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digital_sign_interview.ppt
- 1. Public Integrity Auditing - Digital Signatures by G Jaya Rao Roll No:716178,Research Scholar ,NITW&IDRBT,Hyd
- 2. Public Integrity Auditing -Digital Signatures Digital Signatures • MAC Security services provided by a digital signature Digital signature scheme-RSA Attacks on digital signatures Some applications of digital signatures References
- 3. Message Integrity-Message Authentication Code (MAC) MAC algorithm is a symmetric key cryptographic technique to provide message authentication. For establishing MAC process, the sender and receiver share a symmetric key K. Essentially, a MAC is an encrypted checksum generated on the underlying message that is sent along with a message to ensure message authentication.
- 4. MAC
- 5. 30.5 The symmetric (shared) key in the Diffie-Hellman protocol is K = gxy mod p.
- 7. Limitations of MAC Establishment of Shared Secret. This requires establishment of shared secret among pre-decided legitimate users prior to use of MAC. Inability to Provide Non-Repudiation: Non-repudiation is the assurance that a message originator cannot deny any previously sent messages and commitments or actions. MAC technique does not provide a non-repudiation service. If the sender and receiver get involved in a dispute over message origination, MACs cannot provide a proof that a message was indeed sent by the sender. Both these limitations can be overcome by using the public key based digital signatures discussed in following section.
- 8. DIGITAL SIGNATURES A person signs a document to show that it originated from him or was approved by him. The signature is proof to the recipient that the document comes from the correct entity and nobody else. A sign of authentication: A verified signature on a document. A message can be signed electronically. The electronic signature can prove the authenticity of the sender of the message --->digital signature.
- 11. Security Services 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.
- 12. 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.
- 13. 13.13 Key Generation Key generation in the RSA digital signature scheme is exactly the same as key generation in the RSA RSA digital signature scheme In the RSA digital signature scheme, d is private; e and n are public. Note
- 14. Key-Generation for RSA 1. Generate two large random distinct primes p and q, each roughly the same size 2. Compute n = pq and 3. Select random integer e: 4. Compute unique integer d: 5. Public key is (n, e); Private key is d ( ) ( 1)( 1) n p q 1 , such that gcd( , ) 1 e e 1 , such that 1mod d ed
- 15. 13.15 RSA Signature on the Message Digest Continued The RSA signature on the message digest
- 16. 13.16 ATTACKS ON DIGITAL SIGNATURE
- 21. APPLICATIONS ….. Electronic Mail Data storage Electronic funds transfer Software Distribution
- 22. Limitations The private key must be kept in a secured manner. The process of generation and verification of digital signature requires considerable amount of time. For using the digital signature the user has to obtain private and public key, the receiver has to obtain the digital signature certificate also.