e7610eadfe
Now that the AES salt has been moved to the payload, padding must be adjusted to hide it, lest an attacker guesses that the packet uses symmetric encryption.
364 lines
11 KiB
Go
364 lines
11 KiB
Go
// Copyright 2016 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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// Contains the Whisper protocol Message element.
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package whisperv6
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import (
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"crypto/aes"
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"crypto/cipher"
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"crypto/ecdsa"
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crand "crypto/rand"
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"encoding/binary"
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"errors"
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"strconv"
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"github.com/ethereum/go-ethereum/common"
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"github.com/ethereum/go-ethereum/crypto"
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"github.com/ethereum/go-ethereum/crypto/ecies"
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"github.com/ethereum/go-ethereum/log"
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)
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// Options specifies the exact way a message should be wrapped into an Envelope.
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type MessageParams struct {
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TTL uint32
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Src *ecdsa.PrivateKey
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Dst *ecdsa.PublicKey
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KeySym []byte
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Topic TopicType
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WorkTime uint32
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PoW float64
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Payload []byte
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Padding []byte
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}
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// SentMessage represents an end-user data packet to transmit through the
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// Whisper protocol. These are wrapped into Envelopes that need not be
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// understood by intermediate nodes, just forwarded.
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type sentMessage struct {
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Raw []byte
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}
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// ReceivedMessage represents a data packet to be received through the
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// Whisper protocol.
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type ReceivedMessage struct {
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Raw []byte
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Payload []byte
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Padding []byte
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Signature []byte
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Salt []byte
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PoW float64 // Proof of work as described in the Whisper spec
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Sent uint32 // Time when the message was posted into the network
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TTL uint32 // Maximum time to live allowed for the message
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Src *ecdsa.PublicKey // Message recipient (identity used to decode the message)
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Dst *ecdsa.PublicKey // Message recipient (identity used to decode the message)
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Topic TopicType
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SymKeyHash common.Hash // The Keccak256Hash of the key, associated with the Topic
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EnvelopeHash common.Hash // Message envelope hash to act as a unique id
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}
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func isMessageSigned(flags byte) bool {
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return (flags & signatureFlag) != 0
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}
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func (msg *ReceivedMessage) isSymmetricEncryption() bool {
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return msg.SymKeyHash != common.Hash{}
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}
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func (msg *ReceivedMessage) isAsymmetricEncryption() bool {
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return msg.Dst != nil
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}
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// NewMessage creates and initializes a non-signed, non-encrypted Whisper message.
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func NewSentMessage(params *MessageParams) (*sentMessage, error) {
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msg := sentMessage{}
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msg.Raw = make([]byte, 1, len(params.Payload)+len(params.Padding)+signatureLength+padSizeLimit)
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msg.Raw[0] = 0 // set all the flags to zero
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err := msg.appendPadding(params)
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if err != nil {
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return nil, err
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}
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msg.Raw = append(msg.Raw, params.Payload...)
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return &msg, nil
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}
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// getSizeOfLength returns the number of bytes necessary to encode the entire size padding (including these bytes)
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func getSizeOfLength(b []byte) (sz int, err error) {
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sz = intSize(len(b)) // first iteration
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sz = intSize(len(b) + sz) // second iteration
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if sz > 3 {
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err = errors.New("oversized padding parameter")
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}
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return sz, err
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}
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// sizeOfIntSize returns minimal number of bytes necessary to encode an integer value
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func intSize(i int) (s int) {
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for s = 1; i >= 256; s++ {
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i /= 256
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}
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return s
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}
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// appendPadding appends the pseudorandom padding bytes and sets the padding flag.
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// The last byte contains the size of padding (thus, its size must not exceed 256).
