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Digital Signatures

Digital Signatures. Ajaykumar Poondla CSC 692. Objective. The goal is to present the idea of digital signatures and the two commonly used digital signature algorithms RSA Signature scheme Elgamal Signature scheme. Digital Signatures.

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Digital Signatures

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  1. Digital Signatures Ajaykumar Poondla CSC 692

  2. Objective • The goal is to present the idea of digital signatures and the two commonly used digital signature algorithms • RSA Signature scheme • Elgamal Signature scheme

  3. Digital Signatures • Digital signature is a way of signing an electronic document in much the similar way that we sign conventional documents today.

  4. Advantages • Data Integrity. • Authentication. • Non-Repudiation. • Date-Time stamping.  • Confidentiality.

  5. Digital signature Schemes • RSA signature scheme. • Elgamal signature scheme.

  6. RSA signature scheme • R.L.Rivest, A.Shamir and L.Adleman proposed this method. • Bob computes C = Me mod n. • Bob sends C,M to Alice • Alice computes Cdmod n. • e.d = 1 mod(ø(n)).

  7. Scope of RSA signature Scheme • Used in VISA and Master cards. • Can be broken using the iteration attack. • The difficulty of breaking RSA signature scheme depends on solving the factorization of a large integer into two large prime factors.

  8. Proposed in 1985. • Non-Deterministic scheme. • Based on Discrete Logarithms. Elgamal signature scheme

  9. Details of the Elgamal Scheme • Calculate y = gx mod p • public key is (p, g, y), and the private key is x. • To sign a message, M choose k, such that k is relatively prime to p-1. • Compute a = gkmod p. • Find b in the following equation M = (xa + kb)mod(p –1). To verify the signature, confirm that Yaabmod p = gMmod p.

  10. Scope of Elgamal scheme • The difficulty of breaking Elgamal signature scheme depends on solving the discrete logarithm problem.

  11. References • An Introduction to cryptography and digital signatures. • R.L.Rivest, A.Shamir and L.Adleman A method for obtaining digital signatures and public-key cryptosystem. • ElGamal, T. A Public Key Cryptosystem and a Signature Scheme based on Discrete Logarithms IEEE Transactions on Information Theory, Vol.31, Nr.4, July 1985. • Md5 algorithm. http://rfc.sunsite.dk/rfc/rfc1321.html

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