cryptography full report
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23012010, 01:47 AM
Cryptography full report.doc (Size: 297.5 KB / Downloads: 665) Cryptography ABSTRACT This paper introduces Cryptography Techniques. Cryptography is The science of protecting data & Network Security keeping information private and Secure from unauthorized Users. This paper gives the Fundamental Requirements for the Data Transmission, the security attacks like Interruption, Interception and Modification of the data Transmission. The Cryptographic Process explaining through a generalized function is discussed through which encryption and decryption is done by the various algorithms like RSA algorithm, Hash Functions and many cryptographic algorithms. Presented by Name: T Sampathkumar Name: Sudeep Year: III/IV CSE , Year: III/IV CSE, email: sampaththatikonda@rocketmail.com email : sudeep4u_lp@yahoo.com Introduction The Cryptanalysis is the process of attempting to discover the plain text and/ or the key. Applications of Various Cryptographic Technologies. Why & How to Provide Network Security in the Certificates issuing, The Validity & Trust for Certificate Services, Certificate Revocation in the Internet, Intranet and other Network Communications, the Applications of Network Security to the various Data Transfer techniques and protocols. From the dawn of civilization, to the highly networked societies that we live in Today communication has always been an integral part of our existence. Â¢ Radio communication Â¢ Network communication Â¢ Mobile communication Â¢ Telephonic communication All these methods and means of communication have played an important role in our lives, but in the past few years, network communication, especially over the Internet, has emerged as one of the most powerful Methods of communication with an overwhelming Impact on our lives. Such rapid advances in Communications technology have also given rise to Security threats to individuals and organizations. Fundamental Requirements Confidential: Is the process of keeping information private and Secret so that only the intended recipient is able to understand the information. Authentication: Is the process of providing proof of identity of the sender to the recipient, so that the recipient can be assured that the person sending the information is who and what he or she claims to be. Integrity: Is the method to ensure that information is not tampered with during its transit or its storage on the network. Any unauthorized person should not be able to tamper with the information or change the Information during transit Nonrepudiation: Is the method to ensure that information cannot be disowned. Once the nonrepudiation process is in place, the sender cannot deny being the originator of the data. Security Attacks Interruption: In an attack where one or more of the systems of the organization become unusable due to attacks by unauthorized users. This leads to systems being unavailable for use. Interception: An unauthorized individual intercepts the message content and changes it or uses it for malicious purposes. After this type of attack, the message does not remain confidential. Modification: The content of the message is modified by a third party. This attack affects the integrity of the message. So for maintaining the data secretly while communicating data between two persons or two organizations data is to be converted to other format and the data is to be transmitted. So now we deal with the Cryptography which is process of transmitting data securely without any interruption. Network security is the security of data transmission in the communication. What is Cryptography The term cryptology has its origin in Greek KryptÃƒÂ³s lÃƒÂ³gos , which means hidden word. Cryptography is the science of protecting data, which provides means and methods of converting data into unreadable form, so that Valid User can access Information at the Destination. Cryptography is the science of using mathematics to encrypt and decrypt data. Cryptography enables you to store sensitive information or transmit it across insecure networks (like the Internet) so that it cannot be read by anyone except the intended recipient. While cryptography is the science of securing data, cryptanalysis is the science of analyzing and breaking secure communication. Cryptanalysts are also called attackers. Cryptology embraces both cryptography and cryptanalysis. Cryptography Terminology a) Plaintext: The original intelligible message. b) Cipher text: The transformed message. c) Cipher: An algorithm for transforming an intelligible message to unintelligible by transposition. d) Key: Some critical information used by the cipher, known only to the sender & receiver. e) Encipher Encode) the process of converting plaintext to cipher text using a cipher and a key. f) Decipher Decode) the process of converting cipher text back into plaintext using a cipher & key. g) Cryptanalysis: The study of principles and methods of transforming an unintelligible message back into an intelligible message without knowledge of the key. Also called code breaking h) Cryptology: Both cryptography and cryptanalysis i) Code: an algorithm for transforming an intelligible message into an unintelligible one using codes. j) Hash algorithm: Is an algorithm that converts text string into a string of fixed length. k) Secret Key Cryptography (SKC): Uses a single key for both encryption and decryption l) Public Key Cryptography (PKC): Uses one key for encryption and another for decryption m) Pretty Good Privacy (PGP): PGP is a hybrid cryptosystem. n) Public Key Infrastructure (PKI): PKI feature is Certificate authority. Network Security For Distributed computing Â¢ Logical set of services distributed over the network Â¢ Physical security model does not work anymore For Internet and Web Â¢ Increase of security threat Â¢ More stringent security for Ecommerce and B2B Why network security When networks were not that pervasive, that is when computing devices were running in their own Islands, it was rather easy to deal with security. The only thing they needed to do was to lock the door. Now, as more and more computing devices are getting connected and more and more applications are being built as distributed applications, the physical security model has lost its significance. The advent of the internet and the web has raised the scale and frequency of network Security threats. Common Security Threats Identity interception: It means that someone might steal your identity and use it as their own. Masquerading. If you send your username and password in clear text form, someone might be able to grab it from the network and use it elsewhere with the intention of perpetrating fraud. Replay attack: They might capture your request of withdrawing 1000 dollars from your Bank account and then replay that request over the network. Data interception and manipulation: If someone can read your credit card information while it is on the wire, they could cause a lot of trouble for you. Repudiation: When someone performs a transaction and then deny it later can be a big problem in ecommerce. For example, if you are manufacturer