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Last Updated: Mar 27, 2024
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Cryptography Digital Signature

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Prerita Agarwal
Data Specialist @
23 Jul, 2024 @ 01:30 PM

Introduction

Digital signatures are public-key primitives used in message authentication. In the physical world, handwritten signatures on handwritten or typed documents are common. They are used to connect the signatories to the message.

A digital signature is a technique of attaching a person or entity to digital data. The recipient, as well as any other person, can independently verify this binding.

A digital signature is a cryptographic value calculated using data and a secret key that only the signer possesses.

In the actual world, the receiver of communication needs assurance that the message belongs to the sender and will not deny the message's provenance. This criterion is critical in commercial applications since the chances of a data exchange disagreement are pretty high.

Digital Signatures

A digital signature is a mathematical approach that verifies the integrity and validity of a communication, software, or digital document. It assists us in validating message content and confirming the author's identity and the date and time of signatures. By offering substantially better inherent safety, the digital signature is aimed to address the difficulties of tampering and impersonation (consciously mimicking another person's attributes) in digital interactions.

In computer-based business information authentication, both technology and the law are involved. It also promotes collaboration between people with different professional backgrounds and areas of expertise. Digital signatures differ from previous electronic signatures in terms of method and outcome and in that they are more useful for legal purposes. Some legally identifiable electronic signatures may not be secure as digital signatures, resulting in doubt and conflicts.

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Applications

The following are some of the most compelling reasons to use digital signatures in communication

  • Authentication: Authentication is a technique that confirms a user's identity before allowing them access to a system. Authentication aids in the authentication of message sources in digital signatures.
  • Non-repudiation: The term "non-repudiation" refers to guaranteeing something that cannot be disputed. It assures that someone who signs a contract or communicates with someone else cannot subsequently deny the legitimacy of their signature on a document or in a file or the transmission of a message that they initiated.
  • Integrity: Integrity guarantees that the communication is genuine and correct and protects it against unauthorised changes during delivery.

Digital Signature Algorithms

Three algorithms make into a digital signature:

Name of Algorithm

Description

Key generation algorithm The key generation method chooses a private key randomly from a list of possibilities. This technique generates the private key and the public key corresponding to it.
Signing algorithm A document's signature is created via a signing algorithm.
A signature verifying algorithm The legitimacy of a document is accepted or rejected using a signature verification algorithm.

 

Digital Signature Model

The digital signature system is based on public-key cryptography, as previously stated. The model of the digital signature scheme is depicted in the following illustration −

The following points provide a thorough explanation of the complete procedure:

  • A public-private key pair is created for each individual who uses this system.
  • The key pairs used for encryption/decryption and signing/verification are usually distinct. The signature key is the private key used for signing, whereas the verification key is the public key.
  • Data is sent into the hash function by signer, which creates a hash of the data.
  • The signature algorithm is then provided with  the hash value and signature key, which generates a digital signature for the supplied hash. Both are submitted to the verifier after appending the signature to the data.
  • The digital signature and the verification key are fed into the verification process by the verifier. As an output, the verification algorithm returns a value.
  • The verifier uses the same hash algorithm on the supplied data to create a hash value.
  • This hash value and the output of the verification algorithm are compared for verification. Based on the comparison result, the verifier determines if the digital signature is legitimate.
  • Because a digital signature is made using the signer's "private" key, which no one else has, the signer cannot back out of signing the data in the future.

 

It's worth noting that instead of signing data directly with a signature method, a hash of the data is generally produced. It is sufficient to sign the hash in place of data since the hash represents a unique representation of data. The most crucial justification for utilising hash instead of data for signing is the scheme's efficiency.

Let's pretend that the signature algorithm is RSA (Rivest-Shamir-Adleman). The encryption/signing procedure utilising RSA involves modular exponentiation, as detailed in the public key encryption chapter.

Modular exponentiation is computationally costly and time-intensive when signing huge amounts of data. Because the hash of the data is a short digest of the data, signing a hash is more efficient than signing the whole thing.

How do digital signatures function?

Public key cryptography, often known as asymmetric Cryptography, produces and verifies digital signatures. One can produce two mathematically connected keys using a public key method like RSA. One is a private key, and the other is a public key.

To encrypt the signature-related document, the individual producing the digital signature utilises their own private key. The signer's public key is the sole way to decode that document.

All parties must believe that the person who makes the signature could keep their private key secret using this method. If someone gets access to the signer's private key, they may be able to forge signatures in the signer's name.

