19.4.1. **Comments**
- Release Note: I regret that I haven't had time to add many
new entries here. There are a lot of specialized terms, and
I probably could have doubled the number of entries here.
- Much more work is needed here. In fact, I debated at one
point making the FAQ instead into a kind of "Encycopedia
Cypherpunkia," with a mix of short and long articles on
each of hundreds of topics. Such an organization would
suffer the disadvantages found in nearly all
lexicographically-organized works: confusion of the
concepts.
- Many of the these entries were compiled for a long handout
at the first Cypherpunks meeting, September, 1992. Errors
are obviously present. I'll try to keep correcting them
when I can.
- Schneier's "Applied Cryptography" is of course an excellent
place to browse for terms, special uses, etc.
19.4.2. agoric systems -- open, free market systems in which
voluntary transactions are central.
19.4.3. Alice and Bob -- crypographic protocols are often made
clearer by considering parties A and B, or Alice and Bob,
performing some protocol. Eve the eavesdropper, Paul the
prover, and Vic the verifier are other common stand-in names.
19.4.4. ANDOS -- all or nothing disclosure of secrets.
19.4.5. anonymous credential -- a credential which asserts some right
or privelege or fact without revealing the identity of the
holder. This is unlike CA driver's licenses.
19.4.6. assymmetric cipher -- same as public key cryptosystem.
19.4.7. authentication -- the process of verifying an identity or
credential, to ensure you are who you said you were.
19.4.8. biometric security -- a type of authentication using
fingerprints, retinal scans, palm prints, or other
physical/biological signatures of an individual.
19.4.9. bit commitment -- e.g., tossing a coin and then committing to
the value without being able to change the outcome. The blob
is a cryptographic primitive for this.
19.4.10. BlackNet -- an experimental scheme devised by T. May to
underscore the nature of anonymous information markets. "Any
and all" secrets can be offered for sale via anonymous
mailers and message pools. The experiment was leaked via
remailer to the Cypherpunks list (not by May) and thence to
several dozen Usenet groups by Detweiler. The authorities are
said to be investigating it.
19.4.11. blinding, blinded signatures -- A signature that the signer
does not remember having made. A blind signature is always a
cooperative protocol and the receiver of the signature
provides the signer with the blinding information.
19.4.12. blob -- the crypto equivalent of a locked box. A
cryptographic primitive for bit commitment, with the
properties that a blobs can represent a 0 or a 1, that others
cannot tell be looking whether it's a 0 or a 1, that the
creator of the blob can "open" the blob to reveal the
contents, and that no blob can be both a 1 and a 0. An
example of this is a flipped coin covered by a hand.
19.4.13. BnD --
19.4.14. Capstone --
19.4.15. channel -- the path over which messages are transmitted.
Channels may be secure or insecure, and may have
eavesdroppers (or enemies, or disrupters, etc.) who alter
messages, insert and delete messages, etc. Cryptography is
the means by which communications over insecure channels are
protected.
19.4.16. chosen plaintext attack -- an attack where the cryptanalyst
gets to choose the plaintext to be enciphered, e.g., when
possession of an enciphering machine or algorithm is in the
possession of the cryptanalyst.
19.4.17. cipher -- a secret form of writing, using substitution or
transposition of characters or symbols. (From Arabic "sifr,"
meaning "nothing.")
19.4.18. ciphertext -- the plaintext after it has been encrypted.
19.4.19. Clipper -- the infamous Clipper chip
19.4.20. code -- a restricted cryptosystem where words or letters of a
message are replaced by other words chosen from a codebook.
Not part of modern cryptology, but still useful.
19.4.21. coin flippping -- an important crypto primitive, or protocol,
in which the equivalent of flipping a fair coin is possible.
Implemented with blobs.
19.4.22. collusion -- wherein several participants cooperate to deduce
the identity of a sender or receiver, or to break a cipher.
Most cryptosystems are sensitive to some forms of collusion.
Much of the work on implementing DC Nets, for example,
involves ensuring that colluders cannot isolate message
senders and thereby trace origins and destinations of mail.