of something and you received a 1 million dollar purchase request from a customer, you will want to make sure that person does not deny it after the transaction has been completed. We all know what denial of service means. Network Security Needs Security Needs of an Enterprise Â¢ Single signon Internet and intranet Â¢ Controlled access to corporate information Â¢ Secure business transaction over Internet Â¢ Centralized, easy to use security admin tools Â¢ Transparency of security features Â¢ Interoperable security systems Â¢ Various PKI schemes, Kerbos Common Network Security Needs Â¢ Authentication (Identity verification) Â¢ Access control (Authorization) Â¢ Data confidentiality (Privacy) Â¢ Data integrity (Tamperproofing) Â¢ Nonrepudiation (Proof of transaction) Â¢ Auditing Cryptographic Process Basic Process M is the original message K enc is encryption key M' is the scrambled message K dec is decryption key It is difficult to get M just by knowing M' E and D are related such that E(K enc , M) = M' D(K dec , M') = M D(K dec , E(K enc , M)) = M Plaintextâ€M Cipher textâ€M' Original Plaintextâ€M Decryption functionâ€D Encryption functionâ€E So how does cryptographic process work The idea is rather simple. Let's say you have plaintext M. By providing the encryption key and the encryption function you get cipher text, M'. The cipher text can be decrypted using a decryption function and a decryption key and the result is the original text. In cryptographic process the mathematical property is such that it is practically impossible to derive M from M' unless the key is known. Key Process Techniques SymmetricKey Encryption: One Key Symmetrickey encryption, also called sharedkey encryption or secretkey cryptography, uses a single key that both the sender and recipient possess. This key, used for both encryption and decryption, is called a secret key (also referred to as a symmetric key or session key). Symmetrickey encryption is an efficient method for encrypting large amounts of data. But the drawback is to transfer the Key to Receiver as it is prone to security risks. PublicKey Encryption: Two Keys Two keysâ€a public key and a private key, which are mathematically relatedâ€are used in publickey encryption. To contrast it with symmetrickey encryption, publickey encryption is also sometimes called asymmetrickey encryption. In publickey encryption, the public key can be passed openly between the parties or published in a public repository, but the related private key remains private. Data encrypted with the public key can be decrypted only using the private key. Data encrypted with the private key can be decrypted only using the public key. In Figure 1, a sender has the receiver's public key and uses it to encrypt a message, but only the receiver has the related private key used to decrypt the message. Private Key Method Public Key Method Encryption is done with Public Key and Decryption with another key called Private Key. This is called Public Key Cryptography. Publickey cryptography algorithms RSA: The first, and still most common, PKC implementation, named for the three MIT mathematicians who developed it â€ Ronald Rivest, Adi Shamir, and Leonard Adleman. RSA today is used in hundreds of software products and can be used for key exchange, digital signatures, or encryption of small blocks of data. RSA uses a variable size encryption block and a variable size key. The keypair is derived from a very large number, n, that is the product of two prime numbers chosen according to special rules; these primes may be 100 or more digits in length each, yielding an n with roughly twice as many digits as the prime factors. The public key information includes n and a derivative of one of the factors of n; an attacker cannot determine the prime factors of n (and, therefore, the private key) from this information alone and that is what makes the RSA algorithm so secure. (Some descriptions of PKC erroneously state that RSA's safety is due to the difficulty in factoring large prime numbers. In fact, large prime numbers, like small prime numbers, only have two factors!) The ability for computers to factor large numbers, and therefore attack schemes such as RSA, is rapidly improving and systems today can find the prime factors of numbers with more than 140 digits. The presumed protection of RSA, however, is that users can easily increase the key size to always stay ahead of the computer processing curve. As an aside, the patent for RSA expired in September 2000 which does not appear to have affected RSA's popularity one way or the other. DiffieHellman: After the RSA algorithm Diffie and Hellman came up with their own algorithm. DH is used for secretkey key exchange only, and not for authentication or digital signatures. Digital Signature Algorithm (DSA): The algorithm specified in NIST's Digital Signature Standard (DSS), provides digital signature capability for the authentication of messages. Elliptic Curve Cryptography (ECC): A PKC algorithm based upon elliptic curves. ECC can offer levels of security with small keys comparable to RSA and other PKC methods. It was designed for devices with limited compute power and/or memory, such as smartcards and PDAs Hash functions An improvement on the Public Key scheme is the addition of a one way hash function in the process. A oneway hash function takes variable length input. In this case, a message of any length, even thousands or millions of bits and produces a fixedlength output; say, 160bits. The hash function ensures that, if the information is changed in any way even by just one bit an entirely different output value is produced. Hash functions, also called message digests and oneway encryption, are algorithms that, in some sense, use no key Instead; a fixedlength hash value is computed based upon the plaintext that makes it impossible for either the contents or length of the plaintext to be recovered. Hash algorithms are typically used to provide a digital fingerprint of a file's contents often used to ensure that the file has not been altered by an intruder or virus. Hash functions are also commonly employed by many operating systems so encrypt passwords. Hash functions, then, help preserve the integrity of a file. As long as a secure hash function is used, there is no way to take someone's signature from one document and attach it to another, or to alter a signed message in any way. The slightest change in a signed document will cause the digital signature verification process to fail. Applications Of Cryptography 1. Defense Services 2. Secure Data Manipulation 3. E â€œCommerce 4. Business Transactions 5. Internet Payment Systems 6. Pass Phrasing 7. Secure Internet Comm. 8. User Identification Systems 9. Access Control 10. Computational Security 11.Secure access to Corp Data 12.Data Security. PublicKey Encryption for Digital Signatures A major benefit of public key cryptography is that it provides a method for employing digital signatures. Digital signatures enable the recipient of information to verify the authenticity of the information's origin, and also verify that the information is intact. Thus, public key digital signatures provide authentication