Add support for parsing PKCS#1 priv/pub keys, SEC1 priv keys (#638)

This adds support for parsing RSA public and private keys, and SEC 1 EC
private keys. This should reduce unexpected format errors for library
users.

Signed-off-by: Hayden Blauzvern <hblauzvern@google.com>

pkg/cryptoutils/privatekey.go

@@ -31,7 +31,11 @@ import (
 
 const (
 	// PrivateKeyPEMType is the string "PRIVATE KEY" to be used during PEM encoding and decoding
-	PrivateKeyPEMType                PEMType = "PRIVATE KEY"
+	PrivateKeyPEMType PEMType = "PRIVATE KEY"
+	// ECPrivateKeyPEMType is the string "EC PRIVATE KEY" used to parse SEC 1 EC private keys
+	ECPrivateKeyPEMType PEMType = "EC PRIVATE KEY"
+	// PKCS1PrivateKeyPEMType is the string "RSA PRIVATE KEY" used to parse PKCS#1-encoded private keys
+	PKCS1PrivateKeyPEMType           PEMType = "RSA PRIVATE KEY"
 	encryptedCosignPrivateKeyPEMType PEMType = "ENCRYPTED COSIGN PRIVATE KEY"
 	// EncryptedSigstorePrivateKeyPEMType is the string "ENCRYPTED SIGSTORE PRIVATE KEY" to be used during PEM encoding and decoding
 	EncryptedSigstorePrivateKeyPEMType PEMType = "ENCRYPTED SIGSTORE PRIVATE KEY"
@@ -106,6 +110,10 @@ func UnmarshalPEMToPrivateKey(pemBytes []byte, pf PassFunc) (crypto.PrivateKey,
 	switch derBlock.Type {
 	case string(PrivateKeyPEMType):
 		return x509.ParsePKCS8PrivateKey(derBlock.Bytes)
+	case string(PKCS1PrivateKeyPEMType):
+		return x509.ParsePKCS1PrivateKey(derBlock.Bytes)
+	case string(ECPrivateKeyPEMType):
+		return x509.ParseECPrivateKey(derBlock.Bytes)
 	case string(EncryptedSigstorePrivateKeyPEMType), string(encryptedCosignPrivateKeyPEMType):
 		derBytes := derBlock.Bytes
 		if pf != nil {
@@ -123,7 +131,7 @@ func UnmarshalPEMToPrivateKey(pemBytes []byte, pf PassFunc) (crypto.PrivateKey,
 
 		return x509.ParsePKCS8PrivateKey(derBytes)
 	}
-	return nil, fmt.Errorf("unknown PEM file type: %v", derBlock.Type)
+	return nil, fmt.Errorf("unknown private key PEM file type: %v", derBlock.Type)
 }
 
 // MarshalPrivateKeyToDER converts a crypto.PrivateKey into a PKCS8 ASN.1 DER byte slice
@@ -134,7 +142,7 @@ func MarshalPrivateKeyToDER(priv crypto.PrivateKey) ([]byte, error) {
 	return x509.MarshalPKCS8PrivateKey(priv)
 }
 
-// MarshalPrivateKeyToPEM converts a crypto.PrivateKey into a PEM-encoded byte slice
+// MarshalPrivateKeyToPEM converts a crypto.PrivateKey into a PKCS#8 PEM-encoded byte slice
 func MarshalPrivateKeyToPEM(priv crypto.PrivateKey) ([]byte, error) {
 	derBytes, err := MarshalPrivateKeyToDER(priv)
 	if err != nil {

pkg/cryptoutils/privatekey_test.go

@@ -21,6 +21,9 @@ import (
 	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
+	"strings"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -209,3 +212,85 @@ func TestRSAPrivateKeyPEMRoundtrip(t *testing.T) {
 	}
 	verifyPrivateKeyPEMRoundtrip(t, priv)
 }
+
+func TestUnmarshalPEMToPrivateKey(t *testing.T) {
+	// test PKCS#8 PEM-encoded private keys
+	priv, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatalf("rsa.GenerateKey failed: %v", err)
+	}
+	pkcs8PrivateKey, err := x509.MarshalPKCS8PrivateKey(priv)
+	if err != nil {
+		t.Fatalf("x509.MarshalPKCS8PrivateKey failed: %v", err)
+	}
+	pkcs8PEMBlock := pem.EncodeToMemory(&pem.Block{
+		Type:  "PRIVATE KEY",
+		Bytes: pkcs8PrivateKey,
+	})
+	k, err := UnmarshalPEMToPrivateKey(pkcs8PEMBlock, nil)
+	if err != nil {
+		t.Fatalf("UnmarshalPEMToPrivateKey for PKCS#8 failed: %v", err)
+	}
+	if !priv.Equal(k) {
+		t.Fatalf("private keys for PKCS#8 are not equal")
+	}
+
+	// test PKCS#1 PEM-encoded RSA private keys
+	priv, err = rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatalf("rsa.GenerateKey failed: %v", err)
+	}
+	rsaPrivKey := x509.MarshalPKCS1PrivateKey(priv)
+	pkcs1PEMBlock := pem.EncodeToMemory(&pem.Block{
+		Type:  "RSA PRIVATE KEY",
+		Bytes: rsaPrivKey,
+	})
+	k, err = UnmarshalPEMToPrivateKey(pkcs1PEMBlock, nil)
+	if err != nil {
+		t.Fatalf("UnmarshalPEMToPrivateKey for PKCS#1 failed: %v", err)
+	}
+	if !priv.Equal(k) {
+		t.Fatalf("private keys for PKCS1 are not equal")
+	}
+
+	// test SEC 1 EC private keys
+	ecdsaKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		t.Fatalf("ecdsa.GenerateKey failed: %v", err)
+	}
+	ecPrivKey, err := x509.MarshalECPrivateKey(ecdsaKey)
+	if err != nil {
+		t.Fatalf("x509.MarshalECPrivateKey failed: %v", err)
+	}
+	ecPEMBlock := pem.EncodeToMemory(&pem.Block{
+		Type:  "EC PRIVATE KEY",
+		Bytes: ecPrivKey,
+	})
+	k, err = UnmarshalPEMToPrivateKey(ecPEMBlock, nil)
+	if err != nil {
+		t.Fatalf("UnmarshalPEMToPrivateKey for SEC 1 failed: %v", err)
+	}
+	if !ecdsaKey.Equal(k) {
+		t.Fatalf("private keys for SEC 1 (EC) are not equal")
+	}
+
+	// test Sigstore formatted private keys
+	privSigstorePEM, _, err := GeneratePEMEncodedECDSAKeyPair(elliptic.P256(), StaticPasswordFunc([]byte("pw")))
+	if err != nil {
+		t.Fatalf("GeneratePEMEncodedECDSAKeyPair failed: %v", err)
+	}
+	_, err = UnmarshalPEMToPrivateKey(privSigstorePEM, StaticPasswordFunc([]byte("pw")))
+	if err != nil {
+		t.Fatalf("UnmarshalPEMToPrivateKey for Sigstore encoded key failed: %v", err)
+	}
+
+	// test other PEM formats return an error
+	invalidPEMBlock := pem.EncodeToMemory(&pem.Block{
+		Type:  "RSA PUBLIC KEY",
+		Bytes: rsaPrivKey,
+	})
+	_, err = UnmarshalPEMToPrivateKey(invalidPEMBlock, nil)
+	if err == nil || !strings.Contains(err.Error(), "unknown private key PEM file type") {
+		t.Fatalf("expected error unmarshalling invalid PEM block, got: %v", err)
+	}
+}

