// Construct a general message Cipher
// from a Stream cipher and a cryptographic Hash.
func FromStream(newStream func(key []byte) cipher.Stream,
newHash func() hash.Hash, blockLen, keyLen, hashLen int,
key []byte, options ...interface{}) abstract.Cipher {
sc := streamCipher{}
sc.newStream = newStream
sc.newHash = newHash
sc.blockLen = blockLen
sc.keyLen = keyLen
sc.hashLen = hashLen
sc.h = sc.newHash()
if key == nil {
key = random.Bytes(hashLen, random.Stream)
}
if len(key) > 0 {
sc.Message(nil, nil, key)
}
if len(options) > 0 {
panic("no FromStream options supported yet")
}
return abstract.Cipher{&sc}
}
func (sk *SKEME) mkmac(masterkey, Xb1, Xb2 []byte) (cipher.Stream, []byte) {
keylen := sk.ms.KeySize()
hmac := hmac.New(sk.suite.Hash, masterkey)
hmac.Write(Xb1)
hmac.Write(Xb2)
key := hmac.Sum(nil)[:keylen]
stream := sk.suite.Cipher(key)
mac := random.Bytes(keylen, stream)
return stream, mac
}
func (sk *SKEME) Recv(rm []byte) (bool, error) {
M, err := Decrypt(sk.suite, rm, sk.lpri.Set, sk.lpri.Mine, sk.lpri.Pri,
sk.hide)
if err != nil {
return false, err
}
// Decode the remote DH public key
ptlen := sk.suite.PointLen()
if len(M) < ptlen {
return false, errors.New("SKEME message too short for DH key")
}
if sk.rX == nil {
rXb := M[:ptlen]
rX := sk.suite.Point()
if err := rX.UnmarshalBinary(M[:ptlen]); err != nil {
return false, err
}
sk.rX = rX // remote DH public key
sk.rXb = rXb
// Compute the shared secret and the key-confirmation MACs
DH := sk.suite.Point().Mul(rX, sk.lx)
seed, _ := DH.MarshalBinary()
sk.ms = sk.suite.Cipher(seed)
mkey := random.Bytes(sk.ms.KeySize(), sk.ms)
sk.ls, sk.lmac = sk.mkmac(mkey, sk.lXb, sk.rXb)
sk.rs, sk.rmac = sk.mkmac(mkey, sk.rXb, sk.lXb)
// Transmit our key-confirmation MAC with the next message
sk.lm = append(sk.lm, sk.lmac...)
}
// Decode and check the remote key-confirmation MAC if present
maclo := ptlen
machi := maclo + sk.ms.KeySize()
if len(M) < machi {
return false, nil // not an error, just not done yet
}
if subtle.ConstantTimeCompare(M[maclo:machi], sk.rmac) == 0 {
return false, errors.New("SKEME remote MAC check failed")
}
// Shared key confirmed, good to go!
// (Although remote might still need our key confirmation.)
return true, nil
}
func TestEmbedData(T *testing.T) {
rand := random.Stream
bytes := random.Bytes(50, rand)
points := Embed(bytes)
reconstructed, err := Extract(points)
if err != nil {
T.Fatalf("Error occured during data extraction: %v", err)
}
T.Log(points)
T.Log(bytes)
T.Log(reconstructed)
if !reflect.DeepEqual(bytes, reconstructed) {
T.Fatal("Reconstructed byte slice did not equal original")
}
}
// SpongeCipher builds a general message Cipher from a Sponge function.
func FromSponge(sponge Sponge, key []byte, options ...interface{}) abstract.Cipher {
sc := spongeCipher{}
sc.sponge = sponge
sc.rate = sponge.Rate()
sc.cap = sponge.Capacity()
sc.pad = byte(0x7f) // default, unused by standards
sc.buf = make([]byte, sc.rate+sc.cap)
sc.pos = 0
sc.parseOptions(options)
// Key the cipher in some appropriate fashion
if key == nil {
key = random.Bytes(sponge.Capacity(), random.Stream)
}
if len(key) > 0 {
sc.Message(nil, nil, key)
}
// Setup normal-case domain-separation byte used for message payloads
sc.setDomain(domainPayload, 0)
return abstract.Cipher{&sc}
}
// Start initiates the RandHound protocol run. The client pseudo-randomly
// chooses the server grouping, forms an I1 message for each group, and sends
// it to all servers of that group.