and data integrity. A digital signature also provides nonrepudiation, which means that it prevents the sender from claiming that he or she did not actually send the information. These features are every bit as fundamental to cryptography as privacy, if not more. A digital signature serves the same purpose as a handwritten signature. However, a handwritten signature is easy to counterfeit. A digital signature is superior to a handwritten signature in that it is nearly impossible to counterfeit, plus it attests to the contents of the information as well as to the identity of the signer. PublicKey Encryption for Digital Certificates Digital certificates, or cert., simplify the task of establishing whether a public key truly belongs to the purported owner. A certificate is a form of credential. Examples might be your birth certificate. Each of these has some information on it identifying you and some authorization stating that someone else has confirmed your identity. Some certificates, such as your passport, are important enough confirmation of your identity that you would not want to lose them, lest someone use them to impersonate you. Digital Certificate A digital certificate is data that functions much like a physical certificate. A digital certificate is information included with a person's public key that helps others verify that a key is genuine or valid. Digital certificates are used to thwart attempts to substitute one person's key for another. A digital certificate consists of three things: Â¢ A public key. Â¢ Certificate information. ("Identity" information about the user, such as name, user ID, and so on.) Â¢ One or more digital signatures. The purpose of the digital signature on a certificate is to state that the certificate information has been attested to by some other person or entity. The digital signature does not attest to the authenticity of the certificate as a whole; it vouches only that the signed identity information goes along with, or is bound to, the public key. Thus, a certificate is basically a public key with one or two forms of ID attached, plus a hearty stamp of approval from some other trusted individual. Cryptographic Technologies Based on Layers Â¢ Link layer encryption Â¢ Network layer encryption Â¢ IPSEC, VPN, SKIP Â¢ Transport layer Â¢ SSL, PCT(Private Communication Technology) Â¢ Application layer Â¢ PEM (Privacy Enhanced Mail) Â¢ PGP (Pretty Good Privacy) Â¢ SHTTP Cryptographic process can be implemented at various layers starting from the link Layer all the way up to the application layer. The most popular encryption scheme is SSL and it is implemented at the transport layer. If the encryption is done at the transport layer, any application that is running on the top of the transport layer can be protected. Based on Algorithms Secretkey encryption algorithms (Symmetric algorithms) Â¢ DES (Data Encryption Standard)  56 bit key Â¢ Triple DES 112 bit key Â¢ IDEA (International Data Encryption Algorithm) 128bit key Publickey encryption algorithms (Asymmetric algorithms) DiffieHellman (DH): Exponentiation is easy but computing discrete logarithms from the resulting value is practically impossible RSA: Multiplication of two large prime numbers is easy but factoring the resulting product is practically impossible Public Key Infrastructure (PKI) Introduction The term public key infrastructure (PKI) is used to describe the policies, standards, and software that regulate or manipulate certificates and public and private keys. In practice, PKI refers to a system of digital certificates, certification authorities (CA), and other registration authorities that verify and authenticate the validity of each party involved in an electronic transaction. Standards for PKI are still evolving, even as they are being widely implemented as a necessary element of electronic commerce. This section will help you understand what a PKI is and what services are required to build a PKI. PKI concepts on Certificates Certificate: A public key certificate is a digitally signed statement used for authentication and secure exchange of information on the networks. The issuer and signer of the certificate is known as a certification authority (CA). Certificate has No, Validity, Uses of the Key pair (Public & Secret) Certification Authority: A certification authority (CA) is an entity trusted to issue certificates to a requesting entity. A CA verifies the requester's information according to the policy of the CA, and then uses its private key to apply its digital signature to the certificate. CA Policy: A CA issues certificates to requesters based on a set of established criteria. The set of criteria that a CA uses when processing certificate requests is referred to as CA policy. Typically, a CA publishes its policy in a document known as a Certification Practice Statement (CPS). Types of Certification Authorities Selfsigned CA: The public key in the certificate and the key used to verify the certificate are the same Subordinate CA: The public key in certificate and the key used to verify the certificates are different. Rooted CA: This is trusted unconditionally by a client and is at top of a certification hierarchy. Registration: Registration is the process by which a certificate is issued to the subject, provided that the certificate is in compliance with the criteria established by the CA policy. Certificate enrollment: The procedure that an end entity follows to request and receive a certificate from a CA. The certificate request provides identity information to the CA Certificate Revocation: Certificates have a specified lifetime, but CAs can reduce this lifetime by the process known as certificate revocation. The CAs publishes a certificate revocation list (CRL) that lists serial numbers of certificates that it considers no longer usable. Certificate Chain Validation: In a network, when we generate a request for a new certificate, the information in that request is first passed from the requesting program to Certificate Authority (CA) then passes the appropriate data to a program known as a cryptographic service provider (CSP) A CSP is an independent software module that performs cryptography operations, such as secretkey exchange, digital signing of data, and publickey authentication. Chainbuilding mechanism attempts to build a certification path (a certificate chain) from the endentity certificate, such as a user certificate, up to a CA root certificate. Attacking Cryptography Cryptanalysis Cryptanalysis is the process of attempting to discover the plaintext and/ or the key. The types of Cryptanalysis attacks are Differential Cryptanalysis Attack: The differential cryptanalysis attack looks specifically at pairs of cipher texts whose plaintext has some specific differences. It analyzes these differences as the plaintext propagates through various rounds of Data Encryption Standards (DES) when they are encrypted with the same key. Linear Cryptanalysis Attack: Linear Cryptanalys is attack was invented by Mitsuru Matsui in 1993. This method is based on the concept that if you XOR some of the plaintext bits together, XOR some cipher text bits together, and then XOR the results, you