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group.go
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group.go
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package weshnet
import (
crand "crypto/rand"
"github.com/libp2p/go-libp2p/core/crypto"
"golang.org/x/crypto/nacl/box"
"berty.tech/weshnet/pkg/cryptoutil"
"berty.tech/weshnet/pkg/errcode"
"berty.tech/weshnet/pkg/protocoltypes"
)
const CurrentGroupVersion = 1
// NewGroupMultiMember creates a new Group object and an invitation to be used by
// the first member of the group
func NewGroupMultiMember() (*protocoltypes.Group, crypto.PrivKey, error) {
priv, pub, err := crypto.GenerateEd25519Key(crand.Reader)
if err != nil {
return nil, nil, errcode.ErrCryptoKeyGeneration.Wrap(err)
}
pubBytes, err := pub.Raw()
if err != nil {
return nil, nil, errcode.ErrSerialization.Wrap(err)
}
signing, _, err := crypto.GenerateEd25519Key(crand.Reader)
if err != nil {
return nil, nil, errcode.ErrCryptoKeyGeneration.Wrap(err)
}
signingBytes, err := cryptoutil.SeedFromEd25519PrivateKey(signing)
if err != nil {
return nil, nil, errcode.ErrSerialization.Wrap(err)
}
skSig, err := priv.Sign(signingBytes)
if err != nil {
return nil, nil, errcode.ErrCryptoSignature.Wrap(err)
}
group := &protocoltypes.Group{
PublicKey: pubBytes,
Secret: signingBytes,
SecretSig: skSig,
GroupType: protocoltypes.GroupTypeMultiMember,
}
updateKey, err := cryptoutil.GetLinkKeyArray(group)
if err != nil {
return nil, nil, errcode.ErrCryptoKeyGeneration.Wrap(err)
}
linkKeySig, err := priv.Sign(updateKey[:])
if err != nil {
return nil, nil, errcode.ErrCryptoSignature.Wrap(err)
}
group.LinkKeySig = linkKeySig
return group, priv, nil
}
func openDeviceSecret(m *protocoltypes.GroupMetadata, localMemberPrivateKey crypto.PrivKey, group *protocoltypes.Group) (crypto.PubKey, *protocoltypes.DeviceSecret, error) {
if m == nil || m.EventType != protocoltypes.EventTypeGroupDeviceSecretAdded {
return nil, nil, errcode.ErrInvalidInput
}
s := &protocoltypes.GroupAddDeviceSecret{}
if err := s.Unmarshal(m.Payload); err != nil {
return nil, nil, errcode.ErrDeserialization.Wrap(err)
}
senderDevicePubKey, err := crypto.UnmarshalEd25519PublicKey(s.DevicePK)
if err != nil {
return nil, nil, errcode.ErrDeserialization.Wrap(err)
}
destMemberPubKey, err := crypto.UnmarshalEd25519PublicKey(s.DestMemberPK)
if err != nil {
return nil, nil, errcode.ErrDeserialization.Wrap(err)
}
if !localMemberPrivateKey.GetPublic().Equals(destMemberPubKey) {
return nil, nil, errcode.ErrGroupSecretOtherDestMember
}
mongPriv, mongPub, err := cryptoutil.EdwardsToMontgomery(localMemberPrivateKey, senderDevicePubKey)
if err != nil {
return nil, nil, errcode.ErrCryptoKeyConversion.Wrap(err)
}
nonce := groupIDToNonce(group)
decryptedSecret := &protocoltypes.DeviceSecret{}
decryptedMessage, ok := box.Open(nil, s.Payload, nonce, mongPub, mongPriv)
if !ok {
return nil, nil, errcode.ErrCryptoDecrypt
}
err = decryptedSecret.Unmarshal(decryptedMessage)
if err != nil {
return nil, nil, errcode.ErrDeserialization
}
return senderDevicePubKey, decryptedSecret, nil
}
func groupIDToNonce(group *protocoltypes.Group) *[cryptoutil.NonceSize]byte {
// Nonce doesn't need to be secret, random nor unpredictable, it just needs
// to be used only once for a given {sender, receiver} set and we will send
// only one SecretEntryPayload per {localDevicePrivKey, remoteMemberPubKey}
// So we can reuse groupID as nonce for all SecretEntryPayload and save
// 24 bytes of storage and bandwidth for each of them.
//
// See https://pynacl.readthedocs.io/en/stable/secret/#nonce
// See Security Model here: https://nacl.cr.yp.to/box.html
var nonce [cryptoutil.NonceSize]byte
gid := group.GetPublicKey()
copy(nonce[:], gid)
return &nonce
}