352 lines
9.4 KiB
Go
352 lines
9.4 KiB
Go
package sign
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import (
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"crypto"
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"crypto/x509"
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"encoding/hex"
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"fmt"
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"io"
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"os"
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"time"
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"github.com/digitorus/pdf"
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"github.com/digitorus/pdfsign/revocation"
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"github.com/digitorus/pkcs7"
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"github.com/mattetti/filebuffer"
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)
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type CatalogData struct {
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ObjectId uint32
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Length int64
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RootString string
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}
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type TSA struct {
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URL string
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Username string
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Password string
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}
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type RevocationFunction func(cert, issuer *x509.Certificate, i *revocation.InfoArchival) error
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type SignData struct {
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ObjectId uint32
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Signature SignDataSignature
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Signer crypto.Signer
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DigestAlgorithm crypto.Hash
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Certificate *x509.Certificate
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CertificateChains [][]*x509.Certificate
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TSA TSA
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RevocationData revocation.InfoArchival
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RevocationFunction RevocationFunction
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ExistingSignatures []SignData
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}
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type VisualSignData struct {
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PageId uint32
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ObjectId uint32
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Length int64
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}
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type InfoData struct {
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ObjectId uint32
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Length int64
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}
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//go:generate stringer -type=CertType
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type CertType uint
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const (
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CertificationSignature CertType = iota + 1
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ApprovalSignature
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UsageRightsSignature
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TimeStampSignature
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)
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//go:generate stringer -type=DocMDPPerm
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type DocMDPPerm uint
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const (
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DoNotAllowAnyChangesPerms DocMDPPerm = iota + 1
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AllowFillingExistingFormFieldsAndSignaturesPerms
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AllowFillingExistingFormFieldsAndSignaturesAndCRUDAnnotationsPerms
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)
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type SignDataSignature struct {
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CertType CertType
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DocMDPPerm DocMDPPerm
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Info SignDataSignatureInfo
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}
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type SignDataSignatureInfo struct {
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Name string
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Location string
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Reason string
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ContactInfo string
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Date time.Time
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}
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type SignContext struct {
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Filesize int64
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InputFile io.ReadSeeker
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OutputFile io.Writer
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OutputBuffer *filebuffer.Buffer
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SignData SignData
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CatalogData CatalogData
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VisualSignData VisualSignData
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InfoData InfoData
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PDFReader *pdf.Reader
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NewXrefStart int64
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ByteRangeStartByte int64
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SignatureContentsStartByte int64
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ByteRangeValues []int64
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SignatureMaxLength uint32
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SignatureMaxLengthBase uint32
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}
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func SignFile(input string, output string, sign_data SignData) error {
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input_file, err := os.Open(input)
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if err != nil {
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return err
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}
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defer input_file.Close()
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output_file, err := os.Create(output)
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if err != nil {
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return err
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}
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defer output_file.Close()
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finfo, err := input_file.Stat()
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if err != nil {
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return err
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}
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size := finfo.Size()
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rdr, err := pdf.NewReader(input_file, size)
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if err != nil {
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return err
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}
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return Sign(input_file, output_file, rdr, size, sign_data)
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}
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func Sign(input io.ReadSeeker, output io.Writer, rdr *pdf.Reader, size int64, sign_data SignData) error {
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sign_data.ObjectId = uint32(rdr.XrefInformation.ItemCount) + 2
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// We do size+1 because we insert a newline.
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context := SignContext{
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Filesize: size + 1,
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PDFReader: rdr,
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InputFile: input,
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OutputFile: output,
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VisualSignData: VisualSignData{
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ObjectId: uint32(rdr.XrefInformation.ItemCount),
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},
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CatalogData: CatalogData{
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ObjectId: uint32(rdr.XrefInformation.ItemCount) + 1,
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},
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InfoData: InfoData{
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ObjectId: uint32(rdr.XrefInformation.ItemCount) + 2,
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},
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SignData: sign_data,
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SignatureMaxLengthBase: uint32(hex.EncodedLen(512)),
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}
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// Fetch existing signatures
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existingSignatures, err := context.fetchExistingSignatures()
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if err != nil {
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return err
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}
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context.SignData.ExistingSignatures = existingSignatures
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err = context.SignPDF()
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if err != nil {
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return err
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}
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return nil
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}
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func (context *SignContext) SignPDF() error {
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// set defaults
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if context.SignData.Signature.CertType == 0 {
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context.SignData.Signature.CertType = 1
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}
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if context.SignData.Signature.DocMDPPerm == 0 {
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context.SignData.Signature.DocMDPPerm = 1
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}
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if !context.SignData.DigestAlgorithm.Available() {
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context.SignData.DigestAlgorithm = crypto.SHA256
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}
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context.OutputBuffer = filebuffer.New([]byte{})
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// Copy old file into new buffer.
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_, err := context.InputFile.Seek(0, 0)
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if err != nil {
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return err
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}
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if _, err := io.Copy(context.OutputBuffer, context.InputFile); err != nil {
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return err
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}
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// File always needs an empty line after %%EOF.
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if _, err := context.OutputBuffer.Write([]byte("\n")); err != nil {
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return err
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}
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// Base size for signature.
