RESEARCH ON DIGITAL SIGNATURE Aanchal Chanana, Akash Sharma, Amit Yadav

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1 ABSTRACT RESEARCH ON DIGITAL SIGNATURE Aanchal Chanana, Akash Sharma, Amit Yadav 7 th Semester, Computer Science and Engineering. Dronacharya College Of Engineering, Gurgaon This paper introduces a number of problems faced by business transactions, including financial, legal, and other regulated transactions.these transactions require high assurance when signing documents. When documents are distributed electronically, it is important that recipients can: Verify document authenticity confirming the identity of each person who signed the document Verify document integrity confirming that the document has not been altered in transit KEYWORDS: - digital signature,authenticity,encryption,security,integrity. INTRODUCTION A digital signature is a mathematical scheme for demonstrating the authenticity of a digital message or document. A valid digital signature gives a recipient reason to believe that the message was created by a known sender, such that the sender cannot deny having sent the message (authentication and non-repudiation) and that the message was not altered in transmission.digital signatures are commonly used for software distribution, financial transactions, and in other cases where it is important to detect forgery or tampering. Digital signatures are often used to implement electronic signatures, a broader term that refers to any electronic data that carries the intent of a signature, but not all electronic signatures use digital signatures. In some countries, including the United States, India, and members of the European Union, electronic signatures have legal significance. Digital signatures employ a type of asymmetric cryptography. For messages sent through a nonsecure channel, a properly implemented digital signature gives the receiver reason to believe the message was sent by the claimed sender. Digital signatures are equivalent to traditional handwritten signatures in many respects, but properly implemented digital signatures are more difficult to forge than the handwritten type. Digital signature schemes in the sense used here are cryptographically based, and must be implemented properly to be effective. Digital signatures can also provide non-repudiation, meaning that the signer cannot successfully claim they did not sign a message, while also claiming their private key remains secret; further, some nonrepudiation schemes offer a time stamp for the digital signature, so that even if the private key is exposed, the signature is valid. Digitally signed messages may be anything representable as a bitstring: examples include electronic mail, contracts, or a message sent via some other cryptographic protocol. 13

2 II.COMPONENTS 1. Your public key: This is the part that any one can get a copy of and is part of the verification system. 2. Your name and address: This is necessary for contact information purposes and to enable the viewer to identify the details. 3. Expiration date of the public key: This part of the signature is used to set a shelf life and to ensure that in the event of prolonged abuse of a signature eventually the signature is reset. 4. Name of the company: This section identifies the company that the signature belongs too. 5. Serial number of the Digital ID: This part is a unique number that is bundled to the signature for tracking ad extra identification reasons. 6. Digital signature of the CA (certification Authority): This is a signature that is issued by the authority that issues the certificates. Fig 1:User A is depicted above and has two keys a public key, this key is available to the public for download, and a private key, this key is not available to the public. All keys are used to lock the information in an encrypted mode. The same keys are required to decrypt the data. Another user can encrypt the data using users A s Public Key. User A will use the Private Key to decrypt the message. Without user A s Private Key the data can not be decrypted. Fig 2:This figure depicts the encryption method and decryption method and witch keys are used. 14

