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    Digital Signature Essay

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    Digital Signatures CONTENTS 1. ABSTRACT 2. INTRODUCTION 3. DESIGN PRINCIPLES & EXPLANATION 3. 1. MODULES 3. 2. MODULE DESCRIPTIOIN 4. PROJECT DICTIONARY 4. 1. DATAFLOW DIAGRAMS 5. FORMS & REPORTS 5. 1. I/O SAMPLES 6. BIBILIOGRAPHY 1. ABSTRACT The security of information available to an organization was primarily provided through physical and administrative means. For example, rugged file cabinets with a combination lock were used for storing sensitive documents and personnel screening procedures were employed during the hiring process.

    With the introduction of the computer, the need for automated tools for protecting files and other information stored on the computer became evident. This is especially the case for a shared system and the need is even more acute for a network. Computer networks were primarily used by university researches for sending e-mail, and by corporate employees for sharing printers. Under these conditions, security was not given much attention. Today, since the world is going global, and trillions of data are transferred daily across networks, security is looming on the horizon as a potentially massive problem.

    The generic name for the collection of tools designed to protect data and to thwart hackers is Computer Security. In the project titled “Digital Signatures” security is ensured in the Messaging System of an organization. In this application, if an employee wishes to send confidential information to another employee connected through the intranet of their organization, he first signs the message and then sends it to the recipient. He signs the message using Digital Signatures. The person who receives the message validates the sender and if the message is from an authorized employee, he reads the message.

    The above operation is performed using Digital Signature Algorithm (DSA). This application makes sure that the security services Authentication, Secrecy, Integrity, and Non-repudiation are provided to the user. Therefore, intruders cannot gain access to classified information. 2. INTRODUCTION Scope The project is confined to the intranet in an organization. This application makes sure that security services such as secrecy, authentication, integrity and non-repudiation are provided to the communicating parties. Objective

    This project has been developed keeping in view the security features that need to be implemented in the networks following the fulfillment of these objectives: • To develop an application that deals with the security threats that arise in the network. • To enable the end-users as well as the organizations come out with a safe messaging communication without any threats from intruders or unauthorized people. • To deal with the four inter-related areas of network security namely Secrecy, Authentication, Non-repudiation and Integrity. Project Overview This application makes use of Digital Signature Algorithm (DSA) along with a hash function.

    The hash code is provided as input to a signature function along with a random number generated for this particular signature. The signature function also depends on the sender’s private key and a set of parameters known to a group of communicating principals. This set constitutes a global public key. The result is a signature consisting of two components. At the receiving end, verification is performed. The receiver generates a quantity that is a function of the public-key components, the sender’s public key, and the hash code of the incoming message.

    If this quantity matches with one of the components of the signature, then the signature is validated. This application makes sure that the security services Authentication, Secrecy, Integrity, and Non-repudiation are provided to the user. • This application allows to keep the information out of the hands of unauthorized persons. This is called Secrecy. • It also deals with determining whom a person is communicating with before revealing sensitive information or entering a business deal. This is called Authentication. • Non-repudiation deals with proving that a particular message was sent by a particular person in case he denies it later. Integrity makes sure whether a particular message has been modified or something has been added to it. The project mainly deals with maintenance of the above mentioned security services thereby allowing the users as well as the network organizations to keep track of intrusions and thus enhancing the security services. [pic] Existing system These days almost all organizations around the globe use a messaging system to transfer data among their employees through their exclusive intranet. But the security provided is not of high standards. More and more unauthorized people are gaining access to confidential data.

    Disadvantages: • The validity of sender is not known. • The sender may deny sending a message that he/she has actually sent and similarly the receiver may deny the receipt that he/she has actually received. • Unauthorized people can gain access to classified data. • Intruders can modify the messages or the receiver himself may modify the message and claim that the sender has sent it. Proposed system The system will provide the following security services: Confidentiality: Confidentiality is the protection of transmitted data from passive attacks.

    With respect to the release of message contents, several levels of protection can be identified. The broadest service protects all user data transmitted between two users over a period of time. For example, if a virtual circuit is set up between two systems, this broad protection would prevent the release of any user data transmitted over the virtual circuit. Narrower forms of this service can also be defined, including the protection of a single message or even specific fields within a message. These refinements are less useful than the broad approach and may even be more complex and expensive to implement.

    The other aspect of confidentiality is the protection of traffic flow from analysis. This requires that an attacker not be able to observe the source and destination, frequency, length, or other characteristics of the traffic on a communications facility. Authentication: The authentication service is concerned with assuring that a communication is authentic. In the case of a single message, such as a warning or alarm signal, the function of the authentication service is to assure the recipient that the message is from the source that it claims to be from.

    In the case of an ongoing interaction, such as the connection of a terminal to a host, two aspects are involved. First, at the time of connection initiation, the service assures that the two entities are authentic (i. e. that each is the entity that it claims to be). Second, the service must assure that the connection is not interfered with in such a way that a third party can masquerade as one of the two legitimate parties for the purposes of unauthorized transmission or reception. Integrity: Integrity basically means ensuring that the data messages are not modified.

    An integrity service that deals with a stream of messages assures that messages are received as sent, with no duplication, insertion, modification, reordering or replays. The destruction of data is also covered under this service. Thus the integrity service addresses both message modification and denial of service. Non-repudiation: Non-repudiation prevents either sender or receiver from denying a transmitted message. Thus, when a message is sent, the receiver can prove that the message was in fact sent by the alleged sender.