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context.SignatureMaxLength = context.SignatureMaxLengthBase
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// If not a timestamp signature
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if context.SignData.Signature.CertType != TimeStampSignature {
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switch context.SignData.Certificate.SignatureAlgorithm.String() {
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case "SHA1-RSA":
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case "ECDSA-SHA1":
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case "DSA-SHA1":
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context.SignatureMaxLength += uint32(hex.EncodedLen(128))
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case "SHA256-RSA":
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case "ECDSA-SHA256":
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case "DSA-SHA256":
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context.SignatureMaxLength += uint32(hex.EncodedLen(256))
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case "SHA384-RSA":
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case "ECDSA-SHA384":
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context.SignatureMaxLength += uint32(hex.EncodedLen(384))
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case "SHA512-RSA":
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case "ECDSA-SHA512":
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context.SignatureMaxLength += uint32(hex.EncodedLen(512))
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}
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// Add size of digest algorithm twice (for file digist and signing certificate attribute)
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context.SignatureMaxLength += uint32(hex.EncodedLen(context.SignData.DigestAlgorithm.Size() * 2))
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// Add size for my certificate.
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degenerated, err := pkcs7.DegenerateCertificate(context.SignData.Certificate.Raw)
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if err != nil {
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return fmt.Errorf("failed to degenerate certificate: %w", err)
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}
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context.SignatureMaxLength += uint32(hex.EncodedLen(len(degenerated)))
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// Add size of the raw issuer which is added by AddSignerChain
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context.SignatureMaxLength += uint32(hex.EncodedLen(len(context.SignData.Certificate.RawIssuer)))
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// Add size for certificate chain.
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var certificate_chain []*x509.Certificate
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if len(context.SignData.CertificateChains) > 0 && len(context.SignData.CertificateChains[0]) > 1 {
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certificate_chain = context.SignData.CertificateChains[0][1:]
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}
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if len(certificate_chain) > 0 {
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for _, cert := range certificate_chain {
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degenerated, err := pkcs7.DegenerateCertificate(cert.Raw)
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if err != nil {
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return fmt.Errorf("failed to degenerate certificate in chain: %w", err)
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}
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context.SignatureMaxLength += uint32(hex.EncodedLen(len(degenerated)))
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}
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}
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// Fetch revocation data before adding signature placeholder.
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// Revocation data can be quite large and we need to create enough space in the placeholder.
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if err := context.fetchRevocationData(); err != nil {
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return fmt.Errorf("failed to fetch revocation data: %w", err)
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}
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}
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// Add estimated size for TSA.
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// We can't kow actual size of TSA until after signing.
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//
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// Different TSA servers provide different response sizes, we
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// might need to make this configurable or detect and store.
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if context.SignData.TSA.URL != "" {
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context.SignatureMaxLength += uint32(hex.EncodedLen(9000))
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}
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// Create visual signature (visible or invisible based on CertType)
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//visible := context.SignData.Signature.CertType == CertificationSignature
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// Example usage: passing page number and default rect values
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visual_signature, err := context.createVisualSignature(false, 1, [4]float64{0, 0, 0, 0})
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if err != nil {
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return fmt.Errorf("failed to create visual signature: %w", err)
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}
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context.VisualSignData.Length = int64(len(visual_signature))
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// Write the new visual signature object.
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if _, err := context.OutputBuffer.Write([]byte(visual_signature)); err != nil {
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return err
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}
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catalog, err := context.createCatalog()
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if err != nil {
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return fmt.Errorf("failed to create catalog: %w", err)
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}
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context.CatalogData.Length = int64(len(catalog))
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// Write the new catalog object.
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if _, err := context.OutputBuffer.Write([]byte(catalog)); err != nil {
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return err
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}
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// Create the signature object
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var signature_object string
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var byte_range_start_byte, signature_contents_start_byte int64
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switch context.SignData.Signature.CertType {
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case TimeStampSignature:
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signature_object, byte_range_start_byte, signature_contents_start_byte = context.createTimestampPlaceholder()
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default:
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signature_object, byte_range_start_byte, signature_contents_start_byte = context.createSignaturePlaceholder()
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}
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appended_bytes := context.Filesize + int64(len(catalog)) + int64(len(visual_signature))
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// Positions are relative to old start position of xref table.
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byte_range_start_byte += appended_bytes
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signature_contents_start_byte += appended_bytes
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context.ByteRangeStartByte = byte_range_start_byte
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context.SignatureContentsStartByte = signature_contents_start_byte
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// Write the new signature object.
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if _, err := context.OutputBuffer.Write([]byte(signature_object)); err != nil {
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return fmt.Errorf("failed to create the new signature object: %w", err)
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}
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// Calculate the new start position of the xref table.
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context.NewXrefStart = appended_bytes + int64(len(signature_object))
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if err := context.writeXref(); err != nil {
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return fmt.Errorf("failed to write xref: %w", err)
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}
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if err := context.writeTrailer(); err != nil {
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return fmt.Errorf("failed to write trailer: %w", err)
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}
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if err := context.updateByteRange(); err != nil {
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return fmt.Errorf("failed to update byte range: %w", err)
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}
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if err := context.replaceSignature(); err != nil {
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return err
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}
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if _, err := context.OutputBuffer.Seek(0, 0); err != nil {
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return err
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}
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file_content := context.OutputBuffer.Buff.Bytes()
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if _, err := context.OutputFile.Write(file_content); err != nil {
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return err
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}
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return nil
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}
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