3 Big brother is out there and choosing a high encryption mechanism ensures that any one attempting to decrypt the data would find it unviable to attempt decryption. User A s machine digests the data into a simple string of code after user A s software has encrypted the message digest with his private key. The result is the digital signature. User A s software then appends the digital signature to document. All of the data that was hashed has been signed. User A then passes the digitally signed document to user B. First user B s software decrypts the signature, using User A s public key then changing it back into a message digest. After the decryption if it has decrypted the data to digest level then verifies that user A in fact did sign the data. To stop fraud certificate authorities have been introduced. Certificate authorities can sign User A s public key, ensuring that no one else uses Bobs information or impersonated his key. If a user is uncertain of the digital signature it is possible to verify the digital signature with the certificate authority. Signatures can also be revoked if they are abused or if it is suspected that they are abused. When a digital signature is compromised the user that suspects that the certificate is compromised should report the incident to the certificate authority. III.WORKING Public key cryptography gives a reliable method for digital signing and signature verification based on public/private key pairs. A person can sign a given digital message (file, document, e- mail, and so forth) with his private key. From a technical point of view, the digital signing of a message is performed in two steps: Fig. 3..hash value of the input message is calculated by applying some cryptographic hashing algorithm..the calculated hash-value of a message is extracted from the message. In the second step of digitally signing a message, the information obtained in the first step hash-value of the message (the message digest) is encrypted with the private key of the person who signs the message and thus an encrypted hash-value, also called digital signature is obtained. Step 1: Calculate the Message Digest In the first step of the process, a hash-value of the message (often called the message digest) is calculated by applying some cryptographic hashing algorithm (for example, MD2, MD4, MD5, SHA1, or other). The calculated hash-value of a message is a sequence of bits, usually with a fixed length, extracted in some manner from the message All reliable algorithms for message digest calculation apply such mathematical transformations that when just a single bit from the input message is changed, a completely different digest is obtained. Due to this behavior, these algorithms are very steady in cryptanalytical attacks; in 15

4 other words, it is almost impossible, from a given hash-value of a given message, to find the message itself. This impossibility for retrieval of the input message is pretty logical if we take into account that a hash-value of a message could have a hundred times smaller size than the input message. Actually, the computing resources needed to find a message by its digest are so huge that, practically, it is unfeasible to do it. It is also interesting to know that, theoretically, it is possible for two entirely different messages to have the same hash-value calculated by some hashing algorithm, but the probability for this to happen is so small that in practice it is ignored. Step 2: Calculate the Digital Signature In the second step of digitally signing a message, the information obtained in the first step hashvalue of the message (the message digest) is encrypted with the private key of the person who signs the message and thus an encrypted hash-value, also called digital signature, is obtained. For this purpose, some mathematical cryptographic encrypting algorithm for calculating digital signatures from given message digest is used. The most often used algorithms are RSA (based on the number theory), DSA (based on the theory of the discrete logarithms), and ECDSA (based on the elliptic curves theory). Often, the obtained digital signature is attached to the message in a special format to be verified later if it is necessary. There are several reasons to sign such a hash (or message digest) instead of the whole document. For efficiency: The signature will be much shorter and thus save time since hashing is generally much faster than signing in practice. For compatibility: Messages are typically bit strings, but some signature schemes operate on other domains (such as, in the case of RSA, numbers modulo a composite number N). A hash function can be used to convert an arbitrary input into the proper format. For integrity: Without the hash function, the text "to be signed" may have to be split (separated) in blocks small enough for the signature scheme to act on them directly. However, the receiver of the signed blocks is not able to recognize if all the blocks are present and in the appropriate order. IV.VERIFYING DIGITAL SIGNATURES Digital signature technology allows the recipient of given signed message to verify its real origin and its integrity. The process of digital signature verification is purposed to ascertain if a given message has been signed by the private key that corresponds to a given public key. The digital signature verification cannot ascertain whether the given message has been signed by a given person. If we need to check whether some person has signed a given message, we need to obtain his real public key in some manner. This is possible either by getting the public key in a secure way (for example, on a floppy disk or CD) or with the help of the Public Key Infrastructure by means of a digital certificate. Without having a secure way to obtain the real public key of given person, we don't have a possibility to check whether the given message is really signed by this person. 16

