smallstep-certificates/authority/provisioner/scep.go

package provisioner

import (
	"context"
	"time"

	"github.com/pkg/errors"

	"github.com/smallstep/certificates/authority/policy"
)

// SCEP is the SCEP provisioner type, an entity that can authorize the
// SCEP provisioning flow
type SCEP struct {
	*base
	ID                string   `json:"-"`
	Type              string   `json:"type"`
	Name              string   `json:"name"`
	ForceCN           bool     `json:"forceCN,omitempty"`
	ChallengePassword string   `json:"challenge,omitempty"`
	Capabilities      []string `json:"capabilities,omitempty"`

	// IncludeRoot makes the provisioner return the CA root in addition to the
	// intermediate in the GetCACerts response
	IncludeRoot bool `json:"includeRoot,omitempty"`

	// MinimumPublicKeyLength is the minimum length for public keys in CSRs
	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 0, being DES-CBC
	EncryptionAlgorithmIdentifier int      `json:"encryptionAlgorithmIdentifier,omitempty"`
	Options                       *Options `json:"options,omitempty"`
	Claims                        *Claims  `json:"claims,omitempty"`
	ctl                           *Controller
	secretChallengePassword       string
	encryptionAlgorithm           int
	x509Policy                    policy.X509Policy
}

// GetID returns the provisioner unique identifier.
func (s *SCEP) GetID() string {
	if s.ID != "" {
		return s.ID
	}
	return s.GetIDForToken()
}

// GetIDForToken returns an identifier that will be used to load the provisioner
// from a token.
func (s *SCEP) GetIDForToken() string {
	return "scep/" + s.Name
}

// GetName returns the name of the provisioner.
func (s *SCEP) GetName() string {
	return s.Name
}

// GetType returns the type of provisioner.
func (s *SCEP) GetType() Type {
	return TypeSCEP
}

// GetEncryptedKey returns the base provisioner encrypted key if it's defined.
func (s *SCEP) GetEncryptedKey() (string, string, bool) {
	return "", "", false
}

// GetTokenID returns the identifier of the token.
func (s *SCEP) GetTokenID(ott string) (string, error) {
	return "", errors.New("scep provisioner does not implement GetTokenID")
}

// GetOptions returns the configured provisioner options.
func (s *SCEP) GetOptions() *Options {
	return s.Options
}

// DefaultTLSCertDuration returns the default TLS cert duration enforced by
// the provisioner.
func (s *SCEP) DefaultTLSCertDuration() time.Duration {
	return s.ctl.Claimer.DefaultTLSCertDuration()
}

// Init initializes and validates the fields of a SCEP type.
func (s *SCEP) Init(config Config) (err error) {
	switch {
	case s.Type == "":
		return errors.New("provisioner type cannot be empty")
	case s.Name == "":
		return errors.New("provisioner name cannot be empty")
	}

	// Mask the actual challenge value, so it won't be marshaled
	s.secretChallengePassword = s.ChallengePassword
	s.ChallengePassword = "*** redacted ***"

	// Default to 2048 bits minimum public key length (for CSRs) if not set
	if s.MinimumPublicKeyLength == 0 {
		s.MinimumPublicKeyLength = 2048
	}

	if s.MinimumPublicKeyLength%8 != 0 {
		return errors.Errorf("%d bits is not exactly divisible by 8", s.MinimumPublicKeyLength)
	}

	s.encryptionAlgorithm = s.EncryptionAlgorithmIdentifier // TODO(hs): we might want to upgrade the default security to AES-CBC?
	if s.encryptionAlgorithm < 0 || s.encryptionAlgorithm > 4 {
		return errors.New("only encryption algorithm identifiers from 0 to 4 are valid")
	}

	// TODO: add other, SCEP specific, options?

	// Initialize the x509 allow/deny policy engine
	if s.x509Policy, err = policy.NewX509PolicyEngine(s.Options.GetX509Options()); err != nil {
		return err
	}

	s.ctl, err = NewController(s, s.Claims, config)
	return
}

// AuthorizeSign does not do any verification, because all verification is handled
// in the SCEP protocol. This method returns a list of modifiers / constraints
// on the resulting certificate.
func (s *SCEP) AuthorizeSign(ctx context.Context, token string) ([]SignOption, error) {
	return []SignOption{
		s,
		// modifiers / withOptions
		newProvisionerExtensionOption(TypeSCEP, s.Name, ""),
		newForceCNOption(s.ForceCN),
		profileDefaultDuration(s.ctl.Claimer.DefaultTLSCertDuration()),
		// validators
		newPublicKeyMinimumLengthValidator(s.MinimumPublicKeyLength),
		newValidityValidator(s.ctl.Claimer.MinTLSCertDuration(), s.ctl.Claimer.MaxTLSCertDuration()),
		newX509NamePolicyValidator(s.x509Policy),
	}, nil
}

// GetChallengePassword returns the challenge password
func (s *SCEP) GetChallengePassword() string {
	return s.secretChallengePassword
}

// GetCapabilities returns the CA capabilities
func (s *SCEP) GetCapabilities() []string {
	return s.Capabilities
}

// ShouldIncludeRootInChain indicates if the CA should
// return its intermediate, which is currently used for
// both signing and decryption, as well as the root in
// its chain.
func (s *SCEP) ShouldIncludeRootInChain() bool {
	return s.IncludeRoot
}

// GetContentEncryptionAlgorithm returns the numeric identifier
// for the pkcs7 package encryption algorithm to use.
func (s *SCEP) GetContentEncryptionAlgorithm() int {
	return s.encryptionAlgorithm
}