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// Copyright (C) 2019-2023 Algorand, Inc.
// This file is part of go-algorand
//
// go-algorand is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// go-algorand is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with go-algorand. If not, see <https://www.gnu.org/licenses/>.
package committee
import (
"encoding/binary"
"fmt"
"math/big"
"github.com/algorand/go-algorand/config"
"github.com/algorand/go-algorand/crypto"
"github.com/algorand/go-algorand/data/basics"
"github.com/algorand/go-algorand/logging"
"github.com/algorand/go-algorand/protocol"
"github.com/algorand/sortition"
)
type (
// An UnauthenticatedCredential is a Credential which has not yet been
// authenticated.
UnauthenticatedCredential struct {
_struct struct{} `codec:",omitempty,omitemptyarray"`
Proof crypto.VrfProof `codec:"pf"`
}
// A Credential represents a proof of committee membership.
//
// The multiplicity of this membership is specified in the Credential's
// weight. The VRF output hash (with the owner's address hashed in) is
// also cached.
//
// Upgrades: whether or not domain separation is enabled is cached.
// If this flag is set, this flag also includes original hashable
// credential.
Credential struct {
_struct struct{} `codec:",omitempty,omitemptyarray"`
Weight uint64 `codec:"wt"`
VrfOut crypto.Digest `codec:"h"`
DomainSeparationEnabled bool `codec:"ds"`
Hashable hashableCredential `codec:"hc"`
UnauthenticatedCredential
}
hashableCredential struct {
_struct struct{} `codec:",omitempty,omitemptyarray"`
RawOut crypto.VrfOutput `codec:"v"`
Member basics.Address `codec:"m"`
Iter uint64 `codec:"i"`
}
)
// Verify an unauthenticated Credential that was received from the network.
//
// Verify checks if the given credential is a valid proof of membership
// conditioned on the provided committee membership parameters.
//
// If it is, the returned Credential constitutes a proof of this fact.
// Otherwise, an error is returned.
func (cred UnauthenticatedCredential) Verify(proto config.ConsensusParams, m Membership) (res Credential, err error) {
selectionKey := m.Record.SelectionID
ok, vrfOut := selectionKey.Verify(cred.Proof, m.Selector)
hashable := hashableCredential{
RawOut: vrfOut,
Member: m.Record.Addr,
}
// Also hash in the address. This is necessary to decorrelate the selection of different accounts that have the same VRF key.
var h crypto.Digest
if proto.CredentialDomainSeparationEnabled {
h = crypto.HashObj(hashable)
} else {
h = crypto.Hash(append(vrfOut[:], m.Record.Addr[:]...))
}
if !ok {
err = fmt.Errorf("UnauthenticatedCredential.Verify: could not verify VRF Proof with %v (parameters = %+v, proof = %#v)", selectionKey, m, cred.Proof)
return
}
var weight uint64
userMoney := m.Record.VotingStake()
expectedSelection := float64(m.Selector.CommitteeSize(proto))
if m.TotalMoney.Raw < userMoney.Raw {
logging.Base().Panicf("UnauthenticatedCredential.Verify: total money = %v, but user money = %v", m.TotalMoney, userMoney)
} else if m.TotalMoney.IsZero() || expectedSelection == 0 || expectedSelection > float64(m.TotalMoney.Raw) {
logging.Base().Panicf("UnauthenticatedCredential.Verify: m.TotalMoney %v, expectedSelection %v", m.TotalMoney.Raw, expectedSelection)
} else if !userMoney.IsZero() {
weight = sortition.Select(userMoney.Raw, m.TotalMoney.Raw, expectedSelection, sortition.Digest(h))
}
if weight == 0 {
err = fmt.Errorf("UnauthenticatedCredential.Verify: credential has weight 0")
} else {
res = Credential{
UnauthenticatedCredential: cred,
VrfOut: h,
Weight: weight,
DomainSeparationEnabled: proto.CredentialDomainSeparationEnabled,
}
if res.DomainSeparationEnabled {
res.Hashable = hashable
}
}
return
}
// MakeCredential creates a new unauthenticated Credential given some selector.
func MakeCredential(secrets *crypto.VrfPrivkey, sel Selector) UnauthenticatedCredential {
pf, ok := secrets.Prove(sel)
if !ok {
logging.Base().Error("Failed to construct a VRF proof -- participation key may be corrupt")
return UnauthenticatedCredential{}
}
return UnauthenticatedCredential{Proof: pf}
}
// Less returns true if this Credential is less than the other credential; false
// otherwise (i.e., >=).
// Used for breaking ties when there are multiple proposals.
//
// Precondition: both credentials have nonzero weight
func (cred Credential) Less(otherCred Credential) bool {
i1 := cred.lowestOutput()
i2 := otherCred.lowestOutput()
return i1.Cmp(i2) < 0
}
// Equals compares the hash of two Credentials to determine equality and returns
// true if they're equal.
func (cred Credential) Equals(otherCred Credential) bool {
return cred.VrfOut == otherCred.VrfOut
}
// Selected returns whether this Credential was selected (i.e., if its weight is
// greater than zero).
func (cred Credential) Selected() bool {
return cred.Weight > 0
}
// lowestOutput is used for breaking ties when there are multiple proposals.
// People will vote for the proposal whose credential has the lowest lowestOutput.
//
// We hash the credential and interpret the output as a bigint.
// For credentials with weight w > 1, we hash the credential w times (with
// different counter values) and use the lowest output.
//
// This is because a weight w credential is simulating being selected to be on the
// leader committee w times, so each of the w proposals would have a different hash,
// and the lowest would win.
func (cred Credential) lowestOutput() *big.Int {
var lowest big.Int
h1 := cred.VrfOut
// It is important that i start at 1 rather than 0 because cred.Hashable
// was already hashed with iter = 0 earlier (in UnauthenticatedCredential.Verify)
// for determining the weight of the credential. A nonzero iter provides
// domain separation between lowestOutput and UnauthenticatedCredential.Verify
//
// If we reused the iter = 0 hash output here it would be nonuniformly
// distributed (because lowestOutput can only get called if weight > 0).
// In particular if i starts at 0 then weight-1 credentials are at a
// significant disadvantage because UnauthenticatedCredential.Verify
// wants the hash to be large but tiebreaking between proposals wants
// the hash to be small.
for i := uint64(1); i <= cred.Weight; i++ {
var h crypto.Digest
if cred.DomainSeparationEnabled {
cred.Hashable.Iter = i
h = crypto.HashObj(cred.Hashable)
} else {
var h2 crypto.Digest
binary.BigEndian.PutUint64(h2[:], i)
h = crypto.Hash(append(h1[:], h2[:]...))
}
if i == 1 {
lowest.SetBytes(h[:])
} else {
var temp big.Int
temp.SetBytes(h[:])
if temp.Cmp(&lowest) < 0 {
lowest.Set(&temp)
}
}
}
return &lowest
}
// LowestOutputDigest gives the lowestOutput as a crypto.Digest, which allows
// pretty-printing a proposal's lowest output.
// This function is only used for debugging.
func (cred Credential) LowestOutputDigest() crypto.Digest {
lbytes := cred.lowestOutput().Bytes()
var out crypto.Digest
if len(lbytes) > len(out) {
panic("Cred lowest output too long")
}
copy(out[len(out)-len(lbytes):], lbytes)
return out
}
func (cred hashableCredential) ToBeHashed() (protocol.HashID, []byte) {
return protocol.Credential, protocol.Encode(&cred)
}
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