:03:55 -0500
(originally submitted last week, but lost somewhere in our news system)

A group from NSA and FBI met the other day with a group of us at Bell Labs to
discuss the key escrow proposal.  They were surprisingly forthcoming and open
to discussion and debate, and were willing to at least listen to hard
questions.  They didn't object when asked if we could summarize what we
learned to the net.  Incidentally, the people at the meeting seemed to base a
large part of their understanding of public opinion on Usenet postings.
Postings to RISKS, sci.crypt and talk.politics.crypto seem to actually have an
influence on our government.

Since the many of the points brought up at the meeting have been
discussed in RISKS, it seems appropriate to post a summary here.

A number of things came out at the meeting that we didn't previously know or
that clarified previously released information.  What follows is a rough
summary; needless to say, nothing here should be taken as gospel, or
representing the official positions of anybody.  Also, nothing here should be
taken as an endorsement of key escrow, clipper, or anything else by the
authors; we're just reporting.  These notes are based on the collective memory
of Steve Bellovin, Matt Blaze, Jack Lacy, and Mike Reiter; there may be errors
or misunderstandings.  Please forgive the rough style.  Note also the use of
"~ ~" for 'approximate quotes' (a marvelous Whit Diffie-ism).

NSA's stated goals and motives for all this:
    * DES is at the end of its useful life
    * Sensitive, unclassified government data needs protection
    * This should be made available to US Citizens
    * US business data abroad especially needs protection
    * The new technology should not preclude law enforcement access

They indicated that the thinking was not that criminals would use key escrowed
crypto, but that they should not field a system that criminals could easily
use against them.  The existence of key escrow would deter them from using
crypto in the first place.  The FBI representative said that they expect to
catch "~only the stupid criminals~" through the escrow system.

Another stated reason for key escrow is that they do not think that
even government-spec crypto devices can be kept physically secure.
They do expect enough to be diverted to the black market that they feel
they need a response.  NSA's emphasis was on the foreign black market...

There seems to be a desire to manipulate the market, by having the fixed cost
of key escrow cryptography amortized over the government market.  Any private
sector devices would have to sell a much larger number of units to compete on
price.  (This was somewhere between an implication and an explicit statement
on their part.)

When asked about cryptography in software, "~...if you want US government
cryptography, you must do it with hardware~".

The NSA people were asked whether they would consider evaluating ciphers
submitted by the private sector as opposed to simply proposing a new cipher as
a "black box" as they did with Skipjack.  They said they can't do this
because, among other things, of the extraordinary effort required to properly
test a new cipher.  They said that it often takes from 8-12 years to design,
evaluate and certify a new algorithm, and that Skipjack began development
"~about 10 years ago.~" I asked if we should infer anything from that about
the value of the (limited time and resource) civilian Skipjack review.  They
accepted the question with good humor, but they did say that the civilian
review was at least presented with and able to evaluate some of the results of
NSA's previous internal reviews.

Clipper chips should be available (to product vendors) in June.  You can't
just buy loose chips - they have to be installed in approved products.  Your
application interface has to be approved by NIST for you to get your hands on
the chips.

An interesting point came up about the reverse-engineering resistance of the
chips: they are designed to resist non-destructive reverse engineering.  It
was not clear (from the information presented at the meeting) whether the
chips are equally resistant to destructive reverse-engineering.  That is, the
chips are designed to resist non-destructive reverse engineering to obtain the
unit keys.  They do not believe that it is possible to obtain the unit key of
a particular chip without destroying the chip.  They did not present any
assertions about resistance to destructive reverse engineering, such that
several chips can be taken apart and destroyed in the process, to learn the
Skipjack algorithm. They said the algorithm was patented, but they may have
been joking.  ("~And if that doesn't scare you enough, we'll turn the patent
over to PKP.~")

The resistance to reverse engineering is not considered absolute by NSA.  They
do feel that "~it would require the resources of a national laboratory, and
anyone with that much money can design their own cryptosystem that's just as

They repeated several times that there are "~no plans to regulate the use of
alternate encryption within the US by US citizens.~" They also indicated they
"~weren't naive~" and didn't think that they could if they wanted to.

