Computer Science. The English Language Perspective - Беликова (1176925), страница 33
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CSPRNGs have qualities that other PRNGs do not.CSPRNGs must pass the "next-bit test" in that given the first kbits, there is no polynomial-time algorithm that can predict the(k+1)th bit with probability of success higher than 50%.CSPRNGs must also withstand "state compromises." In theevent that part or all of its state is revealed, it should beimpossible to reconstruct the stream of random numbers priorto the revelation.194There are limitless possibilities for keys used in cryptology. Butthere are only two widely used methods of employing keys:public-key cryptology and secret-key cryptology.
In both ofthese methods (and in all cryptology), the sender (point A) isreferred to as Alice. Point B is known as Bob.In the public-key cryptology (PKC) method, a user choosestwo interrelated keys. He lets anyone who wants to send him amessage know how to encode it using one key. He makes thiskey public.
The other key he keeps to himself. In this manner,anyone can send the user an encoded message, but only therecipient of the encoded message knows how to decode it. Eventhe person sending the message doesn't know what code theuser employs to decode it.PKC is often compared to a mailbox that uses two keys. Oneunlocks the front of the mailbox, allowing anyone with a key todeposit mail. But only the recipient holds the key that unlocksthe back of the mailbox, allowing only him to retrieve themessages.The other usual method of traditional cryptology is secret-keycryptology (SKC).
In this method, only one key is used by bothBob and Alice. The same key is used to both encode and decodethe plaintext. Even the algorithm used in the encoding anddecoding process can be announced over an unsecured channel.The code will remain uncracked as long as the key usedremains secret.SKC is similar to feeding a message into a special mailbox thatgrinds it together with the key. Anyone can reach inside andgrab the cipher, but without the key, he won't be able todecipher it. The same key used to encode the message is alsothe only one that can decode it, separating the key from themessage.Both the secret-key and public-key methods of cryptology haveunique flaws.
The problem with public-key cryptology is thatit's based on the staggering size of the numbers created by thecombination of the key and the algorithm used to encode themessage. These numbers can reach unbelievable proportions.195What's more, they can be made so that in order to understandeach bit of output data, you have to also understand everyother bit as well. This means that to crack a 128-bit key, thepossible numbers used can reach upward to the 1038 power.That's a lot of possible numbers for the correct combination tothe key.The keys used in modern cryptography are so large, in fact, thata billion computers working in conjunction with eachprocessing a billion calculations per second would still take atrillion years to definitively crack a key. This isn't a problemnow, but it soon will be.
Current computers will be replaced inthe near future with quantum computers, which exploit theproperties of physics on the immensely small quantum scale.Since they can operate on the quantum level, these computersare expected to be able to perform calculations and operate atspeeds no computer in use now could possibly achieve. So thecodes that would take a trillion years to break withconventional computers could possibly be cracked in much lesstime with quantum computers. This means that secret-keycryptology (SKC) looks to be the preferred method oftransferring ciphers in the future.But SKC has its problems as well.
The chief problem with SKCis how the two users agree on what secret key to use. It'spossible to send a message concerning which key a user wouldlike to use, but shouldn't that message be encoded, too? Andhow do the users agree on what secret key to use to encode themessage about what secret key to use for the original message?There's almost always a place for an unwanted third party tolisten in and gain information the users don't want that personto have. This is known in cryptology as the key distributionproblem.RSA encryption, named for the surnames of the inventors,relies on multiplication and exponentiation being much fasterthan prime factorization.
The entire protocol is built from twolarge prime numbers. These prime numbers are manipulated togive a public key and private key. Once these keys are196generated they can be used many times. Typically one keepsthe private key and publishes the public key. Anyone can thenencrypt a message using the public key and send it to thecreator of the keys. This person then uses the private key todecrypt the message. Only the one possessing the private keycan decrypt the message.
