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// Contains the Whisper protocol Message element. For formal details please see
// the specs at https://github.com/ethereum/wiki/wiki/Whisper-PoC-1-Protocol-Spec#messages.
package whisper
import (
"crypto/ecdsa"
"math/rand"
"time"
"github.com/ethereum/go-ethereum/crypto"
"github.com/ethereum/go-ethereum/logger"
"github.com/ethereum/go-ethereum/logger/glog"
)
// Message represents an end-user data packet to trasmit through the Whisper
// protocol. These are wrapped into Envelopes that need not be understood by
// intermediate nodes, just forwarded.
type Message struct {
Flags byte // First bit is signature presence, rest reserved and should be random
Signature []byte
Payload []byte
Sent int64
To *ecdsa.PublicKey
}
// Options specifies the exact way a message should be wrapped into an Envelope.
type Options struct {
From *ecdsa.PrivateKey
To *ecdsa.PublicKey
TTL time.Duration
Topics [][]byte
}
// NewMessage creates and initializes a non-signed, non-encrypted Whisper message.
func NewMessage(payload []byte) *Message {
// Construct an initial flag set: bit #1 = 0 (no signature), rest random
flags := byte(rand.Intn(128))
// Assemble and return the message
return &Message{
Flags: flags,
Payload: payload,
Sent: time.Now().Unix(),
}
}
// Wrap bundles the message into an Envelope to transmit over the network.
//
// pow (Proof Of Work) controls how much time to spend on hashing the message,
// inherently controlling its priority through the network (smaller hash, bigger
// priority).
//
// The user can control the amount of identity, privacy and encryption through
// the options parameter as follows:
// - options.From == nil && options.To == nil: anonymous broadcast
// - options.From != nil && options.To == nil: signed broadcast (known sender)
// - options.From == nil && options.To != nil: encrypted anonymous message
// - options.From != nil && options.To != nil: encrypted signed message
func (self *Message) Wrap(pow time.Duration, options Options) (*Envelope, error) {
// Use the default TTL if non was specified
if options.TTL == 0 {
options.TTL = DefaultTimeToLive
}
// Sign and encrypt the message if requested
if options.From != nil {
if err := self.sign(options.From); err != nil {
return nil, err
}
}
if options.To != nil {
if err := self.encrypt(options.To); err != nil {
return nil, err
}
}
// Wrap the processed message, seal it and return
envelope := NewEnvelope(options.TTL, options.Topics, self)
envelope.Seal(pow)
return envelope, nil
}
// sign calculates and sets the cryptographic signature for the message , also
// setting the sign flag.
func (self *Message) sign(key *ecdsa.PrivateKey) (err error) {
self.Flags |= 1 << 7
self.Signature, err = crypto.Sign(self.hash(), key)
return
}
// Recover retrieves the public key of the message signer.
func (self *Message) Recover() *ecdsa.PublicKey {
defer func() { recover() }() // in case of invalid signature
pub, err := crypto.SigToPub(self.hash(), self.Signature)
if err != nil {
glog.V(logger.Error).Infof("Could not get public key from signature: %v", err)
return nil
}
return pub
}
// encrypt encrypts a message payload with a public key.
func (self *Message) encrypt(to *ecdsa.PublicKey) (err error) {
self.Payload, err = crypto.Encrypt(to, self.Payload)
return
}
// hash calculates the SHA3 checksum of the message flags and payload.
func (self *Message) hash() []byte {
return crypto.Sha3(append([]byte{self.Flags}, self.Payload...))
}
// bytes flattens the message contents (flags, signature and payload) into a
// single binary blob.
func (self *Message) bytes() []byte {
return append([]byte{self.Flags}, append(self.Signature, self.Payload...)...)
}
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