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/obscuren/ecies"
)

var clogger = ethlogger.NewLogger("CRYPTOID")

const (
    sskLen int = 16  // ecies.MaxSharedKeyLength(pubKey) / 2
    sigLen int = 65  // elliptic S256
    pubLen int = 64  // 512 bit pubkey in uncompressed representation without format byte
    shaLen int = 32  // hash length (for nonce etc)
    msgLen int = 194 // sigLen + shaLen + pubLen + shaLen + 1 = 194
    resLen int = 97  // pubLen + shaLen + 1
    iHSLen int = 307 // size of the final ECIES payload sent as initiator's handshake
    rHSLen int = 210 // size of the final ECIES payload sent as receiver's handshake
)

// secretRW implements a message read writer with encryption and authentication
// it is initialised by cryptoId.Run() after a successful crypto handshake
// aesSecret, macSecret, egressMac, ingress
type secretRW struct {
    aesSecret, macSecret, egressMac, ingressMac []byte
}

type hexkey []byte

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

var nonceF = func(b []byte) (n int, err error) {
    return rand.Read(b)
}

var step = 0
var detnonceF = func(b []byte) (n int, err error) {
    step++
    copy(b, crypto.Sha3([]byte("privacy"+string(step))))
    fmt.Printf("detkey %v: %v\n", step, hexkey(b))
    return
}

var keyF = func() (priv *ecdsa.PrivateKey, err error) {
    priv, err = ecdsa.GenerateKey(crypto.S256(), rand.Reader)
    if err != nil {
        return
    }
    return
}

var detkeyF = func() (priv *ecdsa.PrivateKey, err error) {
    s := make([]byte, 32)
    detnonceF(s)
    priv = crypto.ToECDSA(s)
    return
}

/*
NewSecureSession(connection, privateKey, remotePublicKey, sessionToken, initiator) is called when the peer connection starts to set up a secure session by performing a crypto handshake.

 connection is (a buffered) network connection.

 privateKey is the local client's private key (*ecdsa.PrivateKey)

 remotePublicKey is the remote peer's node Id ([]byte)

 sessionToken is the token from the previous session with this same peer. Nil if no token is found.

 initiator is a boolean flag. True if the node is the initiator of the connection (ie., remote is an outbound peer reached by dialing out). False if the connection was established by accepting a call from the remote peer via a listener.

 It returns a secretRW which implements the MsgReadWriter interface.
*/
func NewSecureSession(conn io.ReadWriter, prvKey *ecdsa.PrivateKey, remotePubKeyS []byte, sessionToken []byte, initiator bool) (token []byte, rw *secretRW, err error) {
    var auth, initNonce, recNonce []byte
    var read int
    var randomPrivKey *ecdsa.PrivateKey
    var remoteRandomPubKey *ecdsa.PublicKey
    clogger.Debugf("attempting session with %v", hexkey(remotePubKeyS))
    if initiator {
        if auth, initNonce, randomPrivKey, _, err = startHandshake(prvKey, remotePubKeyS, sessionToken); err != nil {
            return
        }
        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
        }
        clogger.Debugf("initiator handshake (sent to %v):\n%v", hexkey(remotePubKeyS), hexkey(auth))
        var response []byte = make([]byte, rHSLen)
        if read, err = conn.Read(response); err != nil || read == 0 {
            return
        }
        if read != rHSLen {
            err = fmt.Errorf("remote receiver's handshake has invalid length. expect %v, got %v", rHSLen, read)
            return
        }
        // write out auth message
        // wait for response, then call complete
        if recNonce, remoteRandomPubKey, _, err = completeHandshake(response, prvKey); err != nil {
            return
        }
        clogger.Debugf("receiver-nonce: %v", hexkey(recNonce))
        remoteRandomPubKeyS, _ := ExportPublicKey(remoteRandomPubKey)
        clogger.Debugf("receiver-random-public-key: %v", hexkey(remoteRandomPubKeyS))

    } else {
        auth = make([]byte, iHSLen)
        clogger.Debugf("waiting for initiator handshake (from %v)", hexkey(remotePubKeyS))
        if read, err = conn.Read(auth); err != nil {
            return
        }
        if read != iHSLen {
            err = fmt.Errorf("remote initiator's handshake has invalid length. expect %v, got %v", iHSLen, read)
            return
        }
        clogger.Debugf("received initiator handshake (from %v):\n%v", hexkey(remotePubKeyS), hexkey(auth))
        // 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
        var response []byte
        if response, recNonce, initNonce, randomPrivKey, remoteRandomPubKey, err = respondToHandshake(auth, prvKey, remotePubKeyS, sessionToken); err != nil {
            return
        }
        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
        }
        clogger.Debugf("receiver handshake (sent to %v):\n%v", hexkey(remotePubKeyS), hexkey(response))
    }
    return newSession(initiator, initNonce, recNonce, auth, randomPrivKey, remoteRandomPubKey)
}

/*
ImportPublicKey creates a 512 bit *ecsda.PublicKey from a byte slice. It accepts the simple 64 byte uncompressed format or the 65 byte format given by calling elliptic.Marshal on the EC point represented by the key. Any other length will result in an invalid public key error.
*/
func ImportPublicKey(pubKey []byte) (pubKeyEC *ecdsa.PublicKey, err error) {
    var pubKey65 []byte
    switch len(pubKey) {
    case 64:
        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
}

/*
ExportPublicKey exports a *ecdsa.PublicKey into a byte slice using a simple 64-byte format. and is used for simple serialisation in network communication
*/
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
}

/* startHandshake is called by if the node is the initiator of the connection.