will get a single bit that is the XOR of some of the key bits. A large number of such plain/cipher texts pairs are used to guess the values of the key bits Brute Force Attack The simplest attack to decipher a DES key is the brute force attack. The brute force attack on the DES algorithm is feasible because of the relatively small key length (56 bit) and everincreasing computational power of the computers. It can break through any cipher by trying all keys that possibly exist. However, in brute force attacks, the time taken to break a cipher is directly proportional to the length of the key. In a brute force attack, keys are randomly generated and applied to the cipher text until the legitimate key is generated. The Average Time Required for Exhaustive Key Search Conclusion Cryptography protects users by providing functionality for the encryption of data and authentication of other users. This technology lets the receiver of an electronic message verify the sender, ensures that a message can be read only by the intended person, and assures the recipient that a message has not be altered in transit. This paper describes the cryptographic concepts of symmetric key encryption, publickey encryption, types of encryption algorithms, hash algorithms, digital signatures, and key exchange. The Cryptography Attacking techniques like Cryptanalysis and Brute Force Attack. This Paper provides information of Network Security Needs and Requirements. Cryptography is a particularly interesting field because of the amount of work that is, by necessity, done in secret. The irony is that today, secrecy is not the key to the goodness of a cryptographic algorithm. Regardless of the mathematical theory behind an algorithm, the best algorithms are those that are well known and welldocumented because they are also welltested and wellstudied! In fact, time is the only true test of good cryptography; any cryptographic scheme that stays in use year after year is most likely a good one. The strength of cryptography lies in the choice (and management) of the keys; longer keys will resist attack better than shorter keys. References: Â¢ Cryptography and Network Security â€œBy William Stallings. Â¢ Introduction to Cryptography â€œBy Aysel Ozgur Â¢ en.wikipedia.org. Â¢ wwwusers.cs.umn.edu/ http:/ Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion



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02042010, 03:51 PM
ABSTRACT
The present century has been one of many scientific discoveries and technological advancements. With the advent of technology came the issue of security. As computing systems became more complicated, there was an increasing need for security. This paper deals with cryptography, which is one of the methods to provide security. It is needed to make sure that information is hidden from anyone for whom it is not intended. It involves the use of a cryptographic algorithm used in the encryption and decryption process. It works in combination with the key to encrypt the plain text. Public key cryptography provides a method to involve digital signatures, which provide authentication and data integrity. To simplify this process an improvement is the addition of hash functions. The main focus of this paper is on quantum cryptography, which has the advantage that the exchange of information can be shown to be secure in a very strong sense, without making assumptions about the intractability of certain mathematical problems. It is an approach of securing communications based on certain phenomena of quantum physics. There are two bases to represent data by this method depending on bit values. There are ways of eavesdropping even on this protocol including the Man â€œintheMiddle attack. The quantum computers could do some really phenomenal things for cryptography if the practical difficulties can be overcome. Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion



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08062010, 01:15 PM
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08032011, 02:15 PM
1.DOC (Size: 131 KB / Downloads: 123) CRYPTOGRAPHY INTRODUCTION: The Explosive growth in computer systems and their interconnection via networks has increased the dependence of both organizations and individuals on the information stored and communicated. This in turn, has lead to a heightened awareness of the need to protect data and resources from disclosures, to guarantee the authenticity of data and messages and to protect the systems from network based attacks. Secondly, the disciplines of cryptography and network security have matured, leading to the development of practical, readily available applications to enforce network security. In distributed systems or in networks, the communication can be possible by carrying data between terminal user and computer and between computer and computer. Network security measures are needed to protect data during their transmission and this can be achieved through cryptography. AN OVERVIEW OF CRYPTOGRAPHY: The word cryptography means “secret writing”. However, the term today refers to the science and of transforming messages to make them secure and immune to attacks. The original message before being transformed is called plaintext. After the message is transformed, it is called cipher text. An encryption algorithm transforms the plaintext to cipher; a decryption algorithm transforms the cipher text back to plaintext. The sender uses an encryption algorithm, and the receiver uses a decryption algorithm These encryption and decryption algorithms are called as ciphers (categories of algorithm). One cipher can serve millions of communicating pairs. A Key is value that the cipher, as an algorithm, operates on. To encrypt a message we need an encryption algorithm, an encryption key, and the plain text. These create the cipher text. To decrypt a message, we need a decryption algorithm, a decryption algorithm and the cipher text. So these reveal the original plaintext. In Cryptography, the encryption/decryption algorithms are public; anyone can access them. The keys are secret. So they need to be protected. Cryptography algorithms can be divided into two groups. • Symmetrickey cryptography (or secret key) algorithm • Publickey cryptography (or asymmetric key) algorithm Symmetric–key cryptography: The symmetrickey cryptography algorithms are so named because the same key can be used in both directions. Here, the same key is used by both sender/receiver. The sender uses this key and an encryption algorithm to encrypt data. The receiver uses the same key and a decryption algorithm to decrypt data. In Symmetrickey cryptography, the algorithm used for decryption is the inverse of the algorithm used for encryption. Advantages: • Symmetric key algorithms are efficient. • It takes less time to encrypt a message using symmetric key algorithm than to encrypt a message using a public key algorithm. • The key is usually small. • It is used to encrypt and decrypt long messages. Disadvantages: • Each pair of users must have a unique symmetric key. For n people, n*(n1)/2 symmetric keys are used. Ex: For 1 million people to communicate, 500 billion symmetric keys are needed. • The