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Fix macOS SCEP client issues

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Fixes #746
This commit is contained in:
Herman Slatman 2022-01-14 10:48:23 +01:00
parent 57f9e54151
commit 9c6580ccd2
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GPG key ID: F4D8A44EA0A75A4F
7 changed files with 108 additions and 39 deletions
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14
authority/authority.go
View file

@ -437,13 +437,6 @@ func (a *Authority) init() error {
}
}
// Check if a KMS with decryption capability is required and available
if a.requiresDecrypter() {
if _, ok := a.keyManager.(kmsapi.Decrypter); !ok {
return errors.New("keymanager doesn't provide crypto.Decrypter")
}
}
// TODO: decide if this is a good approach for providing the SCEP functionality
// It currently mirrors the logic for the x509CAService
if a.requiresSCEPService() && a.scepService == nil {
@ -454,6 +447,7 @@ func (a *Authority) init() error {
if err != nil {
return err
}
options.CertificateChain = append(options.CertificateChain, a.rootX509Certs...)
options.Signer, err = a.keyManager.CreateSigner(&kmsapi.CreateSignerRequest{
SigningKey: a.config.IntermediateKey,
Password: []byte(a.password),
@ -601,6 +595,12 @@ func (a *Authority) IsRevoked(sn string) (bool, error) {
return a.db.IsRevoked(sn)
}
// GetIntermediateCertificate returns the x509 CA intermediate
// certificate.
func (a *Authority) GetIntermediateCertificate() (*x509.Certificate, error) {
return pemutil.ReadCertificate(a.config.IntermediateCert)
}
// requiresDecrypter returns whether the Authority
// requires a KMS that provides a crypto.Decrypter
// Currently this is only required when SCEP is

38
authority/provisioner/scep.go
View file

@ -18,13 +18,20 @@ type SCEP struct {
ForceCN bool `json:"forceCN,omitempty"`
ChallengePassword string `json:"challenge,omitempty"`
Capabilities []string `json:"capabilities,omitempty"`
// IncludeRoots makes the provisioner return the CA root(s) in the GetCACerts response
IncludeRoots bool `json:"includeRoots,omitempty"`
// MinimumPublicKeyLength is the minimum length for public keys in CSRs
MinimumPublicKeyLength int `json:"minimumPublicKeyLength,omitempty"`
Options *Options `json:"options,omitempty"`
Claims *Claims `json:"claims,omitempty"`
claimer *Claimer
MinimumPublicKeyLength int `json:"minimumPublicKeyLength,omitempty"`
// Numerical identifier for the ContentEncryptionAlgorithm as defined in github.com/mozilla-services/pkcs7
// at https://github.com/mozilla-services/pkcs7/blob/33d05740a3526e382af6395d3513e73d4e66d1cb/encrypt.go#L63
// Defaults to 2, being AES-256-CBC
EncryptionAlgorithmIdentifier *int `json:"encryptionAlgorithmIdentifier,omitempty"`
Options *Options `json:"options,omitempty"`
Claims *Claims `json:"claims,omitempty"`
claimer *Claimer
secretChallengePassword string
encryptionAlgorithm int
}
// GetID returns the provisioner unique identifier.
@ -100,6 +107,15 @@ func (s *SCEP) Init(config Config) (err error) {
return errors.Errorf("only minimum public keys exactly divisible by 8 are supported; %d is not exactly divisible by 8", s.MinimumPublicKeyLength)
}
s.encryptionAlgorithm = 2 // default to AES-256-CBC
if s.EncryptionAlgorithmIdentifier != nil {
value := *s.EncryptionAlgorithmIdentifier
if value < 0 || value > 4 {
return errors.Errorf("only encryption algorithm identifiers from 0 to 4 are valid")
}
s.encryptionAlgorithm = value
}
// TODO: add other, SCEP specific, options?
return err
@ -129,3 +145,17 @@ func (s *SCEP) GetChallengePassword() string {
func (s *SCEP) GetCapabilities() []string {
return s.Capabilities
}
// ShouldIncludeRootsInChain indicates if the CA should
// return its intermediate, which is currently used for
// both signing and decryption, as well as the other certs
// in its chain (usually a single root certificate).
func (s *SCEP) ShouldIncludeRootsInChain() bool {
return s.IncludeRoots
}
// GetContentEncryptionAlgorithm returns the numeric identifier
// for the pkcs7 package encryption algorithm to use.
func (s *SCEP) GetContentEncryptionAlgorithm() int {
return s.encryptionAlgorithm
}

