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

Document —> Hashing Algorithm —> Hash Value

                     |

                    (Modify Document)

                     v

Document’ —> Hashing Algorithm —> Different Hash Value

• 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

[Received Document + Signature]

Digital Signature + Public Key —> Decrypted Hash Value

Document —> Hashing Algorithm —> New Hash Value

Compare: [Decrypted Hash] vs [New Hash]

Algorithms Used in Digital Signatures

Algorithm	Key Strength	Hash Function Used	Common Use Cases
RSA	2048-bit	SHA-256	Emails, documents, SSL/TLS
DSA	1024-3072-bit	SHA-2	Digital certificates, government
ECDSA	256-bit	SHA-3	Blockchain, 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

Feature	Basic PKI	Enterprise PKI	Cloud-Based PKI
Certificate Issuance	Manual	Automated	On-demand
Scalability	Limited	High	Very High
Cost	Low	High	Subscription-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.