authenticate each frame before parsing its contents. Each connection
starts with a tag, followed by any number of frames, each starting
with the frame number (32 bits) and payload length (16 bits), and
ending with a MAC (256 bits).
Tags have the following format: 32 bits reserved, 16 bits for the
transport ID, 32 bits for the connection number, 32 bits (set to zero
in the tag) for the frame number, and 16 bits (set to zero in the tag)
for the block number. The tag is encrypted with the tag key in
ECB mode.
Frame numbers for each connection must start from zero and must be
contiguous and strictly increasing. Each frame is encrypted with the
frame key in CTR mode, using the plaintext tag with the appropriate
frame number to initialise the counter.
The maximum frame size is 64 KiB, including header and footer. The
maximum amount of data that can be sent over a connection is 2^32
frames - roughly 2^48 bytes, or 8 terabytes, with the maximum frame
size of 64 KiB. If that isn't sufficient we can add another 16 bits to
the frame counter.
allow writers to starve. If this test passes on Java 5 and 6, we can
get rid of SynchronizedDatabaseComponent and merge
ReadWriteLockDatabaseComponent with DatabaseComponentImpl.
acceptable timestamp of subscribed messages. For a new subscription,
the timestamp is initialised to the current time, so a new subscriber
to a group will not immediately receive any messages. (Subscribing to
a group is therefore more like joining a mailing list than joining a
Usenet group - you only receive messages written after you joined.)
Once the database fills up and starts expiring messages, the
timestamps of subscriptions are updated so that contacts need not send
messages that would expire immediately. This is done using the
*approximate* timestamp of the oldest message in the database, to
avoid revealing the presence or absence of any particular message.
database - unlike transport properties, these are not shared with
contacts. For example, when using email as a transport, the address
for sending and receiving emails would be a transport property, while
the username and password for the email server would be transport
configuration details. Transport plugins can update their
configuration details atomically.
Also clarified the terminology for transport and subscription updates.
arrays, check it before allocating the buffer, and always specify the
maximum length when reading untrusted data - otherwise
CountingConsumer will reject the packet, but not before we've tried to
allocate a buffer of the specified size (up to 2 GB).
called when new messages are available, and a new method
hasSendableMessages(ContactId) that listeners can call to see whether
it's worth trying to create a batch.