One of the special numbers generatedand used in RSA encryption is the modulus, which is theproduct of the two large primes. In order to break this system,one must compute the prime factorization of the modulus,which results in the two primes. The strength of RSAencryption depends on the difficultly to produce this primefactorization. RSA Encryption is the most widely usedasymmetric key encryption system used for electroniccommerce protocols.Notes:One-time pad (другое название Vernam Cipher) – системасимметричного шифрования. Является единственнойсистемой шифрования, для которой доказана абсолютнаякриптографическая стойкость.XOR (Exclusive or) – сложение по модулю 2, логическая ибитовая операция.Pseudo-RandomNumberGenerator–генераторпсевдослучайных чисел.CryptographicallySecurePseudo-RandomNumberGenerator – криптографически безопасный генераторпсевдослучайных чисел.RSA encryption (аббревиатура от имен Rivest, Shamir, andAdleman) – криптографический алгоритм с открытымключом, основывающийся на вычислительной сложностизадачи факторизации больших целых чисел.197Assignments1.
Translate the sentences from the texts into Russian inwriting paying attention to the underlined words andphrases:1. The "one-time pad" encryption algorithm was inventedin the early 1900s, and has since been proven asunbreakable.2. Even when trying every possible key, one would stillhave to review each attempt at decipherment to see ifthe proper key was used.3.
The one-time pad is typically implemented by using amodular addition (XOR) to combine plaintext elementswith key elements.4. Numerous attempts have been made to createseemingly random numbers from a designated key.5. CSPRNGs must pass the "next-bit test" in that given thefirst k bits, there is no polynomial-time algorithm thatcan predict the (k+1)th bit with probability of successhigher than 50%.6. SKC is similar to feeding a message into a specialmailbox that grinds it together with the key.7. RSA encryption, named for the surnames of theinventors, relies on multiplication and exponentiationbeing much faster than prime factorization.8.
One of the special numbers generated and used in RSAencryption is the modulus, which is the product of thetwo large primes. In order to break this system, onemust compute the prime factorization of the modulus,which results in the two primes.1982.
Answer the following questions:1. Is the one-time pad an unbreakable means ofencryption?2. What two assumptions does the unbreakable aspect ofthe one-time pad come from?3. What is the difference between PRNG and CSPRNG?4. What is safer: PKC or SKC?5. What can the strength of RSA encryption depend on?3. Translate into English:Какбынибылисложныинадежныкриптографические системы, их слабое место припрактической реализации - проблема распределенияключей. Для того, чтобы был возможен обменконфиденциальнойинформациеймеждудвумясубъектами ИС, ключ должен быть сгенерирован одним изних,азатемкаким-тообразомопятьжевконфиденциальном порядке передан другому.
Т.е. в общемслучае для передачи ключа опять же требуетсяиспользование какой-то криптосистемы.Для решения этой проблемы на основе результатов,полученных классической и современной алгеброй, былипредложены системы с открытым ключом.Суть их состоит в том, что каждым адресатом ИСгенерируются два ключа, связанные между собой поопределенному правилу. Один ключ объявляетсяоткрытым, а другой закрытым.
Открытый ключпубликуется и доступен любому, кто желает послатьсообщение адресату. Секретный ключ сохраняется в тайне.Исходный текст шифруется открытым ключомадресата и передается ему. Зашифрованный текст впринципе не может быть расшифрован тем же открытым4. Give the summary of the text using the key terms.199FUTURE METHODS OF ENCRYPTIONRead the following words and word combinations and usethem for understanding and translation of the text:eavesdropper - перехватчикto harness — приспособить, поставить на службуspin - вращениеbinary code – двоичный кодcoherent - понятныйto accomplish - выполнятьto discard - отбрасыватьdiscrepancy - несоответствиеparity check — контроль четностиto bounce - отскакиватьspooky — жуткий, зловещийentanglement - переплетениеfiber optic cable – оптоволоконный кабельQuantum CryptologyOne of the great challenges of cryptology is to keep unwantedparties – or eavesdroppers - from learning of sensitiveinformation.
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