How Can We Avoid Installing Unlimited Strength JCE Policy Files While Maintaining Strong Encryption?

Mitigating Reliance on "Unlimited Strength" JCE Policy Files

When deploying applications that employ high-strength encryption (e.g., 256-bit AES), developers often face the challenge of ensuring adequate support for such encryption on end-user machines. While installing the "Unlimited Strength" JCE policy files in the security folder resolves this issue for developers, distributing these files to end-users can be inconvenient or impractical.

Alternatives to Installing Policy Files

Two common approaches exist:

• Skipping the JCE API: Using alternative cryptography libraries like Bouncy Castle avoids the need for policy files, but introduces the burden of an additional 1MB library and a different API.
• Reflection: This unconventional technique involves manipulating the restricted fields of javax.crypto.JceSecurity via reflection. It removes limitations on key strength and allows the application to function without overwriting files on end-user machines.

The Reflection Approach in Detail

The following Java code demonstrates the reflection-based approach:

private static void removeCryptographyRestrictions() {
    // Check if restrictions exist
    if (!isRestrictedCryptography()) {
        return;
    }

    try {
        // ... (Reflection to remove restrictions)
        logger.fine("Successfully removed cryptography restrictions");
    } catch (Exception e) {
        logger.log(Level.WARNING, "Failed to remove cryptography restrictions", e);
    }
}

private static boolean isRestrictedCryptography() {
    // Check for specific Java versions (Oracle Java 7 and 8) where restrictions apply
    // ...
}

Simply calling removeCryptographyRestrictions() from a static initializer or before performing cryptographic operations enables the use of 256-bit ciphers and TLS cipher suites without installing policy files.

Limitations

While the reflection approach effectively bypasses policy file requirements, it remains an imperfect solution:

• It only works on Oracle Java 7 and 8.
• It may not be supported by non-Oracle Java VMs.
• The implementation relies on obfuscation techniques, potentially affecting compatibility with Oracle Java 6.

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