crypto: re-add padding for AES-KW wrapped JWKs

PR-URL: #46563
Reviewed-By: James M Snell <jasnell@gmail.com>
Backport-PR-URL: #47383

lib/internal/crypto/webcrypto.js

@@ -8,6 +8,7 @@ const {
   ReflectApply,
   ReflectConstruct,
   SafeSet,
+  StringPrototypeRepeat,
   SymbolToStringTag,
 } = primordials;
 
@@ -681,7 +682,16 @@ async function wrapKey(format, key, wrappingKey, algorithm) {
   let keyData = await ReflectApply(exportKey, this, [format, key]);
 
   if (format === 'jwk') {
-    keyData = new TextEncoder().encode(JSONStringify(keyData));
+    const ec = new TextEncoder();
+    const raw = JSONStringify(keyData);
+    // As per the NOTE in step 13 https://w3c.github.io/webcrypto/#SubtleCrypto-method-wrapKey
+    // we're padding AES-KW wrapped JWK to make sure it is always a multiple of 8 bytes
+    // in length
+    if (algorithm.name === 'AES-KW' && raw.length % 8 !== 0) {
+      keyData = ec.encode(raw + StringPrototypeRepeat(' ', 8 - (raw.length % 8)));
+    } else {
+      keyData = ec.encode(raw);
+    }
   }
 
   return cipherOrWrap(

test/parallel/test-webcrypto-wrap-unwrap.js

@@ -199,6 +199,10 @@ function getFormats(key) {
 // material length must be a multiple of 8.
 // If the wrapping algorithm is RSA-OAEP, the exported key
 // material maximum length is a factor of the modulusLength
+//
+// As per the NOTE in step 13 https://w3c.github.io/webcrypto/#SubtleCrypto-method-wrapKey
+// we're padding AES-KW wrapped JWK to make sure it is always a multiple of 8 bytes
+// in length
 async function wrappingIsPossible(name, exported) {
   if ('byteLength' in exported) {
     switch (name) {
@@ -207,13 +211,8 @@ async function wrappingIsPossible(name, exported) {
       case 'RSA-OAEP':
         return exported.byteLength <= 446;
     }
-  } else if ('kty' in exported) {
-    switch (name) {
-      case 'AES-KW':
-        return JSON.stringify(exported).length % 8 === 0;
-      case 'RSA-OAEP':
-        return JSON.stringify(exported).length <= 478;
-    }
+  } else if ('kty' in exported && name === 'RSA-OAEP') {
+    return JSON.stringify(exported).length <= 478;
   }
   return true;
 }