distribution of keys between two can be difficult. TRADITIONAL CIPHER: Ciphers that involved either substitution or transposition are referred to as traditional ciphers. SUBSTITUTION CIPHER: A cipher using the substitution method substitutes one symbol with another. If the symbols in the plain text are alphanumeric characters, we replace one character with another. Ex: we replace characters A with D, B with E and so on. If symbols are digits (0 to 9), we can replace 1 with 5, 2 with 6 and so on. Concentrating on the alphabetic characters, substitution can be categorized as either 1) Mono alphabetic or 2) Poly alphabetic substitution. MONO ALPHABETIC SUBSTITUTION: In this substitution, a character in the plain text is always changed to same character in the cipher text. The first recorded cipher text is Caesar cipher. The cipher shifts each character down by three. In the above figure, the encryption algorithm is “shift key characters down” and the decryption algorithm is “shift key characters up”. The key here is 3. The encryption and decryption algorithms are the inverses of each other and the key is same for both the algorithms. Here, we replaced character Y with B. This can be possible not by simply adding the key to the character. Since Y=24, which means that 24+3 is 1, not 27 i.e., modulo of 26. Therefore character with value 1, B is given to Y. In mono alphabetic substitution, a character in the plain text and a character in the cipher text is always one one. ADVANTAGE: • It is very simple. DISADVANTAGES: • The code can be attacked easily. The reason is that method cannot hide the natural frequencies of characters in the language being used. So the attacker can easily break the code. POLY ALPHABETIC SUBSTITUTION: In poly alphabetic substitution, each occurrence of a character can have a different substitute. The relationship between a character in the plaintext to a character in the cipher text is onetomany character A can be changed to D in the beginning of the text, but it could be changed to N at the middle. Let us define our key as “ take the position of the character in the text, divide the by 10, and let the remainder be the shift value.” With this scenario, the character at position 1 will be shifted one character, the character at position 2 will be shifted two characters, and the character in position 14 will be shifted four characters [14 mod 10 is 4]. An example of poly alphabetic substitution is the vigenere cipher. In one version of the cipher, the character in the cipher text is chosen from a twodimensional table (26*26), in which each row is a permutation of 26 characters (A to Z). To change a character, the algorithm finds the character to be encrypted in the first row. It finds the position of the character in the text (mod 26) and uses it as the row number. The algorithm then replaces the character with the character found in the table. A cipher text created by poly alphabetic substitution is harder to attack successfully than a cipher text created by mono alphabetic substitution. A good poly alphabetic substitution may smooth out the frequencies; each character in the cipher text may occur almost the same number of times. However, attacking the code is not difficult; although the encryption changes the frequencies of the characters, the character relationships are still preserved. A good trailanderror attack can break the code. TRANSPOSITIONAL CIPHER: In a transpositional cipher, the characters retain their plaintext from but change their positions to create the cipher text. The text is organized into a twodimensional table, and the columns are interchanged according to a key. For example, we can organize the plaintext into an 8column table and then reorganize the columns according to a key that indicates the interchange rule. The key defines which columns should be swapped. Transpositional cryptography is not very secure either. The character frequencies are preserved, and the attacker can find the plaintext through trail and error. 


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02042011, 04:25 PM
Cryptography.ppt (Size: 796 KB / Downloads: 195) ITNS and CERIAS CISSP Luncheon Series: Cryptography Introduction “Hidden writing” Increasingly used to protect information Can ensure confidentiality • Integrity and Authenticity too History – The Manual Era Dates back to at least 2000 B.C. Pen and Paper Cryptography Examples • Scytale • Atbash • Caesar • Vigenère History – The Mechanical Era Invention of cipher machines Examples • Confederate Army’s Cipher Disk • Japanese Red and Purple Machines • German Enigma History – The Modern Era Computers! Examples • Lucifer • Rijndael • RSA • ElGamal • Speak Like a Crypto Geek Plaintext – A message in its natural format readable by an attacker Ciphertext – Message altered to be unreadable by anyone except the intended recipients Key – Sequence that controls the operation and behavior of the cryptographic algorithm Keyspace – Total number of possible values of keys in a crypto algorithm Speak Like a Crypto Geek (2) Initialization Vector – Random values used with ciphers to ensure no patterns are created during encryption Cryptosystem – The combination of algorithm, key, and key management functions used to perform cryptographic operations Cryptosystem Services Confidentiality Integrity Authenticity Nonrepudiation Access Control Types of Cryptography Streambased Ciphers One at a time, please Mixes plaintext with key stream Good for realtime services Block Ciphers Amusement Park Ride Substitution and transposition Encryption Systems Substitution Cipher Convert one letter to another Cryptoquip Transposition Cipher Change position of letter in text Word Jumble Monoalphabetic Cipher Caesar Encryption Systems Polyalphabetic Cipher Vigenère Modular Mathematics Running Key Cipher Onetime Pads Randomly generated keys Steganography Hiding a message within another medium, such as an image No key is required Example Modify color map of JPEG image Cryptographic Methods Symmetric Same key for encryption and decryption Key distribution problem Asymmetric Mathematically related key pairs for encryption and decryption Public and private keys Cryptographic Methods Hybrid Combines strengths of both methods Asymmetric distributes symmetric key » Also known as a session key Symmetric provides bulk encryption Example: » SSL negotiates a hybrid method Attributes of Strong Encryption Confusion Change key values each round Performed through substitution Complicates plaintext/key relationship Diffusion Change location of plaintext in ciphertext Done through transposition Symmetric Algorithms DES Modes: ECB, CBC, CFB, OFB, CM 3DES AES IDEA Blowfish Symmetric Algorithms RC4 RC5 CAST SAFER Twofish Asymmetric Algorithms DiffieHellman RSA El Gamal Elliptic Curve Cryptography (ECC) Hashing Algorithms MD5 Computes 128bit hash value Widely used for file integrity checking SHA1 Computes 160bit hash value NIST approved message digest algorithm Hashing Algorithms HAVAL Computes between 128 and 256 bit hash Between 3 and 5 rounds RIPEMD160 Developed in Europe published in 1996 Patentfree 


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05042011, 09:37 AM