22
ca/ca.go
View file

@ -417,11 +417,6 @@ func (ca *CA) getTLSConfig(auth *authority.Authority) (*tls.Config, error) {
}
}
certPool := x509.NewCertPool()
for _, crt := range auth.GetRootCertificates() {
certPool.AddCert(crt)
}
// GetCertificate will only be called if the client supplies SNI
// information or if tlsConfig.Certificates is empty.
// When client requests are made using an IP address (as opposed to a domain
@ -432,6 +427,23 @@ func (ca *CA) getTLSConfig(auth *authority.Authority) (*tls.Config, error) {
tlsConfig.Certificates = []tls.Certificate{}
tlsConfig.GetCertificate = ca.renewer.GetCertificateForCA
certPool := x509.NewCertPool()
for _, crt := range auth.GetRootCertificates() {
certPool.AddCert(crt)
}
// adding the intermediate CA to the pool will allow clients that
// fail to send the intermediate for chain building to connect to the CA
// successfully.
shouldAddIntermediateToClientCAPool := true // TODO(hs): make this into a configuration
if shouldAddIntermediateToClientCAPool {
cert, err := auth.GetIntermediateCertificate()
if err != nil {
return nil, err
}
certPool.AddCert(cert)
}
// Add support for mutual tls to renew certificates
tlsConfig.ClientAuth = tls.VerifyClientCertIfGiven
tlsConfig.ClientCAs = certPool

19
scep/api/api.go
View file

@ -212,7 +212,7 @@ func (h *Handler) lookupProvisioner(next nextHTTP) nextHTTP {
// GetCACert returns the CA certificates in a SCEP response
func (h *Handler) GetCACert(ctx context.Context) (SCEPResponse, error) {
certs, err := h.Auth.GetCACertificates()
certs, err := h.Auth.GetCACertificates(ctx)
if err != nil {
return SCEPResponse{}, err
}
@ -289,20 +289,29 @@ func (h *Handler) PKIOperation(ctx context.Context, request SCEPRequest) (SCEPRe
// NOTE: at this point we have sufficient information for returning nicely signed CertReps
csr := msg.CSRReqMessage.CSR
if msg.MessageType == microscep.PKCSReq {
// NOTE: we're blocking the RenewalReq if the challenge does not match, because otherwise we don't have any authentication.
// The macOS SCEP client performs renewals using PKCSreq. The CertNanny SCEP client will use PKCSreq with challenge too, it seems,
// even if using the renewal flow as described in the README.md. MicroMDM SCEP client also only does PKCSreq by default, unless
// a certificate exists; then it will use RenewalReq. Adding the challenge check here may be a small breaking change for clients.
// We'll have to see how it works out.
if msg.MessageType == microscep.PKCSReq || msg.MessageType == microscep.RenewalReq {
challengeMatches, err := h.Auth.MatchChallengePassword(ctx, msg.CSRReqMessage.ChallengePassword)
if err != nil {
return h.createFailureResponse(ctx, csr, msg, microscep.BadRequest, errors.New("error when checking password"))
}
if !challengeMatches {
// TODO: can this be returned safely to the client? In the end, if the password was correct, that gains a bit of info too.
return h.createFailureResponse(ctx, csr, msg, microscep.BadRequest, errors.New("wrong password provided"))
}
}
// TODO: check if CN already exists, if renewal is allowed and if existing should be revoked; fail if not
// TODO: authorize renewal: we can authorize renewals with the challenge password (if reusable secrets are used).
// Renewals OPTIONALLY include the challenge if the existing cert is used as authentication, but client SHOULD omit the challenge.
// This means that for renewal requests we should check the certificate provided to be signed before by the CA. We could
// enforce use of the challenge if we want too. That way we could be more flexible in terms of authentication scheme (i.e. reusing
// tokens from other provisioners, calling a webhook, storing multiple secrets, allowing them to be multi-use, etc).
// Authentication by the (self-signed) certificate with an optional challenge is required; supporting renewals incl. verification
// of the client cert is not.
certRep, err := h.Auth.SignCSR(ctx, csr, msg)
if err != nil {