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func (msg *sentMessage) appendPadding(params *MessageParams) error {
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rawSize := len(params.Payload) + 1
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if params.Src != nil {
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rawSize += signatureLength
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}
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if params.KeySym != nil {
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rawSize += AESNonceLength
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}
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odd := rawSize % padSizeLimit
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if len(params.Padding) != 0 {
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padSize := len(params.Padding)
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padLengthSize, err := getSizeOfLength(params.Padding)
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if err != nil {
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return err
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}
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totalPadSize := padSize + padLengthSize
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buf := make([]byte, 8)
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binary.LittleEndian.PutUint32(buf, uint32(totalPadSize))
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buf = buf[:padLengthSize]
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msg.Raw = append(msg.Raw, buf...)
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msg.Raw = append(msg.Raw, params.Padding...)
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msg.Raw[0] |= byte(padLengthSize) // number of bytes indicating the padding size
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} else if odd != 0 {
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totalPadSize := padSizeLimit - odd
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if totalPadSize > 255 {
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// this algorithm is only valid if padSizeLimit < 256.
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// if padSizeLimit will ever change, please fix the algorithm
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// (please see also ReceivedMessage.extractPadding() function).
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panic("please fix the padding algorithm before releasing new version")
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}
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buf := make([]byte, totalPadSize)
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_, err := crand.Read(buf[1:])
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if err != nil {
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return err
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}
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if totalPadSize > 6 && !validateSymmetricKey(buf) {
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return errors.New("failed to generate random padding of size " + strconv.Itoa(totalPadSize))
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}
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buf[0] = byte(totalPadSize)
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msg.Raw = append(msg.Raw, buf...)
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msg.Raw[0] |= byte(0x1) // number of bytes indicating the padding size
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}
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return nil
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}
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// sign calculates and sets the cryptographic signature for the message,
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// also setting the sign flag.
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func (msg *sentMessage) sign(key *ecdsa.PrivateKey) error {
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if isMessageSigned(msg.Raw[0]) {
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// this should not happen, but no reason to panic
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log.Error("failed to sign the message: already signed")
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return nil
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}
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msg.Raw[0] |= signatureFlag
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hash := crypto.Keccak256(msg.Raw)
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signature, err := crypto.Sign(hash, key)
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if err != nil {
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msg.Raw[0] &= ^signatureFlag // clear the flag
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return err
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}
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msg.Raw = append(msg.Raw, signature...)
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return nil
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}
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// encryptAsymmetric encrypts a message with a public key.
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func (msg *sentMessage) encryptAsymmetric(key *ecdsa.PublicKey) error {
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if !ValidatePublicKey(key) {
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return errors.New("invalid public key provided for asymmetric encryption")
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}
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encrypted, err := ecies.Encrypt(crand.Reader, ecies.ImportECDSAPublic(key), msg.Raw, nil, nil)
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if err == nil {
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msg.Raw = encrypted
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}
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return err
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}
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// encryptSymmetric encrypts a message with a topic key, using AES-GCM-256.
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// nonce size should be 12 bytes (see cipher.gcmStandardNonceSize).
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func (msg *sentMessage) encryptSymmetric(key []byte) (err error) {
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if !validateSymmetricKey(key) {
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return errors.New("invalid key provided for symmetric encryption")
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}
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block, err := aes.NewCipher(key)
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if err != nil {
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return err
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}
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aesgcm, err := cipher.NewGCM(block)
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if err != nil {
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return err
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}
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// never use more than 2^32 random nonces with a given key
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salt := make([]byte, aesgcm.NonceSize())
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_, err = crand.Read(salt)
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if err != nil {
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return err
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} else if !validateSymmetricKey(salt) {
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return errors.New("crypto/rand failed to generate salt")
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}
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msg.Raw = append(aesgcm.Seal(nil, salt, msg.Raw, nil), salt...)
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return nil
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}
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// Wrap bundles the message into an Envelope to transmit over the network.
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func (msg *sentMessage) Wrap(options *MessageParams) (envelope *Envelope, err error) {
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if options.TTL == 0 {
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options.TTL = DefaultTTL
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}
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if options.Src != nil {
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if err = msg.sign(options.Src); err != nil {
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return nil, err
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}
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}
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if options.Dst != nil {
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err = msg.encryptAsymmetric(options.Dst)
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} else if options.KeySym != nil {
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err = msg.encryptSymmetric(options.KeySym)
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} else {
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err = errors.New("unable to encrypt the message: neither symmetric nor assymmetric key provided")
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}
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if err != nil {
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return nil, err
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}
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envelope = NewEnvelope(options.TTL, options.Topic, msg)
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if err = envelope.Seal(options); err != nil {
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return nil, err
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}
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return envelope, nil
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}
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// decryptSymmetric decrypts a message with a topic key, using AES-GCM-256.
