certificates/scep/authority.go

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package scep
import (
"bytes"
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"context"
"crypto/x509"
"errors"
"fmt"
"net/url"
"github.com/smallstep/certificates/authority/provisioner"
database "github.com/smallstep/certificates/db"
"go.step.sm/crypto/pemutil"
"github.com/smallstep/nosql"
microx509util "github.com/micromdm/scep/crypto/x509util"
microscep "github.com/micromdm/scep/scep"
//"github.com/smallstep/certificates/scep/pkcs7"
"go.mozilla.org/pkcs7"
"go.step.sm/crypto/x509util"
)
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var (
certTable = []byte("scep_certs")
)
// Interface is the SCEP authority interface.
type Interface interface {
LoadProvisionerByID(string) (provisioner.Interface, error)
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GetLinkExplicit(provName string, absoluteLink bool, baseURL *url.URL, inputs ...string) string
GetCACertificates() ([]*x509.Certificate, error)
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DecryptPKIEnvelope(ctx context.Context, msg *PKIMessage) error
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SignCSR(ctx context.Context, csr *x509.CertificateRequest, msg *PKIMessage) (*PKIMessage, error)
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CreateFailureResponse(ctx context.Context, csr *x509.CertificateRequest, msg *PKIMessage, info FailInfoName, infoText string) (*PKIMessage, error)
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MatchChallengePassword(ctx context.Context, password string) (bool, error)
GetCACaps(ctx context.Context) []string
}
// Authority is the layer that handles all SCEP interactions.
type Authority struct {
backdate provisioner.Duration
db nosql.DB
prefix string
dns string
// dir *directory
intermediateCertificate *x509.Certificate
service Service
signAuth SignAuthority
}
// AuthorityOptions required to create a new SCEP Authority.
type AuthorityOptions struct {
IntermediateCertificatePath string
Service Service
// Backdate
Backdate provisioner.Duration
// DB is the database used by nosql.
DB nosql.DB
// DNS the host used to generate accurate SCEP links. By default the authority
// will use the Host from the request, so this value will only be used if
// request.Host is empty.
DNS string
// Prefix is a URL path prefix under which the SCEP api is served. This
// prefix is required to generate accurate SCEP links.
Prefix string
}
// SignAuthority is the interface for a signing authority
type SignAuthority interface {
Sign(cr *x509.CertificateRequest, opts provisioner.SignOptions, signOpts ...provisioner.SignOption) ([]*x509.Certificate, error)
LoadProvisionerByID(string) (provisioner.Interface, error)
}
// New returns a new Authority that implements the SCEP interface.
func New(signAuth SignAuthority, ops AuthorityOptions) (*Authority, error) {
if _, ok := ops.DB.(*database.SimpleDB); !ok {
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// If it's not a SimpleDB then go ahead and bootstrap the DB with the
// necessary SCEP tables. SimpleDB should ONLY be used for testing.
tables := [][]byte{certTable}
for _, b := range tables {
if err := ops.DB.CreateTable(b); err != nil {
return nil, fmt.Errorf("%w: error creating table %s", err, string(b))
}
}
}
// TODO: the below is a bit similar as what happens in the core Authority class, which
// creates the full x509 service. However, those aren't accessible directly, which is
// why I reimplemented this (for now). There might be an alternative that I haven't
// found yet.
certificateChain, err := pemutil.ReadCertificateBundle(ops.IntermediateCertificatePath)
if err != nil {
return nil, err
}
return &Authority{
backdate: ops.Backdate,
db: ops.DB,
prefix: ops.Prefix,
dns: ops.DNS,
intermediateCertificate: certificateChain[0],
service: ops.Service,
signAuth: signAuth,
}, nil
}
var (
// TODO: check the default capabilities; https://tools.ietf.org/html/rfc8894#section-3.5.2
defaultCapabilities = []string{
"Renewal",
"SHA-1",
"SHA-256",
"AES",
"DES3",
"SCEPStandard",
"POSTPKIOperation",
}
)
// LoadProvisionerByID calls out to the SignAuthority interface to load a
// provisioner by ID.
func (a *Authority) LoadProvisionerByID(id string) (provisioner.Interface, error) {
return a.signAuth.LoadProvisionerByID(id)
}
// GetLinkExplicit returns the requested link from the directory.
func (a *Authority) GetLinkExplicit(provName string, abs bool, baseURL *url.URL, inputs ...string) string {
// TODO: taken from ACME; move it to directory (if we need a directory in SCEP)?
return a.getLinkExplicit(provName, abs, baseURL, inputs...)
