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Topic: Ciphertext


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RC5

In the News (Thu 25 Apr 19)

  
  Ciphertext-only attack - Wikipedia, the free encyclopedia
For example, if an adversary is sending ciphertext continuously to maintain traffic-flow security, it would be very useful to be able to distinguish real messages from nulls.
In the history of cryptography, early ciphers, implemented using pen-and-paper, were routinely broken using ciphertexts alone.
A cipher whose key space is too small is subject to brute force attack with access to nothing but ciphertext by simply trying all possible keys.
en.wikipedia.org /wiki/Ciphertext-only_attack   (461 words)

  
 CSA: Glossary   (Site not responding. Last check: 2007-11-06)
For these puzzles, the ciphertext to plaintext mapping is such that no ciphertext letter may stand for itself in plaintext.
In the case of a simple substution cipher, ciphertext is made from a clear message (the plaintext) by translating, using a key, the letters of the words one letter at a time.
In the case of a simple substution cipher, plaintext is made from ciphertext by translating, using a deciphering key, the letters of the words one letter at a time.
home.hiwaay.net /~kdunn/problems/csa_help/csah_glo.html   (437 words)

  
 ciphertext feedback - a Whatis.com definition   (Site not responding. Last check: 2007-11-06)
Ciphertext feedback (CFB) is a mode of operation for a block cipher.
In CFB mode, the previous ciphertext block is encrypted and the output is XORed (see XOR) with the current plaintext block to create the current ciphertext block.
Chaining dependencies are similar to CBC, in that reordering ciphertext block sequences alters decryption output, as decryption of one block depends on the decryption of the preceding blocks.
whatis.techtarget.com /gDefinition/0,294236,sid14_gci344946,00.html   (281 words)

  
 CEN 4500C   (Site not responding. Last check: 2007-11-06)
If a forged ciphertext block is inserted between c(n) and c(n+1), a forged message will be generated at (n+1)-th message position and m(n+1) will be garbled.
Because the last ciphertext block of CTR is computed independently to the previous blocks, it will not be affected by precedent plaintext or ciphertext blocks.
In other words, the last ciphertext block does not change even if an intermediate plaintext or ciphertext is modified, because there is no chain in encrypting each block to get the next one.
www.cise.ufl.edu /~sgchen/cen5540fall2004/homework1sol.htm   (956 words)

  
 [No title]   (Site not responding. Last check: 2007-11-06)
Formally, it is a 5-tuple (E, D, M, K, C), where M is the set of plaintext messages, C is the set of ciphertext messages, K is a set of keys, and E: MxK -> C (enciphering functions) and D: CxK -> M (deciphering functions) Example: Caesar cipher.
Substitution cipher: A map from characters in the plaintext to the ciphertext.
Ciphertext = plaintext XOR key Plaintext = key XOR ciphertext It turns out that as long as key is truly random, ciphertext is also random -- no frequency analysis possible.
www.eecs.umich.edu /~aprakash/eecs498/handouts/02-crypto-background.txt   (668 words)

  
 Doctoral Dissertation : Dr.Kanokwan   (Site not responding. Last check: 2007-11-06)
A very good method to provide computer and network security is encryption.Most of the cryptosystems are revealing in the sense that thay give ciphertext which distinctively reveals the fact that it has been encrypted and, thus, invite attention from the potential attackers.
The 29 encryption algorithms are named KSC1 to KSC29 for ease of identification and to honor the KSC group of companies which allowed the author to work on her dissertation while working for the companies.
In KSC23 to KSC28,the ciphertext is in the form of English sentences or passages or paragraphs.
www.phd.au.edu /dissertation/dissertation_kanokwan.html   (649 words)

  
 Figure 2: Assymmetric or Public Key Encryption
Decrypting the ciphertext with your public key proves that the ciphertext had to come from you.
Sue uses your public key to encrypt the plaintext to produce a ciphertext for you.
You use your private key to decrypt the ciphertext to reproduce the plaintext.
www.uic.edu /depts/adn/infwww/html/acccnews/adn26/figure2.html   (137 words)

