/
sign.go
330 lines (270 loc) · 8.64 KB
/
sign.go
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package sign
import (
"crypto"
"crypto/x509"
"encoding/hex"
"fmt"
"io"
"os"
"time"
"github.com/digitorus/pdf"
"github.com/digitorus/pkcs7"
"github.com/shurco/gosign/pkg/pdf/revocation"
"github.com/mattetti/filebuffer"
)
type CatalogData struct {
ObjectId uint32
Length int64
RootString string
}
type TSA struct {
URL string
Username string
Password string
}
type RevocationFunction func(cert, issuer *x509.Certificate, i *revocation.InfoArchival) error
type SignData struct {
ObjectId uint32
Signature SignDataSignature
Signer crypto.Signer
DigestAlgorithm crypto.Hash
Certificate *x509.Certificate
CertificateChains [][]*x509.Certificate
TSA TSA
RevocationData revocation.InfoArchival
RevocationFunction RevocationFunction
}
type VisualSignData struct {
ObjectId uint32
Length int64
}
type InfoData struct {
ObjectId uint32
Length int64
}
type SignDataSignature struct {
CertType uint
DocMDPPerm uint
Info SignDataSignatureInfo
}
const (
CertificationSignature = iota + 1
ApprovalSignature
UsageRightsSignature
)
const (
DoNotAllowAnyChangesPerms = iota + 1
AllowFillingExistingFormFieldsAndSignaturesPerms
AllowFillingExistingFormFieldsAndSignaturesAndCRUDAnnotationsPerms
)
type SignDataSignatureInfo struct {
Name string
Location string
Reason string
ContactInfo string
Date time.Time
}
type SignContext struct {
Filesize int64
InputFile io.ReadSeeker
OutputFile io.Writer
OutputBuffer *filebuffer.Buffer
SignData SignData
CatalogData CatalogData
VisualSignData VisualSignData
InfoData InfoData
PDFReader *pdf.Reader
NewXrefStart int64
ByteRangeStartByte int64
SignatureContentsStartByte int64
ByteRangeValues []int64
SignatureMaxLength uint32
SignatureMaxLengthBase uint32
}
func SignFile(input string, output string, sign_data SignData) error {
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
}
return Sign(input_file, output_file, rdr, size, sign_data)
}
func Sign(input io.ReadSeeker, output io.Writer, rdr *pdf.Reader, size int64, sign_data SignData) error {
sign_data.ObjectId = uint32(rdr.XrefInformation.ItemCount) + 3
// We do size+1 because we insert a newline.
context := SignContext{
Filesize: size + 1,
PDFReader: rdr,
InputFile: input,
OutputFile: output,
VisualSignData: VisualSignData{
ObjectId: uint32(rdr.XrefInformation.ItemCount),
},
CatalogData: CatalogData{
ObjectId: uint32(rdr.XrefInformation.ItemCount) + 1,
},
InfoData: InfoData{
ObjectId: uint32(rdr.XrefInformation.ItemCount) + 2,
},
SignData: sign_data,
SignatureMaxLengthBase: uint32(hex.EncodedLen(512)),
}
err := context.SignPDF()
if err != nil {
return err
}
return nil
}
func (context *SignContext) SignPDF() error {
// set defaults
if context.SignData.Signature.CertType == 0 {
context.SignData.Signature.CertType = 1
}
if context.SignData.Signature.DocMDPPerm == 0 {
context.SignData.Signature.DocMDPPerm = 1
}
if !context.SignData.DigestAlgorithm.Available() {
context.SignData.DigestAlgorithm = crypto.SHA256
}
context.OutputBuffer = filebuffer.New([]byte{})
// Copy old file into new file.
_, err := context.InputFile.Seek(0, 0)
if err != nil {
return err
}
if _, err := io.Copy(context.OutputBuffer, context.InputFile); err != nil {
return err
}
// File always needs an empty line after %%EOF.
if _, err := context.OutputBuffer.Write([]byte("\n")); err != nil {
return err
}
// Base size for signature.
