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Update for Cuckoo filter with tweaked values

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Dirk-Willem van Gulik 2020-04-11 17:42:40 +02:00
parent 6141426ab1
commit 18ce48d516
1 changed files with 34 additions and 9 deletions
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implementation-profiles/profile.md
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@ -39,21 +39,46 @@ Test vector:
H(EphID || t)
109708e29597623f56fd365ba92f1c717ca23994aabd7939822909c465cb10a5 (32 bytes)
### Cuckoo filter and serialisation
### Cuckoo filter and serialisation version 1.00
(Aligned with https://github.com/dirkx/DP-3T-Documents/tree/editable-version/impl/design-2-openssl-C)
The depth of the Cuckoo filter shall be 4.
The hash shall be a SHA256.
The key shall be 32 bytes which are used as follows:
byte 0..3 up to Z bits for the LSB of the Cuckoo hash
byte 4..7 up to Z bits for the MSB of the Cuckoo hash
byte 8.. up to `verifylimit' bytes.
Where <Z> is the number of bits needed for the number of buckets (e.g Z=19 if the buckets are is 524288).
Where verify limit is set as low as is feasible given the acceptable false positive rates.
The Cuckoo filter shall be serialised as:
- Depth: unsigned 32 bit integer (A)
- Number of slots: unsigned 32 bit integer (S)
- Number of buckets: unsigned 32 bit integer (B)
- Buckets B x ( A x slotsID)
- with the slotID an unsigned 32 bit integer.
- Slots(numbered 0 .. slotsID) S x ( key )
- with the key a 31 bit unsigned int;
- the topbit denotes a populated (0) or empty (1) slot.
Magic string 4 bytes D3, D3, 3D, 3D
Major version 1 byte, currently 1 for this version
Minor version 1 byte, currently 0
<Depth> 1 byte, fixed to 4
<verifylimit> 1 byte
<N buckets> 4 bytes, unsigned 32 bit integer, network order
<N slots> 4 bytes, unsigned 32 bit integer, network order
Followed by
<N buckets> with each
<Depth> slots with each
is occupied 1 bit
partial hash 31 bits, network order, of which <Z> are relevant.
verify hash <verifylimit> bytes of the verify hash
With the partial hash being limited to the number of bits needed for N buckets.
And with the Hash
### Cuckoo filter publication
The filter should be published prefixed by an RFC3161 timestamp.