pkg/cryptoutils/publickey.go

@@ -37,6 +37,8 @@ import (
 const (
 	// PublicKeyPEMType is the string "PUBLIC KEY" to be used during PEM encoding and decoding
 	PublicKeyPEMType PEMType = "PUBLIC KEY"
+	// PKCS1PublicKeyPEMType is the string "RSA PUBLIC KEY" used to parse PKCS#1-encoded public keys
+	PKCS1PublicKeyPEMType PEMType = "RSA PUBLIC KEY"
 )
 
 // subjectPublicKeyInfo is used to construct a subject key ID.
@@ -55,6 +57,8 @@ func UnmarshalPEMToPublicKey(pemBytes []byte) (crypto.PublicKey, error) {
 	switch derBytes.Type {
 	case string(PublicKeyPEMType):
 		return x509.ParsePKIXPublicKey(derBytes.Bytes)
+	case string(PKCS1PublicKeyPEMType):
+		return x509.ParsePKCS1PublicKey(derBytes.Bytes)
 	default:
 		return nil, fmt.Errorf("unknown Public key PEM file type: %v. Are you passing the correct public key?",
 			derBytes.Type)

pkg/cryptoutils/publickey_test.go

@@ -21,6 +21,8 @@ import (
 	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
 	"strings"
 	"testing"
 
@@ -252,3 +254,54 @@ func TestValidatePubKeyEd25519(t *testing.T) {
 	}
 	// Only success, ED25519 keys do not support customization
 }
+
+func TestUnmarshalPEMToPublicKey(t *testing.T) {
+	// test PKIX PEM-encoded public keys
+	priv, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatalf("rsa.GenerateKey failed: %v", err)
+	}
+	pkixPubKey, err := x509.MarshalPKIXPublicKey(priv.Public())
+	if err != nil {
+		t.Fatalf("x509.MarshalPKIXPublicKey failed: %v", err)
+	}
+	pkixPEMBlock := pem.EncodeToMemory(&pem.Block{
+		Type:  "PUBLIC KEY",
+		Bytes: pkixPubKey,
+	})
+	k, err := UnmarshalPEMToPublicKey(pkixPEMBlock)
+	if err != nil {
+		t.Fatalf("UnmarshalPEMToPublicKey for PKIX failed: %v", err)
+	}
+	if EqualKeys(priv.Public(), k) != nil {
+		t.Fatalf("public keys for PKIX are not equal")
+	}
+
+	// test PKCS#1 PEM-encoded RSA public keys
+	priv, err = rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatalf("rsa.GenerateKey failed: %v", err)
+	}
+	rsaPubKey := x509.MarshalPKCS1PublicKey(&priv.PublicKey)
+	pkcs1PEMBlock := pem.EncodeToMemory(&pem.Block{
+		Type:  "RSA PUBLIC KEY",
+		Bytes: rsaPubKey,
+	})
+	k, err = UnmarshalPEMToPublicKey(pkcs1PEMBlock)
+	if err != nil {
+		t.Fatalf("UnmarshalPEMToPublicKey for PKCS#1 failed: %v", err)
+	}
+	if EqualKeys(priv.Public(), k) != nil {
+		t.Fatalf("public keys for PKCS1 are not equal")
+	}
+
+	// test other PEM formats return an error
+	invalidPEMBlock := pem.EncodeToMemory(&pem.Block{
+		Type:  "EC PUBLIC KEY",
+		Bytes: rsaPubKey,
+	})
+	_, err = UnmarshalPEMToPublicKey(invalidPEMBlock)
+	if err == nil || !strings.Contains(err.Error(), "unknown Public key PEM file type") {
+		t.Fatalf("expected error unmarshalling invalid PEM block, got: %v", err)
+	}
+}