add support for ignoring certificates with pkcs11

This commit adds a new environment variable,
COSIGN_PKCS11_IGNORE_CERTIFICATE, which will skip loading certificates
into a PKCS11 key when set to "1". This is desirable when you want to
sign with a private key that has a certificate associated with it, but
do not want that certificate to be included with the signature for
verification. Certificates are already optional for keys from non-PKCS11
sources via the --certificate command line flag.

Signed-off-by: dylrich <dylan.richardson@mongodb.com>

pkg/cosign/env/env.go

@@ -44,12 +44,13 @@ func (v Variable) String() string {
 
 const (
 	// Cosign environment variables
-	VariableExperimental     Variable = "COSIGN_EXPERIMENTAL"
-	VariableDockerMediaTypes Variable = "COSIGN_DOCKER_MEDIA_TYPES"
-	VariablePassword         Variable = "COSIGN_PASSWORD"
-	VariablePKCS11Pin        Variable = "COSIGN_PKCS11_PIN"
-	VariablePKCS11ModulePath Variable = "COSIGN_PKCS11_MODULE_PATH"
-	VariableRepository       Variable = "COSIGN_REPOSITORY"
+	VariableExperimental            Variable = "COSIGN_EXPERIMENTAL"
+	VariableDockerMediaTypes        Variable = "COSIGN_DOCKER_MEDIA_TYPES"
+	VariablePassword                Variable = "COSIGN_PASSWORD"
+	VariablePKCS11Pin               Variable = "COSIGN_PKCS11_PIN"
+	VariablePKCS11ModulePath        Variable = "COSIGN_PKCS11_MODULE_PATH"
+	VariablePKCS11IgnoreCertificate Variable = "COSIGN_PKCS11_IGNORE_CERTIFICATE"
+	VariableRepository              Variable = "COSIGN_REPOSITORY"
 
 	// Sigstore environment variables
 	VariableSigstoreCTLogPublicKeyFile Variable = "SIGSTORE_CT_LOG_PUBLIC_KEY_FILE"
@@ -102,6 +103,11 @@ var (
 			Expects:     "string with a module-path",
 			Sensitive:   false,
 		},
+		VariablePKCS11IgnoreCertificate: {
+			Description: "disables loading certificates with PKCS11",
+			Expects:     "1 if loading certificates should be disabled (0 by default)",
+			Sensitive:   false,
+		},
 		VariableRepository: {
 			Description: "can be used to store signatures in an alternate location",
 			Expects:     "string with a repository",

pkg/cosign/pkcs11key/pkcs11key.go

@@ -177,10 +177,15 @@ func GetKeyWithURIConfig(config *Pkcs11UriConfig, askForPinIfNeeded bool) (*Key,
 	// Key's corresponding cert might not exist,
 	// therefore, we do not fail if it is the case.
 	var cert *x509.Certificate
-	if len(config.KeyID) != 0 {
-		cert, _ = ctx.FindCertificate(config.KeyID, nil, nil)
-	} else if len(config.KeyLabel) != 0 {
-		cert, _ = ctx.FindCertificate(nil, config.KeyLabel, nil)
+
+	ignoreCert := env.Getenv(env.VariablePKCS11IgnoreCertificate) == "1"
+
+	if !ignoreCert {
+		if len(config.KeyID) != 0 {
+			cert, _ = ctx.FindCertificate(config.KeyID, nil, nil)
+		} else if len(config.KeyLabel) != 0 {
+			cert, _ = ctx.FindCertificate(nil, config.KeyLabel, nil)
+		}
 	}
 
 	return &Key{ctx: ctx, signer: signer, cert: cert}, nil

test/pkcs11_test.go

@@ -45,6 +45,7 @@ import (
 	"encoding/hex"
 	"encoding/pem"
 	"fmt"
+	"io"
 	"math/big"
 	"os"
 	"strings"
@@ -214,6 +215,64 @@ func TestListKeysUrisCmd(t *testing.T) {
 	}
 }
 
+func TestCertificateIgnored(t *testing.T) {
+	ctx := context.Background()
+
+	tokens, err := GetTokens(ctx, modulePath)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	bTokenFound := false
+	var slotID uint
+	for _, token := range tokens {
+		if token.TokenInfo.Label == tokenLabel {
+			bTokenFound = true
+			slotID = token.Slot
+			break
+		}
+	}
+	if !bTokenFound {
+		t.Fatalf("token with label '%s' not found", tokenLabel)
+	}
+
+	err = importKey(slotID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer deleteKey(slotID)
+
+	pkcs11UriConfig := pkcs11key.NewPkcs11UriConfig()
+	err = pkcs11UriConfig.Parse(uri)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	const envvar = "COSIGN_PKCS11_IGNORE_CERTIFICATE"
+
+	if err := os.Setenv(envvar, "1"); err != nil {
+		t.Fatal(err)
+	}
+
+	defer os.Setenv(envvar, "")
+
+	sk, err := pkcs11key.GetKeyWithURIConfig(pkcs11UriConfig, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer sk.Close()
+
+	cert, err := sk.Certificate()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if cert != nil {
+		t.Fatalf("expected certificate to be ignored while loading")
+	}
+}
+
 func TestSignAndVerify(t *testing.T) {
 	ctx := context.Background()
 
@@ -350,7 +409,7 @@ func importKey(slotID uint) error {
 	keyLabelBytes := []byte(keyLabel)
 
 	r := strings.NewReader(rsaPrivKey)
-	pemBytes, err = os.ReadAll(r)
+	pemBytes, err = io.ReadAll(r)
 	if err != nil {
 		return fmt.Errorf("unable to read pem")
 	}