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certificate_request.go
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certificate_request.go
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package x509util
import (
"crypto"
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"crypto/x509/pkix"
"encoding/asn1"
"encoding/json"
"github.com/pkg/errors"
"golang.org/x/crypto/cryptobyte"
cryptobyte_asn1 "golang.org/x/crypto/cryptobyte/asn1"
)
var (
oidExtensionSubjectAltName = []int{2, 5, 29, 17}
oidChallengePassword = []int{1, 2, 840, 113549, 1, 9, 7}
)
type publicKeyInfo struct {
Raw asn1.RawContent
Algorithm pkix.AlgorithmIdentifier
PublicKey asn1.BitString
}
type tbsCertificateRequest struct {
Raw asn1.RawContent
Version int
Subject asn1.RawValue
PublicKey publicKeyInfo
RawAttributes []asn1.RawValue `asn1:"tag:0"`
}
type certificateRequest struct {
Raw asn1.RawContent
TBSCSR tbsCertificateRequest
SignatureAlgorithm pkix.AlgorithmIdentifier
SignatureValue asn1.BitString
}
// CertificateRequest is the JSON representation of an X.509 certificate. It is
// used to build a certificate request from a template.
type CertificateRequest struct {
Version int `json:"version"`
Subject Subject `json:"subject"`
RawSubject []byte `json:"rawSubject"`
DNSNames MultiString `json:"dnsNames"`
EmailAddresses MultiString `json:"emailAddresses"`
IPAddresses MultiIP `json:"ipAddresses"`
URIs MultiURL `json:"uris"`
SANs []SubjectAlternativeName `json:"sans"`
Extensions []Extension `json:"extensions"`
SignatureAlgorithm SignatureAlgorithm `json:"signatureAlgorithm"`
ChallengePassword string `json:"-"`
PublicKey interface{} `json:"-"`
PublicKeyAlgorithm x509.PublicKeyAlgorithm `json:"-"`
Signature []byte `json:"-"`
Signer crypto.Signer `json:"-"`
}
// NewCertificateRequest creates a certificate request from a template.
func NewCertificateRequest(signer crypto.Signer, opts ...Option) (*CertificateRequest, error) {
pub := signer.Public()
o, err := new(Options).apply(&x509.CertificateRequest{
PublicKey: pub,
}, opts)
if err != nil {
return nil, err
}
// If no template use only the certificate request with the default leaf key
// usages.
if o.CertBuffer == nil {
return &CertificateRequest{
PublicKey: pub,
Signer: signer,
}, nil
}
// With templates
var cr CertificateRequest
if err := json.NewDecoder(o.CertBuffer).Decode(&cr); err != nil {
return nil, errors.Wrap(err, "error unmarshaling certificate")
}
cr.PublicKey = pub
cr.Signer = signer
// Generate the subjectAltName extension if the certificate contains SANs
// that are not supported in the Go standard library.
if cr.hasExtendedSANs() && !cr.hasExtension(oidExtensionSubjectAltName) {
ext, err := createCertificateRequestSubjectAltNameExtension(cr, cr.Subject.IsEmpty())
if err != nil {
return nil, err
}
// Prepend extension to achieve a certificate as similar as possible to
// the one generated by the Go standard library.
cr.Extensions = append([]Extension{ext}, cr.Extensions...)
}
return &cr, nil
}
// NewCertificateRequestFromX509 creates a CertificateRequest from an
// x509.CertificateRequest.
//
// This method is used to create the template variable .Insecure.CR or to
// initialize the Certificate when no templates are used.
// NewCertificateRequestFromX509 will always ignore the SignatureAlgorithm
// because we cannot guarantee that the signer will be able to sign a
// certificate template if Certificate.SignatureAlgorithm is set.
func NewCertificateRequestFromX509(cr *x509.CertificateRequest) *CertificateRequest {
// Set SubjectAltName extension as critical if Subject is empty.
fixSubjectAltName(cr)
return &CertificateRequest{
Version: cr.Version,
Subject: newSubject(cr.Subject),
RawSubject: cr.RawSubject,
DNSNames: cr.DNSNames,
EmailAddresses: cr.EmailAddresses,
IPAddresses: cr.IPAddresses,
URIs: cr.URIs,
Extensions: newExtensions(cr.Extensions),
PublicKey: cr.PublicKey,
PublicKeyAlgorithm: cr.PublicKeyAlgorithm,
Signature: cr.Signature,
// Do not enforce signature algorithm from the CSR, it might not
// be compatible with the certificate signer.
