path: root/p2p/crypto.go

package p2p

import (
    // "binary"
    "crypto/ecdsa"
    "crypto/rand"
    "fmt"
    "io"

    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/crypto/secp256k1"
    ethlogger "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/p2p/discover"
    "github.com/obscuren/ecies"
)

var clogger = ethlogger.NewLogger("CRYPTOID")

const (
    sskLen = 16 // ecies.MaxSharedKeyLength(pubKey) / 2
    sigLen = 65 // elliptic S256
    pubLen = 64 // 512 bit pubkey in uncompressed representation without format byte
    shaLen = 32 // hash length (for nonce etc)

    authMsgLen  = sigLen + shaLen + pubLen + shaLen + 1
    authRespLen = pubLen + shaLen + 1

    eciesBytes = 65 + 16 + 32
    iHSLen     = authMsgLen + eciesBytes  // size of the final ECIES payload sent as initiator's handshake
    rHSLen     = authRespLen + eciesBytes // size of the final ECIES payload sent as receiver's handshake
)

type hexkey []byte

func (self hexkey) String() string {
    return fmt.Sprintf("(%d) %x", len(self), []byte(self))
}

func encHandshake(conn io.ReadWriter, prv *ecdsa.PrivateKey, dial *discover.Node) (
    remoteID discover.NodeID,
    sessionToken []byte,
    err error,
) {
    if dial == nil {
        var remotePubkey []byte
        sessionToken, remotePubkey, err = inboundEncHandshake(conn, prv, nil)
        copy(remoteID[:], remotePubkey)
    } else {
        remoteID = dial.ID
        sessionToken, err = outboundEncHandshake(conn, prv, remoteID[:], nil)
    }
    return remoteID, sessionToken, err
}

// outboundEncHandshake negotiates a session token on conn.
// it should be called on the dialing side of the connection.
//
// privateKey is the local client's private key
// remotePublicKey is the remote peer's node ID
// sessionToken is the token from a previous session with this node.
func outboundEncHandshake(conn io.ReadWriter, prvKey *ecdsa.PrivateKey, remotePublicKey []byte, sessionToken []byte) (
    newSessionToken []byte,
    err error,
) {
    auth, initNonce, randomPrivKey, err := authMsg(prvKey, remotePublicKey, sessionToken)
    if err != nil {
        return nil, err
    }
    if sessionToken != nil {
        clogger.Debugf("session-token: %v", hexkey(sessionToken))
    }

    clogger.Debugf("initiator-nonce: %v", hexkey(initNonce))
    clogger.Debugf("initiator-random-private-key: %v", hexkey(crypto.FromECDSA(randomPrivKey)))
    randomPublicKeyS, _ := exportPublicKey(&randomPrivKey.PublicKey)
    clogger.Debugf("initiator-random-public-key: %v", hexkey(randomPublicKeyS))
    if _, err = conn.Write(auth); err != nil {
        return nil, err
    }
    clogger.Debugf("initiator handshake: %v", hexkey(auth))

    response := make([]byte, rHSLen)
    if _, err = io.ReadFull(conn, response); err != nil {
        return nil, err
    }
    recNonce, remoteRandomPubKey, _, err := completeHandshake(response, prvKey)
    if err != nil {
        return nil, err
    }

    clogger.Debugf("receiver-nonce: %v", hexkey(recNonce))
    remoteRandomPubKeyS, _ := exportPublicKey(remoteRandomPubKey)
    clogger.Debugf("receiver-random-public-key: %v", hexkey(remoteRandomPubKeyS))
    return newSession(initNonce, recNonce, randomPrivKey, remoteRandomPubKey)
}

// authMsg creates the initiator handshake.
func authMsg(prvKey *ecdsa.PrivateKey, remotePubKeyS, sessionToken []byte) (
    auth, initNonce []byte,
    randomPrvKey *ecdsa.PrivateKey,
    err error,
) {
    // session init, common to both parties
    remotePubKey, err := importPublicKey(remotePubKeyS)
    if err != nil {
        return
    }

    var tokenFlag byte // = 0x00
    if sessionToken == nil {
        // no session token found means we need to generate shared secret.
        // ecies shared secret is used as initial session token for new peers
        // generate shared key from prv and remote pubkey
        if sessionToken, err = ecies.ImportECDSA(prvKey).GenerateShared(ecies.ImportECDSAPublic(remotePubKey), sskLen, sskLen); err != nil {
            return
        }
        // tokenFlag = 0x00 // redundant
    } else {
        // for known peers, we use stored token from the previous session
        tokenFlag = 0x01
    }

