From d6a592e10da7f6fc347bb3355f70e89ef2c1b08d Mon Sep 17 00:00:00 2001
From: Robinson <robinson@dorkbox.com>
Date: Fri, 13 Jan 2023 00:50:32 +0100
Subject: [PATCH] Added ability to check if crypto restrictions are in place

---
 src/dorkbox/util/crypto/Crypto.java | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/src/dorkbox/util/crypto/Crypto.java b/src/dorkbox/util/crypto/Crypto.java
index 67aac23..c3ec0ff 100644
--- a/src/dorkbox/util/crypto/Crypto.java
+++ b/src/dorkbox/util/crypto/Crypto.java
@@ -22,6 +22,7 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.nio.ByteBuffer;
 import java.nio.charset.StandardCharsets;
+import java.security.NoSuchAlgorithmException;
 import java.security.Provider;
 import java.security.Security;
 import java.util.Arrays;
@@ -29,6 +30,8 @@ import java.util.Enumeration;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 
+import javax.crypto.Cipher;
+
 import org.bouncycastle.crypto.Digest;
 import org.bouncycastle.crypto.PBEParametersGenerator;
 import org.bouncycastle.crypto.digests.MD5Digest;
@@ -84,6 +87,21 @@ class Crypto {
         }
     }
 
+    /**
+     * Determines if cryptography restrictions apply.
+     * Restrictions apply if the value of {@link Cipher#getMaxAllowedKeyLength(String)} returns a value smaller than {@link Integer#MAX_VALUE} if there are any restrictions according to the JavaDoc of the method.
+     * This method is used with the transform <code>"AES/CBC/PKCS5Padding"</code> as this is an often used algorithm that is <a href="https://docs.oracle.com/javase/8/docs/technotes/guides/security/StandardNames.html#impl">an implementation requirement for Java SE</a>.
+     *
+     * @return <code>true</code> if restrictions apply, <code>false</code> otherwise
+     */
+    public static boolean restrictedCryptography() {
+        try {
+            return Cipher.getMaxAllowedKeyLength("AES/CBC/PKCS5Padding") < Integer.MAX_VALUE;
+        } catch (final NoSuchAlgorithmException e) {
+            throw new IllegalStateException("The transform \"AES/CBC/PKCS5Padding\" is not available (the availability of this algorithm is mandatory for Java SE implementations)", e);
+        }
+    }
+
 
     public static
     byte[] hashFileMD5(File file) {