key length can be obtained from the key

core/src/main/java/hudson/model/UsageStatistics.java

@@ -226,8 +226,8 @@ public class UsageStatistics extends PageDecorator {
             super.in = new CipherInputStream(in,sym);
         }
 
-        public CombinedCipherInputStream(InputStream in, RSAKey key, String algorithm, int keyLength) throws IOException, GeneralSecurityException {
-            this(in,toCipher(key,Cipher.DECRYPT_MODE),algorithm,keyLength);
+        public CombinedCipherInputStream(InputStream in, RSAKey key, String algorithm) throws IOException, GeneralSecurityException {
+            this(in,toCipher(key,Cipher.DECRYPT_MODE),algorithm,key.getModulus().bitLength());
         }
     }
 

test/src/test/java/hudson/model/UsageStatisticsTest.java

@@ -57,7 +57,7 @@ public class UsageStatisticsTest extends HudsonTestCase {
 
         byte[] cipherText = Base64.decode(data.toCharArray());
         InputStreamReader r = new InputStreamReader(new GZIPInputStream(
-                new CombinedCipherInputStream(new ByteArrayInputStream(cipherText),priv,"AES",1024)), "UTF-8");
+                new CombinedCipherInputStream(new ByteArrayInputStream(cipherText),priv,"AES")), "UTF-8");
         JSONObject o = JSONObject.fromObject(IOUtils.toString(r));
         System.out.println(o);
         assertEquals(1,o.getInt("stat"));