Which is the process of breaking the cipher text to obtain the original message?

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With a chosen ciphertext attack, the attacker has access to ciphertext he or she knows about. This information is supplemented with publicly available information and other knowledge he or she has about the message to find the corresponding plaintext.

With adaptive chosen ciphertext, which is similar to chosen ciphertext, the attacker has access to several chosen ciphertexts.

These attack methods provide the basis for most of the other cryptanalysis attacks such as linear and differential cryptanalysis.

Understanding that cryptography, like any other security system, is susceptible to attack, helps in designing, implementing, and maintaining better cryptographic systems.

Ciphertext Relative Length Analysis

Sometimes the ciphertext can provide you with clues to the cleartext even if you don't know how the ciphertext was encrypted. For example, suppose that you have an unknown algorithm that encrypts passwords such that you have available the original password and a ciphertext version of that password. If the length or size of each is the same, then you can infer that the algorithm produces output in a 1:1 ratio to the input. You may even be able to input individual characters to obtain the ciphertext translation for each character. If nothing else, you at least know how many characters to specify for an unknown password if you attempt to break it using a brute force method.

If you know that the length of a message in ciphertext is identical to the length of a message in cleartext, you can leverage this information to pick out pieces of the ciphertext for which you can make guesses about the cleartext. For example, during WWII while the Allies were trying to break the German Enigma codes, they used a method similar to the above because they knew the phrase “Heil Hitler” probably appeared somewhere near the end of each transmission.

Network Design and Components

Cipher text and secret keys are transported over the network and can be harvested for analysis; furthermore they can impersonate a source or, worst case, cause a service denial. Thus, to aid encryption and complex distribution methods, a network needs to be secure and elegant. That is, the network should have applicable appliances that monitor and detect attacks, intelligence that discriminates between degradations/failures and attacks, and also a convention for vigorous countermeasure strategies to outmaneuver the attacker. Consequently, network security is a completely separate topic from data security; however, the devices chosen must complement your infrastructure.

The accumulation of advances in key technologies has enabled companies to envision the implementation of an infrastructure with no limitations. Among these advances are those in materials that underlie electronic components and optical technologies, including optical fibers. Improvements in electronic integrated circuits include both the speed at which these circuits can perform their functions and the achievable complexity that allows a single chip to perform complex tasks. Advances in signal processing techniques that use electronic circuits and software to convert information and information-carrying signals into forms suitable for transport over short or long distances arrange for data to be stored, processed, and transmitted lightning fast. Such advantages have even allowed engineers and scientists to work harder and think further out to develop new technologies to follow suit on hardware and software transformations. Significant progress is required to realize and appreciate the vision of affordable media.

New algorithms and approaches complement the speed of transport networks, coupled with complex connection and session establishment and management. Total network approaches are required to resolve effective management of a cutting-edge infrastructure solution. Large costs are associated with installation and building out of fiber networks needed to provide an objective, robust network. Networks must be scalable and support multiple types of media, including coax, fiber, copper, and wireless, using both the shared media and switched approaches. Premise access must support the multiplexing of video, voice, and data sources requiring varied quality-of-service (QoS) levels and various bandwidths.

Several backbone options and avenues are available, due mostly to the era of electronic trading. These can be comprehensively separated into time division techniques and wavelength division techniques. Determining the potential of each technology would significantly contribute to a company’s success, depending completely on the type of business involved. The time domain limits are determined by the speed of the electro-optic transducers, of the required buffer and memory, and of the switching and control logic required to manage the system. Additionally, high-speed regeneration technologies play a pivotal role in delivering benefits of time-division techniques to the system. Take long distances into consideration: Fiber properties such as loss and dispersion in the fiber limit the capabilities of the fiber span. Optical amplification, attenuators, and dispersion compensator devices can restore impairments induced by the fiber properties and allow the media to match the heat and light of the equipment chosen. Wavelength converters, wavelength filters, and wavelength division multipliers enable use of a greater capacity of the fiber. Optical regeneration techniques permit clock recovery and lead to full regeneration capabilities in the optical domain, avoiding unnecessary optical to electrical conversions.

Pocket Calculator Decryption at the Server

Thus far, the client has used the proper N and E from the server to encrypt “O” (15) as cipher-text 9. This is what is sent on the network. The magic of PKI is being able to get back “O” without using E, only N and D. (Because N is known to and used by both parties, it is never called a key itself.) In this example, N = 33, E = 3, and D = 7. The following is how to get back “P” using only N = 33 and D = 7 at the server end.

1.

Write down the cipher-text value (9) D times and multiply. If the number gets too large for the calculator, we can apply N to get back a more useable number.

9 3 9 3 9 3 9 3 9 3 9 3 9 5 (531,441) 3 9

If we don't want to risk overflowing the calculator, we can apply N at any time as follows:

531,441/33 = 16,104.272 (subtract 16,104) and 0.272 × 33 = 8.976 = 9

(Again, rounding is needed to deal with the annoying decimal fractions that calculators insist on providing.)

So, (9) × 9 = 81. Note how the single (9) replaces 531,441. It is just a coincidence that this turned out to be 9 also.

Divide the final result by N and compute remainder:

81/33 5 2.4545454, so subtract 2

0.4545454 × 33 = 14.99998 = 15

Thus, the plain-text 15 is the letter “O” sent securely using PKI. That's all there is to it! Of course, usually it's a number that's encrypted—but so what? Try the number 19 for yourself. You might have to “normalize” on the encryption side as well, but it still works.

The security in PKI is in the difficulty of finding D given the values of E and N. This example is mathematically trivial to hackers and crackers. But try N = 49,048,499 and E = 61. The answer is D = 2,409,781. Usually, N, E, and D are anywhere from 140 to 156 or more digits long. To deal with text messages, strings of letters can be thought of as numbers. So, “OK” becomes 1511. ASCII is typically used.

Digital signatures employ the same public keys as well. Either key, E or D, can be used to encrypt or decrypt. You just need to use the other to reverse the process (try it with “O”). So, any message encrypted with D can only be decrypted with E (my public key). So, any text that can be decrypted with E (and N) had to come from me as long as my private key D remains secure.

Vigenère Cipher

This cipher was invented by a French diplomat, Blaise de Vigenère, in the 16th century. The Vigenère cipher uses a series of different Caesar ciphers based on a keyword or passphrase. In a Caesar cipher the letters of the alphabet are shifted using one shift value. For example, a Caesar shift by three makes A become D, B become E, and so on. The Vigenère cipher uses several Caesar ciphers, and each cipher has a different shift value (one could be shifted by three, the next shifted by five, and so on).

What does it mean to break a cipher?

What is the process of converting unreadable encoded message cipher text into its original form?

What is the original message to be encrypted called?

What is the process of encoding a plain text to cipher text?