İstanbul borsası için güvenli bir iletişim yazılımı
A Secure communication software for The İstanbul Stock Exchange
- Tez No: 39277
- Danışmanlar: DOÇ.DR. BÜLENT ÖRENCİK
- Tez Türü: Yüksek Lisans
- Konular: Bilgisayar Mühendisliği Bilimleri-Bilgisayar ve Kontrol, Computer Engineering and Computer Science and Control
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1993
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 132
Özet
Özet Bu tezin hazırlanmasındaki temel amaç İstanbul Borsasında işlem yapmaya yetkili aracı kurumların yaptıkları işlemlere ait sözleşme bilgilerini Borsa 'ya hızlı ve güvenli yollardan iletebilmeleri ve Borsa tarafında alınan bilgilerin otomatik olarak veri tabanını güncellemek amacıyla kullanılmasını sağlayabilmektir. Halen manuel olarak yapılmakta olan sözleşme girişi işlemleri tez konusu yazılımın beş üye tarafından kullanılarak,düz mantıkla veri aktaran şeklinin kullanılması ile (kriptolama, otomatik blok boyu ayarlama ve veri sıkıştırma tekniği kullanılmamıştır) bir elemanın iki saatlik iş yükünü ortadan kaldırdığı hesaplanmıştır. Okuyacağınız tez tekstinin birinci bölümünde kriptografinin ana kavramları ve iki ana kriptografi kavram olan blok ve stream kriptolayıcıları tanıtılmaktadır. İkinci bölümde ise hazırlanan tezin ana konusunu oluşturan veri kriptolama standartı (DES) anlatılmaktadır. Son bölümde ise İstanbul Borsası ve sermaye piyasaları hakkında genel bilgi verilerek hazırlanan tez ayrıntıları ile anlatılmıştır.
Özet (Çeviri)
Summary A Secure Communication Software For The Istanbul Stock Exchange Within the computer industry there is a movement toward more secure systems. Cryptography is being used in selected high-risk applications. For example, significant number of cash-issuing terminals employ DES to verify the identity of customers. The cryptographic algorithm can be thought of as an extremely large number of transformations, the particular transformation in effect depending on the cryptographic key being used. Each transformation changes sequences of intelligible data (plaintext) into sequences of apparently random data (ciphertext). The transformation from plaintext to ciphertext is known as encipherment or encryption. Each transformation must have a unique inverse transformation from ciphertext to plaintext is called decipherment or decryption. There are two types of cryptographic algorithms, conventional and public-key. With a conventional algorithm, the enciphering and deciphering case are either identical, or,if different, are such that each key can be easily computed from the other. Thus knowledge of the enciphering key is equivalent to knowledge of the deciphering key -when you have one, you also have the other. A public-key algorithm, on the other hand, permits many users or nodes within a communications system to encipher data using the same public key, but only the specific user or node processing the secret deciphering key can“unlock”or recover the data. In contrast, a conventional cryptographic algorithm provides effective data security between two users or nodes within a communication system only if these users or nods have knowledge of the same secret key. The aim by implementing this thesis is to get a really proven secure communication software and communication protocol for the ISE and its Member Companies. Because in our case the trade data of the individual broker is transmitted to the exchange using our software and protocol of handshaking, via modems, it is very important to transmit data in a secure way so that nobody else the Stock Exchange can be able to have the trade data of transmitter broker.In our application there are three secret variable (constant for each broker). i. A secret 8-bit“KEY”to operate with the“Exchange String”in the OP_SEQUENCE sequence in order to get“Broker 5-bytes Password”, ii. A secret OP_SEQUENCE, which indicates the operation sequence of KEY and incoming 5-bytes“Exchange String”, iii. A 64-bit“Terminal DES key”to encrypt/decrypt PR1,PR2 VIand PR3 (explained in chapter 4) step messages. After answering to a call of a broker first thing to do from the point of view of the broker is to tell the Exchange his Broker Id (3-bytes ASCII character) in the unencrypted form. After that step Exchange can determine the three secret constant for the calling broker and communicate in this communication session with those constants. After receiving the Broker Id. the Stock Exchange sends a 11-bytes data including STX,ETX and FCS characters and 8- bytes by“terminal DES key”encrypted data to the remote side. FCS character is used in every steps of the communication to check the received data and calculated by EX_ORing every byte in the block frame