没有合适的资源?快使用搜索试试~ 我知道了~
首页商业应用推动:现代加密与认证简介
商业应用推动:现代加密与认证简介
5星 · 超过95%的资源 需积分: 10 6 下载量 71 浏览量
更新于2024-08-01
收藏 3.64MB PDF 举报
"本文是一篇关于隐私与认证的密码学综述文章,标题为《隐私与认证:密码学导论》(Privacy and Authentication: An Introduction to Cryptography),发表在1979年3月的《美国电气工程师学会会刊》上。作者针对当时背景下,随着电子通信的迅速普及,商业领域对信息安全需求的提升,对密码学进行了深入的介绍。 首先,文章阐述了密码学的基本信息理论和计算原理,包括古典加密技术如对称密钥系统(如DES)和非对称密钥系统(如RSA)的工作机制,以及它们在信息传输中的关键作用。读者可以从中了解加密算法的核心原理,如密钥管理和加密/解密过程。 接下来,作者对几个重要的现代加密系统进行了分析,探讨了它们的优缺点和在实际应用中的适用性。这可能包括公钥基础设施(PKI)、数字签名、哈希函数等,这些都是确保数据完整性和身份验证的基础。 然后,文章深入讨论了密码学在保护现代系统,如计算机网络和个人设备安全中的重要性。随着网络犯罪活动的增多,密码学在防范数据泄露、防止身份冒充以及实现远程访问控制等方面的作用日益凸显。 最后,作者为读者提供了一份宝贵的阅读指南,推荐了密码学领域的经典文献,以便进一步研究和学习。这可以帮助初学者和专业人士系统地探索密码学的深度,以及跟踪该领域最新的研究成果和发展趋势。 这篇文章不仅适合那些想要了解密码学基础的读者,也对那些寻求在商业环境中应用加密技术的企业和组织具有指导意义。随着数字化时代的到来,隐私和认证的保障成为了信息安全的核心议题,这篇文章因此具有很高的实用价值和历史意义。"
资源详情
资源推荐
402
PROCEEDINGS
OF
THE IEEE,
VOL.
67,
NO.
3,
MARCH
1979
ples representative
of
the variety
of
cryptographic systems
presently or formerly in use, or
of
those planned for
use
in the
future.
In
each case we will describe the operation of the
system, and where possible we
will
outline its cryptanalysis.
More thorough treatments
of
classical cryptanalysis can be
found elsewhere
[
201
-[
221.
A.
Substitution
The simplest encryption technique: simple substitution is
widely used
as
a puzzle. The key
is
a permuted alphabet (e.g.,
BWEKQFMWALUCONPHSIDXTRGZJ)
the letters of which
are substituted for those of the normal alphabet. Using this
alphabet: A is replaced by B, B
is
replaced by
W,
C is replaced
by E, etc. If word divisions are preserved, the plaintext
message
THE QUEEN HAS GIVEN BIRTH TO A HEALTHY SIX
POUND BOY.
is transformed into
DVQ HXQQO VBI MYTQO WYSDV DN B VQBUDVZ IYG
PNXOK WNZ.
As is well
known
to puzzle solvers, simple substitution ciphers
on short alphabets such as Roman or ASCII offer little pro-
tection
to
the underlying plaintext. Substitution cryptograms
can be solved by making frequency tables of letters, letter pairs
(digrams), and letter triples (trigrams). In these tables the high
frequencies
of
such letters as E and T, the low frequencies
of
Q and Z, and the frequent association of vowels with conso-
nants are conspicuous. These allow the identification
of
the
plaintext letterscorresponding to the letters in the cryptogram.
Similar results may be obtained by scanning the ciphertext for
evidence
of
pattern words considered likely to be
in
the plain-
text. Frequent words such as “EVERY,” “THAT,” and
“LOOK”
are conspicuous because of their repeated letters.
As the alphabet size
is
increased, these techniques become
more and more expensive to apply. If instead
of
ASCII with
its 128 7-bit characters, we had chosen the set
of
all 32-bit
words, the compilation
of
a frequency table would have re-
quired an unreasonable amount
of
effort. Unfortunately, the
compilation of such a cipher is also prohibitively expensive.
