Add signed failure responses

scep/api/api.go

@@ -34,9 +34,9 @@ const maxPayloadSize = 2 << 20
 type nextHTTP = func(http.ResponseWriter, *http.Request)
 
 const (
-	certChainHeader = "application/x-x509-ca-ra-cert"
-	leafHeader      = "application/x-x509-ca-cert"
-	pkiOpHeader     = "application/x-pki-message"
+	certChainHeader    = "application/x-x509-ca-ra-cert"
+	leafHeader         = "application/x-x509-ca-cert"
+	pkiOperationHeader = "application/x-pki-message"
 )
 
 // SCEPRequest is a SCEP server request.
@@ -125,10 +125,6 @@ func (h *Handler) Post(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// TODO: fix cases in which we get here and there's no certificate (i.e. wrong password, waiting for cert, etc)
-	// We should generate an appropriate response and it should be signed
-	api.LogCertificate(w, response.Certificate)
-
 	writeSCEPResponse(w, response)
 }
 
@@ -262,9 +258,13 @@ func (h *Handler) PKIOperation(ctx context.Context, request SCEPRequest) (SCEPRe
 	// parse the message using microscep implementation
 	microMsg, err := microscep.ParsePKIMessage(request.Message)
 	if err != nil {
+		// return the error, because we can't use the msg for creating a CertRep
 		return SCEPResponse{}, err
 	}
 
+	// this is essentially doing the same as microscep.ParsePKIMessage, but
+	// gives us access to the p7 itself in scep.PKIMessage. Essentially a small
+	// wrapper for the microscep implementation.
 	p7, err := pkcs7.Parse(microMsg.Raw)
 	if err != nil {
 		return SCEPResponse{}, err
@@ -283,23 +283,25 @@ func (h *Handler) PKIOperation(ctx context.Context, request SCEPRequest) (SCEPRe
 		return SCEPResponse{}, err
 	}
 
+	// NOTE: at this point we have sufficient information for returning nicely signed CertReps
+	csr := msg.CSRReqMessage.CSR
+
 	if msg.MessageType == microscep.PKCSReq {
 
 		challengeMatches, err := h.Auth.MatchChallengePassword(ctx, msg.CSRReqMessage.ChallengePassword)
 		if err != nil {
-			return SCEPResponse{}, err
+			return h.createFailureResponse(ctx, csr, msg, microscep.BadRequest, "error when checking password")
 		}
 
 		if !challengeMatches {
-			return SCEPResponse{}, errors.New("wrong password provided")
+			// 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, "wrong password provided")
 		}
 	}
 
-	csr := msg.CSRReqMessage.CSR
-
 	certRep, err := h.Auth.SignCSR(ctx, csr, msg)
 	if err != nil {
-		return SCEPResponse{}, err
+		return h.createFailureResponse(ctx, csr, msg, microscep.BadRequest, "error when signing new certificate")
 	}
 
 	// //cert := certRep.CertRepMessage.Certificate
@@ -330,6 +332,11 @@ func formatCapabilities(caps []string) []byte {
 
 // writeSCEPResponse writes a SCEP response back to the SCEP client.
 func writeSCEPResponse(w http.ResponseWriter, response SCEPResponse) {
+
+	if response.Certificate != nil {
+		api.LogCertificate(w, response.Certificate)
+	}
+
 	w.Header().Set("Content-Type", contentHeader(response))
 	_, err := w.Write(response.Data)
 	if err != nil {
@@ -346,6 +353,17 @@ func writeError(w http.ResponseWriter, err error) {
 	api.WriteError(w, scepError)
 }
 
+func (h *Handler) createFailureResponse(ctx context.Context, csr *x509.CertificateRequest, msg *scep.PKIMessage, info microscep.FailInfo, infoText string) (SCEPResponse, error) {
+	certRepMsg, err := h.Auth.CreateFailureResponse(ctx, csr, msg, scep.FailInfoName(info), infoText)
+	if err != nil {
+		return SCEPResponse{}, err
+	}
+	return SCEPResponse{
+		Operation: opnPKIOperation,
+		Data:      certRepMsg.Raw,
+	}, nil
+}
+
 func contentHeader(r SCEPResponse) string {
 	switch r.Operation {
 	case opnGetCACert:
@@ -354,7 +372,7 @@ func contentHeader(r SCEPResponse) string {
 		}
 		return leafHeader
 	case opnPKIOperation:
-		return pkiOpHeader
+		return pkiOperationHeader
 	default:
 		return "text/plain"
 	}

scep/authority.go

@@ -56,6 +56,7 @@ type Interface interface {
 	GetCACertificates() ([]*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)
 	MatchChallengePassword(ctx context.Context, password string) (bool, error)
 	GetCACaps(ctx context.Context) []string
 
@@ -376,6 +377,10 @@ func (a *Authority) SignCSR(ctx context.Context, csr *x509.CertificateRequest, m
 				Type:  oidSCEPrecipientNonce,
 				Value: msg.SenderNonce,
 			},
+			pkcs7.Attribute{
+				Type:  oidSCEPsenderNonce,
+				Value: msg.SenderNonce,
+			},
 		},
 	}
 
@@ -419,6 +424,74 @@ func (a *Authority) SignCSR(ctx context.Context, csr *x509.CertificateRequest, m
 	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{
+			pkcs7.Attribute{
+				Type:  oidSCEPtransactionID,
+				Value: msg.TransactionID,
+			},
+			pkcs7.Attribute{
+				Type:  oidSCEPpkiStatus,
+				Value: microscep.FAILURE,
+			},
+			pkcs7.Attribute{
+				Type:  oidSCEPfailInfo,
+				Value: info,
+			},
+			pkcs7.Attribute{
+				Type:  oidSCEPfailInfoText,
+				Value: infoText,
+			},
+			pkcs7.Attribute{
+				Type:  oidSCEPmessageType,
+				Value: microscep.CertRep,
+			},
+			pkcs7.Attribute{
+				Type:  oidSCEPsenderNonce,
+				Value: msg.SenderNonce,
+			},
+			pkcs7.Attribute{
+				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
+}
+
 // MatchChallengePassword verifies a SCEP challenge password
 func (a *Authority) MatchChallengePassword(ctx context.Context, password string) (bool, error) {
 

scep/scep.go

@@ -11,6 +11,18 @@ import (
 	"go.mozilla.org/pkcs7"
 )
 
+// FailInfoName models the name/value of failInfo
+type FailInfoName microscep.FailInfo
+
+// FailInfo models a failInfo object consisting of a
+// name/identifier and a failInfoText, the latter of
+// which can be more descriptive and is intended to be
+// read by humans.
+type FailInfo struct {
+	Name FailInfoName
+	Text string
+}
+
 // SCEP OIDs
 var (
 	oidSCEPmessageType    = asn1.ObjectIdentifier{2, 16, 840, 1, 113733, 1, 9, 2}
@@ -20,6 +32,7 @@ var (
 	oidSCEPrecipientNonce = asn1.ObjectIdentifier{2, 16, 840, 1, 113733, 1, 9, 6}
 	oidSCEPtransactionID  = asn1.ObjectIdentifier{2, 16, 840, 1, 113733, 1, 9, 7}
 	oidChallengePassword  = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 9, 7}
+	oidSCEPfailInfoText   = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 24}
 )
 
 // PKIMessage defines the possible SCEP message types