（信号与信息处理专业论文）混合加密技术应用到信息安全.pdf

国内图书分类号 tn918.4 学校代码： 10213 国际图书分类号：620 密级：公开 工学硕士学位论文 混合加密技术应用到信息安全混合加密技术应用到信息安全 硕士研究生 ： yakoubou dieudonn （杜尼） 导师 ：邹斌 教授 申请学位 ：工学硕士 学科 ：信号与信息处理 所在单位 ：电子与信息程学院 答辩日期 ：2012年7月 授予学位单位 ：哈尔滨工业大学 classified index: tn918.4 u.d.c.: 620 dissertation for the master degree in engineering hybrid encryption technique applied to the information security candidate: yakoubou dieudonne supervisor: prof. zou bin academic degree applied for: master of engineering specialty: information and communication engineering affiliation: school of electronics and information engineering date of defence: july, 2012 degree-conferring-institution: harbin institute of technology dissertation for master degree in engineering, hit - i - 摘 要 信息安全在过去主要是被军方和政府用来防范入侵者。不过最近几年， 商业领域安全的重要性问题也日益突出。加密是一种用来保护信息的标准做 法，但其根本的问题是如何在不被截停或透露给对手的情况下，通过不安全 的网络进行具有较高安全性的信息传递， 以及如何知道在信息传递的过程中， 信息没有被对手更改。在信息安全系统中，对称加密是最古老的方法，广泛 地用于实现获取较大数据量安全的加密。在此方法中，操作者使用相同的密 钥用于信息加密和解密，但另一个问题是如何在不可靠的网络上共享密钥。 非对称加密一种用来解决对称加密中所存在的关键的分布问题的加密 工具。另一方面，非对称加密亦存在一些缺点，如在加密的信息量较大时， 运行速度要明显慢于对称加密。在本篇论文中，重点研究了混合加密技术， 即综合了对称加密和非对称加密优势的组合式加密技术。这种技术提供了信 息保密、验证及完整性等安全方面的服务。此方法可以保证用户共享的密钥 的安全性。在此方法中涉及的用于实现我们的目标的算法是：aes 128、rsa 和散列函数md5。 关键词：密码学、 信息安全性、aes-128 算法，rsa 算法，散列函数 md5 dissertation for master degree in engineering, hit - ii - abstract basically, the security of information was used by military and governments to guard against invaders. however, the importance of this security in the commercial sector has been increasing in recent years. cryptography is a standard way used to secure the information but its fundamental problems are how to communicate the information with high security over unsecured networks without being intercepted or revealed to the adversary and how to know this information have not been changed by an adversary during the transmission process. in the security system of information, the symmetric encryption is the oldest method and widely used in cryptography for securing a large data. in this method, the operators use the same key for encrypting and decrypting the information but the other problem is how to share the key over unreliable networks. asymmetric encryption is one of cryptography tools used to resolve the keys distribution problem experienced by symmetric encryption. on other ways, the asymmetric encryption suffers of some disadvantages such as running markedly slower than symmetric encryption when the encrypted information becomes very large. in this thesis, the focus is on hybrid encryption technique that is a combination of advantages of both symmetric and asymmetric encryption. this technique provides the security services such as confidentiality, authentication and integrity to the information. this method allows to guarantee the security of secret key shared by users. the algorithms involved in this method for achieving our objective are: aes-128, rsa, and hash function md5. keywords: cryptography, information security, aes-128 algorithm, rsa algorithm, hash function md5. dissertation for master degree in engineering, hit - iii - contents 摘 要 . i abstract . ii chapter1 introduction . 1 1. background . 1 1.1 main research contents . 2 1.2. literature review . 3 1.2.1. cryptography overview . 3 1.2.2. symmetric encryption . 4 1.2.3. asymmetric encryption . 7 1.2.4. symmetric and asymmetric encryption . 10 chapter2 basic theory . 13 2. introduction . 13 2.1. rsa algorithm basic theory . 13 2.1.1. keys generation . 13 2.1.2. rsa encryption . 14 2.1.3. rsa decryption . 14 2.1.4. rsa security . 14 2.2. aes algorithm basic theory . 15 2.2.1. aes-128 encryption algorithm . 16 2.2.2. key schedule . 19 2.2.3. the aes-128 decryption algorithm . 20 2.2.4. the aes algorithm security . 21 2.3. hash function md5 basic theory . 22 2.3.1. hash function md5 process . 22 2.3.2. hash function md5 security . 24 chapter3 methodology . 25 3.1 hybrid encryption technique . 25 3.2. the encryption theory (side a) . 26 3.2.1. the aes-128 encryption algorithm . 27 dissertation for master degree in engineering, hit - iv - 3.2.1.1. the aes-128 encryption algorithm process . 27 3.2.2. the hash function md5 . 29 3.2.3. the rsa encryption algorithm . 32 3.3. the decryption theory (side b) . 33 3.3.1. the rsa decryption algorithm . 34 3.3.2. the aes-128 decryption algorithm process . 34 3.4. the decryption theory (side b) . 34 3.4.1. the rsa decryption algorithm . 35 3.4.2. the aes-128 decryption algorithm process . 35 3.4.3. the hash function md5 . 37 3.4.4. the function comparison. 38 chapter4. implementation results, discussion, conclusion. . 39 4.1 implementation results of thesis research . 39 4.2 the encryption results (side a) . 39 4.3 the decryption results (side b) . 42 discussion . 45 conclusion . 46 references . 48 哈尔滨工业大学学位论文原创性声明使用授权说明 . 51 declarations . 52 copyright . 