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// Package sum is a VDAF for aggregating integers in a pre-determined range.
package sum
import (
"math/bits"
"github.com/cloudflare/circl/vdaf/prio3/arith/fp64"
"github.com/cloudflare/circl/vdaf/prio3/internal/cursor"
"github.com/cloudflare/circl/vdaf/prio3/internal/flp"
"github.com/cloudflare/circl/vdaf/prio3/internal/prio3"
)
type (
poly = fp64.Poly
Vec = fp64.Vec
Fp = fp64.Fp
AggShare = prio3.AggShare[Vec, Fp]
InputShare = prio3.InputShare[Vec, Fp]
Nonce = prio3.Nonce
OutShare = prio3.OutShare[Vec, Fp]
PrepMessage = prio3.PrepMessage
PrepShare = prio3.PrepShare[Vec, Fp]
PrepState = prio3.PrepState[Vec, Fp]
PublicShare = prio3.PublicShare
VerifyKey = prio3.VerifyKey
)
// Sum is a verifiable distributed aggregation function in which each
// measurement is an integer in the range [0, maxMeasurement], where
// maxMeasurement defines the largest valid measurement, the aggregated result
// is the sum of all the measurements.
type Sum struct {
p prio3.Prio3[uint64, uint64, *flpSum, Vec, Fp, *Fp]
}
func New(numShares uint8, maxMeasurement uint64, context []byte) (s *Sum, err error) {
const sumID = 2
flp, err := newFlpSum(maxMeasurement)
if err != nil {
return nil, err
}
s = new(Sum)
s.p, err = prio3.New(flp, sumID, numShares, context)
if err != nil {
return nil, err
}
return s, nil
}
func (s *Sum) Params() prio3.Params { return s.p.Params() }
func (s *Sum) Shard(measurement uint64, nonce *Nonce, rand []byte,
) (PublicShare, []InputShare, error) {
return s.p.Shard(measurement, nonce, rand)
}
func (s *Sum) PrepInit(
verifyKey *VerifyKey,
nonce *Nonce,
aggID uint8,
publicShare PublicShare,
inputShare InputShare,
) (*PrepState, *PrepShare, error) {
return s.p.PrepInit(verifyKey, nonce, aggID, publicShare, inputShare)
}
func (s *Sum) PrepSharesToPrep(prepShares []PrepShare) (*PrepMessage, error) {
return s.p.PrepSharesToPrep(prepShares)
}
func (s *Sum) PrepNext(state *PrepState, msg *PrepMessage) (*OutShare, error) {
return s.p.PrepNext(state, msg)
}
func (s *Sum) AggregateInit() AggShare { return s.p.AggregateInit() }
func (s *Sum) AggregateUpdate(aggShare *AggShare, outShare *OutShare) {
s.p.AggregateUpdate(aggShare, outShare)
}
func (s *Sum) Unshard(aggShares []AggShare, numMeas uint) (aggregate *uint64, err error) {
return s.p.Unshard(aggShares, numMeas)
}
type flpSum struct {
flp.FLP[flp.GadgetPolyEvalx2x, poly, Vec, Fp, *Fp]
bits uint
offset Fp
}
func newFlpSum(maxMeasurement uint64) (*flpSum, error) {
bits := uint(bits.Len64(maxMeasurement))
offset := (uint64(1) << uint64(bits)) - 1 - maxMeasurement
s := new(flpSum)
s.bits = bits
err := s.offset.SetUint64(offset)
if err != nil {
return nil, err
}
s.Valid.MeasurementLen = 2 * bits
s.Valid.JointRandLen = 0
s.Valid.OutputLen = 1
s.Valid.EvalOutputLen = 2*bits + 1
s.Gadget = flp.GadgetPolyEvalx2x{}
s.NumGadgetCalls = 2 * bits
s.FLP.Eval = s.Eval
return s, nil
}
func (s *flpSum) Eval(
out Vec, g flp.Gadget[poly, Vec, Fp, *Fp], numCalls uint,
meas, jointRand Vec, numShares uint8,
) {
var input [1]Fp
for i := range meas {
input[0] = meas[i]
g.Eval(&out[i], input[:])
}
measCur := cursor.New(meas)
a := measCur.Next(s.bits).JoinBits()
b := measCur.Next(s.bits).JoinBits()
var invShares Fp
invShares.InvUint64(uint64(numShares))
rangeCheck := &out[len(meas)]
rangeCheck.Mul(&s.offset, &invShares)
rangeCheck.AddAssign(&a)
rangeCheck.SubAssign(&b)
}
func (s *flpSum) Encode(measurement uint64) (Vec, error) {
offset, err := s.offset.GetUint64()
if err != nil {
return nil, err
}
out := make(Vec, s.Valid.MeasurementLen)
outCur := cursor.New(out)
err = outCur.Next(s.bits).SplitBits(measurement)
if err != nil {
return nil, err
}
err = outCur.Next(s.bits).SplitBits(measurement + offset)
if err != nil {
return nil, err
}
return out, nil
}
func (s *flpSum) Truncate(meas Vec) Vec {
return Vec{meas[:s.bits].JoinBits()}
}
func (s *flpSum) Decode(output Vec, numMeas uint) (*uint64, error) {
if len(output) < int(s.Valid.OutputLen) {
return nil, flp.ErrOutputLen
}
n, err := output[0].GetUint64()
if err != nil {
return nil, err
}
return &n, nil
}
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