KEY CRYPTO GRAPHY
802.1i Phase 1: Agreeing on the security policy • supported authentication methods (802.1X, PreShared Key (PSK)), • Security protocols for unicast traffic (CCMP, TKIP etc.) – the pair wise cipher suite, • Security protocols for multicast traffic (CCMP, TKIP etc.) – the group cipher suite, • Support for preauthentication, al lowing users to preauthenticate Before switching to a new access point of the same network for a seamless handover. Phase 2: 802.1X authentication The second phase is 802.1X authentication based on EAP and the specific authentication method agreed earlier: EAP/TLS with client and server certificates (requiring a public key infrastructure), EAP/TTLS or PEAP for hybrid authentication (with certificates only required for servers) etc. 802.1X authentication are initiated when the access point requests client identity data, with the client’s response containing the preferred authentication method. Suitable messages are then exchanged between the client and the authentication server to generate a common master key (MK). At the end of the procedure, a Radius Accept message is send from the authentication server to the access point, containing the MK and a final EAP Success message for the client. Phase 3: Key hierarchy and distribution Connection security relies heavily on secret keys. In RSN, each key has a limited lifetime and overall security is ensured using a collection of various keys, organized into a hierarchy. When a security context is stab lashed after successful authentic tin, temporary (session) keys are created and regularly updated until the security context is closed. Key generation and exchange is the goal of the third phase. • confirm the client’s knowledge of the PMK, • derive a fresh PTK, • install encryption and integrity keys, • encrypt transport of the GTK, • confirm cipher suite selection. Phase 4: RSNA data confidentiality and integrity All the keys generated previously are used in protocols supporting RSNA data confidentiality and integrity: • Temporal Key Hash • CounterMode / Cipher Block Chaining Message Authentication Code Protocol • Wireless Robust Authenticated Protocol An important concept must be understood before detailing these protocols: the difference between an MSDU (MAC Service Data Unit) and an MPDU (MAC Protocol Data Unit). Both refer to a single packet of data, but MSDU represents data before fragmentation, while MPDUs are the multiple data units after fragmentation. The difference is important in TKIP and CCMP encryption, since in TKIP the MIC is calculated from the MSDU, while in CCMP it is calculated from the MPDU. The TKIP KeyMixing Scheme is divided into two phases. Phase 1 involves static data – the secret session key TEK, the transmitter MAC address TA (included to pre vent IV collisions) and the higher 32 bits of the IV. Phase 2 includes the output of Phase 1 and the lower 16 bits of the IV, changing all the bits of the Per Packet Key field for each new IV. The IV value always starts with 0 and is incremented by 1 for each packet sent, with any messages whose TSC is not greater than the last message being discarded. The output of Phase 2 and part of the extended IV (plus a dummy byte) are the input for RC4, generating a key stream that is XORend with the plaintext MPDU, the MIC calculated from the MPDU and the old ICV from WEP. MIC computation uses the Michael algorithm by Niels Ferguson. It was created for TKIP and has a target security level of 20 bits (the algorithm doesn’t use multiplication for performance reasons, as it must be supported on old wire less hardware later to be upgraded to WPA). Due to this limitation, countermeasures are needed to avoid MIC forgery. MIC failures must be kept below two per minute, otherwise a 60 second blackout is enforced and new keys (GTK and PTK) must be established afterwards. Michael computes an 8octet check value called the MIC and appends it to the MSDU prior to transmission. The MIC is calculated from the source address (SA), destination address (DA), plaintext MSDU and the appropriate TMK (depending on the communication side, a different key is used for transmission and reception). CCMP is based on the AES (Advanced Encryption Standard) block cipher suite in its CCM mode of operation, with the key and blocks being 128 bits long. AES is to CCMP what RC4 is to TKIP, but unlike TKIP, which was intended to accommodate existing WEP hard ware, CCMP isn't a compromise, but a new protocol design. CCMP uses counter mode in conjunction with a message authentication method called Cipher Block Chaining (CBCMAC) to produce an MIC. Some interesting features were also added, such as the use of a single key for encryption and authentication (with different initialization vectors) or covering nonencrypted data by the authentication. The CCMP protocol adds 16 bytes to the MPDU: 8 bytes for the CCMP header and 8 bytes for the MIC. The CCMP header is an unencrypted field included between the MAC header and encrypted data, including the 48bit PN (Packet Number = Extended IV) and Group Key Key ID. The PN is incremented by one for each sub sequent MPDU. MIC computation uses the CBCMAC algorithm that encrypts a starting nonce block (computed from the Priority fields, MPDU source address and incremented PN) and XORs subsequent blocks to obtain a final MIC of 64 bits (the final MIC is a 128bit block, since the lower 64 bits are discarded). The MIC is then appended to the plaintext data for AES encryption in counter mode. The counter is constructed from a nonce similar to the MIC one, but with an extra counter field initialized to 1 and incremented for each block. The last protocol is WRAP, also based on AES, but using the OCB (Offset Codebook Mode) authenticated encryption scheme (encryption and authentication in a single computation). OCB was the first mode selected by the IEEE 802.11i working group, but was eventually abandoned due to intellectual property issues and possible licensing fees. CCMP was then adopted as mandatory 


seminar class Active In SP Posts: 5,361 Joined: Feb 2011 
30042011, 10:02 AM
PRESENTED BY,