53 acknowledgement . 54 curriculum vita . 55 dissertation for master degree in engineering, hit - v - nomenclature rsa rivest shamir adleman (the letters rsa are the initials surnames of the researchers that invented this algorithm) aes advanced encryption standard md5 message digest version 5 des data encryption standard n modulus (* )np q ( )n eulers totient function ( ( )(1)*(1)npq e public exponent or encryption exponent d private exponent or decryption exponent gcd greatest common divisor sha-256 secure hash algorithm 256 dissertation for master degree in engineering, hit - 1 - chapter1 introduction 1. background historically, the military and governments were initially the only ones concerned about the security of information. in recent years, the use of information security in the commercial sector has been increasing. each day, millions of users generate and interchange a tremendous amount of information in various domains such as medical reports, financial and legal files, bank services via internet, and e-commerce transactions. the cryptography is one of the tools used to secure the information. in this study, we particularly emphasize on the security of messages. the fundamental problems known to the cryptography are how to transmit the information with high security over unreliable networks without being intercepted and revealed by adversary and how to know that the information have not been manipulated by an unwanted third party during the transmission process. in cryptography, the symmetric encryption 1 is the oldest method widely used for hiding data. in this method, the sender and receiver use the same key for sharing the information and this key must be kept secret. however, other problem is to know how to share this key with high security over unsecured networks. an attempt to resolve these problems is made by focusing on the security of secret key shared by users and providing to the information the security services such as “authentication, confidentiality and integrity”. recalling that, before discovering of the asymmetric encryption by whitfield diffie and martin hellman, the only way for users to communicate was to agree on a secure way for communicating secret key such as trustworthy courier with a briefcase handcuffed to wrist or face-to-face contact. these methods are not effective if the users are located far apart. in 1976, diffie and hellman introduced diffie-hellman key exchange method 2 which resolved the key management problem. however, this method cannot provide the authentication and has become vulnerable to a man-in-the-middle attack 3, 4. thus, the secret key used to dispatch the information remains accessible. dissertation for master degree in engineering, hit - 2 - further, whitfield diffie and martin hellman had invented asymmetric encryption to generate a pair of keys. this concept was developed in order to overcome the drawbacks 5 of symmetric encryption. in asymmetric encryption, one of those keys is used for encryption and the other one for decryption the information. the pass code used for encrypting can be made public and is also referred to as public key. the private key used for decrypting remains secret. furthermore, the asymmetric encryption provides the authentication by signing the document; the details are given in 6. on other hand, the asymmetric encryption suffers some disadvantages 7 such as running apparently slower than symmetric encryption when the encrypted information becomes too vast. thus, to overcome the security information problem, there is need for efficient algorithms and better cryptographic technique so as to achieve the objective. nowadays, various strong types of cryptographic algorithms have been developed and are classified in two groups, such as symmetric encryption algorithms (blowfish 7, idea 7, rc4 7, rc2 7, des 8, tdes 8, cast 9, rc6 9 and aes 10) and asymmetric encryption algorithms (elliptic curve cryptography ecc 7, el gamal 7, rsa 11) that are used in many applications to secure the information. therefore, in this thesis, the focus is on hybrid encryption technique that is defined as a combination of the advantages of symmetric and asymmetric encryption that requires the use of some strong algorithms to protect the secret key and the information. this technique provides to the information the security services such as confidentiality, authentication and integrity. the algorithms involve in this work are follows aes-128, rsa and the hash function md5. 