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