Signing PDF files with Go

This PDF signing library is written in Go. The library is in development, might not work for all PDF files and the API might change, bug reports, contributions and suggestions are welcome.

From the command line

Usage of ./pdfsign:
  -contact string
        Contact information for signatory
  -location string
        Location of the signatory
  -name string
        Name of the signatory
  -reason string
        Reason for signig

Example usage:
        ./pdfsign -name "Jon Doe" sign input.pdf output.pdf certificate.crt private_key.key [chain.crt]
        ./pdfsignverify input.pdf

As library

import "bitbucket.org/digitorus/pdf"

input_file, err := os.Open(input)
if err != nil {
    return err
}
defer input_file.Close()

output_file, err := os.Create(output)
if err != nil {
    return err
}
defer output_file.Close()

finfo, err := input_file.Stat()
if err != nil {
    return err
}
size := finfo.Size()

rdr, err := pdf.NewReader(input_file, size)
if err != nil {
    return err
}

err = sign.Sign(input_file, output_file, rdr, size, sign.SignData{
    Signature: sign.SignDataSignature{
        Info: sign.SignDataSignatureInfo{
            Name:        "John Doe",
            Location:    "Somewhere on the globe",
            Reason:      "My season for siging this document",
            ContactInfo: "How you like",
            Date:        time.Now().Local(),
        },
        CertType:   sign.CertificationSignature,
        DocMDPPerm: sign.AllowFillingExistingFormFieldsAndSignaturesPerms,
    },
    Signer:            privateKey, // crypto.Signer
    Certificate:       certificate, // x509.Certificate
    CertificateChains: certificate_chains, // x509.Certificate.Verify()
    TSA: sign.TSA{
        URL: "https://freetsa.org/tsr",
        Username: "",
        Password: "",
    },

    // The follow options are likely to change in a future release
    //
    // cache revocation data when bulk signing
    RevocationData:     revocation.InfoArchival{}, 
    // custom revocation lookup
    RevocationFunction: sign.DefaultEmbedRevocationStatusFunction,
})
if err != nil {
    log.Println(err)
} else {
    log.Println("Signed PDF written to " + output)
}