including STX and excluding ETX characters. This 8-bytes data includes 3-bytes Exchange Id. ;“I”,“S”,“E”characters, and a 5-bytes“Exchange String”which will be a parameter for the calculation of the brokers secret 5-bytes password. Brokers password is generated by calculating incoming“Exchange String”and“KEY”byte in OP_SEQUENCE operation order. Operations to use are EX-OR, LOGICAL AND, LOGICAL OR, ADD and SUBTRACT. For example if the operation sequence is 1,2,3,4,5 (EX_OR, LOGICAL AND, LOGICAL OR, ADD, SUBTRACT) and KEY is 128 then Broker 5-byte Password should be calculated in the following order; yl = xl A 128 y2 = x2 & 128 y3 = x3 | 128 y4 = x4 + 128 y5 = x5- 128. (Note that xl,x21,x3,x4 and x5 indicate 5-byte Exchange String, where yl,y2,y3,y4 and y5 indicate Broker Password.) After receiving PR1 on the broker side, transmitter software calculates 5-bytes Broker Password and append it to the 3- byte broker code. These 8-bytes message then should be framed with the STX and ETX character. After calculating FCS and appending to the end of the packet PR2 is obtained. The 8-bytes message then encrypted by using the“terminal DES key”and sended to the Exchange. If PR2 received on the Exchange side properly a 64-bit“session DES key”is generated and encrypted using the“terminal DES key”. This 64-bit, 8- bytes data then framed using the same procedures explained above and transmitted to the calling broker. The trade data transmitting begins after this step using the“session DES key”. A basic problem in cryptography is devising procedures to transform messages (plaintext) ino cryptograms (ciphertext) that can withstand intense cryptanalysis-the techniques used by opponents to penetrate encrypted communications and recover the original information. The procedures used to accomplish such transformations involve either a code system or a cipher system. Code systems require a code book or dictionary that translates words, phrases and sentences of plaintext vocabulary into their equivalentciphertext code groups. However, the number of plaintext groups that can be converted depends on the size of the code book. Therefore not every message ca be encoded, and versatility of these code systems is limited. vuOn the other hand, cipher systems are versatile. They require two basic elements; a cryptographic algorithm ; and a set of variable cryptographic keys. A key is relatively short, secret sequence of numbers or characters selected by the user. DES is implemented in our application by using (DE_) ROTATE, (DE_) TRANSPOSE, (DE_)F, (DE_)DES PROCEDURES.“DE_”in parenthesis indicates the same procedures but in the DE_cryption phase. These procedures are explained in the Appendix A in the source programs listing. After our implementation of DES lets have a global knowledge about DES. Known as the Data Encryption Standard (DES) the algorithm enciphers a 64-bit block of plaintext into 64-bit block of ciphertext under control of a 56-bit cryptographic key. The process of encryption consist of 16 rounds of encipherment, each round using a product cipher approach, or cipher function. The interaction of data, cryptographic key K and cipher function g is illustrated in Figure 3-1. The externally supplied key K consist of 64-bits: 56 bits are used by the algorithm and eight bits may be used for parity checking. A different subset of 48 key bits from the 56 bit key is used in each round. The subsets of key bits used for encipherment are denoted K(l),K(2),...,K(16).During decipherment, the keys are used in reverse order (K16) in round one, K(15) in round two, and so forth).The initial and inverse initial permutations allow the algorithm to be implemented more easily on a single chip, provided that the data and the key are serially loaded. DES can be thought of as a huge key-controlled substitution box (S-box) with a 64-bit input and output. With such an S-box, a total number of (264!) different transformations or functions from plaintext to ciphertext are possible. The 56-bit key used with DES thus select only a small subset (256) of the total set's possible functions. A single S-box is impossible to construct. Therefore, DES is implemented by using several smaller S-boxes (6-bit input and 4-bit output) and permuting their concatenated outputs. By repeating the substitutions and permutation process several times, cryptographic strength increases. When referring to the cryptographic transformations of encipherment and decipherment, E denotes encipherment and D denotes decipherment. The notation used to express these operations is Ek(X)=Y which means that ciphertext Y is produced by the encipherment of plaintext X under key K, and Dk(Y)=X which means that ciphertext X is