The permuted alphabet, like the frequency table, is 232 or
about four billion words in length. Substitution ciphers on
large “alphabets” do not, therefore, allow all possible permu-
tations, in order to limit the key to a more reasonable size.
The DES
of
Section
111-1
is
a good example.
B.
Transposition
In transposition, the positions
of
the plaintext letters in the
message rather than the letters
of
the alphabet are permuted.
As an example,
if
the above message
is
broken into five char-
acter groups (including spaces) and the letters in each group
rearranged according
to
the permutation
(i
z)
(i.e., the
third character
of
each group is written first, the first charac-
ter is written second, etc.) the cryptogram becomes
ETQ HEU NESHG AEI NVRBHTIO A TE LAHYTS H
IOPXDUB NXOXXY.
In the case of transpositions, frequency tables
of
letter pairs
and triples reveal the breakup
of
common letter pairs, such
as
the T and H
of
THE, allowing the plaintext to be reconstructed
by seeking permutations which rejoin them. In this way the
key used in transforming the plaintext, and thus the plaintext
itself, can be recovered from the cryptogram alone.
Substitution and transposition, although of little
use
by
themselves, are important components in more complex cipher
systems, some
of
which will be treated in detail later in this
section.
C. Polyalphabetic Ciphers
In an effort to defeat frequency analysis, cryptographers
developed substitution ciphers in which several different sub-
stitution alphabets were used periodically to encipher the
message. For example,
if
5
alphabets are used, letters num-
bered
5n
+i are enciphered in the ith alphabet (e.g., letters
numbered 1, 6, 11, 16,
. .
.
are enciphered in the first alphabet).
A frequency count, either on individual letters or letter pairs,
is now much flatter and provides few clues. This barrier
blocked a general solution
of
polyalphabetic ciphers for over
300
years 123, p. 2071, until the appearance in 1863 of a
book by a Prussian officer, Friedrich Kasiski.
Kasiski’s approach is to determine the period by first looking
for repeated groups
of
three or more ciphertext letters, which
usually occur due to a frequent plaintext trigram (which may
or may not be a word by itself) such as THE (4.5-percent
probability) or ING (1.2-percent probability), occurring twice
in the same phase. For example,
if
the plaintext message
“THEY ARE NOT THERE.” is enciphered using five alphabets,
the two occurrences
of
THE will result in identical ciphertext
since they are 10
=
2
X
5
characters apart. The cryptanalyst
then counts the number of characters between repeated groups.
The period
will
divide all these numbers, except for
a
few
that were not caused by repeated plaintext groups. Factoring
the numbers
of
characters between repeated groups, and
looking for a frequently repeated factor usually identifies
the period rather rapidly.
The assumed period
n
is checked by making a frequency
count on every nth ciphertext letter.
This
is
done for each
of
the
n
possible phases. If each
of
the
n
frequency counts thus
obtained has the highly nonuniform distribution characteristic
of a monoalphabetic substitution the assumed period is correct.
This
is because the periodic use
of
alphabets consists precisely
in enciphering every nth letter in the same alphabet.
Once the period has been determined, the problem can be
solved
as
a set of
n
different simple substitutions. Examples
are worked out in full detail in [23, pp. 209-2131 and [20,
ch. 31.
If a plaintext is enciphered with a periodic polyalphabetic
cipher, and the resulting cryptogram is superenciphered with a
second periodic polyalphabetic cipher with a different period,
the period
of
the resulting cipher will usually be much longer
than the period
of
either component. If the two periods,
81
and
Q2,
are relatively prime (have no common factor) then the
resu1tin.g period will be
111
X
122.
Cryptanalysis of such mul-
tiple loop Vigenere systems is more difficult, but can still be
accomplished
[
241.
D.
Running Key Cipher
In an effort to remove the weakness of periodic polyalpha-
betic ciphers, cryptographers turned to running key ciphers
which are aperiodic polyalphabetics. The key is typically the
name
of
a readily available book, together with a page, line,
and column number (e.g., Proceedings
of
the
IEEE,
October
1976, p. 1488, line
4,
column 19). To encipher the message
DIFFIE AND HELLMAN: AN INTRODUCTION TO CRYPTOGRAPHY
403
“THIS MATERIAL
IS
ENCIPHERED IN A RUNNING KEY.”
we write the message and the text
of
the book (“on a non-
interfering basis over the Defense Satellite
. .
