Generate safe IVs #51086
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Generate safe IVs #51086
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IVs should never be re-used when using CTR. The previous implementation had a 50% probability to generate an IV that was already used after 65536 generations. This happens because std::mt19937 is seeded using a 32bit integer and returns a 32 bits integer. Because of the birthday problem, collisions have a 50% chance after only 2^16 IV's generations. CH uses one IV per file and, for most use cases, 65k files are not as many as they seem. Also, the initial entropy is gathered using std::random_device which is "best-effort" and it's allowed by the standard to return a fixed sequence of numbers.
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Backport #51086 to 23.3: Generate safe IVs
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Backport #51086 to 23.4: Generate safe IVs
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Backport #51086 to 23.5: Generate safe IVs
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Backport #51086 to 22.8: Generate safe IVs
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IVs should never be re-used when using CTR.
The previous implementation had a 50% probability to generate an IV that was already used after 65536 generations. This happens because std::mt19937 is seeded using a 32bit integer and returns a 32 bits integer.
Because of the birthday problem, collisions have a 50% chance after only 2^16 IV's generations.
CH uses one IV per file and, for most use cases, 65k files are not as many as they seem.
Also, the initial entropy is gathered using std::random_device which is "best-effort" and it's allowed by the standard to return a fixed sequence of numbers.
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Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):
Fixed not-so-random IV generation for CTR disk encryption.
@alexey-milovidov