There were 919 authorized wiretaps, and 10,000 pen register monitors, in 1992.
They do not have any figures yet on how often cryptography was used to
frustrate wiretaps.

They do not yet have a production version of the "decoder" box used by law
enforcement.  Initially, the family key will be split (by the same XOR method)
and handled by two different people in the authorized agencies.  There is
presently only one family key.  The specifications of the escrow exploitation
mechanism are not yet final, either; they are considering the possibility of
having the central site strip off the outer layers of encryption, and only
sending the session key back to the decoder box.

The escrow authorities will NOT require presentation of a court order prior to
releasing the keys.  Instead, the agency will fill out a form certifying that
they have a legal authorization.  This is also backed up with a separate
confirmation from the prosecutor's office.  The escrow agencies will supply
any key requested and will not themselves verify that the keys requested are
associated with the particular court order.

As an aside, we've since been informed by a member of the civilian Skipjack
review committee that the rationale for not having the escrow agency see the
actual wiretap order is so that they do not have access to the mapping between
key serial numbers and people/telephones.

Regarding the scale of the escrow exploitation system, they said that they did
not yet have a final operational specification for the escrow protocols, but
did say that the escrow agencies would be expected to deliver keys "~within
about 2 hours~" and are aiming for "~close to real time.~" Initially, the FBI
would have the decoder box, but eventually, depending on costs and demand, any
law enforcement agency authorized to conduct wiretaps would be able to buy
one.  The two escrow agencies will be responsible for verifying the
certification from and securely delivering the key halves to any such police

The NSA did not answer a question as to whether the national security
community would obtain keys from the same escrow mechanism for their (legally
authorized) intelligence gathering or whether some other mechanism would exist
for them to get the keys.

The masks for the Clipper/Capstone chip are unclassified (but are protected by
trade secret) and the chips can be produced in an unclassified foundry.  Part
of the programming in the secure vault includes "~installing part of the
Skipjack algorithm.~" Later discussion indicated that the part of the
algorithm installed in the secure vault are the "S-tables", suggesting that
perhaps unprogrammed Clipper chips can be programmed to implement other 80-bit
key, 32 round ciphers.

The Capstone chip includes an ARM-6 RISC processor that can be used for other
things when no cryptographic functions are performed.  In particular, it can
be used by vendors as their own on-board processor.  The I/O to the processor
is shut off when a crypto operation is in progress.

They passed around a Tessera PCMCIA (type 1) card.  These cards contain a
Capstone chip and can be used by general purpose PC applications.  The cards
themselves might not be export controlled.  (Unfortunately, they took the
sample card back with them...)  The card will digitally sign a challenge from
the host, so you can't substitute a bogus card.  The cards have non-volatile
onboard storage for users' secret keys and for the public keys of a certifying

They are building a library/API for Tessera, called Catapult, that will
provide an interface suitable for many different applications.  They have
prototype email and ftp applications that already uses it.  They intend to
eventually give away source code for this library.  They responded favorably
to the suggestion that they put it up for anonymous ftp.

Applications (which can use the library and which the NSA approves for
government use) will be responsible for managing the LEAF field.  Note that
they intend to apply key escrowed Skipjack to other applications, including
mail and file encryption.  The LEAF would be included in such places as the
mail header or the file attributes.  This implies that it is possible to omit
sending the LEAF -- but the decrypt chip won't work right if it doesn't get

When asked, they indicated that it might be possible wire up a pair of
Clipper/Capstone chips to not transmit the LEAF field, but that the way to do
this is "~not obvious from the interface we give you~" and "~you'd have to be
careful not to make mistakes~".  They gave a lot of attention to obvious ways
to get around the LEAF.

