Validating PAdES Signatures

This guide shows how to validate a digital signature with UniDoc for PAdES compatibility.

Before you begin #

You should get your API key from your UniCloud account.

If this is your first time using UniPDF SDK, follow this guide to set up a local development environment.

Project setup #

Clone the project repository #

In your terminal, clone examples repository. It contains the Go code we will be using for this guide.

git clone https://github.com/unidoc/unipdf-examples.git

Navigate to the signatures folder in the unipdf-examples directory.

cd unipdf-examples/signatures

Configure environment variables #

Replace the UNIDOC_LICENSE_API_KEY with your API credentials from your UniCloud account.

Linux/Mac #

export UNIDOC_LICENSE_API_KEY=PUT_YOUR_API_KEY_HERE

Windows #

set UNIDOC_LICENSE_API_KEY=PUT_YOUR_API_KEY_HERE

How it works #

In the example code above, the import section imports the necessary UniPDF packages and other Go libraries. The init function defined in lines 18-25, loads the API keys and sets the license using license.SetMeteredKey(os.Getenv(`UNIDOC_LICENSE_API_KEY`)).

The main function in lines 29-75, contains the code that is used to validate the signature for PAdES compatibility. In lines 30-34, the input file is parsed from the command line arguments. Then a new PdfReader is created using model.NewPdfReader(file) in line 44. In line 50-53, a new signature handler is created using:

padesHandler, err := sighandler.NewEtsiPAdESLevelB(nil, nil, nil)
if err != nil {
	log.Fatal("Fail: %v\n", err)
}

The signature handler created using NewEtsiPAdESLevelB is used to validate PAdES Baseline B Signature. To validate a PAdES Baseline T Signature, use the NewEtsiPAdESLevelT function instead.

A list of handlers is instantiated in line 55. In lines 60-74, The ValidateSignatures method of the PdfReader is used to validate the signature as follows.

res, err := reader.ValidateSignatures(handlers)
if err != nil {
	log.Fatal("Fail: %v\n", err)
}
if len(res) == 0 {
	log.Fatal("Fail: no signature fields found")
}

if !res[0].IsSigned || !res[0].IsVerified {
	log.Fatal("Fail: validation failed")
}

for i, item := range res {
	fmt.Printf("--- Signature %d\n%s\n", i+1, item.String())
}

The IsSigned and IsVerified fields are checked in line 68. The for loop in line 72-74, iterates through each result and prints the validation results.

Run the code #

To run the code use the following command.

 go run pdf_sign_validate_pades_b_b.go <INPUT_PDF_PATH>