Question : how to random access or skip during decryption

### Problem:

I have a need to handle large files and service a random address range for decryption.
Looking throgh the exampes I dont see an effecient way to do this.
It seems that the underlying encryption data is framed, but the CryptoInputStream doesn't skip in an input stream, and there isnt a support for a Readable Channel that I am aware of

### Solution:
With the existing API - I could use skip in the InputStream, but this will (as I see it) decrypt and throw away the skipped bytes, with extra I/O and CPU load
With an enhanced implementation we could skip on the input stream to the start of a frame and then decrypt that frame (skipping internally to the offset needed by decodng and thowin a few bytes if needed)

### Out of scope:

从现有的 CryptoInputStream API 及其分帧加密输入行为入手，然后将 InputStream.skip 与所请求的 Readable Channel 支持进行比较。完成的标准是：调用方可以通过 seek 到相关帧来处理任意地址范围，并避免对被丢弃字节进行解密和 I/O。

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