1.1 main research contents security of information is one of the entities that passionate several institutions, such as banks, hospitals, military, telecommunication sector, governments etc. the purpose of this study is to attempt to fix the fundamental problems known by cryptography for securing the information, such as “how to transmit the information with high security”, “how to know the information dissertation for master degree in engineering, hit - 3 - transmitted have not been manipulated by an adversary” and “how to share the secret key used by operators over unreliable networks. an attempt to resolve these problems, it is concentrated on hybrid encryption technique that is defined as the combination of the advantages of symmetric and asymmetric encryption applied for securing the information. the use of this method is to provide to the information the security services and it guarantees the security of the secret key shared by users. this method is also effective for fast operation when dealing with the enormous amount of information. it is found out that rsa algorithm, aes algorithm and hash function md5 are effective algorithms that can be used to achieve the objective of this study. therefore, aes algorithm is used in symmetric encryption for encrypting and decrypting large amount of data and it guarantees the confidentiality; rsa is used in asymmetric encryption for securing the secret key of aes and the message digest, this system ensures the authentication; while hash function md5 is used to compute the message digest for checking the integrity of data. the thesis is organized as following: 1. in the second chapter, we deeply enter in basic theories for rsa, aes-128 and hash function md5. 2. the third chapter covers the applied research methodology in this thesis. 3. this research report knots its orientation, in the fourth chapter, by a multidimensional discussion on the outcomes of implementation of hybrid encryption technique using matlab r2008a software and, eventually, a conclusion on some relevant points of our analysis. 1.2. literature review 1.2.1. cryptography overview cryptography 12 is defined as the art for hiding information and making it not obvious. in modern times, cryptography is considered as the one of branches of mathematics which is related to the information security i.e. to provide to the dissertation for master degree in engineering, hit - 4 - information the security services such as confidentiality, authentication and integrity. these words are defined as follows: confidentiality is a method of ensuring that information remains private. for achieving the confidentiality, the operators use the encryption algorithm to convert plaintext into ciphertext and the decryption algorithm to convert ciphertext back to plaintext. integrity ensures that information has not been modified and destroyed or lost in a malicious or accidental manner. authentication allows to verify the users identity and the information source into the networks. in cryptography, the message is called the plaintext and the method used to encrypt this message is the encryption. the ciphertext is defined as the result of the message encrypted. the method used to decrypt the ciphertext is the decryption. encryption and decryption method make respectively the use of keys. cryptography has two important elements: symmetric and asymmetric encryption. both tools play a significant role in modern cryptography. for several critical applications, a combination of both cryptography tools is important. 1.2.2. symmetric encryption the symmetric encryption is the one of the cryptography elements used to protect the information. in symmetric encryption, the users use the same key “secret key” for encrypting and decrypting the data i.e. the sender uses the secret key to encrypt the plaintext, and then the same key is used by recipient to decrypt the ciphertext. fig.1-1 illustrates the encryption and decryption processes. dissertation for master degree in engineering, hit - 5 - figure 1-1 processes of encryption and decryption for symmetric encryption 1.2.2.1. advantages and disadvantages of symmetric encryption the symmetric encryption presented some advantages and disadvantages. according to jessica, j. benz 5, the advantages and disadvantages of symmetric encryption are as follows: 1. advantages the symmetric encryption allows to provide to the information the confidentiality and authentication as long as the key stays secret. the data is encrypted very quickly. symmetric encryption allows to encrypt and to decrypt a message with same key 2. disadvantages if the key is revealed (lost, stolen, guessed etc) the interceptors can decrypt the data that was encrypted using the key. in symmetric encryption, the distributions of keys become a problem, especially if keys change frequently. the keys must be transmitted with extreme security. in the symmetric encryption, the number of keys increases with the square of the number of people that exchange the information; if there are n peoples the keys number is: *(1)/ 2nn. the symmetric keys are subjected