The unit key is generated via Skipjack itself, from random seeds provided by
the two escrow agencies (approximately monthly, though that isn't certain
yet).  They say they prefer a software generation process because its correct
behavior is auditable.

Capstone (but not Clipper) could be configured to allow independent loading of
the two key halves, in separate facilities.  "~It's your money [meaning
American taxpayers].~"

The LEAF field contains 80 bits for the traffic key, encrypted via the unit
key in "~a unique mode <grin>~", 32 bits for the unit id, and a 16 bit
checksum of some sort.  (We didn't waste our breath asking what the checksum
algorithm was.)  This is all encrypted under the family key using "~another
mode <grin>~".

They expressed a great deal of willingness to make any sort of reasonable
changes that vendors needed for their products.  They are trying *very* hard
to get Skipjack and key escrow into lots of products.

Finally, I should make clear that "Clipper" is more properly called the

   [Matt, Thanks for the contribution, and thanks for making careful
   distinctions among the escrow initiative (EEI), the algorithm (Skipjack),
   the telephone implementation (Clipper), and the computer system/network
   implementation (Capstone).  Much of what has been written on the subject
   has been confused because those distinctions were not consistently made.

Re: Campaign and Petition Against Clipper

Dorothy Denning <>
Wed, 09 Feb 1994 17:23:28 -0500 (EST)
CPSR has announced a petition campaign to oppose the Clipper initiative.  I
would like to caution people about signing the petition.  The issues are
extremely complex and difficult.  The Clipper initiative is the result of
considerable deliberation by many intelligent people who appreciate and
understand the concerns that have been expressed and who worked hard to
accommodate the conflicting interests.  The decisions that have been made were
not made lightly.

I would like to respond to some of the statements that CPSR has made
about Clipper in their campaign and petition letters:

     The Clipper proposal, developed in secret by the National Security
     Agency, is a technical standard that will make it easier for
     government agents to wiretap the emerging data highway.

The standard (FIPS 185) is not a standard for the Internet or any other high
speed computer network.  It is for the telephone system.  Quoting from FIPS
185: "Data for purposes of this standard includes voice, facsimile and
computer information communicated in a telephone system.  A telephone system
for purposes of this standard is limited to a system which is circuit switched
and operating at data rates of standard commercial modems over analog voice
circuits or which uses basic-rate ISDN or a similar grade wireless service."

The standard will not make it any easier to tap phones, let alone
computer networks.  All it will do is make it technically possible to
decrypt communications that are encrypted with the standard, assuming
the communications are not superencrypted with something else.  Law
enforcers still need to get a court order just to intercept the
communications in the first place, and advances in technology have made
interception itself more difficult.  The standard will make it much
harder for anyone to conduct illegal taps, including the government.

The purpose of the standard is to provide a very strong encryption algorithm -
something much stronger than DES - and to do so in a way that does not thwart
law enforcement and national security objectives.  Keys are escrowed so that
if someone uses this technology, they cannot use it against national

     Industry groups, professional associations and civil liberties
     organizations have expressed almost unanimous opposition to the
     plan since it was first proposed in April 1993.

     "The public does not like Clipper and will not accept it ..."

     The private sector and the public have expressed nearly unanimous
     opposition to Clipper.

As near as I know, neither CPSR nor any other group has conducted any
systematic poll of industry, professional societies, or the public.  While
many people have voiced opposition, there are many more organizations and
people who have been silent on this issue.  The ACM is in the process of
conducting a study on encryption.  CPSR is a member of the study group, as am
I.  Steve Kent is chair.  Our goal is a report that will articulate the
issues, not a public statement either for or against.  The International
Association for Cryptologic Research has not to my knowledge made any official
statement about Clipper.

     The Administration ignored the overwhelming opposition of the
     general public. When the Commerce Department solicited public
     comments on the proposal last fall, hundreds of people opposed the
     plan while only a few expressed support.

Hundreds of people is hardly overwhelming in a population of 250 million,
especially when most of the letters were the same and came in through the net
following a sample letter that was sent out.

