path: root/whisper/whisperv6/envelope.go

// Copyright 2016 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// Contains the Whisper protocol Envelope element.

package whisperv6

import (
    "crypto/ecdsa"
    "encoding/binary"
    "fmt"
    gmath "math"
    "math/big"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/common/math"
    "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
    TTL    uint32
    Topic  TopicType
    Data   []byte
    Nonce  uint64

    pow float64 // Message-specific PoW as described in the Whisper specification.

    // the following variables should not be accessed directly, use the corresponding function instead: Hash(), Bloom()
    hash  common.Hash // Cached hash of the envelope to avoid rehashing every time.
    bloom []byte
}

// size returns the size of envelope as it is sent (i.e. public fields only)
func (e *Envelope) size() int {
    return EnvelopeHeaderLength + len(e.Data)
}

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

// NewEnvelope wraps a Whisper message with expiration and destination data
// included into an envelope for network forwarding.
func NewEnvelope(ttl uint32, topic TopicType, msg *sentMessage) *Envelope {
    env := Envelope{
        Expiry: uint32(time.Now().Add(time.Second * time.Duration(ttl)).Unix()),
        TTL:    ttl,
        Topic:  topic,
        Data:   msg.Raw,
        Nonce:  0,
    }

    return &env
}

// Seal closes the envelope by spending the requested amount of time as a proof
// of work on hashing the data.
func (e *Envelope) Seal(options *MessageParams) error {
    if options.PoW == 0 {
        // PoW is not required
        return nil
    }

    var target, bestBit int
    if options.PoW < 0 {
        // target is not set - the function should run for a period
        // of time specified in WorkTime param. Since we can predict
        // the execution time, we can also adjust Expiry.
        e.Expiry += options.WorkTime
    } else {
        target = e.powToFirstBit(options.PoW)
    }

    buf := make([]byte, 64)
    h := crypto.Keccak256(e.rlpWithoutNonce())
    copy(buf[:32], h)

    finish := time.Now().Add(time.Duration(options.WorkTime) * time.Second).UnixNano()
    for nonce := uint64(0); time.Now().UnixNano() < finish; {
        for i := 0; i < 1024; i++ {
            binary.BigEndian.PutUint64(buf[56:], nonce)
            d := new(big.Int).SetBytes(crypto.Keccak256(buf))
            firstBit := math.FirstBitSet(d)
            if firstBit > bestBit {
                e.Nonce, bestBit = nonce, firstBit
                if target > 0 && bestBit >= target {
                    return nil
                }
            }
            nonce++
        }
    }

    if target > 0 && bestBit < target {
        return fmt.Errorf("failed to reach the PoW target, specified pow time (%d seconds) was insufficient", options.WorkTime)
    }

    return nil
}

// PoW computes (if necessary) and returns the proof of work target
// of the envelope.
func (e *Envelope) PoW() float64 {
    if e.pow == 0 {
        e.calculatePoW(0)
    }
    return e.pow
}

func (e *Envelope) calculatePoW(diff uint32) {
    buf := make([]byte, 64)
    h := crypto.Keccak256(e.rlpWithoutNonce())
    copy(buf[:32], h)
    binary.BigEndian.PutUint64(buf[56:], e.Nonce)
    d := new(big.Int).SetBytes(crypto.Keccak256(buf))
    firstBit := math.FirstBitSet(d)
    x := gmath.Pow(2, float64(firstBit))
    x /= float64(e.size())
    x /= float64(e.TTL + diff)
    e.pow = x
}

func (e *Envelope) powToFirstBit(pow float64) int {
    x := pow
    x *= float64(e.size())
    x *= float64(e.TTL)
    bits := gmath.Log2(x)
    bits = gmath.Ceil(bits)
    res := int(bits)
    if res < 1 {
        res = 1
    }
    return res
}