    //E(remote-pubk, S(ecdhe-random, ecdh-shared-secret^nonce) || H(ecdhe-random-pubk) || pubk || nonce || 0x0)
    // E(remote-pubk, S(ecdhe-random, token^nonce) || H(ecdhe-random-pubk) || pubk || nonce || 0x1)
    // allocate msgLen long message,
    var msg []byte = make([]byte, authMsgLen)
    initNonce = msg[authMsgLen-shaLen-1 : authMsgLen-1]
    if _, err = rand.Read(initNonce); err != nil {
        return
    }
    // create known message
    // ecdh-shared-secret^nonce for new peers
    // token^nonce for old peers
    var sharedSecret = xor(sessionToken, initNonce)

    // generate random keypair to use for signing
    if randomPrvKey, err = crypto.GenerateKey(); err != nil {
        return
    }
    // sign shared secret (message known to both parties): shared-secret
    var signature []byte
    // signature = sign(ecdhe-random, shared-secret)
    // uses secp256k1.Sign
    if signature, err = crypto.Sign(sharedSecret, randomPrvKey); err != nil {
        return
    }

    // message
    // signed-shared-secret || H(ecdhe-random-pubk) || pubk || nonce || 0x0
    copy(msg, signature) // copy signed-shared-secret
    // H(ecdhe-random-pubk)
    var randomPubKey64 []byte
    if randomPubKey64, err = exportPublicKey(&randomPrvKey.PublicKey); err != nil {
        return
    }
    var pubKey64 []byte
    if pubKey64, err = exportPublicKey(&prvKey.PublicKey); err != nil {
        return
    }
    copy(msg[sigLen:sigLen+shaLen], crypto.Sha3(randomPubKey64))
    // pubkey copied to the correct segment.
    copy(msg[sigLen+shaLen:sigLen+shaLen+pubLen], pubKey64)
    // nonce is already in the slice
    // stick tokenFlag byte to the end
    msg[authMsgLen-1] = tokenFlag

    // encrypt using remote-pubk
    // auth = eciesEncrypt(remote-pubk, msg)
    if auth, err = crypto.Encrypt(remotePubKey, msg); err != nil {
        return
    }
    return
}

// completeHandshake is called when the initiator receives an
// authentication response (aka receiver handshake). It completes the
// handshake by reading off parameters the remote peer provides needed
// to set up the secure session.
func completeHandshake(auth []byte, prvKey *ecdsa.PrivateKey) (
    respNonce []byte,
    remoteRandomPubKey *ecdsa.PublicKey,
    tokenFlag bool,
    err error,
) {
    var msg []byte
    // they prove that msg is meant for me,
    // I prove I possess private key if i can read it
    if msg, err = crypto.Decrypt(prvKey, auth); err != nil {
        return
    }

    respNonce = msg[pubLen : pubLen+shaLen]
    var remoteRandomPubKeyS = msg[:pubLen]
    if remoteRandomPubKey, err = importPublicKey(remoteRandomPubKeyS); err != nil {
        return
    }
    if msg[authRespLen-1] == 0x01 {
        tokenFlag = true
    }
    return
}

// inboundEncHandshake negotiates a session token on conn.
// it should be called on the listening side of the connection.
//
// privateKey is the local client's private key
// sessionToken is the token from a previous session with this node.
func inboundEncHandshake(conn io.ReadWriter, prvKey *ecdsa.PrivateKey, sessionToken []byte) (
    token, remotePubKey []byte,
    err error,
) {
    // we are listening connection. we are responders in the
    // handshake. Extract info from the authentication. The initiator
    // starts by sending us a handshake that we need to respond to. so
    // we read auth message first, then respond.
    auth := make([]byte, iHSLen)
    if _, err := io.ReadFull(conn, auth); err != nil {
        return nil, nil, err
    }
    response, recNonce, initNonce, remotePubKey, randomPrivKey, remoteRandomPubKey, err := authResp(auth, sessionToken, prvKey)
    if err != nil {
        return nil, nil, err
    }
    clogger.Debugf("receiver-nonce: %v", hexkey(recNonce))
    clogger.Debugf("receiver-random-priv-key: %v", hexkey(crypto.FromECDSA(randomPrivKey)))
    if _, err = conn.Write(response); err != nil {
        return nil, nil, err
    }
    clogger.Debugf("receiver handshake:\n%v", hexkey(response))
    token, err = newSession(initNonce, recNonce, randomPrivKey, remoteRandomPubKey)
    return token, remotePubKey, err
}