}
// getLinkExplicit returns an absolute or partial path to the given resource and a base
// URL dynamically obtained from the request for which the link is being calculated.
func (a *Authority) getLinkExplicit(provisionerName string, abs bool, baseURL *url.URL, inputs ...string) string {
// TODO: do we need to provide a way to provide a different suffix/base?
// Like "/cgi-bin/pkiclient.exe"? Or would it be enough to have that as the name?
link := fmt.Sprintf("/%s", provisionerName)
if abs {
// Copy the baseURL value from the pointer. https://github.com/golang/go/issues/38351
u := url.URL{}
if baseURL != nil {
u = *baseURL
}
// If no Scheme is set, then default to http (in case of SCEP)
if u.Scheme == "" {
u.Scheme = "http"
}
// If no Host is set, then use the default (first DNS attr in the ca.json).
if u.Host == "" {
u.Host = a.dns
}
u.Path = a.prefix + link
return u.String()
}
return link
}
// GetCACertificates returns the certificate (chain) for the CA
func (a *Authority) GetCACertificates() ([]*x509.Certificate, error) {
// TODO: this should return: the "SCEP Server (RA)" certificate, the issuing CA up to and excl. the root
// Some clients do need the root certificate however; also see: https://github.com/openxpki/openxpki/issues/73
//
// This means we might need to think about if we should use the current intermediate CA
// certificate as the "SCEP Server (RA)" certificate. It might be better to have a distinct
// RA certificate, with a corresponding rsa.PrivateKey, just for SCEP usage, which is signed by
// the intermediate CA. Will need to look how we can provide this nicely within step-ca.
//
// This might also mean that we might want to use a distinct instance of KMS for doing the key operations,
// so that we can use RSA just for SCEP.
//
// Using an RA does not seem to exist in https://tools.ietf.org/html/rfc8894, but is mentioned in
// https://tools.ietf.org/id/draft-nourse-scep-21.html. Will continue using the CA directly for now.
//
// The certificate to use should probably depend on the (configured) Provisioner and may
// use a distinct certificate, apart from the intermediate.
if a.intermediateCertificate == nil {
return nil, errors.New("no intermediate certificate available in SCEP authority")
}
return []*x509.Certificate{a.intermediateCertificate}, nil
}
// DecryptPKIEnvelope decrypts an enveloped message
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func (a *Authority) DecryptPKIEnvelope(ctx context.Context, msg *PKIMessage) error {
p7c, err := pkcs7.Parse(msg.P7.Content)
if err != nil {
return err
}
envelope, err := p7c.Decrypt(a.intermediateCertificate, a.service.Decrypter)
if err != nil {
return err
}
msg.pkiEnvelope = envelope
switch msg.MessageType {
case microscep.CertRep:
certs, err := microscep.CACerts(msg.pkiEnvelope)
if err != nil {
return err
}
msg.CertRepMessage.Certificate = certs[0] // TODO: check correctness of this
return nil
case microscep.PKCSReq, microscep.UpdateReq, microscep.RenewalReq:
csr, err := x509.ParseCertificateRequest(msg.pkiEnvelope)
if err != nil {
return fmt.Errorf("parse CSR from pkiEnvelope: %w", err)
}
// check for challengePassword
cp, err := microx509util.ParseChallengePassword(msg.pkiEnvelope)
if err != nil {
return fmt.Errorf("scep: parse challenge password in pkiEnvelope: %w", err)
}
msg.CSRReqMessage = &microscep.CSRReqMessage{
RawDecrypted: msg.pkiEnvelope,
CSR: csr,
ChallengePassword: cp,
}
return nil
case microscep.GetCRL, microscep.GetCert, microscep.CertPoll:
return fmt.Errorf("not implemented") //errNotImplemented
}
return nil
}
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// SignCSR creates an x509.Certificate based on a CSR template and Cert Authority credentials
// returns a new PKIMessage with CertRep data
//func (msg *PKIMessage) SignCSR(crtAuth *x509.Certificate, keyAuth *rsa.PrivateKey, template *x509.Certificate) (*PKIMessage, error) {
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//func (a *Authority) SignCSR(ctx context.Context, msg *PKIMessage, template *x509.Certificate) (*PKIMessage, error) {
func (a *Authority) SignCSR(ctx context.Context, csr *x509.CertificateRequest, msg *PKIMessage) (*PKIMessage, error) {
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// TODO: intermediate storage of the request? In SCEP it's possible to request a csr/certificate
// to be signed, which can be performed asynchronously / out-of-band. In that case a client can
// poll for the status. It seems to be similar as what can happen in ACME, so might want to model
// the implementation after the one in the ACME authority. Requires storage, etc.