// Hash returns the SHA3 hash of the envelope, calculating it if not yet done.
func (e *Envelope) Hash() common.Hash {
    if (e.hash == common.Hash{}) {
        encoded, _ := rlp.EncodeToBytes(e)
        e.hash = crypto.Keccak256Hash(encoded)
    }
    return e.hash
}

// DecodeRLP decodes an Envelope from an RLP data stream.
func (e *Envelope) DecodeRLP(s *rlp.Stream) error {
    raw, err := s.Raw()
    if err != nil {
        return err
    }
    // The decoding of Envelope uses the struct fields but also needs
    // to compute the hash of the whole RLP-encoded envelope. This
    // type has the same structure as Envelope but is not an
    // rlp.Decoder (does not implement DecodeRLP function).
    // Only public members will be encoded.
    type rlpenv Envelope
    if err := rlp.DecodeBytes(raw, (*rlpenv)(e)); err != nil {
        return err
    }
    e.hash = crypto.Keccak256Hash(raw)
    return nil
}

// OpenAsymmetric tries to decrypt an envelope, potentially encrypted with a particular key.
func (e *Envelope) OpenAsymmetric(key *ecdsa.PrivateKey) (*ReceivedMessage, error) {
    message := &ReceivedMessage{Raw: e.Data}
    err := message.decryptAsymmetric(key)
    switch err {
    case nil:
        return message, nil
    case ecies.ErrInvalidPublicKey: // addressed to somebody else
        return nil, err
    default:
        return nil, fmt.Errorf("unable to open envelope, decrypt failed: %v", err)
    }
}

// OpenSymmetric tries to decrypt an envelope, potentially encrypted with a particular key.
func (e *Envelope) OpenSymmetric(key []byte) (msg *ReceivedMessage, err error) {
    msg = &ReceivedMessage{Raw: e.Data}
    err = msg.decryptSymmetric(key)
    if err != nil {
        msg = nil
    }
    return msg, err
}

// Open tries to decrypt an envelope, and populates the message fields in case of success.
func (e *Envelope) Open(watcher *Filter) (msg *ReceivedMessage) {
    if watcher == nil {
        return nil
    }

    // The API interface forbids filters doing both symmetric and asymmetric encryption.
    if watcher.expectsAsymmetricEncryption() && watcher.expectsSymmetricEncryption() {
        return nil
    }

    if watcher.expectsAsymmetricEncryption() {
        msg, _ = e.OpenAsymmetric(watcher.KeyAsym)
        if msg != nil {
            msg.Dst = &watcher.KeyAsym.PublicKey
        }
    } else if watcher.expectsSymmetricEncryption() {
        msg, _ = e.OpenSymmetric(watcher.KeySym)
        if msg != nil {
            msg.SymKeyHash = crypto.Keccak256Hash(watcher.KeySym)
        }
    }

    if msg != nil {
        ok := msg.ValidateAndParse()
        if !ok {
            return nil
        }
        msg.Topic = e.Topic
        msg.PoW = e.PoW()
        msg.TTL = e.TTL
        msg.Sent = e.Expiry - e.TTL
        msg.EnvelopeHash = e.Hash()
    }
    return msg
}

// Bloom maps 4-bytes Topic into 64-byte bloom filter with 3 bits set (at most).
func (e *Envelope) Bloom() []byte {
    if e.bloom == nil {
        e.bloom = TopicToBloom(e.Topic)
    }
    return e.bloom
}

// TopicToBloom converts the topic (4 bytes) to the bloom filter (64 bytes)
func TopicToBloom(topic TopicType) []byte {
    b := make([]byte, BloomFilterSize)
    var index [3]int
    for j := 0; j < 3; j++ {
        index[j] = int(topic[j])
        if (topic[3] & (1 << uint(j))) != 0 {
            index[j] += 256
        }
    }

    for j := 0; j < 3; j++ {
        byteIndex := index[j] / 8
        bitIndex := index[j] % 8
        b[byteIndex] = (1 << uint(bitIndex))
    }
    return b
}