The caller provides the public key of the peer as conjuctured from lookup based on IP:port, given as user input or proven by signatures. The caller must have access to persistant information about the peers, and pass the previous session token as an argument to cryptoId.

The first return value is the auth message that is to be sent out to the remote receiver.
*/
func startHandshake(prvKey *ecdsa.PrivateKey, remotePubKeyS, sessionToken []byte) (auth []byte, initNonce []byte, randomPrvKey *ecdsa.PrivateKey, remotePubKey *ecdsa.PublicKey, err error) {
    // session init, common to both parties
    if remotePubKey, err = ImportPublicKey(remotePubKeyS); 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, msgLen)
    initNonce = msg[msgLen-shaLen-1 : msgLen-1]
    fmt.Printf("init-nonce: ")
    if _, err = nonceF(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
    fmt.Printf("init-random-ecdhe-private-key: ")
    if randomPrvKey, err = keyF(); 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[msgLen-1] = tokenFlag

    // encrypt using remote-pubk
    // auth = eciesEncrypt(remote-pubk, msg)

    if auth, err = crypto.Encrypt(remotePubKey, msg); err != nil {
        return
    }

    return
}

/*
respondToHandshake is called by peer if it accepted (but not initiated) the connection from the remote. It is passed the initiator handshake received, the public key and 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 respondToHandshake(auth []byte, prvKey *ecdsa.PrivateKey, remotePubKeyS, sessionToken []byte) (authResp []byte, respNonce []byte, initNonce []byte, randomPrivKey *ecdsa.PrivateKey, remoteRandomPubKey *ecdsa.PublicKey, err error) {
    var msg []byte
    var remotePubKey *ecdsa.PublicKey
    if remotePubKey, err = ImportPublicKey(remotePubKeyS); err != nil {
        return
    }

    // 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
    }

    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[msgLen-shaLen-1 : msgLen-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, resLen)
    // generate shaLen long nonce
    respNonce = resp[pubLen : pubLen+shaLen]
    fmt.Printf("rec-nonce: ")
    if _, err = nonceF(respNonce); err != nil {
        return
    }
    // generate random keypair for session
    fmt.Printf("rec-random-ecdhe-private-key: ")
    if randomPrivKey, err = keyF(); 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[resLen-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
}

/*
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[resLen-1] == 0x01 {
        tokenFlag = true
    }
    return
}

/*
newSession is called after the handshake is completed. The arguments are values negotiated in the handshake and the return value is a new session : a new session Token to be remembered for the next time we connect with this peer. And a MsgReadWriter that implements an encrypted and authenticated connection with key material obtained from the crypto handshake key exchange
*/
func newSession(initiator bool, initNonce, respNonce, auth []byte, privKey *ecdsa.PrivateKey, remoteRandomPubKey *ecdsa.PublicKey) (sessionToken []byte, rw *secretRW, err error) {
    // 3) Now we can trust ecdhe-random-pubk to derive new keys
    //ecdhe-shared-secret = ecdh.agree(ecdhe-random, remote-ecdhe-random-pubk)
    var dhSharedSecret []byte
    pubKey := ecies.ImportECDSAPublic(remoteRandomPubKey)
    if dhSharedSecret, err = ecies.ImportECDSA(privKey).GenerateShared(pubKey, sskLen, sskLen); err != nil {
        return
    }
    var sharedSecret = crypto.Sha3(append(dhSharedSecret, crypto.Sha3(append(respNonce, initNonce...))...))
    sessionToken = crypto.Sha3(sharedSecret)
    var aesSecret = crypto.Sha3(append(dhSharedSecret, sharedSecret...))
    var macSecret = crypto.Sha3(append(dhSharedSecret, aesSecret...))
    var egressMac, ingressMac []byte
    if initiator {
        egressMac = Xor(macSecret, respNonce)
        ingressMac = Xor(macSecret, initNonce)
    } else {
        egressMac = Xor(macSecret, initNonce)
        ingressMac = Xor(macSecret, respNonce)
    }
    rw = &secretRW{
        aesSecret:  aesSecret,
        macSecret:  macSecret,
        egressMac:  egressMac,
        ingressMac: ingressMac,
    }
    clogger.Debugf("aes-secret: %v", hexkey(aesSecret))
    clogger.Debugf("mac-secret: %v", hexkey(macSecret))
    clogger.Debugf("egress-mac: %v", hexkey(egressMac))
    clogger.Debugf("ingress-mac: %v", hexkey(ingressMac))
    return
}

// TODO: optimisation
// should use cipher.xorBytes from crypto/cipher/xor.go for fast xor
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
}