Initial commit, without tests, docs, benchmarks etc
This commit is contained in:
Paul van Brouwershaven
306
signatures.go
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306
signatures.go
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@@ -0,0 +1,306 @@
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// http://wwwimages.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/PDF32000_2008.pdf
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package signatures
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import (
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"bytes"
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"crypto/x509"
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"encoding/asn1"
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"fmt"
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"io"
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"os"
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"io/ioutil"
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// "log"
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// "strings"
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"time"
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"bitbucket.org/digitorus/pdf"
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"github.com/digitorus/timestamp"
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"go.mozilla.org/pkcs7"
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"golang.org/x/crypto/ocsp"
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)
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type RevocationInfoArchival struct {
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CRL RevCRL `asn1:"tag:0,optional,explicit"`
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OCSP RevOCSP `asn1:"tag:1,optional,explicit"`
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OtherRevInfo OtherRevInfo `asn1:"tag:2,optional,explicit"`
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}
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type RevCRL []asn1.RawValue
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type RevOCSP []asn1.RawValue
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type OtherRevInfo struct {
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Type asn1.ObjectIdentifier
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Value []byte
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}
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type Response struct {
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Error string
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DocumentInfo string
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Signers []Signer
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}
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type Signer struct {
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Name string
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Reason string
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Location string
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ContactInfo string
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ValidSignature bool
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TrustedIssuer bool
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RevokedCertificate bool
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Certificates []Certificate
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TimeStamp *timestamp.Timestamp
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}
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type Certificate struct {
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Certificate *x509.Certificate
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VerifyError string
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OCSPResponse *ocsp.Response
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OCSPEmbedded bool
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CRLRevoked time.Time
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CRLEmbedded bool
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}
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func Verify(file *os.File) (apiResp *Response, err error) {
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defer func() {
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if r := recover(); r != nil {
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apiResp = nil
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err = fmt.Errorf("Failed to verify file (%v)", r)
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}
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}()
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apiResp = &Response{}
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finfo, _ := file.Stat()
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size := finfo.Size()
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rdr, err := pdf.NewReader(file, size)
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if err != nil {
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return nil, fmt.Errorf("Failed to open file")
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}
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// AcroForm will contain a SigFlags value if the form contains a digital signature
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t := rdr.Trailer().Key("Root").Key("AcroForm").Key("SigFlags")
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if t.IsNull() {
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return nil, fmt.Errorf("No digital signature in document")
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}
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// Walk over the cross references in the document
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for _, x := range rdr.Xref() {
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// Get the xref object Value
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v := rdr.Resolve(x.Ptr(), x.Ptr())
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// We must have a Filter Adobe.PPKLite
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if v.Key("Filter").Name() != "Adobe.PPKLite" {
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continue
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}
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signer := Signer{
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Name: v.Key("Name").Text(),
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Reason: v.Key("Reason").Text(),
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Location: v.Key("Location").Text(),
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ContactInfo: v.Key("ContactInfo").Text(),
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}
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// (Required) The signature value. When ByteRange is present, the
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// value shall be a hexadecimal string (see 7.3.4.3, “Hexadecimal
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// Strings”) representing the value of the byte range digest.
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// For public-key signatures, Contents should be either a DER-encoded
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// PKCS#1 binary data object or a DER-encoded PKCS#7 binary data object.
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// Space for the Contents value must be allocated before the message
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// digest is computed. (See 7.3.4, “String Objects“)
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p7, err := pkcs7.Parse([]byte(v.Key("Contents").RawString()))
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if err != nil {
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//fmt.Println(err)
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continue
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}
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// An array of pairs of integers (starting byte offset, length in
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// bytes) that shall describe the exact byte range for the digest
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// calculation. Multiple discontiguous byte ranges shall be used to
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// describe a digest that does not include the signature value (the
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// Contents entry) itself.
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for i := 0; i < v.Key("ByteRange").Len(); i++ {
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// As the byte range comes in pairs, we increment one extra
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i++
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// Read the byte range from the raw file and add it to the contents.
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// This content will be hashed with the corresponding algorithm to
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// verify the signature.
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content, err := ioutil.ReadAll(io.NewSectionReader(file, v.Key("ByteRange").Index(i-1).Int64(), v.Key("ByteRange").Index(i).Int64()))
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if err != nil {
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apiResp.Error = fmt.Sprintln("Failed to get ByteRange:", i, err)
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}
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p7.Content = append(p7.Content, content...)
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}
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// Signer certificate
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// http://www.alvestrand.no/objectid/1.2.840.113549.1.9.html
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// http://www.alvestrand.no/objectid/1.2.840.113583.1.1.8.html
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var isn []byte
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for _, s := range p7.Signers {
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isn = s.IssuerAndSerialNumber.IssuerName.FullBytes
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//for _, a := range s.AuthenticatedAttributes {
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//fmt.Printf("A: %v, %#v\n", s.IssuerAndSerialNumber.SerialNumber, a.Type)
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//}
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// Timestamp
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// http://www.alvestrand.no/objectid/1.2.840.113549.1.9.16.2.14.html
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// Timestamp
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// 1.2.840.113549.1.9.16.2.14 - RFC 3161 id-aa-timeStampToken
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for _, attr := range s.UnauthenticatedAttributes {
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//fmt.Printf("U: %v, %#v\n", s.IssuerAndSerialNumber.SerialNumber, attr.Type)
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if attr.Type.Equal(asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 9, 16, 2, 14}) {
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//fmt.Println("Found timestamp")
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signer.TimeStamp, err = timestamp.Parse(attr.Value.Bytes)
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if err != nil {
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apiResp.Error = fmt.Sprintln("Failed to parse timestamp", err)
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}
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break
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}
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}
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}
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// Directory of certificates, including OCSP
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//var ica *x509.Certificate
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certPool := x509.NewCertPool()
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for _, cert := range p7.Certificates {
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certPool.AddCert(cert)
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if bytes.Equal(isn, cert.RawSubject) {
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//ica = cert
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}
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}
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// Verify the digital signature of the pdf file.