48
scep/authority.go
View file

@ -23,7 +23,7 @@ type Interface interface {
LoadProvisionerByID(string) (provisioner.Interface, error)
GetLinkExplicit(provName string, absoluteLink bool, baseURL *url.URL, inputs ...string) string
GetCACertificates() ([]*x509.Certificate, error)
GetCACertificates(ctx context.Context) ([]*x509.Certificate, error)
DecryptPKIEnvelope(ctx context.Context, msg *PKIMessage) error
SignCSR(ctx context.Context, csr *x509.CertificateRequest, msg *PKIMessage) (*PKIMessage, error)
CreateFailureResponse(ctx context.Context, csr *x509.CertificateRequest, msg *PKIMessage, info FailInfoName, infoText string) (*PKIMessage, error)
@ -36,6 +36,7 @@ type Authority struct {
prefix string
dns string
intermediateCertificate *x509.Certificate
caCerts []*x509.Certificate // TODO(hs): change to use these instead of root and intermediate
service *Service
signAuth SignAuthority
}
@ -72,6 +73,8 @@ func New(signAuth SignAuthority, ops AuthorityOptions) (*Authority, error) {
// in its entirety to make this more interoperable with the rest of
// step-ca, I think.
if ops.Service != nil {
authority.caCerts = ops.Service.certificateChain
// TODO(hs): look into refactoring SCEP into using just caCerts everywhere, if it makes sense for more elaborate SCEP configuration. Keeping it like this for clarity (for now).
authority.intermediateCertificate = ops.Service.certificateChain[0]
authority.service = ops.Service
}
@ -82,7 +85,7 @@ func New(signAuth SignAuthority, ops AuthorityOptions) (*Authority, error) {
var (
// TODO: check the default capabilities; https://tools.ietf.org/html/rfc8894#section-3.5.2
defaultCapabilities = []string{
"Renewal",
"Renewal", // NOTE: removing this will result in macOS SCEP client stating the server doesn't support renewal, but it uses PKCSreq to do so.
"SHA-1",
"SHA-256",
"AES",
@ -100,18 +103,13 @@ func (a *Authority) LoadProvisionerByID(id string) (provisioner.Interface, error
// 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?
// Like "/cgi-bin/pkiclient.exe"? Or would it be enough to have that as the name?
link := "/" + provisionerName
if abs {
// Copy the baseURL value from the pointer. https://github.com/golang/go/issues/38351
u := url.URL{}
@ -137,7 +135,7 @@ func (a *Authority) getLinkExplicit(provisionerName string, abs bool, baseURL *u
}
// GetCACertificates returns the certificate (chain) for the CA
func (a *Authority) GetCACertificates() ([]*x509.Certificate, error) {
func (a *Authority) GetCACertificates(ctx context.Context) ([]*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
@ -153,14 +151,27 @@ func (a *Authority) GetCACertificates() ([]*x509.Certificate, error) {
// 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
// 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 {
p, err := provisionerFromContext(ctx)
if err != nil {
return nil, err
}
if len(a.caCerts) == 0 {
return nil, errors.New("no intermediate certificate available in SCEP authority")
}
return []*x509.Certificate{a.intermediateCertificate}, nil
certs := []*x509.Certificate{}
certs = append(certs, a.caCerts[0])
// TODO(hs): we're adding the roots here, but they may be something different than what the RFC means. Clients are responsible to select the right cert(s) to use, though.
if p.ShouldIncludeRootsInChain() && len(a.caCerts) >= 2 {
certs = append(certs, a.caCerts[1:]...)
}
return certs, nil
}
// DecryptPKIEnvelope decrypts an enveloped message
@ -211,8 +222,6 @@ func (a *Authority) DecryptPKIEnvelope(ctx context.Context, msg *PKIMessage) err
// 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) {
//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) {
// TODO: intermediate storage of the request? In SCEP it's possible to request a csr/certificate
@ -220,7 +229,7 @@ func (a *Authority) SignCSR(ctx context.Context, csr *x509.CertificateRequest, m
// 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.
p, err := ProvisionerFromContext(ctx)
p, err := provisionerFromContext(ctx)
if err != nil {
return nil, err
}
@ -292,10 +301,17 @@ func (a *Authority) SignCSR(ctx context.Context, csr *x509.CertificateRequest, m
return nil, err
}
// apparently the pkcs7 library uses a global default setting for the content encryption
// algorithm to use when en- or decrypting data. We need to restore the current setting after
// the cryptographic operation, so that other usages of the library are not influenced by
// this call to Encrypt().
encryptionAlgorithmToRestore := pkcs7.ContentEncryptionAlgorithm
pkcs7.ContentEncryptionAlgorithm = p.GetContentEncryptionAlgorithm()
e7, err := pkcs7.Encrypt(deg, msg.P7.Certificates)
if err != nil {
return nil, err
}
pkcs7.ContentEncryptionAlgorithm = encryptionAlgorithmToRestore
// PKIMessageAttributes to be signed
config := pkcs7.SignerInfoConfig{
@ -434,7 +450,7 @@ func (a *Authority) CreateFailureResponse(ctx context.Context, csr *x509.Certifi
// MatchChallengePassword verifies a SCEP challenge password
func (a *Authority) MatchChallengePassword(ctx context.Context, password string) (bool, error) {
p, err := ProvisionerFromContext(ctx)
p, err := provisionerFromContext(ctx)
if err != nil {
return false, err
}
@ -453,7 +469,7 @@ func (a *Authority) MatchChallengePassword(ctx context.Context, password string)
// GetCACaps returns the CA capabilities
func (a *Authority) GetCACaps(ctx context.Context) []string {
p, err := ProvisionerFromContext(ctx)
p, err := provisionerFromContext(ctx)
if err != nil {
return defaultCapabilities
}

4
scep/common.go
View file

@ -14,9 +14,9 @@ const (
ProvisionerContextKey = ContextKey("provisioner")
)
// ProvisionerFromContext searches the context for a SCEP provisioner.
// provisionerFromContext searches the context for a SCEP provisioner.
// Returns the provisioner or an error.
func ProvisionerFromContext(ctx context.Context) (Provisioner, error) {
func provisionerFromContext(ctx context.Context) (Provisioner, error) {
val := ctx.Value(ProvisionerContextKey)
if val == nil {
return nil, errors.New("provisioner expected in request context")

2
scep/provisioner.go
View file

@ -16,4 +16,6 @@ type Provisioner interface {
GetOptions() *provisioner.Options
GetChallengePassword() string
GetCapabilities() []string
ShouldIncludeRootsInChain() bool
GetContentEncryptionAlgorithm() int
}