commit 30aad19107646ddd8e4b44bb9cc2c3aece754c4f Author: George Kadianakis desnacked@riseup.net Date: Wed Apr 13 14:47:49 2016 +0300

prop224: Revisit how overlap periods work.

Now overlap periods start 6 hours before the start of the next time period. --- proposals/224-rend-spec-ng.txt | 65 ++++++++++++++++++++++++------------------ 1 file changed, 37 insertions(+), 28 deletions(-)

diff --git a/proposals/224-rend-spec-ng.txt b/proposals/224-rend-spec-ng.txt index e270f1d..32d29de 100644 --- a/proposals/224-rend-spec-ng.txt +++ b/proposals/224-rend-spec-ng.txt @@ -639,38 +639,47 @@ Status: Draft the public key and the period.

The time at which a key might first become valid is determined by the - consensus parameter "hsdir-overlap-begins", which is an integer in - range [1,100] with default value 80. This parameter denotes a - percentage of the interval for which no overlap occurs. So for the - default interval (1500 minutes) and default overlap-begins value - (80%), new keys do not become valid for the first 1200 minutes of the - interval. - - The new shared random value must be published *before* the start of - the next overlap interval by at least enough time to ensure that - clients all get it. [TODO: how much earlier?] + consensus parameter "hsdir-overlap-begins", which is an integer in range + [1,100] with default value 75. This parameter denotes a percentage of the + interval for which no overlap occurs. So for the default interval (24 + hours) and default overlap-begins value (75%), new keys do not become valid + for the first 18 hours of the interval. Instead, keys become valid at a + random point in the last 6 hours of the 24 hours interval.

The time at which a key from the next interval becomes valid is determined by taking the first two bytes of

- OFFSET = H("interval-offset" | Key | INT_8(Next_Period_Num)) + OFFSET = H("interval-offset" | KEY | INT_8(NEXT_PERIOD_NUM))

as a big-endian integer, dividing by 65536, and treating that as a fraction of the overlap interval.

- For example, if the period is 1500 minutes long, and overlap interval - is 300 minutes long, and OFFSET begins with [90 50], then the next - key becomes valid at 1200 + 300 * (0x9050 / 65536) minutes, or - approximately 22 hours and 49 minutes after the beginning of the + For example, if the period is 1440 minutes long, and overlap interval + is 360 minutes long, and OFFSET begins with [90 50], then the next + key becomes valid at 1080 + 360 * (0x9050 / 65536) minutes, or + approximately 21 hours and 38 minutes after the beginning of the period.

- Hidden service directories should accept descriptors at least [TODO: - how much?] minutes before they would become valid, and retain them - for at least [TODO: how much?] minutes after the end of the period. + The new shared random value MUST be published *before* the overlap interval + starts so that hidden services have access to the new shared random values + in time and can calculate the upcoming set of responsible HSDirs. In our + system, new shared random values get published at 00:00UTC every day, whereas + the overlap period starts at 06:00 and finishes at 12:00UTC. + + Here is an illustration of the system: + + +------------------------------------------------------------------+ + | | + | 00:00 12:00 00:00 12:00 00:00 12:00 | + | SRV#1 TP#1 SRV#2 TP#2 SRV#3 TP#3 | + | | + | $ |-----------$-----======|-----------$-----======| | + | overlap12 overlap23 | + | | + +------------------------------------------------------------------+

- When a client is looking for a service, it must calculate its key - both for the current and for the subsequent period, to decide whether - the next period's key is valid yet. + Legend: [TP#1 = Time Period #1] + [SRV#1 = Shared Random Value #1]

2.2.3. Where to publish a service descriptor

@@ -737,14 +746,14 @@ Status: Draft Again, nodes from lower-numbered replicas are disregarded when choosing the spread for a replica.

- An HSDir should reject a descriptor if that HSDir is not one of the - first hsdir_spread_accept HSDirs for that node. Since HSDirs can't - derive other replicas of a service, hsdir_spread_accept must be at - least hsdir_n_replicas * hsdir_spread_store. + HSDirs MUST retain hidden service descriptors for 33 hours before expiring + them. That's 24 hours for the time period duration, plus 6 hours for the + maximum overlap period span, plus 3 hours for the maximum acceptable client + clock skew.

- [TODO: Incorporate the findings from proposal 143 here. But watch - out: proposal 143 did not analyze how much the set of nodes changes - over time, or how much client and host knowledge might diverge.] + Hidden services should keep their old introduction circuits open for at + least 3 hours after the descriptor expiration, so that clients with skewed + clocks can still visit them through outdated descriptors.

2.2.4. URLs for anonymous uploading and downloading