Ayesha Farhin 18816402Cryptography.ppt (Size: 491 KB / Downloads: 89) CRYPTOGRAPHY Introduction Cryptography considered as a branch of both mathematics and computer science. Affiliated closely with information theory, computer security, and engineering. Definitions: Cryptography comes from the Greek words Kryptos, meaning hidden, and Graphen, meaning to write. Thus Cryptography is the study of secret (crypto) writing (graphy) Cryptography deals with all aspects of secure messaging, authentication, digital signatures, electronic money, and other applications. The practitioner of Cryptography is called Cryptographer Cryptography Through History Cryptography has a history of at least 4000 years. Ancient Egyptians enciphered some of their hieroglyphic writing on monuments. Ancient Hebrews enciphered certain words in the scriptures. 2000 years ago Julius Caesar used a simple substitution cipher, now known as the Caesar cipher. Roger Bacon in the middle ages described several methods in 1200s. Cryptography Through History Geoffrey Chaucer included several ciphers in his works (e.g. Canterbury Tales). Leon Alberti devised a cipher wheel, and described the principles of frequency analysis in the 1460s. Blaise de Vigenère published a book on cryptology in 1585, & described the polyalphabetic substitution cipher. Increasing use, especially in diplomacy & war over centuries. Areas of Study Computer Security: Cryptanalysis, Cryptology, Cryptography Terminologies: Encryption Decryption Plaintext Cipher Text Cryptanalaysis The study of principles and methods of transforming an unintelligible message back into an intelligible message without knowledge of the key is called Cryptanalysis. Also called “code breaking” sometimes. Practitioners of cryptanalysis are cryptanalysts. Cryptology Cryptology is the branch of mathematics that studies the mathematical foundations of cryptographic methods. Cryptology is actually the study of codes and ciphers. Cryptology = both cryptography and cryptanalysis Definitions: In cryptographic terminology, the message is called plaintext or cleartext. Encoding the contents of the message in such a way that hides its contents from outsiders is called encryption. A method of encryption and decryption is called a cipher  The name cipher originates from the Hebrew word "Saphar," meaning "to number.” The encrypted message is called the ciphertext. The process of retrieving the plaintext from the ciphertext is called decryption. Encryption and decryption usually make use of a key, and the coding method is such that decryption can be performed only by knowing the proper key. The Key All modern algorithms use a key to control encryption and decryption; a message can be decrypted only if the key matches the encryption key. The key used for decryption can be different from the encryption key, but for most algorithms they are the same. Why do we need cryptography? Computers are used by millions of people for many purposes Banking Shopping Tax returns Protesting Military Student records Privacy is a crucial issue in many of these applications Security is to make sure that nosy people cannot read or secretly modify messages intended for other recipients Security issues: some practical situations A sends a file to B: E intercepts it and reads it. How to send a file that looks gibberish to all but the intended receiver? A sends a file to B: E intercepts it, modifies it, and then forwards it to B. How to make sure that the document has been received in exactly the form it has been sent? E sends a file to B pretending it is from A. How to make sure your communication partner is really who she claims to be? Basic situation in cryptography Types Of Attacks: Passive Attack: Carried out by a Passive Attacker who can only read the secret information being exchanged. Active Attack: Carried out by an Active Intruder who can read and modify the secret information Passive Attacks Active Attacks Ciphertextonly Attack This is the situation where the attacker does not know anything about the contents of the message, and must work from ciphertext only. In practice it is quite often possible to make guesses about the plaintext, as many types of messages have fixed format headers. Even ordinary letters and documents begin in a very predictable way. It may also be possible to guess that some ciphertext block contains a common word. Knownplaintext Attack The attacker knows or can guess the plaintext for some parts of the ciphertext. The task is to decrypt the rest of the ciphertext blocks using this information. This may be done by determining the key used to encrypt the data, or via some shortcut. Chosenplaintext Attack The attacker is able to have any text he likes encrypted with the unknown key. The task is to determine the key used for encryption. Some encryption methods, particularly RSA, are extremely vulnerable to chosenplaintext attacks. When such algorithms are used, extreme care must be taken to design the entire system so that an attacker can never have chosen plaintext encrypted. Classical Cryptographic Techniques Three Eras of Cryptography: Classical Traditional Modern We have two basic components of classical ciphers: substitution and transposition. Substitution: In substitution ciphers letters are replaced by other letters. Transposition: In transposition ciphers the letters are arranged in a different order. Caesar CipherA Monoalphabetic Substitution Cipher Replace each letter of message by a letter a fixed distance away e.g. use the 3rd letter on Reputedly used by Julius Caesar. E.g: L FDPH L VDZ L FRQTXHUHG I CAME I SAW I CONQUERED i.e. mapping is A B C D E F G H I J K L M N O P Q R S T U V W X Y Z                           D E F G H I J K L M N O P Q R S T U V W X Y Z A B C Can describe this cipher as: Encryption Ek : i i + k mod 26 Decryption Dk : i i  k mod 26 Polyalphabetic Substitution Cipher Polyalphabetic Substitution  several substitutions are used. Used to hide the statistics of the plaintext. PolyalphabeticSubstitution Example PolyalphabeticSubstitution Example Plaintext  now is the time for every good man Ciphertext  JCQ CZ VXK VCER AQC PCRTX LBQZ QPK Note: The two o’s in good have been enciphered as different letters. Also the three letters “X” in the ciphertext represent different letters in the plaintext. Algorithms Of Modern Crytography Algorithms are basic building blocks on which Crypto Systems are built. Classes of keybased algorithms: Symmetric or Privatekey Systems. Asymmetric or Publickey Systems. Symmetric Algorithms Symmetric algorithms use the same key for encryption and decryption Can be divided into two categories: (1) stream ciphers and (2) block ciphers. Stream ciphers can encrypt a single bit/byte of plaintext at a time. Block ciphers take a number of bits (typically 64 bits in modern ciphers), and encrypt them as a single unit. Example Symmetric Encryption Algorithm  DES The most well known symmetric system is the Data Encryption Standard (DES). Data Encrypt Standard (DES) is a private key system adopted by the U.S. government as a standard “very secure” method of encryption. 64bit plain & cipher text block size 56bit true key plus 8 parity bits Single chip (hardware) implementation  Most implementations now software 16 rounds of transpositions & substitutions Standard for unclassified government data Applications of DES Double DES Effective key length of 112 bits Work factor about the same as single DES Triple DES Encrypt with first key Decrypt with second key Encrypt with first key Very secure used across a wide range of applications, from ATM encryption to email privacy and secure remote access. Private Key Problems Keys must be exchanged before transmission with any recipient or potential recipient of your message. So, to exchange keys you need a secure method of transmission, but essentially what you've done is create a need for another secure method of transmission. Secondly the parties are not protected against each other, if one of the parties leaks the keys it could easily blame the other party for the compromise. Asymmetric Algorithms Use a different key for encryption and decryption, and the decryption key cannot be derived from the encryption key. Asymmetric ciphers also called publickey algorithms permit the encryption key to be public (it can even be published in a newspaper), allowing anyone to encrypt with the key, whereas only the proper recipient (who knows the decryption key) can decrypt the message. The encryption key is also called the Public Key and the decryption key the Private Key or Secret Key. Public Key Encryption Public Key Encryption RSA The best known public key system is RSA, named after its authors, Rivest, Shamir and Adelman. It has recently been brought to light that an RSAlike algorithm was discovered several years before the RSA guys by some official of the British Military Intelligence Cryptography Wing. Comparison of Symmetric and Asymmetric Encryption Other Types: One Time Pad Hash Function Digital Signature Certified Authority ADVANTAGES AND DISADVANTAGES Advantages: 1. The biggest advantage of public key cryptography is the secure nature of the private key. In fact, it never needs to be transmitted or revealed to anyone. 