    Similarly, when a message is received, the sender can prove that the message was in fact received by the alleged receiver. DIGITAL SIGNATURES Message authentication protects two parties who exchange messages from any third party. However, it does not protect the two parties against each other. Several forms of disputes between the two parties are possible. For example, suppose that A sends an authenticated message to B. Consider the following disputes that could arise: 1. B may forge a different message and claim that it came from A.

    B would simply have to create a message and append an authentication code using the key that A and B share. 2. A may deny sending the message. Because it is possible for B to forge a message, there is no way to prove that A did in fact send the message. The most attractive solution to this problem is the Digital Signature. The Digital Signature is analogous to the handwritten signature. It must have the following properties: • It must be able to verify the author and the date and time of the signature. • It must be able to authenticate the contents at the time of the signature. The signature must be verified by third parties, to resolve disputes. Thus, the digital signature function includes the authentication function. Based on the above properties, the following requirements can be formulated for the digital signatures: • The signature must be a bit pattern that depends on the message being signed. • The signature must use some information unique to the sender, to prevent both forgery and denial. • It must be relatively easy to produce the digital signature. • It must be relatively easy to recognize and verify the digital signature. It must be computationally infeasible to forge a digital signature, either by constructing a new message for an existing digital signature or by constructing a fraudulent digital signature for a given message. • It must be practical to retain a copy of the digital signature in storage. A secure hash function, embedded properly in a scheme satisfies these requirements. There are two approaches to implement digital signatures: • DSS approach • RSA approach The Digital Signature Standard (DSS) makes use of the Secure Hash Algorithm (SHA) to present a new digital signature technique, the Digital Signature Algorithm (DSA).

    It uses an algorithm that is designed to provide only the digital signature function. Unlike RSA, it cannot be used for encryption or Key exchange. Nevertheless, it is a public-key technique. RSA Approach In the RSA approach, the message to be signed is input to a hash function that produces a secure hash code of fixed length. This hash code is then encrypted using the sender’s private key to form the signature. Both the message and the signature are then transmitted. The recipient takes the message and produces a hash code. The recipient also decrypts the signature using the sender’s public key.

    If the calculated hash code matches the decrypted signature, the signature is accepted as valid. Because only the sender knows the private key, only the sender could have produced a valid signature. [pic] where M = Message H = Hash Function E = Message Digest at the Sender’s side D = Message Digest at the Receiver’s side KRa = Sender’s Private Key KUa = Sender’s Public Key DSS Approach The Digital Signature Standard approach also makes use of a hash function. The hash code is provided as input to a signature function along with a random number generated for this particular signature.

    The signature function also depends on the sender’s private key and a set of parameters known to a group of communicating principals. This set constitutes a global public key. The result is a signature consisting of two components. [pic] where M = Message H = Hash Function KRa = Sender’s Private Key KUa = Sender’s Public Key KUG = Group Public Key r, s = Signature k = Random Number Sig = Signature Function Ver = Verification Function Disadvantage of RSA over DSA RSA does not use a hash function, it encrypts the message. The length of the encrypted code is same as that of the original message which leads to 100% overhead.

    This implies more processor overload and increase in processing time. DSA uses a hash function which takes large amounts of data and gives a fixed length message digest. This implies less overhead. Hence DSA is preferred over RSA for Digital Signatures. SECURE HASH ALGORITHM (SHA-1) This application makes use of the Secure Hash Algorithm (SHA-1). The SHA-1 algorithm takes as input a message with a maximum length of less than 264 bits and produces as output a 160-bit message digest. The input is processed in 512-bit blocks. The processing consists of the following steps:

    Step 1 : Appending padding bits The message is padded so that its length is congruent to 448 modulo 512 (length = 448 mod 512). Padding is always added, even if the message is already of the desired length. Thus, the number of padding bits is in the range of 1 to 512. The padding consists of a single 1-bit followed by the necessary number of 0-bits. Step 2 : Append Length. A block of 64 bits is appended to the message. This block is treated as an unsigned 64-bit integer (most significant byte first) and contains the length of the original message (before the padding).

    Step 3 : Initialize MD buffer. A 160-bit buffer is used to hold intermediate and final results of the hash function. The buffer can be represented as five 32-bit registers ( A, B, C, D, E ). These registers are initialized to the following 32-bit integers (hexadecimal values): A = 67452301 B = EFCDAB89 C = 98BADCFE D = 10325476 E = C3D2E1F0 These values are stored in big-endian format, which is the most significant byte of a word in the low-address byte position. As 32-bit strings, the initialization values (in hexadecimal values) : word A = 67 45 23 01 ord B = EF CD AB 89 word C = 98 BA DC FE word D = 10 32 54 76 word E = C3 D2 E1 F0 Step 4 : Process message in 512-bit (16-word ) blocks. The heart of the algorithm is a module that consists of four rounds of processing of 20 steps each. The four rounds have a similar structure, but each uses a different primitive logical function, which we refer to as f1, f2, f3, and f4. Each round takes as input the current 512-bit block being processed (Yq) and the 160-bit buffer value ABCDE and updates the contents of the buffer. Each round also makes use of an additive constant Kt, where 0

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