// authResp is called by peer if it accepted (but not
// initiated) the connection from the remote. It is passed the initiator
// handshake received and the session token belonging to the
// remote initiator.
//
// The first return value is the authentication response (aka receiver
// handshake) that is to be sent to the remote initiator.
func authResp(auth, sessionToken []byte, prvKey *ecdsa.PrivateKey) (
    authResp, respNonce, initNonce, remotePubKeyS []byte,
    randomPrivKey *ecdsa.PrivateKey,
    remoteRandomPubKey *ecdsa.PublicKey,
    err error,
) {
    // they prove that msg is meant for me,
    // I prove I possess private key if i can read it
    msg, err := crypto.Decrypt(prvKey, auth)
    if err != nil {
        return
    }

    remotePubKeyS = msg[sigLen+shaLen : sigLen+shaLen+pubLen]
    remotePubKey, _ := importPublicKey(remotePubKeyS)

    var tokenFlag byte
    if sessionToken == nil {
        // no session token found means we need to generate shared secret.
        // ecies shared secret is used as initial session token for new peers
        // generate shared key from prv and remote pubkey
        if sessionToken, err = ecies.ImportECDSA(prvKey).GenerateShared(ecies.ImportECDSAPublic(remotePubKey), sskLen, sskLen); err != nil {
            return
        }
        // tokenFlag = 0x00 // redundant
    } else {
        // for known peers, we use stored token from the previous session
        tokenFlag = 0x01
    }

    // the initiator nonce is read off the end of the message
    initNonce = msg[authMsgLen-shaLen-1 : authMsgLen-1]
    // I prove that i own prv key (to derive shared secret, and read
    // nonce off encrypted msg) and that I own shared secret they
    // prove they own the private key belonging to ecdhe-random-pubk
    // we can now reconstruct the signed message and recover the peers
    // pubkey
    var signedMsg = xor(sessionToken, initNonce)
    var remoteRandomPubKeyS []byte
    if remoteRandomPubKeyS, err = secp256k1.RecoverPubkey(signedMsg, msg[:sigLen]); err != nil {
        return
    }
    // convert to ECDSA standard
    if remoteRandomPubKey, err = importPublicKey(remoteRandomPubKeyS); err != nil {
        return
    }

    // now we find ourselves a long task too, fill it random
    var resp = make([]byte, authRespLen)
    // generate shaLen long nonce
    respNonce = resp[pubLen : pubLen+shaLen]
    if _, err = rand.Read(respNonce); err != nil {
        return
    }
    // generate random keypair for session
    if randomPrivKey, err = crypto.GenerateKey(); err != nil {
        return
    }
    // responder auth message
    // E(remote-pubk, ecdhe-random-pubk || nonce || 0x0)
    var randomPubKeyS []byte
    if randomPubKeyS, err = exportPublicKey(&randomPrivKey.PublicKey); err != nil {
        return
    }
    copy(resp[:pubLen], randomPubKeyS)
    // nonce is already in the slice
    resp[authRespLen-1] = tokenFlag

    // encrypt using remote-pubk
    // auth = eciesEncrypt(remote-pubk, msg)
    // why not encrypt with ecdhe-random-remote
    if authResp, err = crypto.Encrypt(remotePubKey, resp); err != nil {
        return
    }
    return
}

// newSession is called after the handshake is completed. The
// arguments are values negotiated in the handshake. The return value
// is a new session Token to be remembered for the next time we
// connect with this peer.
func newSession(initNonce, respNonce []byte, privKey *ecdsa.PrivateKey, remoteRandomPubKey *ecdsa.PublicKey) ([]byte, error) {
    // 3) Now we can trust ecdhe-random-pubk to derive new keys
    //ecdhe-shared-secret = ecdh.agree(ecdhe-random, remote-ecdhe-random-pubk)
    pubKey := ecies.ImportECDSAPublic(remoteRandomPubKey)
    dhSharedSecret, err := ecies.ImportECDSA(privKey).GenerateShared(pubKey, sskLen, sskLen)
    if err != nil {
        return nil, err
    }
    sharedSecret := crypto.Sha3(dhSharedSecret, crypto.Sha3(respNonce, initNonce))
    sessionToken := crypto.Sha3(sharedSecret)
    return sessionToken, nil
}

// importPublicKey unmarshals 512 bit public keys.
func importPublicKey(pubKey []byte) (pubKeyEC *ecdsa.PublicKey, err error) {
    var pubKey65 []byte
    switch len(pubKey) {
    case 64:
        // add 'uncompressed key' flag
        pubKey65 = append([]byte{0x04}, pubKey...)
    case 65:
        pubKey65 = pubKey
    default:
        return nil, fmt.Errorf("invalid public key length %v (expect 64/65)", len(pubKey))
    }
    return crypto.ToECDSAPub(pubKey65), nil
}

func exportPublicKey(pubKeyEC *ecdsa.PublicKey) (pubKey []byte, err error) {
    if pubKeyEC == nil {
        return nil, fmt.Errorf("no ECDSA public key given")
    }
    return crypto.FromECDSAPub(pubKeyEC)[1:], nil
}

func xor(one, other []byte) (xor []byte) {
    xor = make([]byte, len(one))
    for i := 0; i < len(one); i++ {
        xor[i] = one[i] ^ other[i]
    }
    return xor
}