func (rh *RandHound) Start() error {
var err error
// Set timestamp
rh.time = time.Now()
// Choose client randomness
rand := random.Bytes(rh.Suite().Hash().Size(), random.Stream)
rh.cliRand = rand
// Determine server grouping
rh.server, rh.key, err = rh.Shard(rand, rh.groups)
if err != nil {
return err
}
// Set some group parameters
for i, group := range rh.server {
rh.threshold[i] = 2 * len(group) / 3
rh.polyCommit[i] = make([]abstract.Point, len(group))
g := make([]int, len(group))
for j, server0 := range group {
s0 := server0.RosterIndex
rh.ServerIdxToGroupNum[s0] = i
rh.ServerIdxToGroupIdx[s0] = j
g[j] = s0
}
rh.group[i] = g
}
// Compute session id
rh.sid, err = rh.sessionID(rh.nodes, rh.faulty, rh.purpose, rh.time, rh.cliRand, rh.threshold, rh.Public(), rh.key)
if err != nil {
return err
}
// Multicast first message to grouped servers
for i, group := range rh.server {
index := make([]uint32, len(group))
for j, server := range group {
index[j] = uint32(server.RosterIndex)
}
i1 := &I1{
SID: rh.sid,
Threshold: rh.threshold[i],
Group: index,
Key: rh.key[i],
}
rh.mutex.Lock()
// Sign I1 and store signature in i1.Sig
if err := signSchnorr(rh.Suite(), rh.Private(), i1); err != nil {
rh.mutex.Unlock()
return err
}
rh.i1s[i] = i1
rh.mutex.Unlock()
if err := rh.Multicast(i1, group...); err != nil {
return err
}
}
return nil
}
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
}
func TestSession(T *testing.T) {
numUsers := 5
numNotaries := 2
slot := 0
data, users, notaries := createSetup(numUsers, numNotaries)
userciphers := make([]*UserCipherText, numUsers)
notaryciphers := make([]*NotaryCipherText, numNotaries)
// Create some plaintext bytes and embed them into group elements
bytes := random.Bytes(100, random.Stream)
plaintext := crypto.Embed(bytes)
amount := len(plaintext)
// Let the users construct their ciphertexts
var err error
for i := range users {
if i == slot {
userciphers[i], err = users[i].GetRealCipherText(data, plaintext)
} else {
userciphers[i], err = users[i].GetCoverCipherText(data, amount, slot)
}
}
if err != nil {
T.Fatalf("Failed to create proof: %v", err)
}
// Check the validity of the user ciphertexts
for i, usercipher := range userciphers {
if err := usercipher.Verify(data); err != nil {
T.Logf("Ciphertext of user %d was invalid: %v", i, err)
T.Fail()
}
}
// Let the notaries construct their ciphertexts
for j := range notaries {
notaryciphers[j], err = notaries[j].GetCiphertext(data, amount)
}
if err != nil {
T.Fatalf("Failed to create proof: %v", err)
}
// Check the validity of the notary ciphertexts
for j, notarycipher := range notaryciphers {
if err := notarycipher.Verify(data); err != nil {
T.Logf("Ciphertext of notary %d was invalid: %v", j, err)
T.Fail()
}
}
// Reconstruct plaintext
messages, err := ReconstructMessage(userciphers, notaryciphers)
if err != nil {
T.Logf("Failed to reconstruct plaintext: %v", err)
T.Fail()
}
if len(messages) != len(plaintext) {
T.Fatal("Got wrong amount of points, was %d, should be %d", len(messages), len(plaintext))
}
// Check if the reconstructed plaintext equals the original ones
reconstructed, _ := crypto.Extract(messages)
if !reflect.DeepEqual(bytes, reconstructed) {
T.Fatal("Extracted plaintext does not equal the original")
}
}
