path: root/whisper/envelope.go

// Contains the Whisper protocol Envelope element. For formal details please see
// the specs at https://github.com/ethereum/wiki/wiki/Whisper-PoC-1-Protocol-Spec#envelopes.

package whisper

import (
    "crypto/ecdsa"
    "encoding/binary"
    "fmt"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/crypto/ecies"
    "github.com/ethereum/go-ethereum/rlp"
)

// Envelope represents a clear-text data packet to transmit through the Whisper
// network. Its contents may or may not be encrypted and signed.
type Envelope struct {
    Expiry uint32 // Whisper protocol specifies int32, really should be int64
    TTL    uint32 // ^^^^^^
    Topics [][]byte
    Data   []byte
    Nonce  uint32

    hash common.Hash
}

// NewEnvelope wraps a Whisper message with expiration and destination data
// included into an envelope for network forwarding.
func NewEnvelope(ttl time.Duration, topics [][]byte, msg *Message) *Envelope {
    return &Envelope{
        Expiry: uint32(time.Now().Add(ttl).Unix()),
        TTL:    uint32(ttl.Seconds()),
        Topics: topics,
        Data:   msg.bytes(),
        Nonce:  0,
    }
}

// Seal closes the envelope by spending the requested amount of time as a proof
// of work on hashing the data.
func (self *Envelope) Seal(pow time.Duration) {
    d := make([]byte, 64)
    copy(d[:32], self.rlpWithoutNonce())

    finish, bestBit := time.Now().Add(pow).UnixNano(), 0
    for nonce := uint32(0); time.Now().UnixNano() < finish; {
        for i := 0; i < 1024; i++ {
            binary.BigEndian.PutUint32(d[60:], nonce)

            firstBit := common.FirstBitSet(common.BigD(crypto.Sha3(d)))
            if firstBit > bestBit {
                self.Nonce, bestBit = nonce, firstBit
            }
            nonce++
        }
    }
}

// Valid checks whether the claimed proof of work was indeed executed.
// TODO: Is this really useful? Isn't this always true?
func (self *Envelope) valid() bool {
    d := make([]byte, 64)
    copy(d[:32], self.rlpWithoutNonce())
    binary.BigEndian.PutUint32(d[60:], self.Nonce)

    return common.FirstBitSet(common.BigD(crypto.Sha3(d))) > 0
}

// RlpWithoutNonce returns the RLP encoded envelope contents, except the nonce.
func (self *Envelope) rlpWithoutNonce() []byte {
    enc, _ := rlp.EncodeToBytes([]interface{}{self.Expiry, self.TTL, self.Topics, self.Data})
    return enc
}

// Open extracts the message contained within a potentially encrypted envelope.
func (self *Envelope) Open(key *ecdsa.PrivateKey) (msg *Message, err error) {
    // Split open the payload into a message construct
    data := self.Data

    message := &Message{
        Flags: data[0],
    }
    data = data[1:]

    if message.Flags&128 == 128 {
        if len(data) < 65 {
            return nil, fmt.Errorf("unable to open envelope. First bit set but len(data) < 65")
        }
        message.Signature, data = data[:65], data[65:]
    }
    message.Payload = data

    // Short circuit if the encryption was requested
    if key == nil {
        return message, nil
    }
    // Otherwise try to decrypt the message
    message.Payload, err = crypto.Decrypt(key, message.Payload)
    switch err {
    case nil:
        return message, nil

    case ecies.ErrInvalidPublicKey: // Payload isn't encrypted
        return message, err

    default:
        return nil, fmt.Errorf("unable to open envelope, decrypt failed: %v", err)
    }
}

// Hash returns the SHA3 hash of the envelope, calculating it if not yet done.
func (self *Envelope) Hash() common.Hash {
    if (self.hash == common.Hash{}) {
        enc, _ := rlp.EncodeToBytes(self)
        self.hash = crypto.Sha3Hash(enc)
    }
    return self.hash
}

// rlpenv is an Envelope but is not an rlp.Decoder.
// It is used for decoding because we need to
type rlpenv Envelope

// DecodeRLP decodes an Envelope from an RLP data stream.
func (self *Envelope) DecodeRLP(s *rlp.Stream) error {
    raw, err := s.Raw()
    if err != nil {
        return err
    }
    if err := rlp.DecodeBytes(raw, (*rlpenv)(self)); err != nil {
        return err
    }
    self.hash = crypto.Sha3Hash(raw)
    return nil
}