Add (jwk.Key).Validate (#1005)

* Add (jwk.Key).Validate

* Appease linter

* Update WithValidateKey, and add tests+docs

* appease linter

Changes

@@ -25,6 +25,22 @@ v2.0.16 UNRELEASED
     fail. Therefore this in itself should not pose any security risk, albeit
     allowing some illegally formated messages to be verified.
 
+  * [jwk] `jwk.Key` objects now have a `Validate()` method to validate the data
+    stored in the keys. However, this still does not necessarily mean that the key's
+    are valid for use in cryptographic operations. If `Validate()` is successful,
+    it only means that the keys are in the right _format_, including the presence
+    of required fields and that certain fields are have proper length, etc.
+
+[New Features]
+  * [jws] Added `jws.WithValidateKey()` to force calling `key.Validate()` before
+    signing or verification.
+
+  * [jws] `jws.Sign()` now returns a special type of error that can hold the
+    individual errors from the signers. The stringification is still the same
+    as before to preserve backwards compatibility.
+
+  * [jwk] Added `jwk.IsKeyValidationError` that checks if an error is an error
+    from `key.Validate()`.
 
 v2.0.15 19 20 Oct 2023
 [Bug fixes]

jwk/ecdsa.go

@@ -226,3 +226,48 @@ func (k ecdsaPrivateKey) Thumbprint(hash crypto.Hash) ([]byte, error) {
 		base64.EncodeToString(ybuf),
 	), nil
 }
+
+func ecdsaValidateKey(k interface {
+	Crv() jwa.EllipticCurveAlgorithm
+	X() []byte
+	Y() []byte
+}, checkPrivate bool) error {
+	crv, ok := ecutil.CurveForAlgorithm(k.Crv())
+	if !ok {
+		return fmt.Errorf(`invalid curve algorithm %q`, k.Crv())
+	}
+
+	keySize := ecutil.CalculateKeySize(crv)
+	if x := k.X(); len(x) != keySize {
+		return fmt.Errorf(`invalid "x" length (%d) for curve %q`, len(x), crv.Params().Name)
+	}
+
+	if y := k.Y(); len(y) != keySize {
+		return fmt.Errorf(`invalid "y" length (%d) for curve %q`, len(y), crv.Params().Name)
+	}
+
+	if checkPrivate {
+		if priv, ok := k.(interface{ D() []byte }); ok {
+			if len(priv.D()) != keySize {
+				return fmt.Errorf(`invalid "d" length (%d) for curve %q`, len(priv.D()), crv.Params().Name)
+			}
+		} else {
+			return fmt.Errorf(`missing "d" value`)
+		}
+	}
+	return nil
+}
+
+func (k *ecdsaPrivateKey) Validate() error {
+	if err := ecdsaValidateKey(k, true); err != nil {
+		return NewKeyValidationError(fmt.Errorf(`jwk.ECDSAPrivateKey: %w`, err))
+	}
+	return nil
+}
+
+func (k *ecdsaPublicKey) Validate() error {
+	if err := ecdsaValidateKey(k, false); err != nil {
+		return NewKeyValidationError(fmt.Errorf(`jwk.ECDSAPublicKey: %w`, err))
+	}
+	return nil
+}

jwk/jwk.go

@@ -12,6 +12,7 @@ import (
 	"crypto/rsa"
 	"crypto/x509"
 	"encoding/pem"
+	"errors"
 	"fmt"
 	"io"
 	"math/big"
@@ -757,3 +758,32 @@ func IsPrivateKey(k Key) (bool, error) {
 	}
 	return false, fmt.Errorf("jwk.IsPrivateKey: %T is not an asymmetric key", k)
 }
+
+type keyValidationError struct {
+	err error
+}
+
+func (e *keyValidationError) Error() string {
+	return fmt.Sprintf(`key validation failed: %s`, e.err)
+}
+
+func (e *keyValidationError) Unwrap() error {
+	return e.err
+}
+
+func (e *keyValidationError) Is(target error) bool {
+	_, ok := target.(*keyValidationError)
+	return ok
+}
+
+// NewKeyValidationError wraps the given error with an error that denotes
+// `key.Validate()` has failed. This error type should ONLY be used as
+// return value from the `Validate()` method.
+func NewKeyValidationError(err error) error {
+	return &keyValidationError{err: err}
+}
+
+func IsKeyValidationError(err error) bool {
+	var kve keyValidationError
+	return errors.Is(err, &kve)
+}

