Digital signatures use asymmetric cryptography to authenticate digital messages. They allow a recipient to verify the identity of the sender and confirm the message has not been altered. A digital signature scheme involves key generation, signing, and verification algorithms. Digital signatures provide authentication, integrity, and non-repudiation and are commonly used for software distribution, financial transactions, and other cases requiring detection of forgery or tampering. They offer advantages over traditional ink signatures like inability to forge or erase the signature.

1. Digital Certificates
&
Digital signatures

2. What is a digital signature ?
• 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, and that it was not altered in transit.
• Digital signatures are commonly used for software
distribution, financial transactions, and in other cases
where it is important to detect forgery or tampering.

3. INTRODUCTION
• 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 signature schemes in the sense used here are
cryptographically based, and must be implemented
properly to be effective.

4. • Digitally signed messages may be anything
representable as a bitstring: examples include
electronic mail, contracts, or a message sent via some
other cryptographic protocol
• A digital signature scheme typically consists of three
algorithms:
• A key generation algorithm that selects a private key
uniformly at random from a set of possible private
keys. The algorithm outputs the private key and a
corresponding public key.
• A signing algorithm that, given a message and a
private key, produces a signature.

5. • A signature verifying algorithm that, given a
message, public key and a signature, either accepts or
rejects the message's claim to authenticity.
• Two main properties are required. First, a signature
generated from a fixed message and fixed private key
should verify the authenticity of that message by
using the corresponding public key. Secondly, it
should be computationally infeasible to generate a
valid signature for a party who does not possess the
private key.

7. Uses of Digital Signatures
• Now a days, organisations are moving away
from paper documents with ink signatures or
authenticity stamps, to digital signatures.
• It can provide added assurances of the evidence to
provenance, identity, and status of an electronic
document as well as acknowledging consent and
approval by a signatory.

8. • Below are some common reasons for applying a
digital signature to communications.
• Authentication:-
- Digital signatures can be used to authenticate the
source of messages.
-For example, suppose a bank's branch office sends
instructions to the central office requesting a change
in the balance of an account.
• Integrity:-
▫ The sender and receiver of a message must know
that the message has not been altered during
transmission.

9. • However, if a message is digitally signed, any change
in the message after signature will invalidate the
signature.
• Non-repudiation:-
▫ 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 sign

10. Additional Security Precautions
• Using smart card readers with a separate
keyboard:-
▫ 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.
• Using digital signatures only with trusted
applications:-
One of the main differences between a digital
signature and a written signature is that the user does
not "see" what he signs.

11. WYSIWYS
• WYSIWYS is an shortform for What You See Is
What You Sign, used to describe the property of
digital signatures systems that the content of signed
messages can not be changed, either by accident or
intent.
• What You See Is What You Sign means that the
semantic interpretation of a signed message cannot be
changed.

12. Digital signatures vs. ink on paper signatures
• Ink Paper Signatures • Digital Signatures
• An ink signature could • Digital signatures bind
be replicated from one an electronic identity to
document to another by an electronic document
copying the image and the digital signature
manually or digitally. cannot be copied to
another document.
• Ink Signatures can be • Digital signatures can
easilly erasiable. never be erased.

13. What is Private Key & Public Key ???
• Cryptographic system requiring two separate Keys,
one to lock or encrypt the Plaintext, and one to
unlock or decrypt the Cyber text.
• One of these keys is published or public and the
other is kept private.
• a private key, which only you use. and
• a public key, which other people use.

14. Example: (B's public key)
B
(B's private key)

15. B’s Co-workers
Z
X Y
B’s Public Key
Anyone can get B's Public Key, but B keeps his Private Key to himself

16. "Hey B, how HNFmsEm6Un
are you ?” BejhhyCGKOK
Z
HNFmsEm6U
n "Hey B, how
BejhhyCGKOB are you ?”
cyLK
B

19. Bob Info:
Name
Department
Cubical Number
Certificate Info:
Expiration Date
Serial Number
Bob's Public Key:
B’s Co-Worker

20. Why we use digital signature?
• Guarantees that the person who sent the message is
really the one who sent it.
• By placing the digital signature on a document proves
not only the document is for real, but it also shows
that the signature is not fake or forgery.
• insures data Integrity giving the user piece of mind
that the message or transaction has not been
accidentally or maliciously altered.

21. • ensures confidentiality and ensures that messages can
only be read by authorized intended recipients.
• also verifies date and time so that senders or
recipients can not dispute if the message was actually
sent or received.

22. • The process of checking the validity of digital
signature.
• Advantages
1) Imposter Prevention
2) Message Integrity
3) Legal Requirement