jwe: ensure we always generate appropriate content encryption key sizes

This fixes failures in some ECDH-ES + CBC scenarios. The generator is meant to generate cek's, so it should be the content algorithm's key size, not the key encryption algorithm's key size.
zlonglin · Dec 15, 2020 · 2ed99a5 · 2ed99a5
1 parent f786eda
commit 2ed99a5
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Showing 2 changed files with 4 additions and 6 deletions.
diff --git a/jwe/jwe.go b/jwe/jwe.go
@@ -33,7 +33,6 @@ func Encrypt(payload []byte, keyalg jwa.KeyEncryptionAlgorithm, key interface{},
 	}
 
 	var enc keyenc.Encrypter
-	var keysize int
 	switch keyalg {
 	case jwa.RSA1_5:
 		var pubkey rsa.PublicKey
@@ -45,7 +44,6 @@ func Encrypt(payload []byte, keyalg jwa.KeyEncryptionAlgorithm, key interface{},
 		if err != nil {
 			return nil, errors.Wrap(err, "failed to create RSA PKCS encrypter")
 		}
-		keysize = contentcrypt.KeySize()
 	case jwa.RSA_OAEP, jwa.RSA_OAEP_256:
 		var pubkey rsa.PublicKey
 		if err := keyconv.RSAPublicKey(&pubkey, key); err != nil {
@@ -56,7 +54,6 @@ func Encrypt(payload []byte, keyalg jwa.KeyEncryptionAlgorithm, key interface{},
 		if err != nil {
 			return nil, errors.Wrap(err, "failed to create RSA OAEP encrypter")
 		}
-		keysize = contentcrypt.KeySize()
 	case jwa.A128KW, jwa.A192KW, jwa.A256KW,
 		jwa.A128GCMKW, jwa.A192GCMKW, jwa.A256GCMKW,
 		jwa.PBES2_HS256_A128KW, jwa.PBES2_HS384_A192KW, jwa.PBES2_HS512_A256KW:
@@ -75,7 +72,6 @@ func Encrypt(payload []byte, keyalg jwa.KeyEncryptionAlgorithm, key interface{},
 		if err != nil {
 			return nil, errors.Wrap(err, "failed to create key wrap encrypter")
 		}
-		keysize = contentcrypt.KeySize()
 		// NOTE: there was formerly a restriction, introduced
 		// in PR #26, which disallowed certain key/content
 		// algorithm combinations. This seemed bogus, and
@@ -86,6 +82,7 @@ func Encrypt(payload []byte, keyalg jwa.KeyEncryptionAlgorithm, key interface{},
 			return nil, errors.Errorf("failed to build %s key encrypter", keyalg)
 		}
 
+		var keysize int
 		switch keyalg {
 		case jwa.ECDH_ES:
 			// https://tools.ietf.org/html/rfc7518#page-15
@@ -111,6 +108,7 @@ func Encrypt(payload []byte, keyalg jwa.KeyEncryptionAlgorithm, key interface{},
 		return nil, errors.Errorf(`invalid key encryption algorithm (%s)`, keyalg)
 	}
 
+	keysize := contentcrypt.KeySize()
 	if pdebug.Enabled {
 		pdebug.Printf("Encrypt: keysize = %d", keysize)
 	}

diff --git a/jwx_test.go b/jwx_test.go
@@ -171,9 +171,9 @@ func TestJoseCompatibility(t *testing.T) {
 			{jwa.RSA_OAEP_256, jwa.A256CBC_HS512},
 			// {jwa.ECDH_ES, jwa.A256CBC_HS512},
 			{jwa.ECDH_ES_A128KW, jwa.A128GCM},
-			// {jwa.ECDH_ES_A128KW, jwa.A128CBC_HS256},
+			{jwa.ECDH_ES_A128KW, jwa.A128CBC_HS256},
 			{jwa.ECDH_ES_A256KW, jwa.A256GCM},
-			// {jwa.ECDH_ES_A256KW, jwa.A256CBC_HS512},
+			{jwa.ECDH_ES_A256KW, jwa.A256CBC_HS512},
 			{jwa.A128KW, jwa.A128GCM},
 			{jwa.A128KW, jwa.A128CBC_HS256},
 			{jwa.A256KW, jwa.A256GCM},