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// nonce size should be 12 bytes (see cipher.gcmStandardNonceSize).
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func (msg *ReceivedMessage) decryptSymmetric(key []byte) error {
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// In v6, symmetric messages are expected to contain the 12-byte
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// "salt" at the end of the payload.
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if len(msg.Raw) < AESNonceLength {
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return errors.New("missing salt or invalid payload in symmetric message")
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}
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salt := msg.Raw[len(msg.Raw)-AESNonceLength:]
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block, err := aes.NewCipher(key)
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if err != nil {
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return err
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}
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aesgcm, err := cipher.NewGCM(block)
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if err != nil {
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return err
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}
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if len(salt) != aesgcm.NonceSize() {
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log.Error("decrypting the message", "AES salt size", len(salt))
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return errors.New("wrong AES salt size")
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}
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decrypted, err := aesgcm.Open(nil, salt, msg.Raw[:len(msg.Raw)-AESNonceLength], nil)
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if err != nil {
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return err
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}
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msg.Raw = decrypted
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msg.Salt = salt
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return nil
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}
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// decryptAsymmetric decrypts an encrypted payload with a private key.
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func (msg *ReceivedMessage) decryptAsymmetric(key *ecdsa.PrivateKey) error {
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decrypted, err := ecies.ImportECDSA(key).Decrypt(crand.Reader, msg.Raw, nil, nil)
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if err == nil {
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msg.Raw = decrypted
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}
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return err
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}
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// Validate checks the validity and extracts the fields in case of success
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func (msg *ReceivedMessage) Validate() bool {
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end := len(msg.Raw)
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if end < 1 {
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return false
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}
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if isMessageSigned(msg.Raw[0]) {
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end -= signatureLength
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if end <= 1 {
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return false
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}
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msg.Signature = msg.Raw[end:]
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msg.Src = msg.SigToPubKey()
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if msg.Src == nil {
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return false
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}
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}
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padSize, ok := msg.extractPadding(end)
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if !ok {
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return false
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}
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msg.Payload = msg.Raw[1+padSize : end]
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return true
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}
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// extractPadding extracts the padding from raw message.
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// although we don't support sending messages with padding size
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// exceeding 255 bytes, such messages are perfectly valid, and
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// can be successfully decrypted.
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func (msg *ReceivedMessage) extractPadding(end int) (int, bool) {
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paddingSize := 0
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sz := int(msg.Raw[0] & paddingMask) // number of bytes indicating the entire size of padding (including these bytes)
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// could be zero -- it means no padding
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if sz != 0 {
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paddingSize = int(bytesToUintLittleEndian(msg.Raw[1 : 1+sz]))
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if paddingSize < sz || paddingSize+1 > end {
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return 0, false
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}
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msg.Padding = msg.Raw[1+sz : 1+paddingSize]
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}
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return paddingSize, true
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}
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// Recover retrieves the public key of the message signer.
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func (msg *ReceivedMessage) SigToPubKey() *ecdsa.PublicKey {
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defer func() { recover() }() // in case of invalid signature
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pub, err := crypto.SigToPub(msg.hash(), msg.Signature)
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if err != nil {
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log.Error("failed to recover public key from signature", "err", err)
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return nil
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}
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return pub
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}
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// hash calculates the SHA3 checksum of the message flags, payload and padding.
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func (msg *ReceivedMessage) hash() []byte {
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if isMessageSigned(msg.Raw[0]) {
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sz := len(msg.Raw) - signatureLength
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return crypto.Keccak256(msg.Raw[:sz])
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}
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return crypto.Keccak256(msg.Raw)
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}
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