19.4.23. COMINT --
19.4.24. computationally secure -- where a cipher cannot be broken
with available computer resources, but in theory can be
broken with enough computer resources. Contrast with
unconditionally secure.
19.4.25. countermeasure -- something you do to thwart an attacker
19.4.26. credential -- facts or assertions about some entity. For
example, credit ratings, passports, reputations, tax status,
insurance records, etc. Under the current system, these
credentials are increasingly being cross-linked. Blind
signatures may be used to create anonymous credentials.
19.4.27. credential clearinghouse -- banks, credit agencies,
insurance companies, police departments, etc., that correlate
records and decide the status of records.
19.4.28. cryptanalysis -- methods for attacking and breaking ciphers
and related cryptographic systems. Ciphers may be broken,
traffic may be analyzed, and passwords may be cracked.
Computers are of course essential.
19.4.29. crypto anarchy -- the economic and political system after the
deployment of encryption, untraceable e-mail, digital
pseudonyms, cryptographic voting, and digital cash. A pun on
"crypto," meaning "hidden," and as when Gore Vidal called
William F. Buckley a "crypto fascist."
19.4.30. cryptography -- another name for cryptology.
19.4.31. cryptology -- the science and study of writing, sending,
receiving, and deciphering secret messages. Includes
authentication, digital signatures, the hiding of messages
(steganography), cryptanalysis, and several other fields.
19.4.32. cyberspace -- the electronic domain, the Nets, and computer-
generated spaces. Some say it is the "consensual reality"
described in "Neuromancer." Others say it is the phone
system. Others have work to do.
19.4.33. DC protocol, or DC-Net -- the dining cryptographers protocol.
DC-Nets use multiple participants communicating with the DC
protocol.
19.4.34. DES -- the Data Encryption Standard, proposed in 1977 by the
National Bureau of Standards (now NIST), with assistance from
the National Security Agency. Based on the "Lucifer" cipher
developed by Horst Feistel at IBM, DES is a secret key
cryptosystem that cycles 64-bit blocks of data through
multiple permutations with a 56-bit key controlling the
routing. "Diffusion" and "confusion" are combined to form a
cipher that has not yet been cryptanalyzed (see "DES,
Security of"). DES is in use for interbank transfers, as a
cipher inside of several RSA-based systems, and is available
for PCs.
19.4.35. DES, Security of -- many have speculated that the NSA placed
a trapdoor (or backdoor) in DES to allow it to read DES-
encrypted messages. This has not been proved. It is known
that the original Lucifer algorithm used a 128-bit key and
that this key length was shortened to 64 bits (56 bits plus 8
parity bits), ths making exhaustive search much easier (so
far as is known, brute-force search has not been done, though
it should be feasible today). Shamir and Bihan have used a
technique called "differential cryptanalysis" to reduce the
exhaustive search needed for chosen plaintext attacks (but
with no import for ordinary DES).
19.4.36. differential cryptanalysis -- the Shamir-Biham technique for
cryptanalyzing DES. With a chosen plaintext attack, they've
reduced the number of DES keys that must be tried from about
2^56 to about 2^47 or less. Note, however, that rarely can an
attacker mount a chosen plaintext attack on DES systems.
19.4.37. digital cash, digital money -- Protocols for transferring
value, monetary or otherwise, electronically. Digital cash
usually refers to systems that are anonymous. Digital money
systems can be used to implement any quantity that is
conserved, such as points, mass, dollars, etc. There are
many variations of digital money systems, ranging from VISA
numbers to blinded signed digital coins. A topic too large
for a single glossary entry.
19.4.38. digital pseudonym -- basically, a "crypto identity." A way
for individuals to set up accounts with various organizations
without revealing more information than they wish. Users may
have several digital pseudonyms, some used only once, some
used over the course of many years. Ideally, the pseudonyms
can be linked only at the will of the holder. In the simplest
form, a public key can serve as a digital pseudonym and need
not be linked to a physical identity.
19.4.39. digital signature -- Analogous to a written signature on a
document. A modification to a message that only the signer
can make but that everyone can recognize. Can be used
legally to contract at a distance.