context.SignatureMaxLength = context.SignatureMaxLengthBase
switch context.SignData.Certificate.SignatureAlgorithm.String() {
case "SHA1-RSA":
case "ECDSA-SHA1":
case "DSA-SHA1":
context.SignatureMaxLength += uint32(hex.EncodedLen(128))
case "SHA256-RSA":
case "ECDSA-SHA256":
case "DSA-SHA256":
context.SignatureMaxLength += uint32(hex.EncodedLen(256))
case "SHA384-RSA":
case "ECDSA-SHA384":
context.SignatureMaxLength += uint32(hex.EncodedLen(384))
case "SHA512-RSA":
case "ECDSA-SHA512":
context.SignatureMaxLength += uint32(hex.EncodedLen(512))
}
// Add size of digest algorithm twice (for file digist and signing certificate attribute)
context.SignatureMaxLength += uint32(hex.EncodedLen(context.SignData.DigestAlgorithm.Size() * 2))
// Add size for my certificate.
degenerated, err := pkcs7.DegenerateCertificate(context.SignData.Certificate.Raw)
if err != nil {
return fmt.Errorf("failed to degenerate certificate: %w", err)
}
context.SignatureMaxLength += uint32(hex.EncodedLen(len(degenerated)))
// Add size for certificate chain.
var certificate_chain []*x509.Certificate
if len(context.SignData.CertificateChains) > 0 && len(context.SignData.CertificateChains[0]) > 1 {
certificate_chain = context.SignData.CertificateChains[0][1:]
}
if len(certificate_chain) > 0 {
for _, cert := range certificate_chain {
degenerated, err := pkcs7.DegenerateCertificate(cert.Raw)
if err != nil {
return fmt.Errorf("failed to degenerate certificate in chain: %w", err)
}
context.SignatureMaxLength += uint32(hex.EncodedLen(len(degenerated)))
}
}
// Add estimated size for TSA.
// We can't kow actual size of TSA until after signing.
//
// Different TSA servers provide different response sizes, we
// might need to make this configurable or detect and store.
if context.SignData.TSA.URL != "" {
context.SignatureMaxLength += uint32(hex.EncodedLen(9000))
}
// Fetch revocation data before adding signature placeholder.
// Revocation data can be quite large and we need to create enough space in the placeholder.
if err := context.fetchRevocationData(); err != nil {
return fmt.Errorf("failed to fetch revocation data: %w", err)
}
visual_signature, err := context.createVisualSignature()
if err != nil {
return fmt.Errorf("failed to create visual signature: %w", err)
}
context.VisualSignData.Length = int64(len(visual_signature))
// Write the new catalog object.
if _, err := context.OutputBuffer.Write([]byte(visual_signature)); err != nil {
return err
}
catalog, err := context.createCatalog()
if err != nil {
return fmt.Errorf("failed to create catalog: %w", err)
}
context.CatalogData.Length = int64(len(catalog))
// Write the new catalog object.
if _, err := context.OutputBuffer.Write([]byte(catalog)); err != nil {
return fmt.Errorf("failed to write catalog: %w", err)
}
// Create the signature object
signature_object, byte_range_start_byte, signature_contents_start_byte := context.createSignaturePlaceholder()
info, err := context.createInfo()
if err != nil {
return fmt.Errorf("failed to create info: %w", err)
}
context.InfoData.Length = int64(len(info))
// Write the new catalog object.
if _, err := context.OutputBuffer.Write([]byte(info)); err != nil {
return fmt.Errorf("failed to write info: %w", err)
}
appended_bytes := context.Filesize + int64(len(catalog)) + int64(len(visual_signature)) + int64(len(info))
// Positions are relative to old start position of xref table.
byte_range_start_byte += appended_bytes
signature_contents_start_byte += appended_bytes
context.ByteRangeStartByte = byte_range_start_byte
context.SignatureContentsStartByte = signature_contents_start_byte
// Write the new signature object.
if _, err := context.OutputBuffer.Write([]byte(signature_object)); err != nil {
return fmt.Errorf("failed to create the new signature object: %w", err)
}
// Calculate the new start position of the xref table.
context.NewXrefStart = appended_bytes + int64(len(signature_object))
if err := context.writeXref(); err != nil {
return fmt.Errorf("failed to write xref: %w", err)
}
if err := context.writeTrailer(); err != nil {
return fmt.Errorf("failed to write trailer: %w", err)
}
if err := context.updateByteRange(); err != nil {
return fmt.Errorf("failed to update byte range: %w", err)
}
if err := context.replaceSignature(); err != nil {
return fmt.Errorf("failed to replace signature: %w", err)
}
if _, err := context.OutputBuffer.Seek(0, 0); err != nil {
return err
}
file_content := context.OutputBuffer.Buff.Bytes()
if _, err := context.OutputFile.Write(file_content); err != nil {
return fmt.Errorf("failed to write to output file: %w", err)
}
return nil
}