问题
Setup
- Java doesn't offer out-of-the-box support for the JCE Unlimited Strength Policy Files
- This prevents users from using AES-256, the largest key size of a widely-used encryption standard
- Not including the policy files leads to many problems:
- Unexpected exceptions
- Unsatisfying workarounds:
- Just install them
- Use a different implementation
- Use reflection that may violate the Java License Agreement
- Breakage after JRE updates
- Confusion after installation
- And more!
- All this noise leads to broken and/or buggy programs
Question
- Why are these not provided and treated like a black sheep?
回答1:
- As it turns out, it's not strict crypto export laws, but simply that no one got around to it yet.
- In fact, it's been planned for a long time to not have to jump through these hoops.
- In Java 9, the ceremony will be condensed down to a one-liner:
Security.setProperty("crypto.policy", "unlimited");
回答2:
Now Unlimited cryptography enabled by default in the JDK
The JDK uses the Java Cryptography Extension (JCE) Jurisdiction Policy files to configure cryptographic algorithm restrictions. Previously, the Policy files in the JDK placed limits on various algorithms. This release ships with both the limited and unlimited jurisdiction policy files, with unlimited being the default. The behavior can be controlled via the new 'crypto.policy' Security property found in the /lib/java.security file. Please refer to that file for more information on this property.
See: http://www.oracle.com/technetwork/java/javase/8u161-relnotes-4021379.html#JDK-8170157
回答3:
The US has restrictions on the export of cryptographic technology:
https://en.wikipedia.org/wiki/Export_of_cryptography_from_the_United_States
They used to be very strict -- cryptography was classified as munitions, and you could only download the full strength products from the US and other whitelisted countries.
Restrictions have eased up a lot since then, but some remain, and full strength JCE can't be freely distributed everywhere like the JRE, so it's a separate package.
来源：https://stackoverflow.com/questions/42159690/why-are-the-jce-unlimited-strength-not-included-by-default