5 From a technical point of view, the verification of a digital signature is performed in three steps: Fig 4:hash-value of the signed message is calculated using the hashing algorithm. In the digital signature verification process the digital signature is decrypted with the encryption algorithm by using the public key. Then for the identification, we compare the two hash values. Step 1: Calculate the Current Hash-Value In the first step, a hash-value of the signed message is calculated. For this calculation, the same hashing algorithm is used as was used during the signing process. The obtained hash-value is called the current hash value because it is calculated from the current state of the message. Step 2: Calculate the Original Hash-Value In the second step of the digital signature verification process, the digital signature is decrypted with the same encryption algorithm that was used during the signing process. The decryption is done by the public key that corresponds to the private key used during the signing of the message. As a result, we obtain the original hash-value that was calculated from the original message during the first step of the signing process (the original message digests). Step 3: Compare the Current and the Original Hash-Values In the third step, we compare the current hash-value obtained in the first step with the original hash-value obtained in the second step. If the two values are identical, the verification if successful and proves that the message has been signed with the private key that corresponds to the public key used in the verification process. If the two values differ from onr another, this means that the digital signature is invalid and the verification is unsuccessful. 17

6 V. WHY USE DIGITAL SIGNATURE As organizations move away from paper documents with ink signatures or authenticity stamps, digital signatures can provide added assurances of the evidence to provenance, identity, and status of an electronic document as well as acknowledging informed consent and approval by a signatory. The United States Government Printing Office (GPO) publishes electronic versions of the budget, public and private laws, and congressional bills with digital signatures. Universities including Penn State, University of Chicago, and Stanford are publishing electronic student transcripts with digital signatures. Below are some common reasons for applying a digital signature to communications: Authentication Although messages may often include information about the entity sending a message, that information may not be accurate. Digital signatures can be used to authenticate the source of messages. When ownership of a digital signature secret key is bound to a specific user, a valid signature shows that the message was sent by that user. The importance of high confidence in sender authenticity is especially obvious in a financial context. For example, suppose a bank's branch office sends instructions to the central office requesting a change in the balance of an account. If the central office is not convinced that such a message is truly sent from an authorized source, acting on such a request could be a grave mistake. Integrity In many scenarios, the sender and receiver of a message may have a need for confidence that the message has not been altered during transmission. Although encryption hides the contents of a message, it may be possible to change an encrypted message without understanding it. (Some encryption algorithms, known as nonmalleable ones, prevent this, but others do not.) However, if a message is digitally signed, any change in the message after signature will invalidate the signature. Furthermore, there is no efficient way to modify a message and its signature to produce a new message with a valid signature, because this is still considered to be computationally infeasible by most cryptographic hash functions (see collision resistance). Non-repudiation Non-repudiation, or more specifically non-repudiation of origin, is an important aspect of digital signatures. By this property, an entity that has signed some information cannot at a later time deny having signed it. Similarly, access to the public key only does not enable a fraudulent party to fake a valid signature. To make these assurances, the content must be digitally signed by the content creator, using a signature that satisfies the following criteria: The digital signature is valid. The certificate associated with the digital signature is current (not expired). The signing person or organization, known as the publisher, is trusted. 18

7 The certificate associated with the digital signature is issued to the signing publisher by a reputable certificate authority (CA). VI. SECURITY PRECAUTIONS 1)Putting the private key on a smart card All public key / private key cryptosystems depend entirely on keeping the private key secret. A private key can be stored on a user's computer, and protected by a local password, but this has two disadvantages: the user can only sign documents on that particular computer the security of the private key depends entirely on the security of the computer A more secure alternative is to store the private key on a smart card. Many smart cards are designed to be tamper-resistant (although some designs have been broken, notably by Ross Anderson and his students). In a typical digital signature implementation, the hash calculated from the document is sent to the smart card, whose CPU encrypts the hash using the stored private key of the user, and then returns the encrypted hash. Typically, a user must activate his smart card by entering a personal identification number or PIN code (thus providing two-factor authentication). It can be arranged that the private key never leaves the smart card, although this is not always implemented. If the smart card is stolen, the thief will still need the PIN code to generate a digital signature. This reduces the security of the scheme to that of the PIN system, although it still requires an attacker to possess the card. A mitigating factor is that private keys, if generated and stored on smart cards, are usually regarded as difficult to copy, and are assumed to exist in exactly one copy. Thus, the loss of the smart card may be detected by the owner and the corresponding certificate can be immediately revoked. Private keys that are protected by software only may be easier to copy, and such compromises are far more difficult to detect. 2)Using smart card readers with a separate keyboard Entering a PIN code to activate the smart card commonly requires a numeric keypad. Some card readers have their own numeric keypad. This is safer than using a card reader integrated into a PC, and then entering the PIN using that computer's keyboard. Readers with a numeric keypad are meant to circumvent the eavesdropping threat where the computer might be running a keystroke logger, potentially compromising the PIN code. Specialized card readers are also less vulnerable to tampering with their software or hardware and are often EAL3 certified. 3)Other smart card designs Smart card design is an active field, and there are smart card schemes which are intended to avoid these particular problems, though so far with little security proofs. 4)Using digital signatures only with trusted applications 19

