Computer World. Матросова Т.А. - 103 стр.

UptoLike

ВУЗ: 

УлГТУ | Ульяновск

Составители: 

Рубрика: 

102
dimensions, color spaces, pixel aspect ratios, etc.) and not be limited to classes
of imagery with restrictions on scene content, such as complexity, range of
c olors, or statistic al properties ;
3) have tractable computational complexity, to make feasible software
implementations with viable performance on a range of CPU's, as well as
hardware implementations with viable cost for applications requiring high
performance;
4) have the following modes of operation:
• Sequential encoding: each image component is encoded in a
single left-to-right, top-to-bottom scan;
• Progressive encoding: the image is encoded in multiple scans for
applications in which transmission time is long, and the viewer prefers to
w atch the image build up in mult ip le coars e-to-clear passes;
• Lossless encoding: the image is encoded to guarantee exact
recovery of every source image sample value (even though the result is
low compression compared to the lossy modes);
• Hierarchical encoding: the image is encoded at multiple
resolutions so that lower-resolution versions may be accessed without
first having to decompress the image at its full resolution.
TEXT 11
CRYPTOGRAPHY
Cryptography is the science and art of secret writing – keeping information
secret. When applied in a computing environment, cryptography can protect data
against unauthorized disclosure; it can authenticate the identity of а user or program
requesting service; and it can disclose unauthorized tampering.
Cryptanalysis is the related study of breaking ciphers. Cryptology is the
combined study of cryptography and cryptanalysis.
Cryptography is an indispensable part of modern computer security.
A Brief History of Cryptography
Knowledge of cryptography can be traced back to ancient times. It's not difficult
to understand why: as soon as three people had mastered the art of reading and
writing, there was the possibility that two of them would want to send letters to each
other that the third could not read.
In ancient Greece, the Spartan generals used a form of cryptography so that the
generals could exchange secret messages: the messages were written on narrow
ribbons of parchment that were wound spirally around a cylindrical staff called a
scytale. After the ribbon was unwound, the writing on it could only be read by a
person who had a matching cylinder of exactly the same size. This primitive system
did a reasonably good job of protecting messages from interception and from the
prying eyes of the message courier as well.

Страницы