crypto: clarify missing cipher error

Explain that a cipher is required when a passphrase is provided.

Signed-off-by: Filip Skokan <panva.ip@gmail.com>

Author: panva

lib/internal/crypto/keys.js

@@ -470,7 +470,9 @@ function parseKeyEncoding(enc, keyType, isPublic, objName) {
             encodingNames[type], 'does not support encryption');
         }
       } else if (passphrase !== undefined) {
-        throw new ERR_INVALID_ARG_VALUE(option('cipher', objName), cipher);
+        throw new ERR_INVALID_ARG_VALUE(
+          option('cipher', objName), cipher,
+          'is required when a passphrase is specified');
       }
     }
 

test/parallel/test-crypto-key-objects.js

@@ -1014,7 +1014,8 @@ if (!process.features.openssl_is_boringssl) {
   }, {
     name: 'TypeError',
     code: 'ERR_INVALID_ARG_VALUE',
-    message: "The property 'options.cipher' is invalid. Received undefined"
+    message: "The property 'options.cipher' is required when a " +
+      'passphrase is specified. Received undefined',
   });
 }