Public key infrastructure PKI

Digital Signatures for Beginners: A Step-by-Step Guide into Public key infrastructure PKI

Definition and Explanation of Digital Signatures

A digital signature uses cryptographic methods to verify the identity of the Sender and ensure the integrity of a document or message. Unlike traditional handwritten signatures, which are vulnerable to forgery, digital signatures leverage Public Key Infrastructure (PKI) to offer a secure, tamper-proof way to authenticate digital communications and transactions. They function as a unique digital fingerprint tied to the Sender and the content of the document.

Digital signatures are widely used in secure email communication, software distribution, financial transactions, and legal documents to ensure trust and compliance with regulatory standards.

This article will break down the technical concepts behind digital signatures “PKI”, using easy-to-follow schemas and tables, so even a beginner can understand how they work.

Key Components of Digital Signatures – PKI

1. Public and Private Keys

Digital signatures rely on asymmetric cryptography, which uses two keys:

  • Private Key: Secret and known only to the signer. Used to create the digital signature.
  • Public Key: Shared openly. Used by others to verify the signature.

So, PKI stands for Public key infrastructure.

Schema: How Public and Private Keys Work

[Sender]

Document + Private Key —> Digital Signature

                     |

                     v

[Recipient]

Digital Signature + Public Key —> Verifies Authenticity

  • Key Concept: If the public key successfully verifies the signature, it confirms that the private key (and therefore the signer) created it.

2. Hashing Algorithm

A hashing algorithm transforms the original document into a fixed-length string, called a hash value. Hashing ensures:

  • Integrity: Any change to the document alters the hash value, revealing tampering.

Schema: Hashing Process

  • Popular Hashing Algorithms: SHA-256, SHA-3, MD5 (less secure).

3. Digital Certificates and PKI

A digital certificate, issued by a trusted Certificate Authority (CA), binds a public key to its owner’s identity. The Public Key Infrastructure (PKI) supports this system by:

  • Certificate Authorities (CAs): Issue and verify certificates.
  • Registration Authorities (RAs): Validate user identities before certificates are issued.
  • Certificate Revocation Lists (CRLs): Ensure expired or invalid certificates aren’t used.

Schema: Role of PKI

[CA]

Verifies Identity —> Issues Digital Certificate —> Links Public Key to User

  • Example: When visiting a secure website (HTTPS), your browser verifies the website’s certificate using PKI.

How Digital Signatures Work

1. Creating a Digital Signature

  1. A hash value is generated from the document using a hashing algorithm.
  2. The hash value is encrypted with the sender’s private key using PKI, creating the digital signature.
  3. The signature and document are sent to the recipient.

and don’t forget, Digital signature is not Electronic signature. see the diffrence here.

Schema: Creating a Digital Signature

Document —> Hashing Algorithm —> Hash Value

Hash Value + Private Key —> Digital Signature

Send: [Document + Digital Signature]

2. Verifying a Digital Signature

  1. The recipient decrypts the signature using the sender’s public key, revealing the original hash value.
  2. The recipient hashes the document again to generate a new hash value.
  3. The two hash values are compared:
    • If they match, the signature is valid.
    • If not, the document is tampered or the signature is invalid.

Schema: Verifying a Digital Signature

Algorithms Used in Digital Signatures

AlgorithmKey StrengthHash Function UsedCommon Use Cases
RSA2048-bitSHA-256Emails, documents, SSL/TLS
DSA1024-3072-bitSHA-2Digital certificates, government
ECDSA256-bitSHA-3Blockchain, IoT, mobile apps

Comparison:

RSA: Rivest-Shamir-Adleman is widely known for its strong security but requires larger key sizes, making it computationally slower. In Public Key Infrastructure (PKI) systems, RSA keys are managed for secure digital signatures and encryption. However, the larger key sizes can be cumbersome in some use cases.

DSA: Digital Signature Algorithmis faster in signature generation compared to RSA but is limited to digital signatures and does not support encryption. This makes DSA less versatile. While it is effective in generating signatures, it doesn’t offer the same level of flexibility as RSA in a PKI setup.

ECDSA: Elliptic Curve Digital Signature Algorithm offers the best balance between security and efficiency, especially with smaller key sizes. It is ideal for environments with limited resources, such as mobile devices or blockchain applications. PKI systems efficiently handle ECDSA keys, providing secure digital signatures while minimizing computational demands.