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err = p7.VerifyWithChain(certPool)
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if err != nil {
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err = p7.Verify()
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if err == nil {
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signer.ValidSignature = true
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signer.TrustedIssuer = false
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}
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//apiResp.Error = fmt.Sprintln("Failed to verify signature:", err)
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} else {
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signer.ValidSignature = true
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signer.TrustedIssuer = true
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}
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// PDF signature certificate revocation information attribute (1.2.840.113583.1.1.8)
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var revInfo RevocationInfoArchival
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p7.UnmarshalSignedAttribute(asn1.ObjectIdentifier{1, 2, 840, 113583, 1, 1, 8}, &revInfo)
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// Parse OCSP response
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var ocspStatus = make(map[string]*ocsp.Response)
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for _, o := range revInfo.OCSP {
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resp, err := ocsp.ParseResponse(o.FullBytes, nil)
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if err != nil {
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apiResp.Error = fmt.Sprintln("Failed to parse or verify OCSP response", err)
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ocspStatus[fmt.Sprintf("%x", resp.SerialNumber)] = nil
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} else {
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ocspStatus[fmt.Sprintf("%x", resp.SerialNumber)] = resp
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}
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}
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// Build certificate chains and verify revocation status
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for _, cert := range p7.Certificates {
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var c Certificate
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c.Certificate = cert
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chain, err := cert.Verify(x509.VerifyOptions{
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Intermediates: certPool,
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CurrentTime: cert.NotBefore,
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KeyUsages: []x509.ExtKeyUsage{x509.ExtKeyUsageAny},
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})
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if err != nil {
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c.VerifyError = err.Error()
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}
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if resp, ok := ocspStatus[fmt.Sprintf("%x", cert.SerialNumber)]; ok {
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c.OCSPResponse = resp
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c.OCSPEmbedded = true
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if resp.Status != ocsp.Good {
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signer.RevokedCertificate = true
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}
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if len(chain) > 1 && len(chain[0]) > 1 {
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issuer := chain[0][1]
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if resp.Certificate != nil {
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err = resp.Certificate.CheckSignatureFrom(issuer)
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if err != nil {
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apiResp.Error = fmt.Sprintln("OCSP signing cerificate not from certificate issuer:", err)
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}
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} else {
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// CA Signed response
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err = resp.CheckSignatureFrom(issuer)
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if err != nil {
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apiResp.Error = fmt.Sprintln("Failed to verify OCSP response signature:", err)
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}
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}
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}
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} else {
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// Check OCSP status for certificate out of band
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}
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// Add certificate to result
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signer.Certificates = append(signer.Certificates, c)
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}
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// Certificate revocation lists when included in this document
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for _, crl := range p7.CRLs {
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//var crlissuer *pkix.Name
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//crlissuerdr.FillFromRDNSequence(&crl.TBSCertList.Issuer)
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if len(crl.TBSCertList.RevokedCertificates) > 0 {
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}
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//apiResp.Error = fmt.Sprintf("CRL %v , with %d entries\n", crl.TBSCertList.Issuer, len(crl.TBSCertList.RevokedCertificates))
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// TODO(vanbroup): Check revocation via CRL
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// signer.RevokedCertificate = true
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}
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// Parse CRL file
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for _, c := range revInfo.CRL {
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crl, err := x509.ParseCRL(c.FullBytes)
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if err != nil {
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apiResp.Error = fmt.Sprintln("Failed to parse or verify embedded CRL")
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}
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if len(crl.TBSCertList.RevokedCertificates) > 0 {
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}
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//var crlissuer *pkix.Name
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//crlissuerdr.FillFromRDNSequence(&crl.TBSCertList.Issuer)
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//apiResp.Error = fmt.Sprintf("CRL %v , with %d entries\n", crl.TBSCertList.Issuer, len(crl.TBSCertList.RevokedCertificates))
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// TODO(vanbroup): Check revocation via CRL
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// signer.RevokedCertificate = true
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}
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// If SubFilter is adbe.pkcs7.detached or adbe.pkcs7.sha1, this entry
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// shall not be used, and the certificate chain shall be put in the PKCS#7
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// envelope in Contents.
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//v.Key("Cert").Text()
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apiResp.Signers = append(apiResp.Signers, signer)
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}
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if apiResp == nil {
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err = fmt.Errorf("Document looks to have a signature but got no results")
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}
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return
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}
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func walk(t pdf.Value, pad int) {
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for _, k := range t.Keys() {
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v := t.Key(k)
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if v.Kind() == pdf.Array || v.Kind() == pdf.Dict {
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pad++
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walk(v, pad)
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}
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}
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}
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