8 One of the main differences between a digital signature and a written signature is that the user does not "see" what he signs. The user application presents a hash code to be encrypted by the digital signing algorithm using the private key. An attacker who gains control of the user's PC can possibly replace the user application with a foreign substitute, in effect replacing the user's own communications with those of the attacker. This could allow a malicious application to trick a user into signing any document by displaying the user's original on-screen, but presenting the attacker's own documents to the signing application. To protect against this scenario, an authentication system can be set up between the user's application (word processor, client, etc.) and the signing application. The general idea is to provide some means for both the user application and signing application to verify each other's integrity. For example, the signing application may require all requests to come from digitally signed binaries. 4) WYSIWYS Technically speaking, a digital signature applies to a string of bits, whereas humans and applications "believe" that they sign the semantic interpretation of those bits. In order to be semantically interpreted, the bit string must be transformed into a form that is meaningful for humans and applications, and this is done through a combination of hardware and software based processes on a computer system. The problem is that the semantic interpretation of bits can change as a function of the processes used to transform the bits into semantic content. It is relatively easy to change the interpretation of a digital document by implementing changes on the computer system where the document is being processed. From a semantic perspective this creates uncertainty about what exactly has been signed. WYSIWYS (What You See Is What You Sign) means that the semantic interpretation of a signed message cannot be changed. In particular this also means that a message cannot contain hidden information that the signer is unaware of, and that can be revealed after the signature has been applied. WYSIWYS is a necessary req uirement for the validity of digital signatures, but this requirement is difficult to guarantee because of the increasing complexity of modern computer systems. 5) Digital signatures vs. ink on paper signatures An ink signature could be replicated from one document to another by copying the image manually or digitally, but to have credible signature copies that can resist some scrutiny is a significant manual or technical skill, and to produce ink signature copies that resist professional scrutiny is very difficult. Digital signatures cryptographically bind an electronic identity to an electronic document and the digital signature cannot be copied to another document. Paper contracts sometimes have the ink signature block on the last page, and the previous pages may be replaced after a signature is applied. Digital signatures can be applied to an entire document, such that the digital signature on the last page will indicate tampering if any data on any of the pages have been altered, but this can also be achieved by signing with ink all pages of the contract. Additionally, most digital certificates provided by certificate authorities to end users to sign documents can be obtained by at most gaining access to a victim's inbox. 20