  
 Why Are One-Time Pads Perfectly Secure?   (Site not responding. Last check: 2007-11-06)
As with all symmetric ciphers, the sender must transmit the key to the recipient via some secure and tamperproof channel, otherwise the recipient won't be able to decrypt the ciphertext.
The key for a one-time pad cipher is a string of random bits, usually generated by a cryptographically strong pseudo-random number generator (CSPRNG).
The results of the brute force search of the keyspace is that your staff finds one 8-bit key that decrypts the ciphertext to 'S' and one that decrypts it to 'A'.
world.std.com /~franl/crypto/one-time-pad.html   (494 words)

  
 Securing Threshold Cryptosystems against Chosen Ciphertext Attack - Shoup, Gennaro (ResearchIndex)   (Site not responding. Last check: 2007-11-06)
Abstract: For the most compelling applications of threshold cryptosystems, security against chosen ciphertext attack seems to be a requirement.
However, there appear to be no practical threshold cryptosystems in the literature that are provably chosen-ciphertext secure, even in the idealized random hash function model.
The contribution of this paper is to present two very practical threshold cryptosystems, and to prove that they are secure against chosen ciphertext attack in the random hash function...
citeseer.ist.psu.edu /64084.html   (642 words)

  
 What is a known ciphertext attack?
A known ciphertext attack is an an attack where the cryptanalyst only has access to encrypted ciphertext.
A known ciphertext attack is the easiest of the common cryptanalysis attacks to mount, because is requires the least amount of control over the encryption device.
Conversely, the known ciphertext is the most difficult of the common methods of cryptanalysis to execute successfully, because so little knowledge is known to begin with.
www.tech-faq.com /known-ciphertext-attack.shtml   (148 words)

  
 perl.com: Symmetric Cryptography in Perl
The first ciphertext block is decrypted and XORed with the IV to form the first plaintext block, and each ciphertext block thereafter is XORed with the previous one to form a plaintext block.
Other modes are similar in intent, but vary in detail, including the way errors in transmission affect the ciphertext, and the amount of feedback or dependency on previous blocks.
The effectiveness of this approach depends on the size of the key: the longer it is, the more possible keys there are, and the more guesses will be required, on average, to find the right one.
www.perl.com /pub/a/2001/07/10/crypto.html?page=2   (894 words)

  
 Perl.com: Symmetric Cryptography in Perl
The plaintext to be encrypted must be split into fixed-length blocks (usually 64 or 128 bits long) and fed to the cipher one at a time.
The resulting blocks (of the same length) are concatenated to form the ciphertext.
Because of the highly repetitive nature of most texts, plaintext blocks and their corresponding blocks in the ciphertext tend to be repeated quite often.
www.perl.com /lpt/a/2001/07/10/crypto.html   (1787 words)

  
 [No title]
PLAINTEXT-START and PLAINTEXT-END serve to delineate the extent of the data to be encrypted and CIPHERTEXT-START indicates at what position the encrypted data should be placed.
PLAINTEXT and CIPHERTEXT may be the same vector.") (defgeneric decrypt (contex ciphertext plaintext &key (ciphertext-start 0) ciphertext-end (plaintext-start 0)) (:documentation "Decrypt data located in CIPHERTEXT according to CONTEXT.
CIPHERTEXT-START and CIPHERTEXT-END serve to delineate the exten of the data to be encrypted and PLAINTEXT-START indicates at what position the encrypted data should be placed.
www.cs.rice.edu /~froydnj/lisp/crypt-proposal.lisp   (853 words)

  
 ciphertext - a Whatis.com definition   (Site not responding. Last check: 2007-11-06)
plaintext is what you have before encryption, and ciphertext is the encrypted result.
The term cipher is sometimes used as a synonym for ciphertext, but it more properly means the method of encryption rather than the result.
Eduscapes' "Codes, Ciphers & Secret Messages" includes links to a number of sites where you can practice encrypting or decrypting ciphertext.
whatis.techtarget.com /definition/0,,sid9_gci213853,00.html   (120 words)

  
 TDEScipher/ActiveX Example - Convert Ciphertext to Hex Format
For example the "null" character (andH00 will occur once in every 256 bytes of encrypted data on average) is used as a string terminator in some applications.
Applications where binary or non-printable string characters cause problems include transmission of ciphertext via e-mail, and storage or processing of ciphertext in text fields in some databases.
This example VB project illustrates how to convert ciphertext data into hexadecimal string format.
www.bokler.com /source_code/vb_hexciphertext.html   (547 words)