19.4.40. digital timestamping -- one function of a digital notary
public, in which some message (a song, screenplay, lab
notebook, contract, etc.) is stamped with a time that cannot
(easily) be forged.
19.4.41. dining cryptographers protocol (aka DC protocol, DC nets) --
the untraceable message sending system invented by David
Chaum. Named after the "dining philosophers" problem in
computer science, participants form circuits and pass
messages in such a way that the origin cannot be deduced,
barring collusion. At the simplest level, two participants
share a key between them. One of them sends some actual
message by bitwise exclusive-ORing the message with the key,
while the other one just sends the key itself. The actual
message from this pair of participants is obtained by XORing
the two outputs. However, since nobody but the pair knows the
original key, the actual message cannot be traced to either
one of the participants.
19.4.42. discrete logarithm problem -- given integers a, n, and x,
find some integer m such that a^m mod n = x, if m exists.
Modular exponentiation, the a^m mod n part, is
straightforward (and special purpose chips are available),
but the inverse problem is believed to be very hard, in
general. Thus it is conjectured that modular exponentiation
is a one-way function.
19.4.43. DSS, Digital Signature Standard -- the latest NIST (National
Institute of Standards and Technology, successor to NBS)
standard for digital signatures. Based on the El Gamal
cipher, some consider it weak and poor substitute for RSA-
based signature schemes.
19.4.44. eavesdropping, or passive wiretapping -- intercepting
messages without detection. Radio waves may be intercepted,
phone lines may be tapped, and computers may have RF
emissions detected. Even fiber optic lines can be tapped.
19.4.45. Escrowed Encryption Standard (EES) -- current name for the
key escrow system known variously as Clipper, Capstone,
Skipjack, etc.
19.4.46. factoring -- Some large numbers are difficult to factor. It
is conjectured that there are no feasible--i.e."easy," less
than exponential in size of number-- factoring methods. It is
also an open problem whether RSA may be broken more easily
than by factoring the modulus (e.g., the public key might
reveal information which simplifies the problem).
Interestingly, though factoring is believed to be "hard", it
is not known to be in the class of NP-hard problems.
Professor Janek invented a factoring device, but he is
believed to be fictional.
19.4.47. HUMINT --
19.4.48. information-theoretic security -- "unbreakable" security, in
which no amount of cryptanalysis can break a cipher or
system. One time pads are an example (providing the pads are
not lost nor stolen nor used more than once, of course). Same
as unconditionally secure.
19.4.49. key -- a piece of information needed to encipher or decipher
a message. Keys may be stolen, bought, lost, etc., just as
with physical keys.
19.4.50. key exchange, or key distribution -- the process of sharing a
key with some other party, in the case of symmetric ciphers,
or of distributing a public key in an asymmetric cipher. A
major issue is that the keys be exchanged reliably and
without compromise. Diffie and Hellman devised one such
scheme, based on the discrete logarithm problem.
19.4.51. known-plaintext attack -- a cryptanalysis of a cipher where
plaintext-ciphertext pairs are known. This attack searches
for an unknown key. Contrast with the chosen plaintext
attack, where the cryptanalyst can also choose the plaintext
to be enciphered.
19.4.52. listening posts -- the NSA and other intelligence agencies
maintain sites for the interception of radio, telephone, and
satellite communications. And so on. Many sites have been
identified (cf. Bamford), and many more sites are suspected.
19.4.53. mail, untraceable -- a system for sending and receiving mail
without traceability or observability. Receiving mail
anonymously can be done with broadcast of the mail in
encrypted form. Only the intended recipient (whose identity,
or true name, may be unknown to the sender) may able to
decipher the message. Sending mail anonymously apparently
requires mixes or use of the dining cryptographers (DC)
protocol.
19.4.54. Message Pool
19.4.55. minimum disclosure proofs -- another name for zero knowledge
proofs, favored by Chaum.
19.4.56. mixes -- David Chaum's term for a box which performs the
function of mixing, or decorrelating, incoming and outgoing
electronic mail messages. The box also strips off the outer
envelope (i.e., decrypts with its private key) and remails
the message to the address on the inner envelope. Tamper-
resistant modules may be used to prevent cheating and forced
disclosure of the mapping between incoming and outgoing mail.
