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| -rw-r--r-- | doc/design.md | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/doc/design.md b/doc/design.md index e155762..9030091 100644 --- a/doc/design.md +++ b/doc/design.md @@ -284,11 +284,15 @@ its inclusion proof. 3. The provided tree head is from a known log with enough valid cosignatures. Notice that there are no new outbound network connections for a verifier. -Therefore, a proof of public logging is only as convincing as the tree head that -an inclusion proof leads up to. Sigsum logs have trustworthy tree heads thanks to -using a variant of witness cosigning. A verifier cannot be -tricked into accepting data whose checksum have not been publicly logged -unless the attacker controls more than a threshold of witnesses. +Therefore, a verifier will not be affected by future log downtime since the +signer already collected relevant proofs of public logging. Log downtime may be +caused by temporary operational issues or simply because a shard is done. + +The lack of external communication means that a proof of public logging cannot +be more convincing than the tree head an inclusion proof leads up to. Sigsum +logs have trustworthy tree heads thanks to using a variant of witness cosigning. +A verifier cannot be tricked into accepting data whose checksum have not been +publicly logged unless the attacker controls more than a threshold of witnesses. In a less ideal world sigsum logging can facilitate detection of attacks if a verifier _fails open_ by enforcing the second and third criteria partially. For @@ -353,6 +357,10 @@ set it as large as possible. If a verified timestamp is needed to reason about the time of logging, you may use a cosigned tree head instead [\[TS\]](https://git.sigsum.org/sigsum/commit/?id=fef460586e847e378a197381ef1ae3a64e6ea38b). +A log operator that shuts down a completed shard will not effect verifiers. In +other words, a signer can continue to distribute proofs that were once +collected. This is important because a checksum does not necessarily expire. + #### 4.3 - What is the point of having a domain hint? Domain hints help log operators combat spam. By verifying that every signer controls a domain name that is aware of their public key, rate limits can be |