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* Say what an attacker on the path could do to a link, and what now stops it (098)eunhhu2026-09-291-3/+8
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* Close what an attacker on the path could do to a link, each checkedeunhhu2026-09-291-10/+264
| | | | | | | | | | | | | | | | | | | | | | | | | | | | test-link now also plays an attacker: packets changed on the way, packets of the past sent again from the sender's address and its own, keys and sources not allowed, and a flood of made-up packets. It found: - A nonce used twice: a receiver sealed every answer in its one run, and a sender at rest coming back with the same run got a new slot whose answers began at number 0 again under the same key. Each slot now draws the run its answers are sealed in. - A link stopped for good by one packet of the past: a stream that did not know its last heard (after a restart or a rest) handed over from its first record held, and a stale part of an old one never came whole. It hands over from its first whole record. - Answers taken away: any packet that opened, however old, moved where answers went. Only the newest of its run moves it now; a new address is sent a challenge the sender says back (CHALLENGE, RESPONSE), and until then gets at most three times the bytes that came from it. - An answer made by a packet that did not open: a number heard before was acknowledged before the packet was opened. It is opened first. - An old answer lowering the sender's credit, or its gap making it send again: the sender now sends up to the most heard and credit it was told, and takes a gap only from a word not older than it knows. - Ten thousand made-up packets made ten thousand keys: keys made for a run that did not open now cost a token, 256 a second. Counts now say runs keyed and secrets made.
* Find how large a packet the path carries: 1,452 bytes once a probe is ↵eunhhu2026-09-291-2/+2
| | | | | | | | | | | | | | | acknowledged A link starts at 1,200 bytes; once an RTT is known it sends a PING padded to 1,452 (DPLPMTUD, RFC 8899), alone and with the don't-fragment bit, and uses that size once it is acknowledged. A probe lost is no congestion; it is tried again a second on, three times, then ten minutes on. GSO is asked for each burst (a control message), not the socket, so a packet sent alone is never cut. CUBIC counts in the datagram. On loopback packets fall by 19-27%; the CPU a record falls 13% at 1 KiB and 7% at 16 KiB; in the simulator of a 50 Mbit/s path with 1% loss the goodput rises from 6.1 to 7.0 Mbit/s (5%: 2.3 to 3.0).
* Keep a link's two sides as state alone, the sockets and threads aparteunhhu2026-09-291-0/+300
link/link-protocol.h is the protocol with no socket, thread or clock of its own: packets and time in, packets out. link/link.h carries it over UDP as before. A sender starts small (8 flights, 16 records, a 4 KiB ring) so one thread can hold many. The transport's CPU a record is the same within 2% (five rounds each way, 61 B to 16 KiB). test-link runs both sides through a network of its own: loss, packets held back and doubled, failed saves, an idle sweep, and both sides starting again, every record applied once as sent.