A sequence of many remailings effectively makes tracing
sending and receiving impossible. Contrast this with the
software version, the DC protocol. The "remailers" developed
by Cypherpunks are an approximation of a Chaumian mix.
19.4.57. modular exponentiation -- raising an integer to the power of
another integer, modulo some integer. For integers a, n, and
m, a^m mod n. For example, 5^3 mod 100 = 25. Modular
exponentiation can be done fairly quickly with a sequence of
bit shifts and adds, and special purpose chips have been
designed. See also discrete logarithm.
19.4.58. National Security Agency (NSA) -- the largest intelligence
agency, responsible for making and breaking ciphers, for
intercepting communications, and for ensuring the security of
U.S. computers. Headquartered in Fort Meade, Maryland, with
many listening posts around the world. The NSA funds
cryptographic research and advises other agencies about
cryptographic matters. The NSA once obviously had the world's
leading cryptologists, but this may no longer be the case.
19.4.59. negative credential -- a credential that you possess that you
don't want any one else to know, for example, a bankruptcy
filing. A formal version of a negative reputation.
19.4.60. NP-complete -- a large class of difficult problems. "NP"
stands for nondeterministic polynomial time, a class of
problems thought in general not to have feasible algorithms
for their solution. A problem is "complete" if any other
NP problem may be reduced to that problem. Many important
combinatorial and algebraic problems are NP-complete: the
travelling salesman problem, the Hamiltonian cycle problem,
the graph isomorphism problem, the word problem, and on and
on.
19.4.61. oblivious transfer -- a cryptographic primitive that involves
the probablistic transmission of bits. The sender does not
know if the bits were received.
19.4.62. one-time pad -- a string of randomly-selected bits or symbols
which is combined with a plaintext message to produce the
ciphertext. This combination may be shifting letters some
amount, bitwise exclusive-ORed, etc.). The recipient, who
also has a copy of the one time pad, can easily recover the
plaintext. Provided the pad is only used once and then
destroyed, and is not available to an eavesdropper, the
system is perfectly secure, i.e., it is information-
theoretically secure. Key distribution (the pad) is
obviously a practical concern, but consider CD-ROM's.
19.4.63. one-way function -- a function which is easy to compute in
one direction but hard to find any inverse for, e.g. modular
exponentiation, where the inverse problem is known as the
discrete logarithm problem. Compare the special case of trap
door one-way functions. An example of a one-way operation
is multiplication: it is easy to multiply two prime numbers
of 100 digits to produce a 200-digit number, but hard to
factor that 200-digit number.
19.4.64. P ?=? NP -- Certainly the most important unsolved problem
in complexity theory. If P = NP, then cryptography as we know
it today does not exist. If P = NP, all NP problems are
"easy."
19.4.65. padding -- sending extra messages to confuse eavesdroppers
and to defeat traffic analysis. Also adding random bits to
a message to be enciphered.
19.4.66. PGP
19.4.67. plaintext -- also called cleartext, the text that is to be
enciphered.
19.4.68. Pool
19.4.69. Pretty Good Privacy (PGP) -- Phillip Zimmerman's
implementation of RSA, recently upgraded to version 2.0, with
more robust components and several new features. RSA Data
Security has threatened PZ so he no longer works on it.
Version 2.0 was written by a consortium of non-U.S. hackers.
19.4.70. prime numbers -- integers with no factors other than
themselves and 1. The number of primes is unbounded. About
1% of the 100 decimal digit numbers are prime. Since there
are about 10^70 particles in the universe, there are about
10^23 100 digit primes for each and every particle in the
universe!
19.4.71. probabalistic encryption -- a scheme by Goldwasser, Micali,
and Blum that allows multiple ciphertexts for the same
plaintext, i.e., any given plaintext may have many
ciphertexts if the ciphering is repeated. This protects
against certain types of known ciphertext attacks on RSA.
