1. Seminar
on
Digital Signature
Submitted to: Submitted by:
Prof. K.K.Agarwal Khushboo Dexit

2. Outline
1. Digital Signature
2. Why Digital Signature?
3. Conventional Signature Vs. Digital
Signature
4. Digital Signature Schemes
5. Public Key Encryption
6. How digital Signature works?
7. Digital Certificates
8. Certifying Authority
9. Private Key Protection

3. Digital Signature
• A digital signature is a mathematical scheme for demonstrating
the authenticity of a digital message or document.
• A digital signature is an electronic signature.
• A digital signature is basically a way to ensure that an electronic
document.
• A digital signature is a type of public key cryptography.

4. Why Digital Signature?

5. Conventional Signature Vs. Digital
Signature
 A signature is physically part of the document being signed. A
digital signature is not attached physically to the message that is
signed.
 A signature is verified by comparing it to authentic signatures.
Digital signatures can be verified using a publicly known
verification algorithm.
 A copy of a signed paper document can usually be distinguished
from an original. A “copy” of a signed digital message is identical
to the original.

6. Digital Signature Schemes
The following are the widely used Schemes for Digital Signature:
• RSA Scheme
• ElGamal Scheme
• Schnorr Scheme
• Digital Signature Standard (DSS)

7. Public Key Encryption
• Involves 2 distinct keys:
 public
 private
• It is also called “asymmetric cryptography”.
• Two keys are mathematically related.
Public Key Private Key
Cipher text
Plaintext Encryption Decryption Plaintext

8. Message Encryption
(User A sends message to User B)
Public Key Directory
User B’s Public Key
Encrypted
Text Text
Encryption
User A

9. Transfer Encrypted Data
User B
User A
Insecure Channel
Encrypted Encrypted
Text Text

10. Decryption with your Private key
Private key stored in
Encrypted your personal computer
Text
User B
User B’s
Private key
Decryption
Original Text

11. How to use 2 different keys?
• Just an example:
– Public Key = 4, Private Key = 1/4, message M = 5
– Encryption:
• Cipher text C = M * Public Key
• 5 * 4 = 20
– Decryption:
• Plaintext M = C * Private Key
• 20 * ¼ = 5

12. A cryptosystem uses the private and public keys of the
receiver.
A digital signature uses the private and public keys of the
sender.
So Digital Signature uses a Reverse Public Key Cryptography.

13. How digital Signature works?
Transmit via the Internet
User A
Use A’s private key to sign the document
Verify the signature User B received
by A’s public key stored the document with
at the directory signature attached
User B

15. Example of Digital Signature
• I agree
efcc61c1c03db8d8ea8569545c073c814a0ed755
• My place of birth is at Gwalior.
fe1188eecd44ee23e13c4b6655edc8cd5cdb6f25
• I am 62 years old.
0e6d7d56c4520756f59235b6ae981cdb5f9820a0
• I am an Engineer.
ea0ae29b3b2c20fc018aaca45c3746a057b893e7

16. Digital Certificates
• Digital Certificate is a data with digital signature from one
trusted Certification Authority (CA).
• This digital certificate contains:
Who owns this certificate
Who signed this certificate
The expired date
User name & email address

17. Certifying Authority
• Trusted Third Party.
• An organization which issues public key certificates.
• Assures the identity of the parties to whom it issues
certificates.
• Maintains online access to the public key certificates issued
• A trusted agent who certifies public keys for general use
(Corporation or Bank).

18. Private Key Protection
Hardware tokens
Soft Token
Smart card