The steps for establishing a digital signature are as follows:

  • Choose a file to be signed digitally.
  • The message or file content's hash value is computed. The digital signature is formed by encrypting the message or file content using the sender's private key.
  • The actual message or file content is now delivered with the digital signature.
  • The digital signature is decrypted by the recipient using the sender's public key.
  • The message or file content is now available to the receiver, who may compute it.
  • Comparing the content of these calculated messages or files to the original calculated messages. For the sake of consistency, the comparison must be the same.

 

Different document processing platforms support types of Digital Signatures Different digital signatures. They're outlined below:

Certified Signatures

The documents with validated digital signatures have a distinctive blue ribbon across the top. The certified signature includes the document signer's and certificate issuer's names, signifying the document's authorship and authenticity.

Approval Signatures

The approving digital signatures on a document can be utilised in the business workflow of an organisation. They aid in the organization's approval process optimization. The technique entails collecting our and other people's approvals and integrating them into the PDF document. Details such as an image of our physical signature, place, date, and official seal should be included in the approved signatures.

Visible Digital Signature

A user can sign a single document using a visible digital signature. In the same manner that signatures are signed on physical copies, this signature appears.

Invisible Digital Signature

The invisible digital signatures are shown by a blue ribbon in the taskbar within a document. We can utilise invisible digital signatures when we don't have or don't want to exhibit our signature but still need to ensure the document's validity, integrity, and origin.

Encryption with Digital Signature

To achieve secrecy in many digital conversations, it is preferable to exchange encrypted messages rather than plain text ones. A sender's public (encryption) key is available in the open domain in a public key encryption system; thus, anybody may impersonate him and transmit an encrypted message to the recipient.

As a result, users that utilise PKC (Public-key cryptography) for encryption must look for digital signatures in addition to encrypted data to ensure message authenticity and non-repudiation.

By combining digital signatures with an encryption mechanism, this may be preserved. Let's take a quick look at how to fulfill these criteria. Here are the two options:

  • Sign-then-encrypt and encrypt-then-sign are the two options.
  • Encrypt-then-sign(Anyone may check the validity if you encrypt-then-sign, but only the receiver can decode it.)

 

The sign-then-encrypt crypto technique may be used by the receiver to spoof the sender's identity and transfer data to a third party. As a result, this procedure is not recommended. Encrypt-then-sign is a more reliable and extensively used method. This is illustrated in the figure below.

After receiving the encrypted data and signature, the recipient validates the signature using the sender's public key. The recipient obtains the data by decrypting it with his private key.

FAQs

1. What do you mean by digital signature?

Ans: A digital signature is a method of tying a person or entity to digital data. The recipient, as well as any other person, can independently verify this binding.

A digital signature is a cryptographic value computed from data and a secret key only the signer has access to.

2. What are the types of digital signature? Name them.

Ans: There are four digital signature types mentioned below:

  1. Certified Signature
  2. Approval Signature
  3. Visible Signature
  4. Invisible Signature

 

3. What do you mean by visible digital signature?

Ans: A user can sign a single document digitally using a visible digital signature. In the same manner that signatures are signed on physical documents, this signature appears.

4. Define certified signatures.

Ans: The documents with validated digital signatures have a distinctive blue ribbon across the top. The certified signature includes the document signer's and certificate issuer's names, signifying the document's authorship and authenticity.

5. What is authentication in the digital signature?

Ans: Authentication is a technique that confirms a user's identity before allowing them access to a system. Authentication aids in the authentication of message sources in digital signatures.

Key Takeaways

In this article, we have discussed the concept of digital signatures including the model of digital signature and the application of digital signature. We have also discussed its types. So basically, a digital signature is a mathematical approach that verifies the integrity and validity of a communication, software, or digital document.

We hope that this blog has helped you enhance your knowledge regarding Cryptography Digital Signature and if you would like to learn more, check out our article on What is Cryptography, Cyber Attacks and their types and Cryptosystem

Recommended Readings:

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Topics covered
1.
Introduction
2.
Digital Signatures
3.
Applications
4.
Digital Signature Algorithms
5.
Digital Signature Model
6.
How do digital signatures function?
6.1.
Certified Signatures
6.2.
Approval Signatures
6.3.
Visible Digital Signature
6.4.
Invisible Digital Signature
7.
Encryption with Digital Signature
8.
FAQs
9.
Key Takeaways