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// Package x509ext provides functions for (un)marshalling X.509 extensions not
// supported by the crypto/x509 package.
package x509ext
import (
"crypto/x509/pkix"
"encoding/asn1"
"errors"
"fmt"
"github.com/google/go-attestation/oid"
)
// RFC 4043
//
// https://tools.ietf.org/html/rfc4043
var (
oidPermanentIdentifier = []int{1, 3, 6, 1, 5, 5, 7, 8, 3}
)
// OtherName ::= SEQUENCE {
// type-id OBJECT IDENTIFIER,
// value [0] EXPLICIT ANY DEFINED BY type-id }
type otherName struct {
TypeID asn1.ObjectIdentifier
Value asn1.RawValue
}
func marshalOtherName(typeID asn1.ObjectIdentifier, value interface{}) (asn1.RawValue, error) {
valueBytes, err := asn1.MarshalWithParams(value, "explicit,tag:0")
if err != nil {
return asn1.RawValue{}, err
}
otherName := otherName{
TypeID: typeID,
Value: asn1.RawValue{FullBytes: valueBytes},
}
bytes, err := asn1.MarshalWithParams(otherName, "tag:0")
if err != nil {
return asn1.RawValue{}, err
}
return asn1.RawValue{FullBytes: bytes}, nil
}
// PermanentIdentifier represents an ASN.1 encoded "permanent identifier" as
// defined by RFC4043.
//
// PermanentIdentifier ::= SEQUENCE {
// identifierValue UTF8String OPTIONAL,
// assigner OBJECT IDENTIFIER OPTIONAL
// }
//
// https://datatracker.ietf.org/doc/html/rfc4043
type PermanentIdentifier struct {
IdentifierValue string `asn1:"utf8,optional"`
Assigner asn1.ObjectIdentifier `asn1:"optional"`
}
func parsePermanentIdentifier(der []byte) (PermanentIdentifier, error) {
var permID PermanentIdentifier
if _, err := asn1.UnmarshalWithParams(der, &permID, "explicit,tag:0"); err != nil {
return PermanentIdentifier{}, err
}
return permID, nil
}
// SubjectAltName contains GeneralName variations not supported by the
// crypto/x509 package.
//
// https://datatracker.ietf.org/doc/html/rfc5280
type SubjectAltName struct {
DirectoryNames []pkix.Name
PermanentIdentifiers []PermanentIdentifier
}
// ParseSubjectAltName parses a pkix.Extension into a SubjectAltName struct.
func ParseSubjectAltName(ext pkix.Extension) (*SubjectAltName, error) {
var out SubjectAltName
dirNames, otherNames, err := parseSubjectAltName(ext)
if err != nil {
return nil, fmt.Errorf("parseSubjectAltName: %v", err)
}
out.DirectoryNames = dirNames
for _, otherName := range otherNames {
if otherName.TypeID.Equal(oidPermanentIdentifier) {
permID, err := parsePermanentIdentifier(otherName.Value.FullBytes)
if err != nil {
return nil, fmt.Errorf("parsePermanentIdentifier: %v", err)
}
out.PermanentIdentifiers = append(out.PermanentIdentifiers, permID)
}
}
return &out, nil
}
// https://datatracker.ietf.org/doc/html/rfc5280#page-35
func parseSubjectAltName(ext pkix.Extension) (dirNames []pkix.Name, otherNames []otherName, err error) {
err = forEachSAN(ext.Value, func(generalName asn1.RawValue) error {
switch generalName.Tag {
case 0: // otherName
var otherName otherName
if _, err := asn1.UnmarshalWithParams(generalName.FullBytes, &otherName, "tag:0"); err != nil {
return fmt.Errorf("OtherName: asn1.UnmarshalWithParams: %v", err)
}
otherNames = append(otherNames, otherName)
case 4: // directoryName
var rdns pkix.RDNSequence
if _, err := asn1.Unmarshal(generalName.Bytes, &rdns); err != nil {
return fmt.Errorf("DirectoryName: asn1.Unmarshal: %v", err)
}
var dirName pkix.Name
dirName.FillFromRDNSequence(&rdns)
dirNames = append(dirNames, dirName)
default:
return fmt.Errorf("expected tag %d", generalName.Tag)
}
return nil
})
return
}
// Borrowed from the x509 package.
func forEachSAN(extension []byte, callback func(ext asn1.RawValue) error) error {
var seq asn1.RawValue
rest, err := asn1.Unmarshal(extension, &seq)
if err != nil {
return err
} else if len(rest) != 0 {
return errors.New("x509: trailing data after X.509 extension")
}
if !seq.IsCompound || seq.Tag != 16 || seq.Class != 0 {
return asn1.StructuralError{Msg: "bad SAN sequence"}
}
rest = seq.Bytes
for len(rest) > 0 {
var v asn1.RawValue
rest, err = asn1.Unmarshal(rest, &v)
if err != nil {
return err
}
if err := callback(v); err != nil {
return err
}
}
return nil
}
// MarshalSubjectAltName converts a SubjectAltName struct into a pkix.Extension.
func MarshalSubjectAltName(san *SubjectAltName) (pkix.Extension, error) {
var generalNames []asn1.RawValue
for _, permID := range san.PermanentIdentifiers {
val, err := marshalOtherName(oidPermanentIdentifier, permID)
if err != nil {
return pkix.Extension{}, err
}
generalNames = append(generalNames, val)
}
for _, dirName := range san.DirectoryNames {
bytes, err := asn1.MarshalWithParams(dirName.ToRDNSequence(), "explicit,tag:4")
if err != nil {
return pkix.Extension{}, err
}
generalNames = append(generalNames, asn1.RawValue{FullBytes: bytes})
}
val, err := asn1.Marshal(generalNames)
if err != nil {
return pkix.Extension{}, err
}
return pkix.Extension{
Id: oid.SubjectAltName,
Value: val,
}, nil
}
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