19.4.72. proofs of identity -- proving who you are, either your true
name, or your digital identity. Generally, possession of the
right key is sufficient proof (guard your key!). Some work
has been done on "is-a-person" credentialling agencies, using
the so-called Fiat-Shamir protocol...think of this as a way
to issue unforgeable digital passports. Physical proof of
identity may be done with biometric security methods. Zero
knowledge proofs of identity reveal nothing beyond the fact
that the identity is as claimed. This has obvious uses for
computer access, passwords, etc.
19.4.73. protocol -- a formal procedure for solving some problem.
Modern cryptology is mostly about the study of protocols for
many problems, such as coin-flipping, bit commitment (blobs),
zero knowledge proofs, dining cryptographers, and so on.
19.4.74. public key -- the key distributed publicly to potential
message-senders. It may be published in a phonebook-like
directory or otherwise sent. A major concern is the validity
of this public key to guard against spoofing or
impersonation.
19.4.75. public key cryptosystem -- the modern breakthrough in
cryptology, designed by Diffie and Hellman, with
contributions from several others. Uses trap door one-way
functions so that encryption may be done by anyone with
access to the "public key" but decryption may be done only by
the holder of the "private key." Encompasses public key
encryption, digital signatures, digital cash, and many other
protocols and applications.
19.4.76. public key encryption -- the use of modern cryptologic
methods to provided message security and authentication. The
RSA algorithm is the most widely used form of public key
encryption, although other systems exist. A public key may be
freely published, e.g., in phonebook-like directories, while
the corresponding private key is closely guarded.
19.4.77. public key patents -- M.I.T. and Stanford, due to the work
of Rivest, Shamir, Adleman, Diffie, Hellman, and Merkle,
formed Public Key Partners to license the various public key,
digital signature, and RSA patents. These patents, granted in
the early 1980s, expire in the between 1998 and 2002. PKP has
licensed RSA Data Security Inc., of Redwood City, CA, which
handles the sales, etc.
19.4.78. quantum cryptography -- a system based on quantum-mechanical
principles. Eavesdroppers alter the quantum state of the
system and so are detected. Developed by Brassard and
Bennett, only small laboratory demonstrations have been made.
19.4.79. remailers -- software versions of Chaum's "mixes," for the
sending of untraceable mail. Various features are needed to
do this: randomized order of resending, encryption at each
stage (picked in advance by the sender, knowing the chain of
remailers), padding of message sizes. The first remailer was
written by E. Hughes in perl, and about a dozen or so are
active now, with varying feature sets.
19.4.80. reputations -- the trail of positive and negative
associations and judgments that some entity accrues. Credit
ratings, academic credentials, and trustworthiness are all
examples. A digital pseudonym will accrue these reputation
credentials based on actions, opinions of others, etc. In
crypto anarchy, reputations and agoric systems will be of
paramount importance. There are many fascinating issues of
how reputation-based systems work, how credentials can be
bought and sold, and so forth.
19.4.81. RSA -- the main public key encryption algorithm, developed by
Ron Rivest, Adi Shamir, and Kenneth Adleman. It exploits the
difficulty of factoring large numbers to create a private key
and public key. First invented in 1978, it remains the core
of modern public key systems. It is usually much slower than
DES, but special-purpose modular exponentiation chips will
likely speed it up. A popular scheme for speed is to use RSA
to transmit session keys and then a high-speed cipher like
DES for the actual message text.
- Description -- Let p and q be large primes, typically with
more than 100 digits. Let n = pq and find some e such that
e is relatively prime to (p - 1)(q - 1). The set of numbers
p, q, and e is the private key for RSA. The set of numbers
n and e forms the public key (recall that knowing n is not
sufficient to easily find p and q...the factoring problem).
A message M is encrypted by computing M^e mod n. The owner
of the private key can decrypt the encrypted message by
exploiting number theory results, as follows. An integer d
is computed such that ed =1 (mod (p - 1)(q - 1)). Euler
proved a theorem that M^(ed) = M mod n and so M^(ed) mod n
= M. This means that in some sense the integers e and d are
"inverses" of each other. [If this is unclear, please see
one of the many texts and articles on public key
encryption.]
19.4.82. secret key cryptosystem -- A system which uses the same key
to encrypt and decrypt traffic at each end of a communication
link. Also called a symmetric or one-key system. Contrast
with public key cryptosystem.