jwk/jwk_internal_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 
 	"github.com/lestrrat-go/jwx/v2/cert"
+	"github.com/lestrrat-go/jwx/v2/internal/base64"
 	"github.com/lestrrat-go/jwx/v2/internal/json"
 	"github.com/lestrrat-go/jwx/v2/jwa"
 	"github.com/stretchr/testify/assert"
@@ -129,9 +130,18 @@ func TestIterator(t *testing.T) {
 		{
 			Extras: map[string]interface{}{
 				ECDSACrvKey: jwa.P256,
-				ECDSAXKey:   []byte("MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4"),
-				ECDSAYKey:   []byte("4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM"),
-				ECDSADKey:   []byte("870MB6gfuTJ4HtUnUvYMyJpr5eUZNP4Bk43bVdj3eAE"),
+				ECDSAXKey: (func() []byte {
+					s, _ := base64.DecodeString("MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4")
+					return s
+				})(),
+				ECDSAYKey: (func() []byte {
+					s, _ := base64.DecodeString("4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM")
+					return s
+				})(),
+				ECDSADKey: (func() []byte {
+					s, _ := base64.DecodeString("870MB6gfuTJ4HtUnUvYMyJpr5eUZNP4Bk43bVdj3eAE")
+					return s
+				})(),
 			},
 			Func: func() Key {
 				return newECDSAPrivateKey()
@@ -140,8 +150,14 @@ func TestIterator(t *testing.T) {
 		{
 			Extras: map[string]interface{}{
 				ECDSACrvKey: jwa.P256,
-				ECDSAXKey:   []byte("MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4"),
-				ECDSAYKey:   []byte("4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM"),
+				ECDSAXKey: (func() []byte {
+					s, _ := base64.DecodeString("MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4")
+					return s
+				})(),
+				ECDSAYKey: (func() []byte {
+					s, _ := base64.DecodeString("4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM")
+					return s
+				})(),
 			},
 			Func: func() Key {
 				return newECDSAPublicKey()
@@ -184,6 +200,7 @@ func TestIterator(t *testing.T) {
 			}
 
 			if !assert.NoError(t, json.Unmarshal(buf, key2), `json.Unmarshal should succeed`) {
+				t.Logf("%s", buf)
 				return
 			}
 

jwk/jwk_test.go

@@ -2217,3 +2217,54 @@ func TestGH947(t *testing.T) {
 	var exported []byte
 	require.Error(t, k.Raw(&exported), `(okpkey).Raw with 0-length OKP key should fail`)
 }
+
+func TestValidation(t *testing.T) {
+	{
+		key, err := jwxtest.GenerateRsaJwk()
+		require.NoError(t, err, `jwx.GenerateRsaJwk should succeed`)
+		require.NoError(t, key.Validate(), `key.Validate should succeed (vanilla key)`)
+
+		require.NoError(t, key.Set(jwk.RSADKey, []byte(nil)), `key.Set should succeed`)
+		require.Error(t, key.Validate(), `key.Validate should fail`)
+	}
+
+	{
+		key, err := jwxtest.GenerateEcdsaJwk()
+		require.NoError(t, err, `jwx.GenerateEcdsaJwk should succeed`)
+		require.NoError(t, key.Validate(), `key.Validate should succeed`)
+
+		x := key.(jwk.ECDSAPrivateKey).X()
+		require.NoError(t, key.Set(jwk.ECDSAXKey, x[:len(x)/2]), `key.Set should succeed`)
+		require.Error(t, key.Validate(), `key.Validate should fail`)
+
+		require.NoError(t, key.Set(jwk.ECDSAXKey, x), `key.Set should succeed`)
+		require.NoError(t, key.Validate(), `key.Validate should succeed`)
+
+		require.NoError(t, key.Set(jwk.ECDSADKey, []byte(nil)), `key.Set should succeed`)
+		require.Error(t, key.Validate(), `key.Validate should fail`)
+	}
+
+	{
+		key, err := jwxtest.GenerateEd25519Jwk()
+		require.NoError(t, err, `jwx.GenerateEd25519Jwk should succeed`)
+		require.NoError(t, key.Validate(), `key.Validate should succeed`)
+		x := key.(jwk.OKPPrivateKey).X()
+		require.NoError(t, key.Set(jwk.OKPXKey, []byte(nil)), `key.Set should succeed`)
+		require.Error(t, key.Validate(), `key.Validate should fail`)
+
+		require.NoError(t, key.Set(jwk.OKPXKey, x), `key.Set should succeed`)
+		require.NoError(t, key.Validate(), `key.Validate should succeed`)
+
+		require.NoError(t, key.Set(jwk.OKPDKey, []byte(nil)), `key.Set should succeed`)
+		require.Error(t, key.Validate(), `key.Validate should fail`)
+	}
+
+	{
+		key, err := jwxtest.GenerateSymmetricJwk()
+		require.NoError(t, err, `jwx.GenerateSymmetricJwk should succeed`)
+		require.NoError(t, key.Validate(), `key.Validate should succeed`)
+
+		require.NoError(t, key.Set(jwk.SymmetricOctetsKey, []byte(nil)), `key.Set should succeed`)
+		require.Error(t, key.Validate(), `key.Validate should fail`)
+	}
+}

