fix: update key usage error message to make it clear (#169)

Resolves #164 
Signed-off-by: Junjie Gao <junjiegao@microsoft.com>

---------

Signed-off-by: Junjie Gao <junjiegao@microsoft.com>

x509/cert_validations.go

@@ -20,20 +20,10 @@ import (
  "crypto/x509"
  "errors"
  "fmt"
+ "strings"
  "time"
 )
 
-var kuLeafCertBlocked = x509.KeyUsageContentCommitment |
- x509.KeyUsageKeyEncipherment |
- x509.KeyUsageDataEncipherment |
- x509.KeyUsageKeyAgreement |
- x509.KeyUsageCertSign |
- x509.KeyUsageCRLSign |
- x509.KeyUsageEncipherOnly |
- x509.KeyUsageDecipherOnly
-var kuLeafCertBlockedString = "ContentCommitment, KeyEncipherment, DataEncipherment, KeyAgreement, " +
- "CertSign, CRLSign, EncipherOnly, DecipherOnly"
-
 // ValidateCodeSigningCertChain takes an ordered code-signing certificate chain
 // and validates issuance from leaf to root
 // Validates certificates according to this spec:
@@ -184,10 +174,36 @@ func validateLeafKeyUsage(cert *x509.Certificate) error {
  return err
  }
  if cert.KeyUsage&x509.KeyUsageDigitalSignature == 0 {
- return fmt.Errorf("certificate with subject %q: key usage must have the bit positions for digital signature set", cert.Subject)
+ return fmt.Errorf("The certificate with subject %q is invalid. The key usage must have the bit positions for \"Digital Signature\" set", cert.Subject)
+ }
+
+ var invalidKeyUsages []string
+ if cert.KeyUsage&x509.KeyUsageContentCommitment != 0 {
+ invalidKeyUsages = append(invalidKeyUsages, `"ContentCommitment"`)
+ }
+ if cert.KeyUsage&x509.KeyUsageKeyEncipherment != 0 {
+ invalidKeyUsages = append(invalidKeyUsages, `"KeyEncipherment"`)
+ }
+ if cert.KeyUsage&x509.KeyUsageDataEncipherment != 0 {
+ invalidKeyUsages = append(invalidKeyUsages, `"DataEncipherment"`)
+ }
+ if cert.KeyUsage&x509.KeyUsageKeyAgreement != 0 {
+ invalidKeyUsages = append(invalidKeyUsages, `"KeyAgreement"`)
+ }
+ if cert.KeyUsage&x509.KeyUsageCertSign != 0 {
+ invalidKeyUsages = append(invalidKeyUsages, `"CertSign"`)
+ }
+ if cert.KeyUsage&x509.KeyUsageCRLSign != 0 {
+ invalidKeyUsages = append(invalidKeyUsages, `"CRLSign"`)
+ }
+ if cert.KeyUsage&x509.KeyUsageEncipherOnly != 0 {
+ invalidKeyUsages = append(invalidKeyUsages, `"EncipherOnly"`)
+ }
+ if cert.KeyUsage&x509.KeyUsageDecipherOnly != 0 {
+ invalidKeyUsages = append(invalidKeyUsages, `"DecipherOnly"`)
  }
- if cert.KeyUsage&kuLeafCertBlocked != 0 {
- return fmt.Errorf("certificate with subject %q: key usage must not have the bit positions for %s set", cert.Subject, kuLeafCertBlockedString)
+ if len(invalidKeyUsages) > 0 {
+ return fmt.Errorf("The certificate with subject %q is invalid. The key usage must be \"Digital Signature\" only, but found %s", cert.Subject, strings.Join(invalidKeyUsages, ", "))
  }
  return nil
 }

x509/cert_validations_test.go

@@ -15,7 +15,9 @@ package x509
 
 import (
  "crypto/x509"
+ "crypto/x509/pkix"
  _ "embed"
+ "encoding/asn1"
  "testing"
  "time"
 
@@ -510,7 +512,7 @@ var kuNoDigitalSignatureLeaf = parseCertificateFromString(kuNoDigitalSignatureLe
 
 func TestFailKuNoDigitalSignatureLeaf(t *testing.T) {
  err := validateLeafCertificate(kuNoDigitalSignatureLeaf, x509.ExtKeyUsageCodeSigning)
- assertErrorEqual("certificate with subject \"CN=Hello\": key usage must have the bit positions for digital signature set", err, t)
+ assertErrorEqual("The certificate with subject \"CN=Hello\" is invalid. The key usage must have the bit positions for \"Digital Signature\" set", err, t)
 }
 