produced by the decipherment of ciphertext Y under key K. VUlwhich means that ciphertext X is produced by the decipherment of ciphertext Y under key K. In DES, a cryptographic relationship exists among the plaintext, ciphertext and cryptographic keys on one hand and the complements of those quantities on the other hand. That relationship, called the complementary property of DES, can be expressed as Ek(X) = [Ek-(X)] ' where ( ' ) represent complementation, or bit inversion. Because of the complementary property of DES, if an analyst could obtain Ek(X) and Ek(X') for an arbitrary X, he could reduce the size of the key space he must search from 256 to 255.Therefor, the key space could be exhausted in 255 trials instead of 256 trials. However, depending on the implementation, it may not be possible for an opponent to obtain plaintext X and its complement X' enciphered under the unknown cipher key. Generally, the steps of substitution and permutation in the DES algorithm have the following relationship to the algorithm1 s strength. Deterministic attacks (purely mathematical and non statistical in nature) are deterred mainly by the use of nonlinear functions in the substitutions process. Statistical attacks are deterred mainly by the permutation of bits after each step of substitution (smoothing out the statistics).In the strict sense, both deterministic and statistical attacks are deterred by a combination of substitution and permutation. Organizations in both the public and private sectors have become increasingly dependent on electronic data processing. Vast amounts of digital data are now gathered and stored in large computer databases and transmitted between computers and terminal devices linked together in complex communications networks. Without appropriate safeguards, these data are susceptible to interception during transmission, or they may be physically removed or copied while in storage. This could result in unwanted exposures of data and potential invasions of privacy. Data are also susceptible to unauthorized deletion, modification, or addition during transmission or storage. This can result in illicit access to computing recourses and services, falsification of personal data or business records, or the conduct of fraudulent transactions, including increases in credit authorizations, modifications of funds transfers, and the issuance of unauthorized payments. Legislators, recognizing that the confidentiality and integrity of certain data must be protected, have passed laws to help prevent these problems. But laws alone cannot prevent attacks or eliminate threats to data processing systems. Additional steps must be taken to preserve the secrecy and integrity of computer data. Amount the computer security measures that should be considered is cryptography, which embraces methods of rendering data unintelligible to unauthorized parties. Cryptography is the only known practical method for protecting information transmitted through communications networks IXthat use land lines, communications satellites, and microwave facilities. In some instances it can be the most economical way to protect the stored data. Cryptographic procedures can also be used for message authentication, digital signatures, and personal identification for authorizing electronic funds transfer and credit card transactions. It is proven that with five of the high volume broker and using the old version of the transmitter/receiver software (no cryptography, no automatic block length selection used) two operator hours can be saved. The thesis text is divided into three chapters. In chapter one, two common known cipher; block ciphers and the stream ciphers are described and compared. Both block and stream ciphers can be used in communication and data processing systems. With a block cipher, data are encrypted and decrypted in blocks, whose length are predetermined by the algorithm's designer. With a stream cipher, the algorithm's user determines the length of data to be encrypted and decrypted. This flexibility requires that stream ciphers,in addition to the algorithm and the key, employ another parameter defined as an initializing vector. In that chapter the details of two public-key algorithm RSA and Trapdoor, Knapsack is also given. DES is described in chapter two. And in the last chapter after defining Exchange and Capital Markets, the written software is explained. As a result the transmitter/receiver and handshaking protocols can be used generally by changing the PR1 (“I”,“S”,“E”characters) and broker codes to transmit/receive any ASCII file from any node in a particular computer system to the host computer.
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