expanded fri_test.go and implemented more for the fri verifier

field/field.go

@@ -1,6 +1,8 @@
 package field
 
 import (
+	"math/big"
+
 	"github.com/consensys/gnark-crypto/ecc"
 	"github.com/consensys/gnark/frontend"
 	"github.com/consensys/gnark/std/math/emulated"
@@ -28,3 +30,9 @@ func NewFieldAPI(api frontend.API) frontend.API {
 	}
 	return field
 }
+
+var r EmulatedField
+
+func EmulatedFieldModulus() *big.Int {
+	return r.Modulus()
+}

plonky2_verifier/fri.go

@@ -1,9 +1,9 @@
 package plonky2_verifier
 
 import (
-	"fmt"
 	"gnark-ed25519/field"
 	. "gnark-ed25519/field"
+	"gnark-ed25519/poseidon"
 	"math"
 
 	"github.com/consensys/gnark/frontend"
@@ -34,16 +34,19 @@ type FriChip struct {
 	field frontend.API
 	qe    *QuadraticExtensionAPI
 
+	poseidonChip *poseidon.PoseidonChip
+
 	friParams               *FriParams
 	verifierOnlyCircuitData *VerifierOnlyCircuitData
 }
 
-func NewFriChip(api frontend.API, field frontend.API, qe *QuadraticExtensionAPI, friParams *FriParams) *FriChip {
+func NewFriChip(api frontend.API, field frontend.API, qe *QuadraticExtensionAPI, poseidonChip *poseidon.PoseidonChip, friParams *FriParams) *FriChip {
 	return &FriChip{
-		api:       api,
-		field:     field,
-		qe:        qe,
-		friParams: friParams,
+		api:          api,
+		field:        field,
+		qe:           qe,
+		poseidonChip: poseidonChip,
+		friParams:    friParams,
 	}
 }
 
@@ -52,9 +55,6 @@ func (f *FriChip) assertLeadingZeros(powWitness F, friConfig FriConfig) {
 	// Note that this is assuming that the Goldilocks field is being used.  Specfically that the
 	// field is 64 bits long
 	maxPowWitness := uint64(math.Pow(2, float64(64-friConfig.ProofOfWorkBits))) - 1
-	f.field.Println(powWitness)
-	fmt.Println(maxPowWitness)
-	fmt.Println(friConfig.ProofOfWorkBits)
 	f.field.AssertIsLessOrEqual(powWitness, field.NewFieldElement(maxPowWitness))
 }
 
@@ -70,10 +70,63 @@ func (f *FriChip) fromOpeningsAndAlpha(openings *FriOpenings, alpha QuadraticExt
 	return reducedOpenings
 }
 
-func (f *FriChip) verifyMerkleProofToCap(leafData []F, leafIndex F, merkleCap MerkleCap, proof *MerkleProof) {
+func (f *FriChip) hashOrNoop(data []F) Hash {
+	var elements Hash
+	if len(data) <= 4 {
+		// Pad the data to have a size of 4
+		for i, inputElement := range data {
+			elements[i] = inputElement
+		}
+		for i := len(data); i < 4; i++ {
+			elements[i] = f.qe.ZERO_F
+		}
+
+		return elements
+	} else {
+		hashOutput := f.poseidonChip.HashNToMNoPad(data, 4)
+
+		if len(hashOutput) != len(elements) {
+			panic("The length of hashOutput and elements is different")
+		}
+
+		for i, hashField := range hashOutput {
+			elements[i] = hashField
+		}
+
+		return elements
+	}
 }
 
