Worker: fix potentially incorrect signatures for some small payloads #742
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There was an issue with small payloads (well potentially larger too, but exceedingly unlikely) which could cause the payloads to not serialize correctly which could cause signatures to be incorrect in same rare scenarios likely only affecting small payloads. If memory serves, serde parses and stringifies json in a non-deterministic way. Normally it would be deterministic, but it also maintains an internal cache of "json structures", and if it thinks that it can reuse one it does. This means that if there's a "cache hit", which I'm not sure about the circumstances, it can reuse one of those and therefore generate a different string. Why does it matter? Because instead of using the string representation of the payload, we were passing a `Json::Value` around and stringifying and parsing it in multiple places. This is both inefficient, and incorrect. Cryptographic hashes (like the ones used by the Svix signature scheme) are very sensitive to even the slightest changes, not to mention reordering, so we must use the same payload everywhere. We can't just hope it'll be the same when strinigifying later.
svix-gabriel
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tasn
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Dec 27, 2022
…742) There was an issue with small payloads (well potentially larger too, but exceedingly unlikely) which could cause the payloads to not serialize correctly which could cause signatures to be incorrect in same rare scenarios likely only affecting small payloads. If memory serves, serde parses and stringifies json in a non-deterministic way. Normally it would be deterministic, but it also maintains an internal cache of "json structures", and if it thinks that it can reuse one it does. This means that if there's a "cache hit", which I'm not sure about the circumstances, it can reuse one of those and therefore generate a different string. Why does it matter? Because instead of using the string representation of the payload, we were passing a `Json::Value` around and stringifying and parsing it in multiple places. This is both inefficient, and incorrect. Cryptographic hashes (like the ones used by the Svix signature scheme) are very sensitive to even the slightest changes, not to mention reordering, so we must use the same payload everywhere. We can't just hope it'll be the same when strinigifying later.
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There was an issue with small payloads (well potentially larger too, but exceedingly unlikely) which could cause the payloads to not serialize correctly which could cause signatures to be incorrect in same rare scenarios likely only affecting small payloads.
If memory serves, serde parses and stringifies json in a non-deterministic way. Normally it would be deterministic, but it also maintains an internal cache of "json structures", and if it thinks that it can reuse one it does. This means that if there's a "cache hit", which I'm not sure about the circumstances, it can reuse one of those and therefore generate a different string.
Why does it matter? Because instead of using the string representation of the payload, we were passing a
Json::Valuearound and stringifying and parsing it in multiple places. This is both inefficient, and incorrect. Cryptographic hashes (like the ones used by the Svix signature scheme) are very sensitive to even the slightest changes, not to mention reordering, so we must use the same payload everywhere. We can't just hope it'll be the same when strinigifying later.