2. Why We Need Digital Signature.
• A real life example could be the case of a user C, posing as a user A, sending a funds
transfer request(from A’s account to C’s account) to bank B. The bank might happily transfer
the funds from A’s account to C’s account, after all, it would think that user A has requested
for the funds transfer.
A I am user A B
C
3. • User A could send a funds transfer request to bank B over the internet. After the bank
performs the funds transfer as per A’s instructions, A could claim that he never sent the fund
transfer instructions to the bank. Thus, A denies, his funds transfer instructions. That is the
reason, we need digital signature.
A B
I never send that message,
which you claim to have
recieved
4. Digital Signature
• A digital signature is a mathematical technique used for message authentication,
non-repudation and message intregity.
• Digital signature are based on public key cryptography, also known as asymmetric
crypography.
• Using a public key algorithm, two keys are generated-- one public and one private.
• For encryption and decryption, the person who creates the digital signature uses a private
key to encrypt signature-related data. The only way to decrypt that data is with the signer’s
public key.
• If the recipient can’t open the document with the signer’s public key, that indicates there’s a
problem with the document or the signature. This is how digital signatures are authenticated.
• {Note: It is not used for confidentiality.}
6. Confidentiality
• A digital signature does not provide confidential communication. If confidentiality is required, the
message and the signature must be encrypted using either a secret-key or public-key
cryptosystem.
Original Message Hash algorithm Hash code Encryption
Private key A
Digitally Signed
Document
Encryption
Public key B
Encrypted
Message
Decrypted
Message
Original Message Hash Algo
Decryption
Hash Code
Hash Code
Digital Signature
Decryption
Private key B Public key A
Signature are valid
when hash code are
equal
7. Application of digital signature
• Order through internet.
• Online Contract / agreement.
• Online payment.
• Transfer Of Authenticate information.
• Transfer of government. documents etc.