9 Important paper documents are signed in ink with all involved parties meeting in person, with additional identification forms other than the actual presence (like driver's licence, passports, fingerprints, etc.), and most usually with the presence of a respected notary that knows the involved parties, the signing often happens in a building which has security cameras and other forms of identification and physical security. The security that is added by this type of ink on paper signatures cannot be currently matched by digital only signatures. VII. ADVANTAGES AND DISADVANTAGES The following are the main benefits of using digital signatures: Speed: Businesses no longer have to wait for paper documents to be sent by courier. Contracts are easily written, completed, and signed by all concerned parties in a little amount of time no matter how far the parties are geographically. Costs: Using postal or courier services for paper documents is much more expensive compared to using digital signatures on electronic documents. Security: The use of digital signatures and electronic documents reduces risks of documents being intercepted, read, destroyed, or altered while in transit. Authenticity: An electronic document signed with a digital signature can stand up in court just as well as any other signed paper document. Tracking: A digitally signed document can easily be tracked and located in a short amount of time. Non-Repudiation: Signing an electronic document digitally identifies you as the signatory and that cannot be later denied. Imposter prevention: No one else can forge your digital signature or submit an electronic document falsely claiming it was signed by you. Time-Stamp: By time-stamping your digital signatures, you will clearly know when the document was signed. Message integrity: By having a digital signature you are in fact showing and simply proving the document to be valid. You are assuring the recipient that the document is free from forgery or false information. Legal requirements: Using a digital signature satisfies some type of legal requirement for the document in question. A digital signature takes care of any formal legal aspect of executing the document. Just like all other electronic products, digital signatures have some disadvantages that go with them. These include: Expiry: Digital signatures, like all technological products, are highly dependent on the technology it is based on. In this era of fast technological advancements, many of these tech products have a short shelf life. Certificates: In order to effectively use digital signatures, both senders and recipients may have to buy digital certificates at a cost from trusted certification authorities. Software: To work with digital certificates, senders and recipients have to buy verification software at a cost. 21

10 Law: In some states and countries, laws regarding cyber and technology-based issues are weak or even non-existent. Trading in such jurisdictions becomes very risky for those who use digitally signed electronic documents. Compatibility: There are many different digital signature standards and most of them are incompatible with each other and this complicates the sharing of digitally signed documents VIII. CONCLUSION Utilizing digital certificates and encryption, users can easily and securely communicate on the Internet. This combination of ease of use and security lays the foundation for commerce. As users gain confidence and experience using these tools, Internet Commerce, much like encryption, will grow exponentially.we also conclude that : 1)Minimizes the risk of dealing with imposters. 2)Minimizes the risk of undetected message tampering and forgery. 3)Retains a high degree of information security. IX.REFERENCES 1)Biddle B. (1996) 'Digital Signature Legislation: Some Reasons for Concern' Privacy Right Clearinghouse, April 2)1996Clarke R. 'Cryptography in Plain Text', Privacy Law & Policy Reporter 3, 2 (May 1996), pp , 30-33, at 3)Froomkin A.M. (1996) 'The Essential Role of Trusted Third Parties in Electronic Commerce' Oregon L. Rev. 75,1 (Spring, 1996) )Greenleaf, G. (1996a) `Privacy Principles - Irrelevant in cyberspace?' (1996) 3 PLPR )Greenleaf G. (1996b) `OECD Cryptography Guidelines near finalisation' (Unofficial extracts from the OECD December 1996 Draft Cryptography Policy Guidelines) (1996) 3 PLPR 126 6)OTA (1995) 'Issue Update on Information Security and Privacy in Network Environments', Chapter 2: Overview Of The 1994 OTA Report On Information Security And Privacy, June 1995, at: ftp://otabbs.ota.gov/pub/infosec.update/07ch2.txt and ftp://otabbs.ota.gov/pub/pdf/infosec.update and mirrored at: and 7)PKAF Report (1996) 'Strategies for the Implementation of a Public Key Authentication Framework (PKAF) in Australia', Miscellaneous Publication SAA MP , Standards Australia, October 1996, 88 pp. 8)Schneier B. (1996) 'Applied Cryptography' Wiley, 2nd Ed., )Utah Digital Signature Act, 1995, at 10)Walsh Report (1996) 'Review of Policy Relating to Encryption Technologies' Attorney- General's Department, Security Division, October 1996, ISBN , 96 pp. 22