2. It enables the use of digital certificates and digital timestamps, which is a very secure technique of signature authorization. Disadvantages: Transmission time for documents encrypted using public key cryptography are significantly slower then symmetric cryptography. In fact, transmission of very large documents is prohibitive. The key sizes must be significantly larger than symmetric cryptography to achieve the same level of protection. Public key cryptography is susceptible to impersonation attacks. Future Developments: Quantum cryptography and DNA cryptography DNA cryptography is a new born cryptographic field emerged with the research of DNA computing, in which DNA is used as information carrier and the modern biological technology is used as implementation tool. The vast parallelism and extraordinary information density inherent in DNA molecules are explored for cryptographic purposes such as encryption, authentication, signature, and so on. Quantum cryptography Quantum cryptography attempts to achieve the same security of information as other forms of cryptography but through the use of photons, or packets of light. The process, though still in experimental stages, makes use of the polarization nature of light and is proving to be a very promising defense against eavesdropping 


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30042011, 03:54 PM
Presented By: Yogita Dey Amardeep Kahali Dipanjan Devnagar Minhaajuddin Ahmad Khan Cryptography.pptx (Size: 1.36 MB / Downloads: 62) Cryptography Background Information Security requirements have changed in recent times Traditionally provided by physical and administrative mechanisms Computer use requires automated tools to protect files and other stored information Use of networks and communications links requires measures to protect data during transmission Need for Information Security Defending against external/internal hackers Defending against industrial espionage Securing Ecommerce Securing bank accounts/electronic transfers Securing intellectual property Avoiding liability Threats to Information Security Pervasiveness of email/networks Online storage of sensitive information Insecure technologies (e.g. wireless) Trend towards paperless society Weak legal protection of email privacy Essential Terms Cryptography Encryption (code) Plain text Cipher text Decryption (decode) Cipher text Plain text Cryptanalysis Cryptology Cryptographic Algorithms Symmetric Key or secret key: Involves use of one key. Asymmetric key or public key: Involves use of two keys viz. public and private. Message Digest. Hash Functions. Symmetric Key Cryptography Traditional Ciphers Substitution Mono alphabetic e.g. Caesar cipher Poly alphabetic e.g. Vigenère cipher, Hill cipher Modern Ciphers Simple Modern Ciphers XOR Cipher Rotation Cipher Sbox (Substitution) Pbox (Permutation) Two types of symmetric ciphers Stream ciphers Encrypt one bit at time Block ciphers Break plaintext message in equalsize blocks Encrypt each block as a unit Stream Ciphers Combine each bit of keystream with bit of plaintext to get bit of ciphertext m(i) = ith bit of message ks(i) = ith bit of keystream c(i) = ith bit of ciphertext c(i) = ks (i) m(i) m(i) = ks (i) c(i) RC5 Stream Cipher Feistel like network Variable block size (32,63 or 128 bits) Key size (0 to 2040 bits) Use of data dependent rotations Really simple 12round RC5 (with 64bit blocks) is susceptible to a differential attack using 244 chosen plaintexts Block Ciphers Message to be encrypted is processed in blocks of k bits (e.g., 64bit blocks). 1to1 mapping is used to map kbit block of plaintext to kbit block of ciphertext Example with k=3 Data Encryption Standard (DES) US encryption standard designed by IBM [NIST 1993] 56bit symmetric key, 64bit plaintext input Block cipher with cipher block chaining 56bitkeyencrypted phrase decrypted (brute force) in less than a day No known good analytic attack Data Encryption Standard (DES) Advanced Encryption Standard (AES) New (Nov. 2001) symmetrickey NIST standard, replacing DES Based on Rijndael Algorithm Processes data in 128 bit blocks 128, 192, or 256 bit keys Brute force decryption taking 1 sec on DES, takes 149 trillion years for AES Asymmetric Key Cryptography RSA (Rivest, Shamir, Adelman) DH (DiffieHellman Key Agreement Algorithm) ECDH (Elliptic Curve DiffieHellman Key Agreement Algorithm) RPK (Raike Public Key) Choose two distinct prime numbers p and q. Compute n = pq Compute φ(n) = (p – 1)(q – 1) Choose an integer e such that 1 < e < φ(n) and e and φ(n) are coprime Determine d = e1 mod φ(n) e is released as the public key exponent and d is kept as the private key exponent A hybrid encryption technology Message is encrypted using a private key algorithm (IDEA) Key is then encrypted using a public key algorithm (RSA) For file encryption, only IDEA algorithm is used PGP is free for home use Digital Signatures Made by encrypting a message digest (cryptographic checksum) with the sender’s private key Receiver decrypts with the sender’s public key (roles of private and public keys are flipped) Prevents Impostor attacks Content tampering Timing modification Currently Available Technologies MD4 and MD5 (Message Digest) SHA1 (Secure Hash Algorithm version 1) DSA (The Digital Signature Algorithm) ECDSA (Elliptic Curve DSA) Kerberos OPS (Open Profiling Standard) VeriSign Digital IDs Benefits of Cryptographic Technologies Data secrecy Data integrity Authentication of message originator Electronic certification and digital signature Nonrepudiation Potential Problems False sense of security if badly implemented Government regulation of cryptographic technologies/export restrictions Encryption prohibited in some countries All public key schemes are susceptible to brute force attacks…only the work factor varies With decreasing cost of computer power and mathematical discoveries, work factor is decreasing Remarks Encryption does not guarantee security! Many ways to beat a crypto system NOT dependent on cryptanalysis, such as: Viruses, worms, hackers, etc. TEMPEST attacks Unauthorized physical access to secret keys Cryptography is only one element of comprehensive computer security 


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