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p, err := ProvisionerFromContext(ctx)
if err != nil {
return nil, err
}
// check if CSRReqMessage has already been decrypted
if msg.CSRReqMessage.CSR == nil {
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if err := a.DecryptPKIEnvelope(ctx, msg); err != nil {
return nil, err
}
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csr = msg.CSRReqMessage.CSR
}
// Template data
data := x509util.NewTemplateData()
data.SetCommonName(csr.Subject.CommonName)
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data.SetSANs(csr.DNSNames)
data.SetCertificateRequest(csr)
// Get authorizations from the SCEP provisioner.
ctx = provisioner.NewContextWithMethod(ctx, provisioner.SignMethod)
signOps, err := p.AuthorizeSign(ctx, "")
if err != nil {
return nil, fmt.Errorf("error retrieving authorization options from SCEP provisioner: %w", err)
}
opts := provisioner.SignOptions{
// NotBefore: provisioner.NewTimeDuration(o.NotBefore),
// NotAfter: provisioner.NewTimeDuration(o.NotAfter),
}
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templateOptions, err := provisioner.TemplateOptions(p.GetOptions(), data)
if err != nil {
return nil, fmt.Errorf("error creating template options from SCEP provisioner: %w", err)
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}
signOps = append(signOps, templateOptions)
certChain, err := a.signAuth.Sign(csr, opts, signOps...)
if err != nil {
return nil, fmt.Errorf("error generating certificate for order %w", err)
}
cert := certChain[0]
// create a degenerate cert structure
deg, err := degenerateCertificates([]*x509.Certificate{cert})
if err != nil {
return nil, err
}
e7, err := pkcs7.Encrypt(deg, msg.P7.Certificates)
if err != nil {
return nil, err
}
// PKIMessageAttributes to be signed
config := pkcs7.SignerInfoConfig{
ExtraSignedAttributes: []pkcs7.Attribute{
{
Type: oidSCEPtransactionID,
Value: msg.TransactionID,
},
{
Type: oidSCEPpkiStatus,
Value: microscep.SUCCESS,
},
{
Type: oidSCEPmessageType,
Value: microscep.CertRep,
},
{
Type: oidSCEPrecipientNonce,
Value: msg.SenderNonce,
},
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{
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Type: oidSCEPsenderNonce,
Value: msg.SenderNonce,
},
},
}
signedData, err := pkcs7.NewSignedData(e7)
if err != nil {
return nil, err
}
// add the certificate into the signed data type
// this cert must be added before the signedData because the recipient will expect it
// as the first certificate in the array
signedData.AddCertificate(cert)
authCert := a.intermediateCertificate
// sign the attributes
if err := signedData.AddSigner(authCert, a.service.Signer, config); err != nil {
return nil, err
}
certRepBytes, err := signedData.Finish()
if err != nil {
return nil, err
}
cr := &CertRepMessage{
PKIStatus: microscep.SUCCESS,
RecipientNonce: microscep.RecipientNonce(msg.SenderNonce),
Certificate: cert,
degenerate: deg,
}
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// create a CertRep message from the original
crepMsg := &PKIMessage{
Raw: certRepBytes,
TransactionID: msg.TransactionID,
MessageType: microscep.CertRep,
CertRepMessage: cr,
}
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// TODO: save more data?
