# What Is a Digital Signature? How PKI-Based Signatures Work in the Philippines


A **digital signature** is a specific type of [electronic signature](/blog/glossary/electronic-signature/) that uses [Public Key Infrastructure (PKI)](/blog/glossary/public-key-infrastructure/) and cryptographic algorithms to verify the signer's identity and ensure that a document has not been tampered with after signing. It provides the highest level of security, authentication, and non-repudiation among signature types.

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## How Digital Signatures Work

Digital signatures rely on asymmetric cryptography -- a mathematical process using two related keys:

### The Signing Process

1. **Hash creation** -- A cryptographic hash function creates a unique "fingerprint" (hash value) of the document
2. **Encryption** -- The signer's **private key** encrypts the hash, creating the digital signature
3. **Attachment** -- The encrypted hash is attached to the document along with the signer's digital certificate

### The Verification Process

1. **Decryption** -- The recipient uses the signer's **public key** to decrypt the signature
2. **Hash comparison** -- The decrypted hash is compared to a fresh hash of the received document
3. **Validation** -- If the hashes match, the document is authentic and unaltered; if they don't match, the document has been tampered with

This process ensures three things:
- **Authentication** -- The document came from the claimed signer
- **Integrity** -- The document has not been altered since signing
- **Non-repudiation** -- The signer cannot deny having signed the document

For a deeper technical explanation, see our article on [how advanced cryptographic technology prevents document fraud](/blog/how-advanced-cryptographic-technology-helps-prevent-document-fraud/).

## Digital Signature vs. Electronic Signature

| Feature | Electronic Signature | Digital Signature |
|---------|---------------------|-------------------|
| Technology | Any electronic mark or process | Cryptographic (PKI-based) |
| Identity verification | Varies (can be weak) | Certificate-based (strong) |
| Tamper detection | Not inherent | Built-in via hash comparison |
| Non-repudiation | Weak | Strong |
| Legal weight | Valid under [RA 8792](/blog/glossary/ra-8792/) | Stronger presumption under RA 8792 |
| Complexity | Simple | Requires PKI infrastructure |
| Cost | Lower | Higher (certificate costs) |

**Key takeaway:** All digital signatures are electronic signatures, but not all electronic signatures are digital signatures. For a complete comparison, see [the difference between digital and electronic signatures](/blog/what-is-the-difference-between-digital-signature-and-electronic-signature/).

## Legal Basis in the Philippines

Digital signatures are recognized under [RA 8792 (the Electronic Commerce Act)](/blog/glossary/ra-8792/). Under the law and its implementing rules:

- Digital signatures using PKI receive a **stronger presumption of validity** than simple electronic signatures
- The signer is presumed to have intended to authenticate the document
- Any alteration to the document after signing is detectable, which strengthens evidentiary weight under the [Rules on Electronic Evidence](/blog/glossary/rules-on-electronic-evidence/)

In the context of [e-notarization](/blog/glossary/e-notarization/), [A.M. No. 24-10-14-SC](/blog/glossary/am-no-24-10-14-sc/) requires that electronic notarial acts use secure electronic signatures -- making digital signatures the preferred method for notarized documents.

## Use Cases

Digital signatures are recommended for documents that require the highest level of security and legal enforceability:

- **Notarized documents** -- [E-notarization](/blog/glossary/e-notarization/) uses digital signatures for both the principal and the ENP
- **Court filings** -- [Making digital signatures court-ready](/blog/how-to-make-your-digital-signatures-court-ready-in-the-philippines/) requires PKI-level security
- **Financial transactions** -- Bank and investment documents, [budget sign-offs](/blog/streamline-your-budget-sign-offs-with-secure-digital-workflows/)
- **Corporate governance** -- [Board resolutions](/blog/glossary/board-resolution/), [secretary's certificates](/blog/glossary/secretarys-certificate/), and SEC filings
- **Government submissions** -- Regulatory filings and compliance documents
- **High-value contracts** -- Agreements where [dispute mitigation](/blog/mitigating-contract-disputes-with-tamper-proof-digital-signatures/) is critical

## Digital Certificates

A digital signature requires a **digital certificate** -- an electronic credential issued by a Certificate Authority (CA) that binds a person's identity to their public key. The certificate contains:

- The signer's name and identifying information
- The signer's public key
- The issuing Certificate Authority's name
- The certificate's validity period
- The CA's digital signature (proving the certificate is authentic)

In the Philippines, digital certificates for use in legal and government contexts should come from accredited or recognized certificate authorities.

## Related Terms

- [Electronic Signature](/blog/glossary/electronic-signature/)
- [Public Key Infrastructure (PKI)](/blog/glossary/public-key-infrastructure/)
- [Document Audit Trail](/blog/glossary/document-audit-trail/)
- [E-Notarization](/blog/glossary/e-notarization/)
- [Electronic Notarial Seal](/blog/glossary/electronic-notarial-seal/)

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[NotarialOS](https://notarialos.com) uses PKI-based digital signatures to ensure that every document signed and notarized on the platform is cryptographically secure, legally valid, and tamper-proof.