SignatureAlgorithm: 0,
}
}
// GetCertificateRequest returns the signed x509.CertificateRequest.
func (c *CertificateRequest) GetCertificateRequest() (*x509.CertificateRequest, error) {
cert := c.GetCertificate().GetCertificate()
asn1Data, err := x509.CreateCertificateRequest(rand.Reader, &x509.CertificateRequest{
Subject: cert.Subject,
RawSubject: cert.RawSubject,
DNSNames: cert.DNSNames,
IPAddresses: cert.IPAddresses,
EmailAddresses: cert.EmailAddresses,
URIs: cert.URIs,
ExtraExtensions: cert.ExtraExtensions,
SignatureAlgorithm: x509.SignatureAlgorithm(c.SignatureAlgorithm),
}, c.Signer)
if err != nil {
return nil, errors.Wrap(err, "error creating certificate request")
}
// If a challenge password is provided, encode and prepend it as a challenge
// password attribute.
//
// The challengePassword attribute doesn't follow the ASN.1 encoding of
// [pkix.AttributeTypeAndValueSET] used in the deprecated
// [x509.CertificateRequest.Attributes], so this requires some low-level
// ASN.1 operations.
if c.ChallengePassword != "" {
asn1Data, err = c.addChallengePassword(asn1Data)
if err != nil {
return nil, err
}
}
// This should not fail
return x509.ParseCertificateRequest(asn1Data)
}
// addChallengePassword unmarshals the asn1Data into a certificateRequest and
// creates a new one with the challengePassword.
func (c *CertificateRequest) addChallengePassword(asn1Data []byte) ([]byte, error) {
// Build challengePassword attribute (RFC 2985 section-5.4). The resulting
// bytes will be added as an asn1.RawValue in the RawAttributes.
var builder cryptobyte.Builder
builder.AddASN1(cryptobyte_asn1.SEQUENCE, func(child *cryptobyte.Builder) {
child.AddASN1ObjectIdentifier(oidChallengePassword)
child.AddASN1(cryptobyte_asn1.SET, func(value *cryptobyte.Builder) {
switch {
case isPrintableString(c.ChallengePassword, true, true):
value.AddASN1(cryptobyte_asn1.PrintableString, func(s *cryptobyte.Builder) {
s.AddBytes([]byte(c.ChallengePassword))
})
case isUTF8String(c.ChallengePassword):
value.AddASN1(cryptobyte_asn1.UTF8String, func(s *cryptobyte.Builder) {
s.AddBytes([]byte(c.ChallengePassword))
})
default:
value.SetError(errors.New("error marshaling challenge password: password is not valid"))
}
})
})
b, err := builder.Bytes()
if err != nil {
return nil, errors.Wrap(err, "error marshaling challenge password")
}
challengePasswordAttr := asn1.RawValue{
FullBytes: b,
}
// Parse certificate request
var csr certificateRequest
rest, err := asn1.Unmarshal(asn1Data, &csr)
if err != nil {
return nil, err
} else if len(rest) != 0 {
return nil, errors.New("error unmarshalling certificate request: trailing data")
}
sigAlgo := csr.SignatureAlgorithm
tbsCSR := tbsCertificateRequest{
Version: csr.TBSCSR.Version,
Subject: csr.TBSCSR.Subject,
PublicKey: csr.TBSCSR.PublicKey,
RawAttributes: csr.TBSCSR.RawAttributes,
}
// Prepend challengePassword attribute
tbsCSR.RawAttributes = append([]asn1.RawValue{challengePasswordAttr}, tbsCSR.RawAttributes...)
