Pool options

	A	B	C	D	E	F
1		Upgrade from IP	DNS SRV records	Shared domain name	NTS-KE generating cookies	NTS-KE load balancer
2	Key material
3	Pool domain tls certificates	No one	No one	All ntp providers	Pool only	Pool only
4	Provider domain tls certificate	Ntp provider (1)	Ntp provider	None needed	None needed	Ntp provider
5	Cookie keys	Ntp provider	Ntp provider	Ntp provider	Ntp provider + pool	Ntp provider
6	Session keys	Ntp provider	Ntp provider	Ntp provider (2)	Ntp provider + pool	Ntp provider + pool
7	Environment requirements
8	Needs client DNSSec validation (3)	Yes	Yes	No	No	No
9	Security implications
10	Non-pool providers can't MITM	Yes	Yes	Yes	Yes	Yes
11	Ntp provider can't MITM	Yes	Yes	No	Yes	Yes
12	Pool can't read/modify client traffic	Maybe (5)	Maybe (5)	Maybe (5)	No	No
13	Ntp provider can't read/modify others' traffic	Yes	Yes	No	Yes	Yes
14	Implementation
15	Requires server modifications	No	No	No	Maybe (4)	Yes
16	Requires client modifications	Yes	Yes	No	No	No
17	NTS Pool is interchangable with ordinary server	Yes	No	Yes	Yes	Yes
18	Load scaling
19	Pool TLS handshakes (6)	0	0	0	N	N+O(K) (7)
20	NTP Provider TLS handshakes (6)	N/K	N/K	N/K	0	O(1) (7)
21	Client TLS sessions	1	1	1	1	1
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23	Notes:
24	1) This needs to be an IP certificate, which requires IP ownership. This may be hard/impossible for the average pool server operator.
25	2) Because of the shared certificates, any ntp provider in the pool can MITM all the traffic to it. This renders the setup insecure!
26	3) DNSSec validation is not yet standard on most computers, and notably has significant issues in systemd.
27	4) Key material that is rotated quite often needs to be exchanged with the pool, which is probably best done automatically.
28	5) A pool can always only return ntp providers it controls, hence giving it access to client traffic.
29	6) N is the number of clients, K the number of NTP providers
30	7) Number of TLS handshakes depends on loadbalancing characteristics of pool provider
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