// Pick a uint32 uniformly at random
func randUint32() uint32 {
return random.Uint32(random.Stream)
}
func (rh *RandHound) handleR1(r1 WR1) error {
msg := &r1.R1
idx := r1.RosterIndex
grp := rh.ServerIdxToGroupNum[idx]
pos := rh.ServerIdxToGroupIdx[idx]
rh.mutex.Lock()
defer rh.mutex.Unlock()
// Verify R1 message signature
if err := verifySchnorr(rh.Suite(), rh.key[grp][pos], msg); err != nil {
return err
}
// Verify that server replied to the correct I1 message
if err := verifyMessage(rh.Suite(), rh.i1s[grp], msg.HI1); err != nil {
return err
}
// Record R1 message
rh.r1s[idx] = msg
// Prepare data for recovery of polynomial commits and verification of shares
n := len(msg.EncShare)
poly := make([][]byte, n)
index := make([]int, n)
encShare := make([]abstract.Point, n)
encProof := make([]ProofCore, n)
for i := 0; i < n; i++ {
poly[i] = msg.CommitPoly
index[i] = msg.EncShare[i].Pos
encShare[i] = msg.EncShare[i].Val
encProof[i] = msg.EncShare[i].Proof
}
// Init PVSS and recover polynomial commits
H, _ := rh.Suite().Point().Pick(nil, rh.Suite().Cipher(rh.sid))
pvss := NewPVSS(rh.Suite(), H, rh.threshold[grp])
polyCommit, err := pvss.Commits(poly, index)
if err != nil {
return err
}
// Record polynomial commits
rh.polyCommit[idx] = polyCommit
// Return, if we already committed to secrets previously
if len(rh.chosenSecret) > 0 {
return nil
}
// Verify encrypted shares
good, _, err := pvss.Verify(H, rh.key[grp], polyCommit, encShare, encProof)
if err != nil {
return err
}
// Record valid encrypted shares per secret/server
for _, g := range good {
if _, ok := rh.secret[idx]; !ok {
rh.secret[idx] = make([]int, 0)
}
rh.secret[idx] = append(rh.secret[idx], msg.EncShare[g].Target)
}
// Check if there is at least a threshold number of reconstructable secrets
// in each group. If yes proceed to the next phase. Note the double-usage
// of the threshold which is used to determine if enough valid shares for a
// single secret are available and if enough secrets for a given group are
// available
goodSecret := make(map[int][]int)
for i, group := range rh.server {
var secret []int
for _, server := range group {
j := server.RosterIndex
if share, ok := rh.secret[j]; ok && rh.threshold[i] <= len(share) {
secret = append(secret, j)
}
}
if rh.threshold[i] <= len(secret) {
goodSecret[i] = secret
}
}
// Proceed, if there are enough good secrets
if len(goodSecret) == rh.groups {
// Reset secret for the next phase (see handleR2)
rh.secret = make(map[int][]int)
// Choose secrets that contribute to collective randomness
for i := range rh.server {
// Randomly remove some secrets so that a threshold of secrets remains
rand := random.Bytes(rh.Suite().Hash().Size(), random.Stream)
prng := rh.Suite().Cipher(rand)
secret := goodSecret[i]
for j := 0; j < len(secret)-rh.threshold[i]; j++ {
k := int(random.Uint32(prng) % uint32(len(secret)))
secret = append(secret[:k], secret[k+1:]...)
}
rh.chosenSecret[i] = secret
}
log.Lvlf3("Grouping: %v", rh.group)
log.Lvlf3("ChosenSecret: %v", rh.chosenSecret)
// Transformation of commitments from int to uint32 to avoid protobuff errors
var chosenSecret = make([][]uint32, len(rh.chosenSecret))
for i := range rh.chosenSecret {
var l []uint32
for j := range rh.chosenSecret[i] {
l = append(l, uint32(rh.chosenSecret[i][j]))
}
chosenSecret[i] = l
}
// Prepare a message for each server of a group and send it
for i, group := range rh.server {
for j, server := range group {
// Among the good secrets chosen previously collect all valid
// shares, proofs, and polynomial commits intended for the
// target server
var encShare []Share
var polyCommit []abstract.Point
for _, k := range rh.chosenSecret[i] {
r1 := rh.r1s[k]
pc := rh.polyCommit[k]
encShare = append(encShare, r1.EncShare[j])
polyCommit = append(polyCommit, pc[j])
}
i2 := &I2{
Sig: crypto.SchnorrSig{},
SID: rh.sid,
ChosenSecret: chosenSecret,
EncShare: encShare,
PolyCommit: polyCommit,
}
if err := signSchnorr(rh.Suite(), rh.Private(), i2); err != nil {
return err
}
rh.i2s[server.RosterIndex] = i2
if err := rh.SendTo(server, i2); err != nil {
return err
}
}
}
}
return nil
}