-func (f *FriChip) verifyInitialProof(xIndex F, proof *FriInitialTreeProof, initialMerkleCaps []MerkleCap) {
+func (f *FriChip) verifyMerkleProofToCapWithCapIndex(leafData []F, leafIndexBits []frontend.Variable, capIndex F, merkleCap MerkleCap, proof *MerkleProof) {
+	currentDigest := f.hashOrNoop(leafData)
+
+	if len(leafIndexBits) != len(proof.Siblings) {
+		panic("len(leafIndexBits) != len(proof.Siblings)")
+	}
+
+	fourZeros := [4]F{f.qe.ZERO_F, f.qe.ZERO_F, f.qe.ZERO_F, f.qe.ZERO_F}
+	for i, bit := range leafIndexBits {
+		sibling := proof.Siblings[i]
+
+		var leftSiblingState poseidon.PoseidonState
+		copy(leftSiblingState[0:4], sibling[0:4])
+		copy(leftSiblingState[4:8], currentDigest[0:4])
+		copy(leftSiblingState[8:12], fourZeros[0:4])
+		leftHash := f.poseidonChip.Poseidon(leftSiblingState)
+		leftHashCompress := leftHash[0:4]
+
+		var rightSiblingState poseidon.PoseidonState
+		copy(rightSiblingState[0:4], currentDigest[0:4])
+		copy(rightSiblingState[4:8], sibling[0:4])
+		copy(rightSiblingState[8:12], fourZeros[0:4])
+		rightHash := f.poseidonChip.Poseidon(rightSiblingState)
+		rightHashCompress := rightHash[0:4]
+
+		currentDigest = f.api.Select(bit, leftHashCompress, rightHashCompress).(Hash)
+	}
+}
+
+func (f *FriChip) verifyInitialProof(xIndexBits []frontend.Variable, proof *FriInitialTreeProof, initialMerkleCaps []MerkleCap, capIndex F) {
 	if len(proof.EvalsProofs) != len(initialMerkleCaps) {
 		panic("length of eval proofs in fri proof should equal length of initial merkle caps")
 	}
@@ -82,7 +135,28 @@ func (f *FriChip) verifyInitialProof(xIndex F, proof *FriInitialTreeProof, initi
 		evals := proof.EvalsProofs[i].Elements
 		merkleProof := proof.EvalsProofs[i].MerkleProof
 		cap := initialMerkleCaps[i]
-		f.verifyMerkleProofToCap(evals, xIndex, cap, &merkleProof)
+		f.verifyMerkleProofToCapWithCapIndex(evals, xIndexBits, capIndex, cap, &merkleProof)
+	}
+}
+
+// / We decompose FRI query indices into bits without verifying that the decomposition given by
+// / the prover is the canonical one. In particular, if `x_index < 2^field_bits - p`, then the
+// / prover could supply the binary encoding of either `x_index` or `x_index + p`, since they are
+// / congruent mod `p`. However, this only occurs with probability
+// /     p_ambiguous = (2^field_bits - p) / p
+// / which is small for the field that we use in practice.
+// /
+// / In particular, the soundness error of one FRI query is roughly the codeword rate, which
+// / is much larger than this ambiguous-element probability given any reasonable parameters.
+// / Thus ambiguous elements contribute a negligible amount to soundness error.
+// /
+// / Here we compare the probabilities as a sanity check, to verify the claim above.
+func (f *FriChip) assertNoncanonicalIndicesOK() {
+	numAmbiguousElems := uint64(math.MaxUint64) - EmulatedFieldModulus().Uint64() + 1
+	queryError := f.friParams.Config.rate()
+	pAmbiguous := float64(numAmbiguousElems) / float64(EmulatedFieldModulus().Uint64())
+	if pAmbiguous < queryError*1e-5 {
+		panic("A non-negligible portion of field elements are in the range that permits non-canonical encodings. Need to do more analysis or enforce canonical encodings.")
 	}
 }
 
@@ -95,11 +169,17 @@ func (f *FriChip) verifyQueryRound(
 	n uint64,
 	roundProof *FriQueryRound,
 ) {
-	f.verifyInitialProof(xIndex, &roundProof.InitialTreesProof, initialMerkleCaps)
+	nLog := log2Strict(uint(n))
+
+	f.assertNoncanonicalIndicesOK()
+	xIndexBits := f.qe.field.ToBinary(xIndex, nLog)
+	capIndex := f.qe.field.FromBinary(xIndexBits[len(xIndexBits)-int(f.friParams.Config.CapHeight):]...).(F)
+
+	f.verifyInitialProof(xIndexBits, &roundProof.InitialTreesProof, initialMerkleCaps, capIndex)
 }
 
 func (f *FriChip) VerifyFriProof(
-	openings *FriOpenings,
+	openings FriOpenings,
 	friChallenges *FriChallenges,
 	initialMerkleCaps []MerkleCap,
 	friProof *FriProof,
@@ -116,9 +196,9 @@ func (f *FriChip) VerifyFriProof(
 	); */
 
 	// Check POW
-	f.assertLeadingZeros(friProof.PowWitness, f.friParams.Config)
+	f.assertLeadingZeros(friChallenges.FriPowResponse, f.friParams.Config)
 
-	precomputedReducedEvals := f.fromOpeningsAndAlpha(openings, friChallenges.FriAlpha)
+	precomputedReducedEvals := f.fromOpeningsAndAlpha(&openings, friChallenges.FriAlpha)
 
 	// Size of the LDE domain.
 	n := uint64(math.Pow(2, float64(f.friParams.DegreeBits+f.friParams.Config.RateBits)))

plonky2_verifier/fri_test.go

@@ -2,6 +2,7 @@ package plonky2_verifier
 
 import (
 	. "gnark-ed25519/field"
+	"gnark-ed25519/poseidon"
 	"testing"
 
