path: root/whisper/whisperv6/message.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 Message element.

package whisperv6

import (
    "crypto/aes"
    "crypto/cipher"
    "crypto/ecdsa"
    crand "crypto/rand"
    "encoding/binary"
    "errors"
    mrand "math/rand"
    "strconv"

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

// MessageParams specifies the exact way a message should be wrapped
// into an Envelope.
type MessageParams struct {
    TTL      uint32
    Src      *ecdsa.PrivateKey
    Dst      *ecdsa.PublicKey
    KeySym   []byte
    Topic    TopicType
    WorkTime uint32
    PoW      float64
    Payload  []byte
    Padding  []byte
}

// SentMessage represents an end-user data packet to transmit through the
// Whisper protocol. These are wrapped into Envelopes that need not be
// understood by intermediate nodes, just forwarded.
type sentMessage struct {
    Raw []byte
}

// ReceivedMessage represents a data packet to be received through the
// Whisper protocol and successfully decrypted.
type ReceivedMessage struct {
    Raw []byte

    Payload   []byte
    Padding   []byte
    Signature []byte
    Salt      []byte

    PoW   float64          // Proof of work as described in the Whisper spec
    Sent  uint32           // Time when the message was posted into the network
    TTL   uint32           // Maximum time to live allowed for the message
    Src   *ecdsa.PublicKey // Message recipient (identity used to decode the message)
    Dst   *ecdsa.PublicKey // Message recipient (identity used to decode the message)
    Topic TopicType

    SymKeyHash   common.Hash // The Keccak256Hash of the key
    EnvelopeHash common.Hash // Message envelope hash to act as a unique id
}

func isMessageSigned(flags byte) bool {
    return (flags & signatureFlag) != 0
}

func (msg *ReceivedMessage) isSymmetricEncryption() bool {
    return msg.SymKeyHash != common.Hash{}
}

func (msg *ReceivedMessage) isAsymmetricEncryption() bool {
    return msg.Dst != nil
}

// NewSentMessage creates and initializes a non-signed, non-encrypted Whisper message.
func NewSentMessage(params *MessageParams) (*sentMessage, error) {
    const payloadSizeFieldMaxSize = 4
    msg := sentMessage{}
    msg.Raw = make([]byte, 1,
        flagsLength+payloadSizeFieldMaxSize+len(params.Payload)+len(params.Padding)+signatureLength+padSizeLimit)
    msg.Raw[0] = 0 // set all the flags to zero
    msg.addPayloadSizeField(params.Payload)
    msg.Raw = append(msg.Raw, params.Payload...)
    err := msg.appendPadding(params)
    return &msg, err
}

// addPayloadSizeField appends the auxiliary field containing the size of payload
func (msg *sentMessage) addPayloadSizeField(payload []byte) {
    fieldSize := getSizeOfPayloadSizeField(payload)
    field := make([]byte, 4)
    binary.LittleEndian.PutUint32(field, uint32(len(payload)))
    field = field[:fieldSize]
    msg.Raw = append(msg.Raw, field...)
    msg.Raw[0] |= byte(fieldSize)
}

// getSizeOfPayloadSizeField returns the number of bytes necessary to encode the size of payload
func getSizeOfPayloadSizeField(payload []byte) int {
    s := 1
    for i := len(payload); i >= 256; i /= 256 {
        s++
    }
    return s
}

// appendPadding appends the padding specified in params.
// If no padding is provided in params, then random padding is generated.
func (msg *sentMessage) appendPadding(params *MessageParams) error {
    if len(params.Padding) != 0 {
        // padding data was provided by the Dapp, just use it as is
        msg.Raw = append(msg.Raw, params.Padding...)
        return nil
    }

    rawSize := flagsLength + getSizeOfPayloadSizeField(params.Payload) + len(params.Payload)
    if params.Src != nil {
        rawSize += signatureLength
    }
    odd := rawSize % padSizeLimit
    paddingSize := padSizeLimit - odd
    pad := make([]byte, paddingSize)
    _, err := crand.Read(pad)
    if err != nil {
        return err
    }
    if !validateDataIntegrity(pad, paddingSize) {
        return errors.New("failed to generate random padding of size " + strconv.Itoa(paddingSize))
    }
    msg.Raw = append(msg.Raw, pad...)
    return nil
}

// sign calculates and sets the cryptographic signature for the message,
// also setting the sign flag.
func (msg *sentMessage) sign(key *ecdsa.PrivateKey) error {
    if isMessageSigned(msg.Raw[0]) {
        // this should not happen, but no reason to panic
        log.Error("failed to sign the message: already signed")
        return nil
    }

    msg.Raw[0] |= signatureFlag // it is important to set this flag before signing
    hash := crypto.Keccak256(msg.Raw)
    signature, err := crypto.Sign(hash, key)
    if err != nil {
        msg.Raw[0] &= (0xFF ^ signatureFlag) // clear the flag
        return err
    }
    msg.Raw = append(msg.Raw, signature...)
    return nil
}

// encryptAsymmetric encrypts a message with a public key.
func (msg *sentMessage) encryptAsymmetric(key *ecdsa.PublicKey) error {
    if !ValidatePublicKey(key) {
        return errors.New("invalid public key provided for asymmetric encryption")
    }
    encrypted, err := ecies.Encrypt(crand.Reader, ecies.ImportECDSAPublic(key), msg.Raw, nil, nil)
    if err == nil {
        msg.Raw = encrypted
    }
    return err
}