_, err = newCert(a.db, CertOptions{
Leaf: certChain[0],
Intermediates: certChain[1:],
})
if err != nil {
fmt.Println(err)
return nil, err
}
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return crepMsg, nil
}
// CreateFailureResponse creates an appropriately signed reply for PKI operations
func (a *Authority) CreateFailureResponse(ctx context.Context, csr *x509.CertificateRequest, msg *PKIMessage, info FailInfoName, infoText string) (*PKIMessage, error) {
config := pkcs7.SignerInfoConfig{
ExtraSignedAttributes: []pkcs7.Attribute{
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{
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Type: oidSCEPtransactionID,
Value: msg.TransactionID,
},
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{
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Type: oidSCEPpkiStatus,
Value: microscep.FAILURE,
},
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{
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Type: oidSCEPfailInfo,
Value: info,
},
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{
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Type: oidSCEPfailInfoText,
Value: infoText,
},
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{
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Type: oidSCEPmessageType,
Value: microscep.CertRep,
},
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{
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Type: oidSCEPsenderNonce,
Value: msg.SenderNonce,
},
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{
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Type: oidSCEPrecipientNonce,
Value: msg.SenderNonce,
},
},
}
signedData, err := pkcs7.NewSignedData(nil)
if err != nil {
return nil, err
}
// sign the attributes
if err := signedData.AddSigner(a.intermediateCertificate, a.service.Signer, config); err != nil {
return nil, err
}
certRepBytes, err := signedData.Finish()
if err != nil {
return nil, err
}
cr := &CertRepMessage{
PKIStatus: microscep.FAILURE,
FailInfo: microscep.BadRequest,
RecipientNonce: microscep.RecipientNonce(msg.SenderNonce),
}
// create a CertRep message from the original
crepMsg := &PKIMessage{
Raw: certRepBytes,
TransactionID: msg.TransactionID,
MessageType: microscep.CertRep,
CertRepMessage: cr,
}
return crepMsg, nil
}
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// MatchChallengePassword verifies a SCEP challenge password
func (a *Authority) MatchChallengePassword(ctx context.Context, password string) (bool, error) {
p, err := ProvisionerFromContext(ctx)
if err != nil {
return false, err
}
if p.GetChallengePassword() == password {
return true, nil
}
// TODO: support dynamic challenges, i.e. a list of challenges instead of one?
// That's probably a bit harder to configure, though; likely requires some data store
// that can be interacted with more easily, via some internal API, for example.
return false, nil
}
// GetCACaps returns the CA capabilities
func (a *Authority) GetCACaps(ctx context.Context) []string {
p, err := ProvisionerFromContext(ctx)
if err != nil {
return defaultCapabilities
}
caps := p.GetCapabilities()
if len(caps) == 0 {
return defaultCapabilities
}
// TODO: validate the caps? Ensure they are the right format according to RFC?
// TODO: ensure that the capabilities are actually "enforced"/"verified" in code too:
// check that only parts of the spec are used in the implementation belonging to the capabilities.
// For example for renewals, which we could disable in the provisioner, should then also
// not be reported in cacaps operation.
return caps
}
// degenerateCertificates creates degenerate certificates pkcs#7 type
func degenerateCertificates(certs []*x509.Certificate) ([]byte, error) {
var buf bytes.Buffer
for _, cert := range certs {
buf.Write(cert.Raw)
}
degenerate, err := pkcs7.DegenerateCertificate(buf.Bytes())
if err != nil {
return nil, err
}
return degenerate, nil
}
// Interface guards
var (
_ Interface = (*Authority)(nil)
)