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package scep
import (
"crypto"
"crypto/rsa"
"crypto/x509"
"errors"
)
type Options struct {
// Roots contains the (federated) CA roots certificate(s)
Roots []*x509.Certificate `json:"-"`
// Intermediates points issuer certificate, along with any other bundled certificates
// to be returned in the chain for consumers.
Intermediates []*x509.Certificate `json:"-"`
// SignerCert points to the certificate of the CA signer. It usually is the same as the
// first certificate in the CertificateChain.
SignerCert *x509.Certificate `json:"-"`
// Signer signs CSRs in SCEP. Configured in the ca.json key property.
Signer crypto.Signer `json:"-"`
// Decrypter decrypts encrypted SCEP messages. Configured in the ca.json key property.
Decrypter crypto.Decrypter `json:"-"`
// DecrypterCert points to the certificate of the CA decrypter.
DecrypterCert *x509.Certificate `json:"-"`
// SCEPProvisionerNames contains the currently configured SCEP provioner names. These
// are used to be able to load the provisioners when the SCEP authority is being
// validated.
SCEPProvisionerNames []string
}
type comparablePublicKey interface {
Equal(crypto.PublicKey) bool
}
// Validate checks the fields in Options.
func (o *Options) Validate() error {
switch {
case len(o.Intermediates) == 0:
return errors.New("no intermediate certificate available for SCEP authority")
case o.SignerCert == nil:
return errors.New("no signer certificate available for SCEP authority")
}
// the signer is optional, but if it's set, its public key must match the signer
// certificate public key.
if o.Signer != nil {
// check if the signer (intermediate CA) certificate has the same public key as
// the signer. According to the RFC it seems valid to have different keys for
// the intermediate and the CA signing new certificates, so this might change
// in the future.
signerPublicKey := o.Signer.Public().(comparablePublicKey)
if !signerPublicKey.Equal(o.SignerCert.PublicKey) {
return errors.New("mismatch between signer certificate and public key")
}
}
// decrypter can be nil in case a signing only key is used; validation complete.
if o.Decrypter == nil {
return nil
}
// If a decrypter is available, check that it's backed by an RSA key. According to the
// RFC: https://tools.ietf.org/html/rfc8894#section-3.1, SCEP can be used with something
// different than RSA, but requires the encryption to be performed using the challenge
// password in that case. An older version of specification states that only RSA is
// supported: https://tools.ietf.org/html/draft-nourse-scep-23#section-2.1.1. Other
// algorithms do not seem to be supported in certnanny/sscep, but it might work
// in micromdm/scep. Currently only RSA is allowed, but it might be an option
// to try other algorithms in the future.
decrypterPublicKey, ok := o.Decrypter.Public().(*rsa.PublicKey)
if !ok {
return errors.New("only RSA keys are (currently) supported as decrypters")
}
// check if intermediate public key is the same as the decrypter public key.
// In certnanny/sscep it's mentioned that the signing key can be different
// from the decrypting (and encrypting) key. These options are only used and
// validated when the intermediate CA is also used as the decrypter, though,
// so they should match.
if !decrypterPublicKey.Equal(o.SignerCert.PublicKey) {
return errors.New("mismatch between certificate chain and decrypter public keys")
}
return nil
}
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