115 lines
3.8 KiB
Go
115 lines
3.8 KiB
Go
package sign
|
|
|
|
import (
|
|
"bytes"
|
|
"encoding/hex"
|
|
"io"
|
|
"strconv"
|
|
"strings"
|
|
|
|
"github.com/digitorus/pkcs7"
|
|
)
|
|
|
|
var signatureMaxLength = uint32(11742)
|
|
var signatureByteRangePlaceholder = "/ByteRange[0 ********** ********** **********]"
|
|
|
|
func (context *SignContext) createSignaturePlaceholder() (signature string, byte_range_start_byte int64, signature_contents_start_byte int64) {
|
|
signature = strconv.Itoa(int(context.SignData.ObjectId)) + " 0 obj\n"
|
|
signature += "<< /Type /Sig"
|
|
signature += " /Filter /Adobe.PPKLite"
|
|
signature += " /SubFilter /adbe.pkcs7.detached"
|
|
|
|
byte_range_start_byte = int64(len(signature)) + 1
|
|
|
|
// Create a placeholder for the byte range string, we will replace it later.
|
|
signature += " " + signatureByteRangePlaceholder
|
|
|
|
signature_contents_start_byte = int64(len(signature)) + 11
|
|
|
|
// Create a placeholder for the actual signature content, we wil replace it later.
|
|
signature += " /Contents<" + strings.Repeat("0", int(signatureMaxLength)) + ">"
|
|
|
|
if !context.SignData.Signature.Approval {
|
|
signature += " /Reference [" // array of signature reference dictionaries
|
|
signature += " << /Type /SigRef"
|
|
if context.SignData.Signature.CertType > 0 {
|
|
signature += " /TransformMethod /DocMDP"
|
|
signature += " /TransformParams <<"
|
|
signature += " /Type /TransformParams"
|
|
signature += " /P " + strconv.Itoa(int(context.SignData.Signature.CertType))
|
|
signature += " /V /1.2"
|
|
} else {
|
|
signature += " /TransformMethod /UR3"
|
|
signature += " /TransformParams <<"
|
|
signature += " /Type /TransformParams"
|
|
signature += " /V /2.2"
|
|
}
|
|
|
|
signature += " >>" // close TransformParams
|
|
signature += " >>"
|
|
signature += " ]" // end of reference
|
|
}
|
|
|
|
if context.SignData.Signature.Info.Name != "" {
|
|
signature += " /Name " + pdfString(context.SignData.Signature.Info.Name)
|
|
}
|
|
if context.SignData.Signature.Info.Location != "" {
|
|
signature += " /Location " + pdfString(context.SignData.Signature.Info.Location)
|
|
}
|
|
if context.SignData.Signature.Info.Reason != "" {
|
|
signature += " /Reason " + pdfString(context.SignData.Signature.Info.Reason)
|
|
}
|
|
if context.SignData.Signature.Info.ContactInfo != "" {
|
|
signature += " /ContactInfo " + pdfString(context.SignData.Signature.Info.ContactInfo)
|
|
}
|
|
signature += " /M " + pdfDateTime(context.SignData.Signature.Info.Date)
|
|
signature += " >>"
|
|
signature += "\nendobj\n"
|
|
|
|
return signature, byte_range_start_byte, signature_contents_start_byte
|
|
}
|
|
|
|
func (context *SignContext) createSignature() ([]byte, error) {
|
|
|
|
// Sadly we can't efficiently sign a file, we need to read all the bytes we want to sign.
|
|
context.OutputFile.Seek(0, 0)
|
|
sign_buf := bytes.NewBuffer(nil)
|
|
io.Copy(sign_buf, context.OutputFile)
|
|
file_content := sign_buf.Bytes()
|
|
|
|
// Collect the parts to sign.
|
|
sign_content := make([]byte, 0)
|
|
sign_content = append(sign_content, file_content[context.ByteRangeValues[0]:(context.ByteRangeValues[0]+context.ByteRangeValues[1])]...)
|
|
sign_content = append(sign_content, file_content[context.ByteRangeValues[2]:(context.ByteRangeValues[2]+context.ByteRangeValues[3])]...)
|
|
|
|
// Initialize pkcs7 signer.
|
|
signed_data, err := pkcs7.NewSignedData(sign_content)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
|
|
// Add the signer and sign the data.
|
|
if err := signed_data.AddSignerChain(context.SignData.Certificate, context.SignData.Signer, context.SignData.CertificateChain, pkcs7.SignerInfoConfig{}); err != nil {
|
|
return nil, err
|
|
}
|
|
|
|
// PDF needs a detached signature, meaning the content isn't included.
|
|
signed_data.Detach()
|
|
|
|
return signed_data.Finish()
|
|
}
|
|
|
|
func (context *SignContext) replaceSignature() error {
|
|
signature, err := context.createSignature()
|
|
if err != nil {
|
|
return err
|
|
}
|
|
|
|
dst := make([]byte, hex.EncodedLen(len(signature)))
|
|
hex.Encode(dst, signature)
|
|
|
|
context.OutputFile.WriteAt(dst, context.ByteRangeValues[0] + context.ByteRangeValues[1] + 1)
|
|
|
|
return nil
|
|
}
|