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Week 7

Digital signatures provide authentication and integrity for digital messages. A digital signature is created by hashing a message and encrypting the hash with a private key. This attaches a code that acts as a signature to verify the source and integrity of the message. The Digital Signature Algorithm (DSA) was introduced as an alternative to RSA for creating digital signatures using unique mathematical functions rather than encryption/decryption. Requirements for a valid digital signature include being message dependent, unique to the sender, easy to produce/verify, and infeasible to forge. Digital signatures are important for message authentication, ensuring data integrity, and non-repudiation.

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80 views9 pages

Week 7

Digital signatures provide authentication and integrity for digital messages. A digital signature is created by hashing a message and encrypting the hash with a private key. This attaches a code that acts as a signature to verify the source and integrity of the message. The Digital Signature Algorithm (DSA) was introduced as an alternative to RSA for creating digital signatures using unique mathematical functions rather than encryption/decryption. Requirements for a valid digital signature include being message dependent, unique to the sender, easy to produce/verify, and infeasible to forge. Digital signatures are important for message authentication, ensuring data integrity, and non-repudiation.

Uploaded by

Hala Gharib
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Week-7

Digital Signatures
Digital signature
A digital signature is an authentication
mechanism that enables the creator of a message
to attach a code that acts as a signature. Typically
the signature is formed by taking the hash of the
message and encrypting the message with the
creator’s private key. The signature guarantees
the source and integrity of the message.
Digital Signature Algorithm (DSA)
A digital signature algorithm (DSA) refers to a
standard for digital signatures. It was introduced
in 1991 by the National Institute of Standards
and Technology (NIST) as a better method of
creating digital signatures. Along with RSA,
DSA is considered one of the most preferred
digital signature algorithms used today.
Generic Model of Digital Signature Process
DSA does not encrypt message digests using private key or decrypt
message digests using public key. Instead, it uses unique mathematical
functions to create a digital signature consisting of two 160-bit numbers,
which are originated from the message digests and the private key.
DSAs make use of the public key for authenticating the signature, but the
authentication process is more complicated when compared with RSA.
The digital signature procedures for RSA and DSA are usually regarded as
being equal in strength. Because DSAs are exclusively used for digital
signatures and make no provisions for encrypting data, it is typically not
subject to import or export restrictions, which are often enforced on RSA
cryptography.
Attacks and Forgeries
Attacks:
• Key-only attack
• Known message attack
• Generic chosen message attack
• Directed chosen message attack
• Adaptive chosen message attack
Forgeries:
• Universal forgery
• Selective forgery
• Existential forgery
Digital Signature Requirements
On the basis of the properties and attacks just discussed, we can
formulate the following requirements for a digital signature.
• The signature must be a bit pattern that depends on the messa
ge being signed.
• The signature must use some information unique to
the sender to prevent both forgery and denial.
• It must be relatively easy to produce the digital signature.
• It must be relatively easy to recognize and verify the digital si
gnature.
• It must be computationally infeasible to forge a digital
signature, either by
constructing a new message for an existing digital
signature or by constructing
a fraudulent digital signature for a given message.

• It must be practical to retain a copy of the digital signatur


e in storage.
Importance of Digital Signature

• Message authentication
• Data Integrity
• Non-repudiation

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