  
 Equivalence Between Semantic Security and Indistinguishability Against Chosen Ciphertext Attacks - Watanabe, Shikata, ...   (Site not responding. Last check: 2007-11-06)
Abstract: The aim of this work is to examine the relation between the notions of semantic security and indistinguishability against chosen ciphertext attacks.
For this purpose, a new security notion called non-dividability is introduced independent of attack models, and is shown to be equivalent to both of the two notions.
Watanabe, J. Shikata and H. Imai, Equivalence between semantic security and indistinguishability against chosen ciphertext attacks, In Proceedings of International Workshop on Practice and Theory in Public Key Cryptosystems { PKC 2003, Lecture Notes in Computer Science Vol.
citeseer.ist.psu.edu /watanabe02equivalence.html   (418 words)

  
 Package: pgp   (Site not responding. Last check: 2007-11-06)
Decrypt a block of data using PGP and PGPdaemon.
ciphertext_length : The length of the input ciphertext data.
Returns: A pointer to the ciphertext data on success, else NULL.
www.atnf.csiro.au /computing/software/karma/lib/pgp.html   (156 words)

  
 What are plaintext and ciphertext?
Decryption is the process of turning ciphertext into plaintext.
A cryptanalyst in possession of a piece of plaintext and the resulting ciphertext can attempt to mount a known plaintext attack.
A cryptanalyst in who possesses only the ciphertext can attempt the more difficult known ciphertext attack.
www.tech-faq.com /plaintext-ciphertext.shtml   (150 words)

  
 [No title]   (Site not responding. Last check: 2007-11-06)
The character in the corresponding cell is the ciphertext character Repeat for the second plaintext character, and second key letter, and so on.
Then a retired Prussian cavalry officer named Kasiski noticed that repetitions occur in the ciphertext when characters of the key appear over the same characters in the ciphertext.
Each letter of the plaintext alphabet was allocated a number of 2-letter ciphertext translations; the number was roughly proportional to the frequency of occurrence of the letter in typical plaintext.
www.rivier.edu /faculty/bhiggs/web/cs572aweb/Slides/Cryptology.ppt   (1289 words)

  
 [No title]   (Site not responding. Last check: 2007-11-06)
A cipher is breakable if is possible to determine systematically the key (or the plaintext) from pairs plaintext, ciphertext given.
It is very difficult to estimate the amount of effort required to cryptanalize ciphertext successfully.
That is, no matter how much computational power an opponent has, it is impossible for him or her to decrypt the cyphertext, simply because the required information is not there.
euclid.barry.edu /~zuniga/courses/cs477/chapter2-1.ppt   (1176 words)

  
 [No title]   (Site not responding. Last check: 2007-11-06)
Example:Keyword: Carrots The letters for Carrots are, in order of appearance, c a r o t s Thus the columnar table using the keyword, carrots, is: CAROTSBDEFGHIJKLMNPQUVWXYZCiphertext Table We now write the ciphertext column by column under the plaintext (regular alphabet).
Your Coding Work: Use this table to write out your keyword and ciphertext.
Show your work here: Your Ciphertext, step 2: Write this on a slip of paper for your decoding partner Your Decoding Partner’s Ciphertext & Your Decoding Work: Your Decoding Partner’s Secret Message:     PAGE 4 Topic 6.3, page  PAGE 1 Keyword letters in order of appearance.
www.wou.edu /~burtonl/courses/math392/6.3.doc   (647 words)

  
 [No title]   (Site not responding. Last check: 2007-11-06)
What will happen if two ciphertext blocks are swapped?
c(n) also gets decrypted, and then XORed with c(n-1) to produce m(n) What will happen if two ciphertext blocks are swapped?
If two ciphertext blocks are neighboring and swapped, then three message blocks will be garbled.
www.cise.ufl.edu /~sgchen/cen5540fall2004/homework1sol.doc   (577 words)

  
 CIPHERTEXT-ONLY CRYPTANALYSIS OF ENIGMA
The Germans were right to mandate short Enigma messages, since the uneven distribution of plaintext was not fully concealed by the plugboards -- at least for the number of plugs normally in use.
In messages using fewer plugs, less ciphertext is needed for a solution.
Conversely, messages using more plugs require more text; only one very long message using 13 plugs has been solved by this method, and that probably by chance.
www.fortunecity.com /skyscraper/coding/379/gillog1.htm   (2196 words)

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