jwk/okp.go

@@ -187,3 +187,41 @@ func (k okpPrivateKey) Thumbprint(hash crypto.Hash) ([]byte, error) {
 		base64.EncodeToString(k.x),
 	), nil
 }
+
+func validateOKPKey(key interface {
+	Crv() jwa.EllipticCurveAlgorithm
+	X() []byte
+}) error {
+	if key.Crv() == jwa.InvalidEllipticCurve {
+		return fmt.Errorf(`invalid curve algorithm`)
+	}
+
+	if len(key.X()) == 0 {
+		return fmt.Errorf(`missing "x" field`)
+	}
+
+	if priv, ok := key.(interface{ D() []byte }); ok {
+		if len(priv.D()) == 0 {
+			return fmt.Errorf(`missing "d" field`)
+		}
+	}
+	return nil
+}
+
+func (k *okpPublicKey) Validate() error {
+	k.mu.RLock()
+	defer k.mu.RUnlock()
+	if err := validateOKPKey(k); err != nil {
+		return NewKeyValidationError(fmt.Errorf(`jwk.OKPPublicKey: %w`, err))
+	}
+	return nil
+}
+
+func (k *okpPrivateKey) Validate() error {
+	k.mu.RLock()
+	defer k.mu.RUnlock()
+	if err := validateOKPKey(k); err != nil {
+		return NewKeyValidationError(fmt.Errorf(`jwk.OKPPrivateKey: %w`, err))
+	}
+	return nil
+}

jwk/rsa.go

@@ -241,3 +241,43 @@ func rsaThumbprint(hash crypto.Hash, key *rsa.PublicKey) ([]byte, error) {
 	}
 	return h.Sum(nil), nil
 }
+
+func validateRSAKey(key interface {
+	N() []byte
+	E() []byte
+}, checkPrivate bool) error {
+	if len(key.N()) == 0 {
+		// Ideally we would like to check for the actual length, but unlike
+		// EC keys, we have nothing in the key itself that will tell us
+		// how many bits this key should have.
+		return fmt.Errorf(`missing "n" value`)
+	}
+	if len(key.E()) == 0 {
+		return fmt.Errorf(`missing "e" value`)
+	}
+	if checkPrivate {
+		if priv, ok := key.(interface{ D() []byte }); ok {
+			if len(priv.D()) == 0 {
+				return fmt.Errorf(`missing "d" value`)
+			}
+		} else {
+			return fmt.Errorf(`missing "d" value`)
+		}
+	}
+
+	return nil
+}
+
+func (k *rsaPrivateKey) Validate() error {
+	if err := validateRSAKey(k, true); err != nil {
+		return NewKeyValidationError(fmt.Errorf(`jwk.RSAPrivateKey: %w`, err))
+	}
+	return nil
+}
+
+func (k *rsaPublicKey) Validate() error {
+	if err := validateRSAKey(k, false); err != nil {
+		return NewKeyValidationError(fmt.Errorf(`jwk.RSAPublicKey: %w`, err))
+	}
+	return nil
+}

jwk/symmetric.go

@@ -58,3 +58,10 @@ func (k *symmetricKey) PublicKey() (Key, error) {
 	}
 	return newKey, nil
 }
+
+func (k *symmetricKey) Validate() error {
+	if len(k.Octets()) == 0 {
+		return NewKeyValidationError(fmt.Errorf(`jwk.SymmetricKey: missing "k" field`))
+	}
+	return nil
+}