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Presented byMohsin (09-CSS-46)
ShriPrakash(08-CSS-66)
DIGITAL SIGNATURE
Digital Signature1
Paper v/s Digital Signature2
Hash Function3
4
Area of application5
Overview
Implementation
Digital Signature
digital signature is a technique for establishing the
origin of a particular message in order to settle later
disputes about what message was sent.
Hash value of a message when encrypted with the
private key of a person is his digital signature on
that e-Document.
LOGO
Paper v/s Digital Signature
Parameter Paper Electronic
Authenticity May be forged Can not be copied
Integrity Signature
independent of the
document
Signature depends
on the contents of
the document
Non-
repudiation
a. Handwriting
expert needed
b. Error prone
a. Any computer
user
b. Error free
V/s
Hash Function
Hash function is a mathematical function that
generally has the following three properties :-
Condenses arbitrary long inputs into a fixed length
output.
Is one-way.
It is hard to find two inputs with the same
output.
LOGO
Proposed Scheme
Implementation
Sender uses SHA (Secure Hash Algorithm) hash function to calculate
a message digest (M).
M=SHA(massage)
Now generate digital signature using CRT-RSA algorithm with
Modified Approach by BlÄomer, Otto and Seifert .
Key generation :-
1. Select two distinct prime numbers p and q
2. Compute n = pq.
3. Compute euler’s phi totient, φ = (p-1)(q-1)
4. Select public key e < n such that gcd(e, phi)=1
5. Compute d = e^(-1) mod phi.
LOGO
Implementation
6. Calculate t1 and t2 to compute mP = M^d mod pt1 and
mQ = m^d mod qt2 such that
a) gcd(t1,t2)=1.
b) gcd(d,φ(t1))=gcd(d,φ(t2))=1.
c) t1 and t2 are squarefree.
d) ti#3 mod 4 for i@{1,2}.
e) t2 doesn’t divide X= pt1*((pt1)^(-1) mod qt2),
where pt1=p*t1 and qt2=q*t2.
7. Compute dP= d mod φ(pt1).
8. Compute dQ= d mod φ(qt2).
9. Compute et1 = dP^(-1) mod φ(t1).
10. Compute et2 = dQ^(-1) mod φ(t2).
11. Compute mP= M^(dP) mod pt1.
12. Compute mQ= M^(dQ) mod qt2.
LOGO9
7. Compute qt2Inv = qt2^(-1) mod pt1.
8. Compute h = (qt2Inv * (mP-mQ)) mod pt1.
9. Compute s= mQ+ h* qt2.
10. Compute c1=(M-(s^et1)+1) mod t2.
11. Compute c2=(M-(s^et2)+1) mod t1.
12. Return:
Sig = (s^(c1*c2)) mod N ,if c1=c2=1;
Error ,otherwise
Implementation
LOGO10
Implementation
Verification:-
1. Compute M’=Sig^e mod N.
2. Compare M and M’ ,where M is the hash of the received message.
3. If(M # M’) then accept.
LOGO
Area of Application
Issuing forms and licenses Filing tax returns online
Online Government orders/treasury orders Registration
Online file movement system Public information records
E-voting Railway reservations & ticketing
E-education Online money orders
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