.”)
one above the
other as shown below and add them mod-26, by regarding A
asO,Basl,*--,Zas25.
Plaintext:
THIS MATERIAL
IS
ENCIPHERED IN A RUNNING KEY.
Key
:
ONAN ONINTERF ER INGBASISOV ER T HEDEFEN SES.
Ciphertext:
HUIF ANBRKMRQ MJ MAIJPZMJSY ME T YYQRNRT CIQ.
Spaces are usually deleted from the ciphertext to hinder cryp-
tanalysis. Decryption is carried out by subtracting the key
from the ciphertext mod-26.
Although a Kasiski solution
is
no longer possible due to the
aperiodic selection of the 26 alphabets used (one for each
of
the 26 possible values of the running key), Bazeries [23, p.
2461 solved running key ciphers in the late 1890’s. Friedman
published a solution in 191
8
[
251 and added additional tech-
niques in
his
Military Cryptanalysis
[
221
.
There are two basic
approaches. The more powerful
of
the two depends on the
cryptanalyst knowing a probable
word,
one which probably
occurs in the plaintext.
In
military communications the words
BATTALION, COMPANY, ATTACK, etc., are probable.
In
a
message relating
to
bidding on
oil
leases, probable words are
OFFSHORE, COMPETITION, LEASES, etc. Lacking even
this, the cryptanalyst can use common words or groups
of
letters such
as
OFTHE, TION, WHICH, etc. If a number
of
probable words are tried, one
will
usually produce success.
To test for the existence of a probable word the cryptanalyst
subtracts it from the ciphertext, mod-26, in all possible loca-
tions. If the word is present, this process produces the key
when tried at the proper location. When tried at an incorrect
location (and all locations are incorrect
if
the probable word
is
not present), the cryptanalyst finds a random looking result.
Considering the ciphertext in our example, HUIFANB
.
.
.
TCIQ, the cryptanalyst might use CIPHER as a probable word
or partial word. Since the word ENCIPHERED did occur,
when the cryptanalyst subtracts CIPHER from IJPZMJ he
will
obtain GBASIS. The inclusion
of
the word BASIS is indicative
of
success, and the cryptanalyst then tries to extend either the
plaintext or the key in either direction (e.g., by trying
INGBASIS
to
get ENCIPHER). When CIPHER
is
subtracted
off
at the point just before the correct one (i.e., ciphertext
AIJPZM) the cryptanalyst finds the key would have to have
been YAUIVV, an impossibility.
Occasional false alarms will occur, especially with short
probable words, but these will be detected as analysis pro-
ceeds since they
will
not allow reasonable extensions. It
should be noted that our example is
too
short
to
allow an
easy solution and is being used solely for illustrative purposes.
The second approach
to
solving a running key cipher is
to
note that each ciphertext letter tends
to
represent certain
plaintext-key letter pairs.
In
our example, ciphertext
M
occurs
5
times, and each time results from the pair I-E or
E-I.
This
is rather unusual, but indicative
of
the approach.
Each ciphertext
M
can represent A-M, B-L, C-K, D-J, E-I,
F-H, G-G, N-Z, 0-Y, P-X, Q-W, R-V,
S-U,
T-T and the
reversals thereof (i.e., M-A, L-B, etc.). It
is
seen that E-I,
I-E, and T-T are the only pairs’ where both letters in the pair
are highly probable. Calculation shows that these three pairings
account for 64 percent
of
the occurrences
of
ciphertext
M.
At
the other extreme only
0.1
percent
of
the time that ciphertext
M
occurs does it stand for the pair
Q-W.
The ten lowest prob
ability pairs (Q-W, W-Q, Z-N, N-Z, K-C, C-K, J-D, D-J, X-P,
and P-X) account for only 2 percent
of
the occurrences of
ciphertext
M.
Therefore, while there are 26 possible pair substitutes for
each letter
of
the ciphertext, and 26” possible pairs of message
and key
to
try on an
n
letter cryptogram, most
of
these can
be
tentatively discarded without introducing
too
great an error
into the solution.
