This document discusses digital signatures. A digital signature is a code attached to an electronic document that verifies the contents and sender's identity using public key encryption. It involves two processes - creation and verification. For creation, a hash of the message is encrypted with the sender's private key. For verification, the receiver decrypts the signature with the public key and compares the hash to ensure the message wasn't altered. Digital signatures provide authentication of the sender and integrity of the data. They are used in applications that require assurance of an individual's identity or confirmation of an affirmative act.

1. Digital Signature
Jisha George A.
Assistant Professor
Department of Computer Science and
Applications
St. Mary’s College Thrissur

2. Digital Signature, Jisha George A, St.Mary’s College
DEFINITION
 A digital code (generated and authenticated by public key
encryption) which is attached to an electronically transmitted
document to verify its contents and the sender's identity.

3. Public Key Cryptography and its Demerits
Public Key Cryptogragraphy-
 The sender is assigned 2 keys- one public and one private.
 Original message is encrypted using the public key.
 The recipient of the message requires the private key to decrypt the
message and can determine whether the message has been altered or
not.
Demerits-
 This method guarantees the integrity of the data. But not guarantee the
identity of the sender.
Digital Signature,Jisha George A,St.Mary’s College

4. Digital Signature- Merits
 Digital Signature is the solution for authenticity in various fields
 Provide data integrity- allowing the data to remain in the same
state which it was transmitted
Digital Signature, Jisha George A,St.Mary’s College

5. Digital Signatures Involves 2 Processes
Digital Signature, Jisha George A, St.Mary’s College
Digital signature creation
(performed by the signer)
Digital signature verification
(performed by the receiver)

6. Digital Signature Creation
 In order to compute the digital signature a one way hashing
algorithm may be used to first calculate a message digest.
 Message Digest is a unique number that can only be calculated
from the contents of the original message.
 Once message digest is calculated the sender’s private key is used
to encrypt the message digest
ENCRYPTED MESSAGE DIGEST IS KNOWN AS DIGITAL
SIGNATURE
Digital Signature, Jisha George A, St.Mary’s College

7. Digital Signature Verification
 Process of checking the digital signature by reference to the
original message and given public key
 Determine whether the digital signature was created for that same
message using the private key corresponding to the referenced
public key
 Verification of the digital signature is accomplished by computing
a new hash result of the original message by means of the same
hash function used to create the digital signature
Digital Signature, Jisha George A, St.Mary’s College

8. Digital Signature Verification continues…
Then, using the public key and the new hash result, the verifier
checks:
(i) whether the digital signature was created using the corresponding
Private Key and
(ii) whether the newly computed hash result matches the original
hash result which was transformed into the digital signature
during the signing process
Digital Signature, Jisha George A, St.Mary’s College

9. Certification Authority
 Performs the task of managing the key pairs.
 Issues a certificate which links an individual or entity to its public
key and in some cases to private key
 Offer grades of certificate
Digital Signature, Jisha George A, St.Mary’s College

10. When and Where A Digital Signature is Used?
 Signer Authentication : Digital Signature identify the authenticity
of a sender since a public and private key pair is associated with an
identified signer
 Message Authentication : Digital Signature Verification reveals
any tampering of the message
 Affirmative Act : Creating a digital signature requires the signer to
use the signer's private key and the signer is consummating a
transaction with legal consequences
 Assurance :The processes of creating and verifying a digital
signature assures the signer’s identity
Digital Signature, Jisha George A, St.Mary’s College

11. Digital Signature, Jisha George A, St.Mary’s College
REFERENCE
 E Commerce , An Indian Perspective by P.T. Joseph
 Computer Networking , A top Down Approach by Kurose|Rose