nuts-foundation/nuts-node

/*
 * Copyright (C) 2023 Nuts community
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 */

package pki

import (
    "crypto/tls"
    "crypto/x509"
    "errors"
    "github.com/nuts-foundation/nuts-node/core"
    "time"
)

// errors
var (
    ErrCRLMissing    = errors.New("crl is missing")
    ErrCRLExpired    = errors.New("crl has expired")
    ErrCertRevoked   = errors.New("certificate is revoked")
    ErrCertUntrusted = errors.New("certificate's issuer is not trusted")
    // ErrDenylistMissing occurs when the denylist cannot be downloaded
    ErrDenylistMissing = errors.New("denylist cannot be retrieved")

    // ErrCertBanned means the certificate was banned by a denylist rather than revoked by a CRL
    ErrCertBanned = errors.New("certificate is banned")
)

// Denylist implements a global certificate rejection
type Denylist interface {
    // LastUpdated provides the time at which the denylist was last retrieved
    LastUpdated() time.Time

    // Update fetches a new copy of the denylist
    Update() error

    // URL returns the URL of the denylist
    URL() string

    // ValidateCert returns an error if a certificate should not be used
    ValidateCert(cert *x509.Certificate) error

    // Subscribe registers a callback that is triggered everytime the denylist is updated
    Subscribe(f func())
}

type Validator interface {
    // Validate returns an error if any of the certificates in the chain has been revoked, or if the request cannot be processed.
    // ErrCertRevoked and ErrCertUntrusted indicate that at least one of the certificates is revoked, or signed by a CA that is not in the truststore.
    // ErrCRLMissing and ErrCRLExpired signal that at least one of the certificates cannot be validated reliably.
    // If the certificate was revoked on an expired CRL, it wil return ErrCertRevoked.
    // Ignoring all errors except ErrCertRevoked changes the behavior from hard-fail to soft-fail. Without a truststore, the Validator is a noop if set to soft-fail
    // The certificate chain is expected to be sorted leaf to root.
    Validate(chain []*x509.Certificate) error

    // SetVerifyPeerCertificateFunc sets config.ValidatePeerCertificate to use Validate.
    SetVerifyPeerCertificateFunc(config *tls.Config) error

    // AddTruststore adds all CAs to the truststore for validation of CRL signatures. It also adds all CRL Distribution Endpoints found in the chain.
    // CRL Distribution Points encountered during operation, such as on end user certificates, are only added to the monitored CRLs if their issuer is in the truststore.
    AddTruststore(chain []*x509.Certificate) error

    // SubscribeDenied registers a callback that is triggered everytime the denylist is updated.
    // This can be used to revalidate all certificates on long-lasting connections by calling Validate on them again.
    SubscribeDenied(f func())
}

// Provider is an interface for providing PKI services (e.g. TLS configuration, certificate validation).
type Provider interface {
    Validator
    // CreateTLSConfig creates a tls.Config for outbound connections. It returns nil (and no error) if TLS is disabled.
    CreateTLSConfig(cfg core.TLSConfig) (*tls.Config, error)
}