A digital certificate is an electronic document issued by a trusted certificate authority that binds the identity of a person, organization or server to a public encryption key. The certificate operates within a public key infrastructure (PKI): a system of entities, policies and technologies that issue, manage and revoke certificates. This system makes it possible to verify that a signature came from its owner, that a document has not changed since it was signed, and that the website you are connecting to is the one it claims to be.

We wrote this article for technical managers and developers who build systems that rely on electronic signatures or integrate them into their platforms. It explains how a digital certificate works technically, what the components of a public key infrastructure are, how it relates to the Saudi framework, and what to review when choosing a provider or building an integration.

Quick summary

• A digital certificate binds a verified identity to a public key, and is signed by a certificate authority so that others can trust it.
• Public key infrastructure is built on a key pair: a private key that signs and a public key that verifies.
• The chain of trust starts at a root certificate authority, passes through intermediate authorities, and ends with the user's or server's certificate.
• A certificate's value depends on protecting the private key, verifying identity before issuance, and revocation and timestamping mechanisms.
• At Signit, we operate as a trust service provider licensed by the Digital Government Authority (DGA), and we verify signers' identities through Nafath, Absher and Wathq.

What is a digital certificate, and what does it contain?

A digital certificate is a structured electronic file that contains its owner's public key and identity data, and is signed by a certificate authority with its own private key to attest that this binding is valid.

Most certificates in use today follow the international X.509 standard, which defines the structure of the fields inside the certificate. The most important of these fields are the certificate holder's name, the issuer's name, the serial number, the validity period, the public key, the permitted uses of the key, and the issuer's signature over all of the above.

How does public key infrastructure work?

Public key infrastructure works on the principle of asymmetric cryptography: each party has a mathematically linked key pair, and whatever the private key signs can only be verified by the corresponding public key.

The private key stays with its owner alone and is used to create the signature. The public key is published inside the certificate, and any party can use it for verification. It is practically impossible to derive the private key from the public key, and this is what makes the system secure.

When a document is signed, the whole document is not encrypted. First, the document's hash is calculated: a short, fixed-length value that changes completely if a single character in the document changes. This hash is then signed with the private key. During verification, the other party recalculates the document's hash and uses the public key to decrypt the signature and compare the two hashes. If they match, two things are true: the signature came from the owner of the private key, and the document has not changed.

The certificate answers a question that cryptography alone cannot: who does this public key belong to? Without it, anyone could create a key pair and claim any identity.

What is the chain of trust, and how is it structured?

The chain of trust is the sequence that links a user's certificate to a trusted root certificate authority through one or more intermediate certificate authorities.

At the top of the chain sits the root certificate authority (Root CA). Its certificate is self-signed and pre-installed in operating systems, browsers and document readers, or approved within a national framework. To protect its key, the root authority does not issue user certificates directly; instead, it issues certificates to intermediate authorities that handle day-to-day issuance. At the end of the chain comes the user's or server's certificate.

When an application verifies a signature, it traces the chain upward: Is the signer's certificate signed by a valid intermediate authority? Is the intermediate authority signed by a trusted root authority? And has no certificate in the chain been revoked? If any link is broken, verification fails.

In Saudi Arabia, there is a national public key infrastructure operated by the National Center for Digital Certification (NCDC), while the Digital Government Authority regulates trust services and licenses their providers. This is why it matters that the certificates underpinning signatures are issued within a locally licensed framework. To learn more, read the article "Licensed trust service provider".

How does a digital certificate protect your identity online?

A digital certificate protects identity because it makes impersonation technically difficult: no one can sign in your name without your private key, and no website can claim another entity's identity without a certificate issued to that entity.

This protection shows up in everyday uses. When you browse a bank's website, the certificate is used in the TLS protocol to prove that the server really belongs to the bank and to encrypt the connection. When a contract is signed electronically, the certificate binds the signature to the signer's identity and reveals any later modification to the document. In document sealing, the organization's certificate proves that the document was issued by it.

But a certificate does not protect against everything. If the private key is stolen, the thief can sign in the owner's name until the certificate is revoked. And if a certificate is issued to someone without sufficient verification of their identity, it binds a key to an unconfirmed identity. That is why a certificate's value depends on what happens before and after it is issued.

What happens before and after a certificate is issued?

Before issuance, the applicant's identity must be verified. After issuance, the private key must be protected, the certificate's status must be verifiable, and evidence of the signing time must be preserved.

Identity verification is the foundation. The certificate attests that the key belongs to a specific person, and the value of that attestation depends on the strength of the verification. In the Saudi context, integration with Nafath and Absher gives this verification an official reference. For details, read the article "Nafath and Absher".

Private key protection is usually achieved through hardware security modules (HSM): dedicated devices that generate and store keys and perform signing operations internally, without the key ever leaving the device. In cloud signing, the trust service provider stores the user's key in these devices, and the key is activated only after the user authenticates.

Revocation makes it possible to invalidate a certificate before it expires, when the key is lost or the holder's details change. Revocation status is checked through certificate revocation lists (CRL) or the Online Certificate Status Protocol (OCSP).

Timestamping binds the signature to a verified time issued by a trusted timestamping authority. This solves a practical problem: years after a certificate has expired, how do we prove that the signature was made while it was valid? The timestamp is the evidence, and it is the basis for long-term validation of signed documents.

What should the technical team review when choosing a provider or building an integration?

The technical team reviews the provider's license and the source of its certificates, how keys are protected, the strength of identity verification, support for timestamping and long-term validation, where data is hosted, and how easy integration is.

What are the common mistakes in handling digital certificates?

Confusing a signature image with a digital signature. Many systems place an image of a signature on a PDF file and treat that as an electronic signature, without any certificate or cryptographic hash. That image does not prove who placed it, and it does not reveal any later modification. A real digital signature is embedded in the structure of the document itself and verified programmatically. To learn more, read the article "The difference between digital and electronic signatures".

Another is neglecting to check revocation status. Some developers verify the signature mathematically and check the chain of trust, but do not check that the certificate had not been revoked at the time of signing. The result is accepting a signature made with a certificate whose owner had already reported the key as stolen.

Some teams make the mistake of ignoring timestamping. The signature looks sound today, but once the certificate expires, it becomes impossible to prove that it was made while the certificate was valid. In long-term contracts, this becomes a real gap in any dispute.

Finally, the separation between identity and authority is sometimes overlooked. The certificate proves that a particular person signed, but not that they have the authority to bind the organization. That aspect is governed by the delegation of authority matrix and internal workflows.

How does a technical team start implementing certificate-based signing?

The team starts by defining use cases and the level of assurance required for each, then chooses a licensed provider and builds the integration, with full verification testing before launch.

To connect this implementation to the full contract lifecycle, read the article "Contract management from draft to archive".

Frequently asked questions

Conclusion

The digital certificate is the link that binds an encryption key to a real identity, and public key infrastructure is the system that makes this binding trustworthy. The strength of the whole system is determined by its weakest link: identity verification before issuance, private key protection, revocation checking, and timestamping. A technical team that attends to these links builds signatures that stand up to audits and disputes.