// Marshal tbsCertificateRequest
tbsCSRContents, err := asn1.Marshal(tbsCSR)
if err != nil {
return nil, errors.Wrap(err, "error creating certificate request")
}
tbsCSR.Raw = tbsCSRContents
// Get the hash used previously
var hashFunc crypto.Hash
found := false
sigAlgoOID := sigAlgo.Algorithm
for _, m := range signatureAlgorithmMapping {
if sigAlgoOID.Equal(m.oid) {
hashFunc = m.hash
found = true
break
}
}
if !found {
return nil, errors.Errorf("error creating certificate request: unsupported signature algorithm %s", sigAlgoOID)
}
// Sign tbsCertificateRequest
signed := tbsCSRContents
if hashFunc != 0 {
h := hashFunc.New()
h.Write(signed)
signed = h.Sum(nil)
}
var signature []byte
signature, err = c.Signer.Sign(rand.Reader, signed, hashFunc)
if err != nil {
return nil, errors.Wrap(err, "error creating certificate request")
}
// Build new certificate request and marshal
asn1Data, err = asn1.Marshal(certificateRequest{
TBSCSR: tbsCSR,
SignatureAlgorithm: sigAlgo,
SignatureValue: asn1.BitString{
Bytes: signature,
BitLength: len(signature) * 8,
},
})
if err != nil {
return nil, errors.Wrap(err, "error creating certificate request")
}
return asn1Data, nil
}
// GetCertificate returns the Certificate representation of the
// CertificateRequest.
//
// GetCertificate will not specify a SignatureAlgorithm, it's not possible to
// guarantee that the certificate signer can sign with the CertificateRequest
// SignatureAlgorithm.
func (c *CertificateRequest) GetCertificate() *Certificate {
return &Certificate{
Subject: c.Subject,
DNSNames: c.DNSNames,
EmailAddresses: c.EmailAddresses,
IPAddresses: c.IPAddresses,
URIs: c.URIs,
SANs: c.SANs,
Extensions: c.Extensions,
PublicKey: c.PublicKey,
PublicKeyAlgorithm: c.PublicKeyAlgorithm,
SignatureAlgorithm: 0,
}
}
// GetLeafCertificate returns the Certificate representation of the
// CertificateRequest, including KeyUsage and ExtKeyUsage extensions.
//
// GetLeafCertificate will not specify a SignatureAlgorithm, it's not possible
// to guarantee that the certificate signer can sign with the CertificateRequest
// SignatureAlgorithm.
func (c *CertificateRequest) GetLeafCertificate() *Certificate {
keyUsage := x509.KeyUsageDigitalSignature
if _, ok := c.PublicKey.(*rsa.PublicKey); ok {
keyUsage |= x509.KeyUsageKeyEncipherment
}
cert := c.GetCertificate()
cert.KeyUsage = KeyUsage(keyUsage)
cert.ExtKeyUsage = ExtKeyUsage([]x509.ExtKeyUsage{
x509.ExtKeyUsageServerAuth,
x509.ExtKeyUsageClientAuth,
})
return cert
}
// hasExtendedSANs returns true if the certificate contains any SAN types that
// are not supported by the golang x509 library (i.e. RegisteredID, OtherName,
// DirectoryName, X400Address, or EDIPartyName)
//
// See also https://datatracker.ietf.org/doc/html/rfc5280.html#section-4.2.1.6
func (c *CertificateRequest) hasExtendedSANs() bool {
for _, san := range c.SANs {
if !(san.Type == DNSType || san.Type == EmailType || san.Type == IPType || san.Type == URIType || san.Type == AutoType || san.Type == "") {
return true
}
}
return false
}
// hasExtension returns true if the given extension oid is in the certificate.
func (c *CertificateRequest) hasExtension(oid ObjectIdentifier) bool {
for _, e := range c.Extensions {
if e.ID.Equal(oid) {
return true
}
}
return false
}
// CreateCertificateRequest creates a simple X.509 certificate request with the
// given common name and sans.
func CreateCertificateRequest(commonName string, sans []string, signer crypto.Signer) (*x509.CertificateRequest, error) {
dnsNames, ips, emails, uris := SplitSANs(sans)
asn1Data, err := x509.CreateCertificateRequest(rand.Reader, &x509.CertificateRequest{
Subject: pkix.Name{
CommonName: commonName,
},
DNSNames: dnsNames,
IPAddresses: ips,
EmailAddresses: emails,
URIs: uris,
}, signer)
if err != nil {
return nil, errors.Wrap(err, "error creating certificate request")
}
// This should not fail
return x509.ParseCertificateRequest(asn1Data)
}
// fixSubjectAltName makes sure to mark the SAN extension to critical if the
// subject is empty.
func fixSubjectAltName(cr *x509.CertificateRequest) {
if subjectIsEmpty(cr.Subject) {
for i, ext := range cr.Extensions {
if ext.Id.Equal(oidExtensionSubjectAltName) {
cr.Extensions[i].Critical = true
}
}
}
}