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Add validation to SCEP Options

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This commit is contained in:
Herman Slatman 2021-03-26 15:22:04 +01:00
parent b97f024f8a
commit 65aab963c9
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1 changed files with 53 additions and 13 deletions
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66
scep/options.go
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@ -2,30 +2,70 @@ package scep
import (
"crypto"
"crypto/rsa"
"crypto/x509"
"github.com/pkg/errors"
)
type Options struct {
// CertificateChain is the issuer certificate, along with any other bundled certificates
// to be returned in the chain for consumers. Configured in ca.json crt property.
// to be returned in the chain for consumers. Configured in the ca.json crt property.
CertificateChain []*x509.Certificate
// Signer signs CSRs in SCEP. Configured in ca.json key property.
// Signer signs CSRs in SCEP. Configured in the ca.json key property.
Signer crypto.Signer `json:"-"`
// Decrypter decrypts encrypted SCEP messages. Configured in ca.json key property.
// Decrypter decrypts encrypted SCEP messages. Configured in the ca.json key property.
Decrypter crypto.Decrypter `json:"-"`
}
// Validate checks the fields in Options.
func (o *Options) Validate() error {
// var typ Type
// if o == nil {
// typ = Type(SoftCAS)
// } else {
// typ = Type(o.Type)
// }
// // Check that the type can be loaded.
// if _, ok := LoadCertificateAuthorityServiceNewFunc(typ); !ok {
// return errors.Errorf("unsupported cas type %s", typ)
// }
if o.CertificateChain == nil {
return errors.New("certificate chain not configured correctly")
}
if len(o.CertificateChain) < 1 {
return errors.New("certificate chain should at least have one certificate")
}
// 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. 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 than RSA 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.
intermediate := o.CertificateChain[0]
if intermediate.PublicKeyAlgorithm != x509.RSA {
return errors.New("only the RSA algorithm is (currently) supported")
}
// TODO: add checks for key usage?
signerPublicKey, ok := o.Signer.Public().(*rsa.PublicKey)
if !ok {
return errors.New("only RSA public keys are (currently) supported as signers")
}
// check if the 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.
if !signerPublicKey.Equal(intermediate.PublicKey) {
return errors.New("mismatch between certificate chain and signer public keys")
}
decrypterPublicKey, ok := o.Decrypter.Public().(*rsa.PublicKey)
if !ok {
return errors.New("only RSA public keys are (currently) supported as decrypters")
}
// check if intermedate 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. Currently that's not supported.
if !decrypterPublicKey.Equal(intermediate.PublicKey) {
return errors.New("mismatch between certificate chain and decrypter public keys")
}
return nil
}