     The technical standard is subject to misuse and compromise. It
     would provide government agents with copies of the keys that
     protect electronic communications. "It is a nightmare for computer

I have been one of the reviewers of the standard.  We have completed our
review of the encryption algorithm, SKIPJACK, and concluded it was very
strong.  While we have not completed our review of the key escrow system, from
what I have seen so far, I anticipate that it will provide an extremely high
level of security for the escrowed keys.

     The underlying technology was developed in secret by the NSA, an
     intelligence agency responsible for electronic eavesdropping, not
     privacy protection. Congressional investigations in the 1970s
     disclosed widespread NSA abuses, including the illegal
     interception of millions of cables sent by American citizens.

NSA is also responsible for the development of cryptographic codes to protect
the nation's most sensitive classified information.  They have an excellent
track record in conducting this mission.  I do not believe that our
requirements for protecting private information are greater than those for
protecting classified information.  I do not know the facts of the 1970s
incident that is referred to here, but it sounds like it occurred before
passage of the 1978 Foreign Intelligence Surveillance Act.  This act requires
intelligence agencies to get a court order in order to intercept
communications of American citizens.  I am not aware of any recent evidence
that the NSA is engaging in illegal intercepts of Americans.

     Computer security experts question the integrity of the
     technology.  Clipper was developed in secret and its
     specifications are classified.

The 5 of us who reviewed the algorithm unanimously agreed that it was very
strong.  We will publish a final report when we complete or full evaluation.
Nothing can be concluded from a statement questioning the technology by
someone who has not seen it regardless of whether that person is an expert in

     NSA overstepped its legal authority in developing the standard.  A
     1987 law explicitly limits the intelligence agency's power to set
     standards for the nation's communications network.

The 1987 Computer Security Act states that NIST "shall draw on the technical
advice and assistance (including work products) of the National Security

     There is no evidence to support law enforcement's claims that new
     technologies are hampering criminal investigations. CPSR recently
     forced the release of FBI documents that show no such problems.

CPSR obtained some documents from a few FBI field offices.  Those offices
reported no problems.  CPSR did not get reports from all field offices and did
not get reports from local law enforcement agencies.  I can tell you that it
is a fact that new communications technologies, including encryption, have
hampered criminal investigations.  I personally commend law enforcement for
trying to get out in front of this problem.

     If the plan goes forward, commercial firms that hope to develop
     new products will face extensive government obstacles.
     Cryptographers who wish to develop new privacy enhancing
     technologies will be discouraged.

The standard is voluntary -- even for the government.

     Mr. Rotenberg said "We want the public to understand the full
     implications of this plan.  Today it is only a few experts and
     industry groups that understand the proposal.

I support this objective.  Unfortunately, it is not possible for most of us to
be fully informed of the national security implications of uncontrolled
encryption.  For very legitimate reasons, these cannot be fully discussed and
debated in a public forum.  It is even difficult to talk about the full
implications of encryption on law enforcement.  This is why it is important
that the President and Vice-President be fully informed on all the issues, and
for the decisions to be made at that level.  The Feb. 4 decision was made
following an inter-agency policy review, headed by the National Security
Council, that examined these issues using considerable input from industry,
CPSR, EFF, and individuals as well as from law enforcement and intelligence
agencies.  In the absence of understanding the national security issues, I
believe we need to exercise some caution in believing that we can understand
the full implications of encryption on society.

As part of the Feb. 4 announcement, the Administration announced the
establishment of an Interagency Working Group on Encryption and
Telecommunications, chaired by the White House Office of Science and
Technology Policy and National Security Council, with representatives from
Commerce, Justice, State, Treasury, FBI, NSA, OMB, and the National Economic
Council.  The group is to work with industry and public interest groups to
develop new encryption technologies and to review and refine encryption
policy.  The NRC's Computer Science and Telecommunications Board will also be
conducting a study of encryption policy.

These comments may be distributed.

Dorothy Denning, Georgetown University

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