Transcript Digital Signatures

DIGITAL SIGNATURES
By Umair Sadiq
WHAT IS A DIGITAL SIGNATURE?

A signature to validate any electronic data.
Its not modified
 It belongs to signatory
 Signatory cannot repudiate

PICTORIAL OVERVIEW
VARIOUS ALGORITHMS
RSA
 DSA (US Federal Govt Standard)
 Elliptic Curve DSA
 ElGamal (based on computing discrete
logarithm),
 Pointcheval-Stern (a variant of ElGamal)

Note: Unlocking the key requires solution to a
mathematically hard problem like factoring the
product of large primes or computing discrete
logarithms
A SIMPLIFIED SCENARIO

Encryption, (e,n)

Decryption, (d,n)
code  msg e mod n
msg  code d mod n 

 msg
 msg
 (mod n)
e d
 ed   (n)
POTENTIAL THREATS AND SOLUTIONS

Man-in-the-middle-attack
a person intercepts and modifies messages in both
direction and uses its own generated set of keys
 digital certificates are used to authenticate keys


Timing attacks
with the knowledge of hardware and decipher time
becomes possible to deduce the key
 it is rectified by combining decryption with a random
computation

CONCLUSION

Where digital signature provide a safe way to
authenticate electronic piece of information, it is
important to use an algorithm that has been put
to rigorous testing and has proven its validity
over a period of time.
REFERENCES
http://csrc.nist.gov/publications/fips/fips1862/fips186-2-change1.pdf
 http://www.abanet.org/scitech/ec/isc/dsgtutorial.html
 http://gdp.globus.org/gt4tutorial/multiplehtml/ch09s03.html
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