// encryptSymmetric encrypts a message with a topic key, using AES-GCM-256.
// nonce size should be 12 bytes (see cipher.gcmStandardNonceSize).
func (msg *sentMessage) encryptSymmetric(key []byte) (err error) {
    if !validateDataIntegrity(key, aesKeyLength) {
        return errors.New("invalid key provided for symmetric encryption, size: " + strconv.Itoa(len(key)))
    }
    block, err := aes.NewCipher(key)
    if err != nil {
        return err
    }
    aesgcm, err := cipher.NewGCM(block)
    if err != nil {
        return err
    }
    salt, err := generateSecureRandomData(aesNonceLength) // never use more than 2^32 random nonces with a given key
    if err != nil {
        return err
    }
    encrypted := aesgcm.Seal(nil, salt, msg.Raw, nil)
    msg.Raw = append(encrypted, salt...)
    return nil
}

// generateSecureRandomData generates random data where extra security is required.
// The purpose of this function is to prevent some bugs in software or in hardware
// from delivering not-very-random data. This is especially useful for AES nonce,
// where true randomness does not really matter, but it is very important to have
// a unique nonce for every message.
func generateSecureRandomData(length int) ([]byte, error) {
    x := make([]byte, length)
    y := make([]byte, length)
    res := make([]byte, length)

    _, err := crand.Read(x)
    if err != nil {
        return nil, err
    } else if !validateDataIntegrity(x, length) {
        return nil, errors.New("crypto/rand failed to generate secure random data")
    }
    _, err = mrand.Read(y)
    if err != nil {
        return nil, err
    } else if !validateDataIntegrity(y, length) {
        return nil, errors.New("math/rand failed to generate secure random data")
    }
    for i := 0; i < length; i++ {
        res[i] = x[i] ^ y[i]
    }
    if !validateDataIntegrity(res, length) {
        return nil, errors.New("failed to generate secure random data")
    }
    return res, nil
}

// Wrap bundles the message into an Envelope to transmit over the network.
func (msg *sentMessage) Wrap(options *MessageParams) (envelope *Envelope, err error) {
    if options.TTL == 0 {
        options.TTL = DefaultTTL
    }
    if options.Src != nil {
        if err = msg.sign(options.Src); err != nil {
            return nil, err
        }
    }
    if options.Dst != nil {
        err = msg.encryptAsymmetric(options.Dst)
    } else if options.KeySym != nil {
        err = msg.encryptSymmetric(options.KeySym)
    } else {
        err = errors.New("unable to encrypt the message: neither symmetric nor assymmetric key provided")
    }
    if err != nil {
        return nil, err
    }

    envelope = NewEnvelope(options.TTL, options.Topic, msg)
    if err = envelope.Seal(options); err != nil {
        return nil, err
    }
    return envelope, nil
}

// decryptSymmetric decrypts a message with a topic key, using AES-GCM-256.
// nonce size should be 12 bytes (see cipher.gcmStandardNonceSize).
func (msg *ReceivedMessage) decryptSymmetric(key []byte) error {
    // symmetric messages are expected to contain the 12-byte nonce at the end of the payload
    if len(msg.Raw) < aesNonceLength {
        return errors.New("missing salt or invalid payload in symmetric message")
    }
    salt := msg.Raw[len(msg.Raw)-aesNonceLength:]

    block, err := aes.NewCipher(key)
    if err != nil {
        return err
    }
    aesgcm, err := cipher.NewGCM(block)
    if err != nil {
        return err
    }
    decrypted, err := aesgcm.Open(nil, salt, msg.Raw[:len(msg.Raw)-aesNonceLength], nil)
    if err != nil {
        return err
    }
    msg.Raw = decrypted
    msg.Salt = salt
    return nil
}

// decryptAsymmetric decrypts an encrypted payload with a private key.
func (msg *ReceivedMessage) decryptAsymmetric(key *ecdsa.PrivateKey) error {
    decrypted, err := ecies.ImportECDSA(key).Decrypt(crand.Reader, msg.Raw, nil, nil)
    if err == nil {
        msg.Raw = decrypted
    }
    return err
}

// ValidateAndParse checks the message validity and extracts the fields in case of success.
func (msg *ReceivedMessage) ValidateAndParse() bool {
    end := len(msg.Raw)
    if end < 1 {
        return false
    }

    if isMessageSigned(msg.Raw[0]) {
        end -= signatureLength
        if end <= 1 {
            return false
        }
        msg.Signature = msg.Raw[end : end+signatureLength]
        msg.Src = msg.SigToPubKey()
        if msg.Src == nil {
            return false
        }
    }

    beg := 1
    payloadSize := 0
    sizeOfPayloadSizeField := int(msg.Raw[0] & SizeMask) // number of bytes indicating the size of payload
    if sizeOfPayloadSizeField != 0 {
        payloadSize = int(bytesToUintLittleEndian(msg.Raw[beg : beg+sizeOfPayloadSizeField]))
        if payloadSize+1 > end {
            return false
        }
        beg += sizeOfPayloadSizeField
        msg.Payload = msg.Raw[beg : beg+payloadSize]
    }

    beg += payloadSize
    msg.Padding = msg.Raw[beg:end]
    return true
}

// SigToPubKey returns the public key associated to the message's
// signature.
func (msg *ReceivedMessage) SigToPubKey() *ecdsa.PublicKey {
    defer func() { recover() }() // in case of invalid signature

    pub, err := crypto.SigToPub(msg.hash(), msg.Signature)
    if err != nil {
        log.Error("failed to recover public key from signature", "err", err)
        return nil
    }
    return pub
}

// hash calculates the SHA3 checksum of the message flags, payload size field, payload and padding.
func (msg *ReceivedMessage) hash() []byte {
    if isMessageSigned(msg.Raw[0]) {
        sz := len(msg.Raw) - signatureLength
        return crypto.Keccak256(msg.Raw[:sz])
    }
    return crypto.Keccak256(msg.Raw)
}