ECDSA vs RSA and DSA: When it comes to modern use cases where both performance and security matter, ECDSA is becoming the go-to over RSA and DSA. It offers smaller key sizes and faster processing, all while maintaining strong security. PKI systems manage ECDSA keys with ease, making it a top choice for secure digital signatures

FeatureBasic PKIEnterprise PKICloud-Based PKI
Certificate IssuanceManualAutomatedOn-demand
ScalabilityLimitedHighVery High
CostLowHighSubscription-based

Key Insights:

  • For small businesses, cloud-based PKI offers flexibility and cost-effectiveness.
  • Large enterprises benefit from full control with on-premise PKI.

Linking It All Together

The digital signature process integrates cryptographic algorithms, hashing, and PKI as follows:

  1. Public/Private Key Pair: Ensures authentication and non-repudiation.
  2. Hashing Algorithm: Protects document integrity.
  3. Digital Certificate: Builds trust through identity verification.

By understanding these components, you can evaluate and compare digital signature solutions based on:

  • Security (key strength, hashing algorithm).
  • Efficiency (processing speed, scalability).
  • Trust (CA reputation, certificate validation process).

Use cases and examples

One practical example of PKI-based digital signature implementation can be seen with PandaDoc, a widely trusted document management platform used by businesses around the world. PandaDoc offers both electronic signatures and advanced digital signatures that leverage Public Key Infrastructure (PKI) to ensure the authenticity, integrity, and non-repudiation of documents. Known for its high level of security and compliance with global standards (including eIDAS and UETA/ESIGN), PandaDoc allows companies to send, sign, and manage legally binding documents with confidence. Whether integrated into CRMs or used as a standalone tool, PandaDoc is relied upon by thousands of organizations globally to secure their digital workflows.

Other reputable platforms offering secure electronic and digital signature solutions include BoldSign, Signable, and SignWell, all widely used and compliant with international e-signature regulations.

Conclusion

Digital signatures are important for secure digital communication. By learning the basics of public/private keys, hashing, and PKI, even beginners can see how powerful and flexible this technology is. PKI helps manage keys and certificates to verify the identity of users and organizations. With this understanding, you can choose the right digital signature solution for your needs.

Frequently Asked Questions (FAQs)

A digital signature is a secure cryptographic method that verifies the authenticity and integrity of digital documents. It uses asymmetric encryption, a hashing algorithm, and PKI (Public Key Infrastructure) to create a tamper-evident seal.
In contrast, an electronic signature can be as simple as typing your name or uploading a scanned signature, offering less security and no cryptographic verification.

Digital = Secure, Verified, Tamper-Proof
📝 Electronic = Simple Approval Method

PKI (Public Key Infrastructure) is the system that supports the secure use of digital signatures. It includes:

  • Private and public key pairs
  • Digital certificates issued by Certificate Authorities (CAs)
  • Certificate Revocation Lists (CRLs) and validation protocols

PKI ensures that the signer’s identity is verified and that only trusted parties can issue or validate signatures, making it the backbone of digital trust.

Here’s how the process works:

Compares both hashes. If they match, the signature is valid and the document is untampered.

The sender creates a hash of the document.

The hash is encrypted using the sender’s private key, forming the digital signature.

The document and signature are sent to the recipient.

The recipient:

Decrypts the signature using the sender’s public key to get the original hash.

Generates a new hash of the received document.

Hashing algorithms like SHA-256 transform a document into a unique string of characters called a hash value. This hash:

  • Acts like a digital fingerprint.
  • Will change completely if even one character in the document changes.
  • Ensures the integrity of the document during verification.

Common algorithms include SHA-256 (most widely used), SHA-3, and MD5 (now considered insecure).

Here are the three major algorithms used:

AlgorithmStrengthUse CasesPros
RSA2048-bitEmails, SSL, docsStrong, widely adopted
DSA1024–3072-bitGov. use, digital certificatesFast for signing
ECDSA256-bitBlockchain, IoT, mobileHigh security + efficiency

ECDSA is often preferred today for its small key size, fast performance, and robust security, especially in mobile and resource-constrained environments.

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