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/*
* ZLint Copyright 2024 Regents of the University of Michigan
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy
* of the License at http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
* implied. See the License for the specific language governing
* permissions and limitations under the License.
*/
package rfc
import (
"fmt"
"sort"
"strings"
"github.com/zmap/zcrypto/x509"
"github.com/zmap/zlint/v3/lint"
"github.com/zmap/zlint/v3/util"
)
type ecdsaInvalidKU struct{}
func init() {
lint.RegisterCertificateLint(&lint.CertificateLint{
LintMetadata: lint.LintMetadata{
Name: "n_ecdsa_ee_invalid_ku",
Description: "ECDSA end-entity certificates MAY have key usages: digitalSignature, nonRepudiation and keyAgreement",
Citation: "RFC 5480 Section 3",
Source: lint.RFC5480,
EffectiveDate: util.CABEffectiveDate,
},
Lint: NewEcdsaInvalidKU,
})
}
func NewEcdsaInvalidKU() lint.LintInterface {
return &ecdsaInvalidKU{}
}
// Initialize is a no-op for this lint.
// CheckApplies returns true when the certificate is a subscriber cert using an
// ECDSA public key algorithm.
func (l *ecdsaInvalidKU) CheckApplies(c *x509.Certificate) bool {
return util.IsSubscriberCert(c) && c.PublicKeyAlgorithm == x509.ECDSA && util.HasKeyUsageOID(c)
}
// Execute returns a Notice level lint.LintResult if the ECDSA end entity certificate
// being linted has Key Usage bits set other than digitalSignature,
// nonRepudiation/contentCommentment, and keyAgreement.
func (l *ecdsaInvalidKU) Execute(c *x509.Certificate) *lint.LintResult {
// RFC 5480, Section 3 "Key Usage Bits" says:
//
// If the keyUsage extension is present in an End Entity (EE)
// certificate that indicates id-ecPublicKey in SubjectPublicKeyInfo,
// then any combination of the following values MAY be present:
//
// digitalSignature;
// nonRepudiation; and
// keyAgreement.
//
// So we set up `allowedKUs` to match. Note that per RFC 5280: recent editions
// of X.509 renamed "nonRepudiation" to "contentCommitment", which is the name
// of the Go x509 constant we use here alongside the digitalSignature and
// keyAgreement constants.
allowedKUs := map[x509.KeyUsage]bool{
x509.KeyUsageDigitalSignature: true,
x509.KeyUsageContentCommitment: true,
x509.KeyUsageKeyAgreement: true,
}
var invalidKUs []string
for ku, kuName := range util.KeyUsageToString {
if c.KeyUsage&ku != 0 {
if !allowedKUs[ku] {
invalidKUs = append(invalidKUs, kuName)
}
}
}
if len(invalidKUs) > 0 {
// Sort the invalid KUs to allow consistent ordering of Details messages for
// unit testing
sort.Strings(invalidKUs)
return &lint.LintResult{
Status: lint.Notice,
Details: fmt.Sprintf(
"Certificate had unexpected key usage(s): %s",
strings.Join(invalidKUs, ", ")),
}
}
return &lint.LintResult{
Status: lint.Pass,
}
}
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