The cryptanalyst substitutes the several highest probability
pairs that correspond
to
each ciphertext letter and attempts
to find adjacent pairs which have a high digram probability.
He then tries extending this path to produce good trigrams,
etc.
The fact that running key ciphers can
be
solved is proof that
English is at least 50-percent redundant, since two
n
character
texts (the plaintext and the running key)
can
be recovered
from a single
n
character string (the cryptogram).
This
ob-
servation leads
to
an obvious, but little used method for
strengthening a running key cipher: use two or more successive
encipherments with different running keys. Since English is
about 75-percent redundant
[
131,
[
141, four encipherments
would be secure against
all
attacks. There cannot
be
a way for
the cryptanalyst
to
recover the plaintext since, by symmetry,
he could then also recover the four running keys, implying
that English
is
at least 80-percent redundant.
While techniques at least as clumsy as this were often used
(e.g., see Kahn’s description
of
a Russian spy cipher [23, pp.
669-6701), none
of
them offer its ironclad guarantee
of
security. It is therefore somewhat surprising that multiple
running key ciphers were not more widely used. Today,
they are
of
little value because
of
the availability
of
inexpensive,
more easily used electronic techniques.
In the limit as the number of running keys tends
to
infinity,
the mod-26 sum approaches a totally random character
se-
quence, which can be regarded
as
the key in a one time tape
system. It is now clear why the cryptanalyst
is
unable to learn
anything about plaintext which has been enciphered with a
one time tape. If he could learn even 1 percent
of
the plain-
text, he could learn (by symetry) 1 percent
of
each key, for an
infinite information gain from a finite message.
E.
Codes
Cryptographic techniques Like substitution and transposition
which operate on the plaintext without regard to
its
linguistic
structure are called ciphers and the cryptotext they produce
is
referred
to
as
ciphertext. A cryptographic system which oper-
ates on larger linguistic units of the plaintext, such as words or
phrases,
is
called a code. A code usually consists of a
list
of
words and phrases together with corresponding random groups
of
numbers or letters called codegroups. Since codegroups are
typically shorter than the expressions they represent, codes
offer the advantage
of
data compression
as
well
as
secrecy.
If used properly, codes are far more difficult
to
break than
other classical paper and pencil systems. There are three basic
reasons for their success. Probably the most important is the
large amount of key involved. A typical cipher system em-
ploys at most a few hundred bits of key. For example, the
key
to
a simple substitution cipher is a permuted alphabet,
representing fewer than 90 bits, while a good-sized code book
剩余31页未读,继续阅读
欧阳20180801
- 粉丝: 3
- 资源: 6
上传资源 快速赚钱
- 我的内容管理 展开
- 我的资源 快来上传第一个资源
- 我的收益 登录查看自己的收益
- 我的积分 登录查看自己的积分
- 我的C币 登录后查看C币余额
- 我的收藏
- 我的下载
- 下载帮助
最新资源
- JSP+SSM科研管理系统响应式网站设计案例
- 推荐一款超级好用的嵌入式串口调试工具
- PHP域名多维查询平台:高效精准的域名搜索工具
- Citypersons目标检测数据集:Yolo格式下载指南
- 掌握MySQL面试必备:程序员面试题解析集锦
- C++软件开发培训:核心技术资料深度解读
- SmartSoftHelp二维码工具:生成与解析条形码
- Android Spinner控件自定义字体大小的方法
- Ubuntu Server on Orangepi3 LTS 官方镜像发布
- CP2102 USB驱动程序的安装与更新指南
- ST-link固件升级指南:轻松更新程序步骤
- Java实现的质量管理系统Demo功能分析与操作
- Everything高效文件搜索工具:快速精确定位文件
- 基于B/S架构的酒店预订系统开发实践
- RF_Setting(E22-E90(SL)) V1.0中性版功能解析
- 高效转换M3U8到MP4:免费下载工具发布
资源上传下载、课程学习等过程中有任何疑问或建议,欢迎提出宝贵意见哦~我们会及时处理!
点击此处反馈
安全验证
文档复制为VIP权益,开通VIP直接复制
信息提交成功