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// Copyright 2022 The Sigstore Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package cryptoutils
import (
"crypto/x509"
"crypto/x509/pkix"
"encoding/asn1"
"errors"
"fmt"
)
var (
// OIDOtherName is the OID for the OtherName SAN per RFC 5280
OIDOtherName = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 57264, 1, 7}
// SANOID is the OID for Subject Alternative Name per RFC 5280
SANOID = asn1.ObjectIdentifier{2, 5, 29, 17}
)
// OtherName describes a name related to a certificate which is not in one
// of the standard name formats. RFC 5280, 4.2.1.6:
//
// OtherName ::= SEQUENCE {
// type-id OBJECT IDENTIFIER,
// value [0] EXPLICIT ANY DEFINED BY type-id }
//
// OtherName for Fulcio-issued certificates only supports UTF-8 strings as values.
type OtherName struct {
ID asn1.ObjectIdentifier
Value string `asn1:"utf8,explicit,tag:0"`
}
// MarshalOtherNameSAN creates a Subject Alternative Name extension
// with an OtherName sequence. RFC 5280, 4.2.1.6:
//
// SubjectAltName ::= GeneralNames
// GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName
// GeneralName ::= CHOICE {
//
// otherName [0] OtherName,
// ... }
func MarshalOtherNameSAN(name string, critical bool) (*pkix.Extension, error) {
o := OtherName{
ID: OIDOtherName,
Value: name,
}
bytes, err := asn1.MarshalWithParams(o, "tag:0")
if err != nil {
return nil, err
}
sans, err := asn1.Marshal([]asn1.RawValue{{FullBytes: bytes}})
if err != nil {
return nil, err
}
return &pkix.Extension{
Id: SANOID,
Critical: critical,
Value: sans,
}, nil
}
// UnmarshalOtherNameSAN extracts a UTF-8 string from the OtherName
// field in the Subject Alternative Name extension.
func UnmarshalOtherNameSAN(exts []pkix.Extension) (string, error) {
var otherNames []string
for _, e := range exts {
if !e.Id.Equal(SANOID) {
continue
}
var seq asn1.RawValue
rest, err := asn1.Unmarshal(e.Value, &seq)
if err != nil {
return "", err
} else if len(rest) != 0 {
return "", fmt.Errorf("trailing data after X.509 extension")
}
if !seq.IsCompound || seq.Tag != asn1.TagSequence || seq.Class != asn1.ClassUniversal {
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
}
// skip all GeneralName fields except OtherName
if v.Tag != 0 {
continue
}
var other OtherName
if _, err := asn1.UnmarshalWithParams(v.FullBytes, &other, "tag:0"); err != nil {
return "", fmt.Errorf("could not parse requested OtherName SAN: %w", err)
}
if !other.ID.Equal(OIDOtherName) {
return "", fmt.Errorf("unexpected OID for OtherName, expected %v, got %v", OIDOtherName, other.ID)
}
otherNames = append(otherNames, other.Value)
}
}
if len(otherNames) == 0 {
return "", errors.New("no OtherName found")
}
if len(otherNames) != 1 {
return "", errors.New("expected only one OtherName")
}
return otherNames[0], nil
}
// GetSubjectAlternateNames extracts all subject alternative names from
// the certificate, including email addresses, DNS, IP addresses, URIs,
// and OtherName SANs
func GetSubjectAlternateNames(cert *x509.Certificate) []string {
sans := []string{}
sans = append(sans, cert.DNSNames...)
sans = append(sans, cert.EmailAddresses...)
for _, ip := range cert.IPAddresses {
sans = append(sans, ip.String())
}
for _, uri := range cert.URIs {
sans = append(sans, uri.String())
}
// ignore error if there's no OtherName SAN
otherName, _ := UnmarshalOtherNameSAN(cert.Extensions)
if len(otherName) > 0 {
sans = append(sans, otherName)
}
return sans
}
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