BoxBuffer wraps either BoxReader for reading or BufferWriter for writing.
Thus it is capable of doing either reading or writing, but not both.
Change-Id: Id57370755a586bfdef1291a23af29f5b1feec903
FixedEncryptorSource takes hardcoded key id and content key.
Implemented an AES Encryptor using OpenSSL.
Change-Id: I59ba9a41fc0f40925d697045dd1b147b7351c2f9
The BufferWriter is capable of appending various data types to buffer.
No optimization is done yet. We may consider optimize it for
appending (adding data to the tail) later.
Change-Id: I3b8e749e410c7ea4d4f2fb855e27744131c63cb0
Kongqun Yang