[UP-487] Example for PAdES B-T signing. (#231)

* [UP-487] Example for PAdES B-T signing.

* Added new examples to README.md

signatures/README.md

@@ -9,7 +9,9 @@ Examples for digital signing of PDF files with UniDoc:
 - [pdf_sign_appearance.go](pdf_sign_appearance.go) Example of creating signature appearance fields.
 - [pdf_sign_validate.go](pdf_sign_validate.go) Example of signature validation.
 - [pdf_sign_pem_multicert.go](pdf_sign_pem_multicert.go) Example of signing using a certificate chain and a private key, extracted from PEM files.
-
+- [pdf_sign_pades_b_b.go](pdf_sign_pades_b_b.go) Example of signing with a PAdES B-B compatible digital signature.
+- [pdf_sign_pades_b_t.go](pdf_sign_pades_b_t.go) Example of signing with a PAdES B-T compatible digital signature.
+- [pdf_sign_validate_pades_b_b.go](pdf_sign_validate_pades_b_b.go) Example of PAdES signature validation.
 For LTV enabling digital signatures, see the [LTV](ltv) guide and samples.
 
 ## pdf_sign_hsm_pkcs11_cgo.go

signatures/pdf_sign_pades_b_t.go

@@ -0,0 +1,140 @@
+/*
+ * This example showcases how to create a  PAdES B-T compatible digital signature for a PDF file.
+ *
+ * $ ./pdf_sign_pades_b_t <FILE.PFX> <PASSWORD> <FILE.PEM> <INPUT_PDF_PATH> <OUTPUT_PDF_PATH>
+ */
+package main
+
+import (
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"time"
+
+	"golang.org/x/crypto/pkcs12"
+
+	"github.com/unidoc/unipdf/v3/annotator"
+	"github.com/unidoc/unipdf/v3/common/license"
+	"github.com/unidoc/unipdf/v3/core"
+	"github.com/unidoc/unipdf/v3/model"
+	"github.com/unidoc/unipdf/v3/model/sighandler"
+)
+
+func init() {
+	// Make sure to load your metered License API key prior to using the library.
+	// If you need a key, you can sign up and create a free one at https://cloud.unidoc.io
+	err := license.SetMeteredKey(os.Getenv(`UNIDOC_LICENSE_API_KEY`))
+	if err != nil {
+		panic(err)
+	}
+}
+
+const usagef = "Usage: %s PFX_FILE PASSWORD PEM_FILE INPUT_PDF_PATH OUTPUT_PDF_PATH\n"
+
+func main() {
+	args := os.Args
+	if len(args) < 6 {
+		fmt.Printf(usagef, os.Args[0])
+		return
+	}
+	pfxPath := args[1]
+	password := args[2]
+	pemPath := args[3]
+	inputPath := args[4]
+	outputPath := args[5]
+
+	// Get private key and X509 certificate from the PFX file.
+	pfxData, err := ioutil.ReadFile(pfxPath)
+	if err != nil {
+		log.Fatal("Fail: %v\n", err)
+	}
+
+	priv, cert, err := pkcs12.Decode(pfxData, password)
+	if err != nil {
+		log.Fatal("Fail: %v\n", err)
+	}
+
+	// Get cacert certificate from the PEM file.
+	caCertF, err := ioutil.ReadFile(pemPath)
+	if err != nil {
+		log.Fatal("Fail: %v\n", err)
+	}
+
+	certDERBlock, _ := pem.Decode(caCertF)
+
+	cacert, err := x509.ParseCertificate(certDERBlock.Bytes)
+
+	if err != nil {
+		log.Fatal("Fail: %v\n", err)
+		return
+	}
+
+	// Create reader.
+	file, err := os.Open(inputPath)
+	if err != nil {
+		log.Fatal("Fail: %v\n", err)
+	}
+	defer file.Close()
+
+	reader, err := model.NewPdfReader(file)
+	if err != nil {
+		log.Fatal("Fail: %v\n", err)
+	}
+
+	// Create appender.
+	appender, err := model.NewPdfAppender(reader)
+	if err != nil {
+		log.Fatal("Fail: %v\n", err)
+	}
+
+	// Set timestamp server.
+	timestampServerURL := "https://freetsa.org/tsr"
+
+	// Create signature handler.
+	handler, err := sighandler.NewEtsiPAdESLevelT(priv.(*rsa.PrivateKey), cert, cacert, timestampServerURL)
+	if err != nil {
+		log.Fatal("Fail: %v\n", err)
+	}
+
+	// Create signature.
+	signature := model.NewPdfSignature(handler)
+	signature.SetName("PAdES B-T Signature PDF")
+	signature.SetReason("TestPAdESPDF")
+	signature.SetDate(time.Now(), "")
+
+	if err := signature.Initialize(); err != nil {
+		log.Fatal("Fail: %v\n", err)
+	}
+
+	// Create signature field and appearance.
+	opts := annotator.NewSignatureFieldOpts()
+	opts.FontSize = 10
+	opts.Rect = []float64{10, 25, 75, 60}
+
+	field, err := annotator.NewSignatureField(
+		signature,
+		[]*annotator.SignatureLine{
+			annotator.NewSignatureLine("Name", "John Doe"),
+			annotator.NewSignatureLine("Date", "2023.05.08"),
+			annotator.NewSignatureLine("Reason", "PAdES signature test"),
+		},
+		opts,
+	)
+	field.T = core.MakeString("Self signed PDF")
+
+	if err = appender.Sign(1, field); err != nil {
+		log.Fatal("Fail: %v\n", err)
+	}
+
+	// Write output PDF file.
+	err = appender.WriteToFile(outputPath)
+	if err != nil {
+		log.Fatal("Fail: %v\n", err)
+	}
+
+	log.Printf("PDF file successfully signed. Output path: %s\n", outputPath)
+}

signatures/pdf_sign_validate_pades_b_b.go

@@ -46,7 +46,7 @@ func main() {
 		log.Fatal("Fail: %v\n", err)
 	}
 
-	// Create signature handler.
+	// Create signature handler. It is possible to validate B-T level the same way if you create NewEtsiPAdESLevelT here
 	padesHandler, err := sighandler.NewEtsiPAdESLevelB(nil, nil, nil)
 	if err != nil {
 		log.Fatal("Fail: %v\n", err)