The Study of Digital Signature in Cryptography

ABSTRACT: Digital signature methodology provides cryptographic services like entity authentication, authenticated key transmission and authenticated key agreement. A Digital Signature is used to provide authentication, non-repudiation & integrity over the digital data in data exchanged and to validate the recipient for the authorized identity over open network. The goal of a Digital signature algorithm is to provide security for message or data. Keywords : Digital signature, Authentication, Non-repudiation, Integrity

INTRODUCTION The information is highly secret which requires a great security, thus, an extensive security measures have to be adopted. Many algorithms and techniques can be used to secure our data or information from threats. These kinds of technologies and algorithms are collectively known as Cryptography. Cryptography system can be widely categorized into two parts first one is symmetric key cryptography (single key system) which is possessed by both the sender and receiver and another one is public key system (asymmetric key cryptography) in which uses of two keys are provided, first is public key which is common for both the sender and receiver and other one is private key which is known to the individual only.

DIGITAL SIGNATURE The authenticity of many legal, financial, and other documents is done by the presence or absence of an authorized handwritten signature.“Digital Signature” is the best solution for authenticity in various fields. A. Digital Signature is an authentication mechanism that enables the creator of a message to attach a code that acts as a signature. The signature is formed by taking the hash of the message and encrypting the message with the creator’s private key. The signature guarantees the source and integrity of the message. It must have the following properties: It must verify the author and the date and time of the signature It must to authenticate the contents at the time of the signature It must be verifiable by third parties to resolve disputes.

IMPORTANCE OF DIGITAL SIGNATURE Out of all cryptographic primitives, the digital signature using public key cryptography is considered as very important and useful tool to achieve information security. Apart from ability to provide non-repudiation of message, the digital signature also provides message authentication and data integrity. Let us briefly see how this is achieved by the digital signature − Message authentication − When the verifier validates the digital signature using public key of a sender, he is assured that signature has been created only by sender who possess the corresponding secret private key and no one else.

Data Integrity − In case an attacker has access to the data and modifies it, the digital signature verification at receiver end fails. The hash of modified data and the output provided by the verification algorithm will not match. Hence, receiver can safely deny the message assuming that data integrity has been breached. Non-repudiation − Since it is assumed that only the signer has the knowledge of the signature key, he can only create unique signature on a given data. Thus the receiver can present data and the digital signature to a third party as evidence if any dispute arises in the future.

APPROACHES Digital signature algorithm (DSA) is the part of Digital Signature Standard (DSS) approach, which is developed by the U.S. National Security Agency (NSA).DSA is a Federal Information Processing Standard for digital signatures. In August 1991 DSA is developed by the National Institute of Standards and Technology (NIST).There are two different approaches to the Digital Signature The RSA Approach. The DSS Approach. The 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. The DSS Approach The DSS approach also makes use of hash function. The hash code is provided as input to a signature function along with a random number k 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 communication principals. We can consider this set to constitute a global public key. The result is a signature consisting of two components, labeled s and r.

ADVANTAGES AND DISADVANTAGES OF DIGITAL SIGNATURE Advantages With the use of digital signature we can remove the chance of committing scam because the digital signature cannot be changed. Moreover the forging Signature is impossible. · By having a digital signature we are proving the Document to be legal We are assuring the receiver that The document is free from fake or false information. Increases the speed and correctness of transactions. Disadvantages · Cost-you must have the essential software to instruct The signatures, and if you're using hardware so that Customers can sign physically, then the cost goes up Even further. Digital signatures are an extra cost That should be weighed against their possible security Benefits. · Preparation and troubleshooting -if your employees aren't Sure how to use a digital signature, then you'll have to Spend time training them about how the signature Process works. Additionally, as with all computer digital Signature 118 Related applications, sooner or later there will be a Hiccups in the system and you'll need someone to Troubleshoot.

CONCLUSION The Digital Signature which is based on RSA and DSA approach has been done. Digital signatures will be championed by many players that the public distrusts, including national security agencies. New variant of algorithms of digital signature that are based on many hard problems like the elliptic curve, disconnected logarithm and prime factorization has also been discussed. Based on the relative analysis, we show the performances based on many characteristics.