Cryptography Reference
In-Depth Information
to statistical cryptanalysis. It can be cracked by a ciphertext attack with known
text structures on a computer within fractions of seconds.
Symmetric encryption
The common type of encryption, where one single secret key
is used for both encryption and decryption. These methods are secure when
used in combination with session keys. A problem is normally the key distri-
bution.
System V
A UNIX variant mainly used in the commercial area (examples include SCO
UNIX, UnixWare, and Irix). It was extensively unified with BSD from Release
V.4 and higher.
Topic analysis
A new type of interception method that classifies documents automati-
cally by their contents so that huge amounts of data can be searched in a targeted
way. This is mainly significant for national intelligence organizations, but it can
also be used within security concepts of commercial or industrial organizations
(secret information is automatically encrypted, and access privileges are regu-
lated by contents). The method is based, among others, on the
N-gram analysis
developed by the NSA.
Traffic analysis
A type of analysis that logs parameters of a message, such as sender,
receiver, time and date, length, etc., rather than its contents (because it is encrypted,
for example). Someone can collect huge amounts of such data and yield an aston-
ishing amount of insightful information.
Transposition
A special permutation, namely the transposition of two elements (each
permutation can be represented as a sequence of a finite number of transpositions).
In cryptology, a
transposition cipher
is an encryption method that permutes
fixed-length blocks.
Trigram
See 'polygraphic substitution'.
Triple-DES
A variant of DES that does triple encryption, but uses only two DES keys:
ciphertext = DES
key
_
1
(DES
−
1
key
_
2
(DES
key
_
1
(plaintext)))
This method is intended to solve the problem with the DES key length that had
been found to be too short, while ensuring optimal hardware compatibility (see
Section 5.2.1).
Trojan cryptography
A term used by the author of this topic for implementations of
cryptographic software or hardware that allow the vendor to unsurveillably listen
in on encrypted messages.
