# elgamal digital signature ques10

The ElGamal Digital Signature Define GF(p) =F p System public key: p is a prime such that the discrete log problem in F p is infeasible, , a primitive element in F p. * a â F p User Bob: Selects x, 0 < x < p with (x, p-1) = 1 as his private key. 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. 1.The receiver performs the 1st part of verification called $v_1$ using the equation, 2.The receiver performs the 2nd part of verification called as $v_2$ using the equation, $v_1 = e_1^M mod p$ = $10^{14} mod 19$ = 16, $v_2 = e_2^{s_1} s_1^{(s_2)}mod p = 4^3 X 3^4 mod p$ = 5184 mod 19 = 16. Differentiate Digital signature and Digital certificate. This binding can be independently verified by receiver as well as any third party. For verification, this hash value and output of verification algorithm are compared. The verification algorithm gives some value as output. The output result is the witness of the signature validity or invalidity. The Elgamal digital signature scheme employs a public key consisting of the triple {y,p,g) and a private key x, where these numbers satisfy. The user process all fields except the last one of the received digital certificate to a message digest algorithms. 3. Digital signatures are the public-key primitives of message authentication. Digital signatures are a cryptographic tool to sign messages and verify message signatures in order to provide proof of authenticity for digital messages or electronic documents. As discussed in public key encryption chapter, the encryption/signing process using RSA involves modular exponentiation. Go ahead and login, it'll take only a minute. iii. Find answer to specific questions by searching them here. It should be noticed that instead of signing data directly by signing algorithm, usually a hash of data is created. For slides, a problem set and more on learning cryptography, visit www.crypto-textbook.com Recall from Chapter 10, that the ElGamal encryption scheme is designed to enable encryption by a userâs public key with decryption by the userâs private key. iii. This specific variant of ElGamal has been proposed in 1990 by Agnew, Mullin and Vanstone (the article is called "Improved Digital Signature Scheme based on Discrete Exponentiation"; I could not find a freely downloadable version). Analysis of ElGamal Digital Signature Algorithm You must be logged in to read the answer. This scheme used the same keys but a different algorithm. ElGamal cryptosystem can be defined as the cryptography algorithm that uses the public and private key concept to secure the communication occurring between two systems. Its strength lies in the difficulty of calculating discrete logarithms (DLP Problem). In many digital communications, it is desirable to exchange an encrypted messages than plaintext to achieve confidentiality. Compute as his public key.y =ax 4. CryptoCalculator. Blockchain Calc. It's the best way to discover useful content. You must be logged in to read the answer. They are used to bind signatory to the message. Working of RSA digital signature scheme: Sender A wants to send a message M to the receiver B along with the digital signature S calculated over the message M. Step1: The sender A uses the message digest algorithm to calculate the message digest MD1 over the original message M. With digital signatures, the receiver can verify that the information is not modified. Elgamal digital signature scheme Generation parameters (keys) 1. The algorithm creates two digital signatures, these two signatures, are used in the verification phase. Let us assume RSA is used as the signing algorithm. Digital signature is a cryptographic value that is calculated from the data and a secret key known only by the signer. Calculate the random generator of the multiplicative . This binding can be independently verified by receiver as well as any third party. You'll get subjects, question papers, their solution, syllabus - All in one app. elgamal digital signature scheme Before examining the NIST Digital Signature standard, it will be helpful to under- stand the ElGamal and Schnorr signature schemes. Since $v_1$=$v_2$, the signature is valid. Signing large data through modular exponentiation is computationally expensive and time consuming. Ask Question Asked today. iii. The model of digital signature scheme is depicted in the following illustration: The following points explain the entire process in detail: i. ii. Go ahead and login, it'll take only a minute. v. Verifier feeds the digital signature and the verification key into the verification algorithm. ElGamal signatures are much longer than DSS and Schnorr signatures. Since digital signature is created by ‘private’ key of signer and no one else can have this key; the signer cannot repudiate signing the data in future. Like the ElGamal scheme DSA is a digital signature scheme with an appendix meaning that the message cannot be easily recovered from the signature itself. vii. In 1985, ElGamal [6] proposed a public key cryptosystem and a digital signature scheme based on the difficulty of solving the Discrete Logarithm Problem in the multiplicative group of an appropriate finite field. Let $e_1$ = 10, $e_2$ = 4, p=19, M=14, d=16 & r=5, Then, $s_1 = e_1^{R} modp $= $10^5mod19$= 3, $s_2 =(M-d X s_1) X r^{-1}mod (p-1) = (14-16 X 3) X 5^{-1}mod (18) $= 4. Each person adopting this scheme has a public-private key pair. By adding public-key encryption to digital signature scheme, we can create a cryptosystem that can provide the four essential elements of security namely − Privacy, Authentication, Integrity, and Non-repudiation. ElGamal digital signature scheme with the ElGamal digital signature scheme after adding a random number, then analyzed and verified its security that is improved, it turns out that the private key x and random number k are unknown to the attacker. B. However, in the case of digital signatures, the recipient must have a relationship with the sender or hosting site. Secure File and Messages. The key generation process is the same as that of EI-gamal algorithms. As with the ElGamal digital signature scheme, the Schnorr signature scheme is based on discrete logarithms . iv. After ensuring the validity of the signature, he then retrieves the data through decryption using his private key. Hence, this method is not preferred. Choose a random prime p. 2. M = xa + ks mod (p â 1). 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