 var kuWrongValuesLeafPem = "-----BEGIN CERTIFICATE-----\n" +
@@ -534,7 +536,7 @@ var kuWrongValuesLeaf = parseCertificateFromString(kuWrongValuesLeafPem)
 
 func TestFailKuWrongValuesLeaf(t *testing.T) {
  err := validateLeafCertificate(kuWrongValuesLeaf, x509.ExtKeyUsageCodeSigning)
- assertErrorEqual("certificate with subject \"CN=Hello\": key usage must not have the bit positions for ContentCommitment, KeyEncipherment, DataEncipherment, KeyAgreement, CertSign, CRLSign, EncipherOnly, DecipherOnly set", err, t)
+ assertErrorEqual("The certificate with subject \"CN=Hello\" is invalid. The key usage must be \"Digital Signature\" only, but found \"CertSign\", \"CRLSign\"", err, t)
 }
 
 var rsaKeyTooSmallLeafPem = "-----BEGIN CERTIFICATE-----\n" +
@@ -699,3 +701,75 @@ func assertErrorEqual(expected string, err error, t *testing.T) {
  t.Fatalf("Expected error \"%v\" but was \"%v\"", expected, err)
  }
 }
+
+func TestValidateLeafKeyUsage(t *testing.T) {
+ extensions := []pkix.Extension{{
+ Id: asn1.ObjectIdentifier{2, 5, 29, 15}, // OID for KeyUsage
+ Critical: true,
+ }}
+
+ tests := []struct {
+ name string
+ cert *x509.Certificate
+ expectedErrMsg string
+ }{
+ {
+ name: "Valid DigitalSignature usage",
+ cert: &x509.Certificate{
+ Subject: pkix.Name{CommonName: "Test CN"},
+ KeyUsage: x509.KeyUsageDigitalSignature,
+ Extensions: extensions,
+ },
+ expectedErrMsg: "",
+ },
+ {
+ name: "Valid ContentCommitment usage",
+ cert: &x509.Certificate{
+ Subject: pkix.Name{CommonName: "Test CN"},
+ KeyUsage: x509.KeyUsageDigitalSignature | x509.KeyUsageContentCommitment,
+ Extensions: extensions,
+ },
+ expectedErrMsg: "The certificate with subject \"CN=Test CN\" is invalid. The key usage must be \"Digital Signature\" only, but found \"ContentCommitment\"",
+ },
+ {
+ name: "Missing DigitalSignature usage",
+ cert: &x509.Certificate{
+ Subject: pkix.Name{CommonName: "Test CN"},
+ KeyUsage: x509.KeyUsageCertSign,
+ Extensions: extensions,
+ },
+ expectedErrMsg: "The certificate with subject \"CN=Test CN\" is invalid. The key usage must have the bit positions for \"Digital Signature\" set",
+ },
+ {
+ name: "Invalid KeyEncipherment usage",
+ cert: &x509.Certificate{
+ Subject: pkix.Name{CommonName: "Test CN"},
+ KeyUsage: x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment,
+ Extensions: extensions,
+ },
+ expectedErrMsg: "The certificate with subject \"CN=Test CN\" is invalid. The key usage must be \"Digital Signature\" only, but found \"KeyEncipherment\"",
+ },
+ {
+ name: "Multiple Invalid usages",
+ cert: &x509.Certificate{
+ Subject: pkix.Name{CommonName: "Test CN"},
+ KeyUsage: x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment | x509.KeyUsageDataEncipherment | x509.KeyUsageKeyAgreement | x509.KeyUsageCertSign | x509.KeyUsageCRLSign | x509.KeyUsageEncipherOnly | x509.KeyUsageDecipherOnly | x509.KeyUsageEncipherOnly | x509.KeyUsageDecipherOnly,
+ Extensions: extensions,
+ },
+ expectedErrMsg: "The certificate with subject \"CN=Test CN\" is invalid. The key usage must be \"Digital Signature\" only, but found \"KeyEncipherment\", \"DataEncipherment\", \"KeyAgreement\", \"CertSign\", \"CRLSign\", \"EncipherOnly\", \"DecipherOnly\"",
+ },
+ }
+
+ for _, tt := range tests {
+ t.Run(tt.name, func(t *testing.T) {
+ err := validateLeafKeyUsage(tt.cert)
+ if err != nil && tt.expectedErrMsg == "" {
+ t.Fatalf("expected no error, but got: %s", err)
+ } else if err == nil && tt.expectedErrMsg != "" {
+ t.Fatalf("expected error %q, but got none", tt.expectedErrMsg)
+ } else if err != nil && err.Error() != tt.expectedErrMsg {
+ t.Fatalf("expected error %q, but got: %s", tt.expectedErrMsg, err)
+ }
+ })
+ }
+}