19.4.83. SIGINT --
19.4.84. smart cards -- a computer chip embedded in credit card. They
can hold cash, credentials, cryptographic keys, etc. Usually
these are built with some degree of tamper-resistance. Smart
cards may perform part of a crypto transaction, or all of it.
Performing part of it may mean checking the computations of a
more powerful computer, e.g., one in an ATM.
19.4.85. spoofing, or masquerading -- posing as another user. Used for
stealing passwords, modifying files, and stealing cash.
Digital signatures and other authentication methods are
useful to prevent this. Public keys must be validated and
protected to ensure that others don't subsititute their own
public keys which users may then unwittingly use.
19.4.86. steganography -- a part of cryptology dealing with hiding
messages and obscuring who is sending and receiving messages.
Message traffic is often padded to reduce the signals that
would otherwise come from a sudden beginning of messages.
"Covered writing."
19.4.87. symmetric cipher -- same as private key cryptosystem.
19.4.88. tamper-responding modules, tamper-resistant modules (TRMs) --
sealed boxes or modules which are hard to open, requiring
extensive probing and usually leaving ample evidence that the
tampering has occurred. Various protective techniques are
used, such as special metal or oxide layers on chips, armored
coatings, embedded optical fibers, and other measures to
thwart analysis. Popularly called "tamper-proof boxes." Uses
include: smart cards, nuclear weapon initiators,
cryptographic key holders, ATMs, etc.
19.4.89. tampering, or active wiretapping -- intefering with messages
and possibly modifying them. This may compromise data
security, help to break ciphers, etc. See also spoofing.
19.4.90. Tessera
19.4.91. token -- some representation, such as ID cards, subway
tokens, money, etc., that indicates possession of some
property or value.
19.4.92. traffic analysis -- determining who is sending or receiving
messages by analyzing packets, frequency of packets, etc. A
part of steganography. Usually handled with traffic padding.
19.4.93. traffic analysis -- identifying characteristics of a message
(such as sender, or destination) by watching traffic.
Remailers and encryption help to foil traffic analysys.
19.4.94. transmission rules -- the protocols for determining who can
send messages in a DC protocol, and when. These rules are
needed to prevent collision and deliberate jamming of the
channels.
19.4.95. trap messages -- dummy messages in DC Nets which are used to
catch jammers and disrupters. The messages contain no private
information and are published in a blob beforehand so that
the trap message can later be opened to reveal the disrupter.
(There are many strategies to explore here.)
19.4.96. trap-door -- In cryptography, a piece of secret information
that allows the holder of a private key to invert a normally
hard to invert function.
19.4.97. trap-door one way functions -- functions which are easy to
compute in both the forward and reverse direction but for
which the disclosure of an algorithm to compute the function
in the forward direction does not provide information on how
to compute the function in the reverse direction. More simply
put, trap-door one way functions are one way for all but the
holder of the secret information. The RSA algorithm is the
best-known example of such a function.
19.4.98. unconditional security -- same as information-theoretic
security, that is, unbreakable except by loss or theft of the
key.
19.4.99. unconditionally secure -- where no amount of intercepted
ciphertext is enough to allow the cipher to be broken, as
with the use of a one-time pad cipher. Contrast with
computationally secure.
19.4.100. URLs
19.4.101. voting, cryptographic -- Various schemes have been devised
for anonymous, untraceable voting. Voting schemes should have
several properties: privacy of the vote, security of the vote
(no multiple votes), robustness against disruption by jammers
or disrupters, verifiability (voter has confidence in the
results), and efficiency.
19.4.102. Whistleblowers
19.4.103. zero knowledge proofs -- proofs in which no knowledge of the
actual proof is conveyed. Peggy the Prover demonstrates to
Sid the Skeptic that she is indeed in possession of some
piece of knowledge without actually revealing any of that
knowledge. This is useful for access to computers, because
eavesdroppers or dishonest sysops cannot steal the knowledge
given. Also called minimum disclosure proofs. Useful for
proving possession of some property, or credential, such as
age or voting status, without revealing personal information.
By Tim May, see README
HTML by Jonathan Rochkind