Signatures on documents are not restricted to the procedure that involves printing out a document, signing it physically, scanning it, and then returning it. In today’s world, there are ways through which people can digitally sign documents and perform all tasks related to documents without involving any paper at all.
But what is a digital signature? How is it done, and how is it different from adding an image of your physical signature to a PDF document?
This guide aims at answering all these questions by discussing digital signatures in layman language, the working of digital signatures, the difference between digital signatures and electronic signatures, and signing PDF documents online.
What Is a Digital Signature?
The digital signature is a cryptographic technique employed to ensure the legitimacy and integrity of the digital information.
In simpler terms, the digital signature is a way that answers two questions:
- •Who is the signatory of this document?
- •Is there any change made in the document after it has been signed?
The digital signatures employ public key cryptography to create and validate the signatures. As per NIST, digital signatures may be employed to authenticate the identity of the signer and detect any tampering with signed data.
Thus, the digital signatures prove useful for documents such as contracts, agreements, business forms, approvals, certificates, and many other types of documents.
How Does a Digital Signature Work?
Though the technology of a digital signature may be complicated, its concept is fairly simple to comprehend.
A digital signature typically consists of a set of two keys for cryptography:
- •Private key: The signer uses this key to make the digital signature.
- •Public key: This key verifies the digital signature.
The keys belong to public key cryptography, which utilizes different keys to sign and verify signatures.
The signing process works like this:
1. The document is prepared
The signer opens the document, such as a PDF, and prepares it for signing.
2. A unique representation of the document is created
Cryptographic algorithms process the document's data to create a value commonly called a hash.
The hash represents the contents of the document. If the document is changed, its resulting hash will also change.
3. The signature is created
The signer's private key is used as part of the cryptographic process that creates the digital signature.
4. Signature is verified
In the case when the recipient receives the signed document, the signature can be checked using the public key.
In case of successful verification, this becomes a proof that the signature belongs to the signer and the signed data is not changed.
According to NIST, the digital signature is a tool that can detect any modification of the document and authenticate the identity of the signer.
What Is a Digital Certificate?
A digital certificate helps connect a public key with an identified person or entity.
This is akin to a digital certificate, which contains data about the owner of a public key. Such certificates can be generated by trusted third-party certificate authorities and may include information like the public key, identification information, valid period, and digital signature of the certificate authority.
A signature certificate is specifically intended for verifying digital signatures.
This certificate-based system is one reason a true certificate-based digital signature is different from simply placing a picture of a signature on a PDF.
Digital Signature vs Electronic Signature
The terms digital signature and electronic signature can be interchangeable at times, yet they don't always mean the same thing.
Electronic signatures can be more of a general term. For instance, an electronic signature could entail typing one's name, drawing a signature, clicking an agreement button, or any other means by which one intends to sign.
A digital signature is, technically, the use of cryptography to create a signature.
In addition, a digital signature could use a digital certificate in order to authenticate the identity of the signer and protect the integrity of the signed document.
So, a simple way to remember the difference is:
Electronic signature = a general way of electronically signing.
Digital signature = cryptography-based signing and verification process.
The specific legal definitions and requirements can differ from country to country or even per document type and regulation requirements. Adobe makes similar distinctions between basic electronic signatures and digital signatures based on certificates.
Is a Picture of Your Signature a Digital Signature?
No.
Attaching an image of your handwritten signature to a PDF is only a visual representation of a signature, but not necessarily a cryptographic one.
For instance, you could scan your signature and attach the image to the document. However, even though it makes the document appear signed, the image lacks the cryptographic properties of a digital certificate.
This matters especially when the document requires greater assurance in identity or the document needs protection from tampering.
Why Use Digital Signatures?
Digital signatures can improve document processing efficiency while also serving as a way of authenticating and assuring integrity.
Common uses include:
Business agreements
Companies can use digitally signed documents in their contracts and agreements.
Financial documents
Digital signatures can be applied to invoice processing, authorizations, and other financial documents.
Human resources
Documents related to employment and personnel policies can also be digitally signed.
Education
Educational institutions can use digitally signed documents for application process, certifications, approvals and other administrative tasks.
Professional documents
Consultants, freelancers, agencies, and other professionals can sign their documents without printing and scanning.
What Are the Benefits of Digital Signatures?
There may be several benefits to using digital signatures.
Faster document workflows
Documents can be signed and returned electronically instead of being printed, scanned, and emailed.
Better document integrity
Cryptographic verification can help detect unauthorized changes to signed information.
Easier verification
Recipients can use signature information and certificates to verify a digital signature.
Less paper
Digital document workflows can reduce the need for printing and physical document handling.
Easier remote collaboration
Teams working in different locations can exchange and sign documents digitally.
How to Sign a PDF Digitally
The exact process depends on the PDF signing solution and the type of signature required.
A typical PDF signing workflow looks like this:
- Open or upload the PDF.
- Choose the signing option.
- Add the required signature information.
- Complete any required identity or certificate verification.
- Apply the signature.
- Review the signed PDF.
- Save or share the completed document.
If you just want to insert a visual signature in the PDF document, the above process will be somewhat simplified.
Are Digital Signatures Secure?
Digital signatures are designed to provide security properties such as authentication and integrity.
But security is not all about the signature algorithm. Security will also depend on how the private key, certificate, identity, software, and signing system are managed.
In its advice on applications for digital signatures, NIST stresses the need to authenticate the public keys, ensure the management of the private keys, and verify the identity of the key-pair holder.
Users should, thus, know the kind of digital signature they are using when dealing with critical documents.
Digital Signatures in Everyday PDF Work
PDFs are extensively used in creating contracts, forms, reports, invoices, applications, certificates, and business documents.
In signing a document, the objective would be more than just making the signature visible. It may also be necessary for the recipient to be sure that the document came from the right source, and that the document has not been tampered with.
This is where digital signatures technology becomes handy.
Frequently Asked Questions
What is the digital signature of a PDF?
The digital signature of a PDF refers to the cryptographic signature used on the file. It will depend on how it was signed whether it will help in authentication and detecting any alteration of the signed file.
Are a digital signature and an electronic signature the same?
Not always. Electronic signature is a general term used, but a certificate-based digital signature involves cryptographic methods for signing and verifying the file.
Can I sign my own handwritten signature on a PDF?
Yes, most PDF applications allow for the addition of your handwritten or image-based signature, but that doesn’t mean it is the same as adding a certificate-based digital signature to it.
Can a digital signature show whether a document was changed?
Digital signatures are designed to detect unauthorized modifications to signed data.
What is a digital certificate?
A digital certificate is a digital credential that associates an identity with a public key. It can be issued and digitally signed by a trusted certification authority.
Are digital signatures legally valid?
Legal validity depends on the country, applicable laws, document type, identity verification method, and signature technology being used. A digital signature should not automatically be assumed to have the same legal effect in every jurisdiction.
Conclusion
Digital signatures are a crucial aspect of contemporary document workflows. They use cryptography techniques and key pairs, as well as digital certificates in some instances, to provide proof of identity and integrity of the signed content.
In the case of regular PDF usage, distinguishing between visual signature, electronic signature, and digital signature that uses digital certificate may be useful when choosing the way to sign a document.
As PDF document workflow becomes more frequent nowadays, knowledge of PDF signature process may prove very useful.
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