 	"github.com/consensys/gnark/frontend"
@@ -13,11 +14,66 @@ type TestFriCircuit struct{}
 func (circuit *TestFriCircuit) Define(api frontend.API) error {
 	proofWithPis := DeserializeProofWithPublicInputs("./data/fibonacci/proof_with_public_inputs.json")
 	commonCircuitData := DeserializeCommonCircuitData("./data/fibonacci/common_circuit_data.json")
+	verifierOnlyCircuitData := DeserializeVerifierOnlyCircuitData("./data/fibonacci/verifier_only_circuit_data.json")
 
 	field := NewFieldAPI(api)
+	qe := NewQuadraticExtensionAPI(field, commonCircuitData.DegreeBits)
+	poseidonChip := poseidon.NewPoseidonChip(api, field)
+	friChip := NewFriChip(api, field, qe, poseidonChip, &commonCircuitData.FriParams)
+
+	friChallenges := FriChallenges{
+		FriAlpha: QuadraticExtension{
+			NewFieldElementFromString("14641715242626918707"),
+			NewFieldElementFromString("10574243340537902930"),
+		},
+		FriBetas:       []QuadraticExtension{},
+		FriPowResponse: NewFieldElement(82451580476419),
+		FriQueryIndicies: []F{
+			NewFieldElement(6790812084677375942),
+			NewFieldElement(12394212020331474798),
+			NewFieldElement(16457600747000998582),
+			NewFieldElement(1543271328932331916),
+			NewFieldElement(12115726870906958644),
+			NewFieldElement(6775897107605342797),
+			NewFieldElement(15989401564746021030),
+			NewFieldElement(10691676456016926845),
+			NewFieldElement(1632499470630032007),
+			NewFieldElement(1317292355445098328),
+			NewFieldElement(18391440812534384252),
+			NewFieldElement(17321705613231354333),
+			NewFieldElement(6176487551308859603),
+			NewFieldElement(7119835651572002873),
+			NewFieldElement(3903019169623116693),
+			NewFieldElement(4886491111111487546),
+			NewFieldElement(4087641893164620518),
+			NewFieldElement(13801643080324181364),
+			NewFieldElement(16993775312274189321),
+			NewFieldElement(9268202926222765679),
+			NewFieldElement(10683001302406181735),
+			NewFieldElement(13359465725531647963),
+			NewFieldElement(4523327590105620849),
+			NewFieldElement(4883588003760409588),
+			NewFieldElement(187699146998097671),
+			NewFieldElement(14489263557623716717),
+			NewFieldElement(11748359318238148146),
+			NewFieldElement(13636347200053048758),
+		},
+	}
+
+	initialMerkleCaps := []MerkleCap{
+		verifierOnlyCircuitData.ConstantSigmasCap,
+		proofWithPis.Proof.WiresCap,
+		proofWithPis.Proof.PlonkZsPartialProductsCap,
+		proofWithPis.Proof.QuotientPolysCap,
+	}
+
+	friChip.VerifyFriProof(
+		proofWithPis.Proof.Openings.ToFriOpenings(),
+		&friChallenges,
+		initialMerkleCaps,
+		&proofWithPis.Proof.OpeningProof,
+	)
 
-	friChip := NewFriChip(api, field, commonCircuitData.Config.FriConfig)
-	friChip.VerifyFriProof(&proofWithPis.Proof.OpeningProof)
 	return nil
 }
 

plonky2_verifier/structs.go

@@ -75,6 +75,10 @@ type FriConfig struct {
 	// TODO: add FriReductionStrategy
 }
 
+func (fc *FriConfig) rate() float64 {
+	return 1.0 / float64((uint64(1) << fc.RateBits))
+}
+
 type FriParams struct {
 	Config             FriConfig
 	Hiding             bool

plonky2_verifier/utils.go

@@ -1,7 +1,9 @@
 package plonky2_verifier
 
 import (
+	"fmt"
 	. "gnark-ed25519/field"
+	"math/bits"
 )
 
 func reduceWithPowers(qe *QuadraticExtensionAPI, terms []QuadraticExtension, scalar QuadraticExtension) QuadraticExtension {
@@ -19,3 +21,12 @@ func reduceWithPowers(qe *QuadraticExtensionAPI, terms []QuadraticExtension, sca
 
 	return sum
 }
+
+// Computes `log_2(n)`, panicking if `n` is not a power of two.
+func log2Strict(n uint) int {
+	res := bits.TrailingZeros(n)
+	if n>>res != 1 {
+		panic(fmt.Sprintf("Not a power of two: %d", n))
+	}
+	return res
+}