forked from cwtch.im/tapir
102 lines
3.6 KiB
Go
102 lines
3.6 KiB
Go
package applications
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import (
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"crypto/subtle"
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"cwtch.im/tapir"
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"cwtch.im/tapir/primitives"
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"encoding/json"
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"git.openprivacy.ca/openprivacy/libricochet-go/log"
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"git.openprivacy.ca/openprivacy/libricochet-go/utils"
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"golang.org/x/crypto/ed25519"
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"golang.org/x/crypto/sha3"
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"time"
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)
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// AuthMessage is exchanged between peers to obtain the Auth Capability
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type AuthMessage struct {
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LongTermPublicKey ed25519.PublicKey
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EphemeralPublicKey ed25519.PublicKey
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}
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// AuthCapability defines the Authentication Capability granted by AuthApp
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const AuthCapability = "AUTH"
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// AuthApp is the concrete Application type that handles Authentication
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type AuthApp struct {
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}
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// NewInstance creates a new instance of the AuthApp
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func (ea AuthApp) NewInstance() tapir.Application {
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return new(AuthApp)
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}
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// Init runs the entire AuthApp protocol, at the end of the protocol either the connection is granted AUTH capability
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// or the connection is closed.
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func (ea AuthApp) Init(connection tapir.Connection) {
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longTermPubKey := ed25519.PublicKey(connection.ID().PublicKeyBytes())
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ephemeralIdentity, _ := primitives.InitializeEphemeralIdentity()
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authMessage := AuthMessage{LongTermPublicKey: longTermPubKey, EphemeralPublicKey: ephemeralIdentity.PublicKey()}
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serialized, _ := json.Marshal(authMessage)
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connection.Send(serialized)
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message := connection.Expect()
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var remoteAuthMessage AuthMessage
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err := json.Unmarshal(message, &remoteAuthMessage)
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if err != nil {
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connection.Close()
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return
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}
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// If we are an outbound connection we can perform an additional check to ensure that the server sent us back the correct long term
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// public key
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if connection.IsOutbound() && utils.GetTorV3Hostname(remoteAuthMessage.LongTermPublicKey) != connection.Hostname() {
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log.Errorf("The remote server (%v) has attempted to authenticate with a different public key %v", connection.Hostname(), utils.GetTorV3Hostname(remoteAuthMessage.LongTermPublicKey))
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connection.Close()
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return
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}
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// Perform the triple-diffie-hellman exchange.
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key := primitives.Perform3DH(connection.ID(), &ephemeralIdentity, remoteAuthMessage.LongTermPublicKey, remoteAuthMessage.EphemeralPublicKey, connection.IsOutbound())
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connection.SetEncryptionKey(key)
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// Wait to Sync (we need to ensure that both the Local and Remote server have turned encryption on
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// otherwise our next Send will fail.
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time.Sleep(time.Second)
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// TODO: Replace this with proper transcript primitive
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challengeRemote, err := json.Marshal(remoteAuthMessage)
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if err != nil {
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connection.Close()
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return
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}
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challengeLocal, err := json.Marshal(authMessage)
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if err != nil {
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connection.Close()
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return
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}
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challenge := sha3.New512()
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if connection.IsOutbound() {
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challenge.Write(challengeLocal)
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challenge.Write(challengeRemote)
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} else {
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challenge.Write(challengeRemote)
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challenge.Write(challengeLocal)
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}
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// Since we have set the encryption key on the connection the connection will encrypt any messages we send with that key
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// To test that the remote peer has done the same we calculate a challenge hash based on the transcript so far and send it to them
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// We expect the remote to do the same, and compare the two.
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// If successful we extend our auth capability to the connection and reassert the hostname.
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challengeBytes := challenge.Sum([]byte{})
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connection.Send(challengeBytes)
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remoteChallenge := connection.Expect()
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if subtle.ConstantTimeCompare(challengeBytes, remoteChallenge) == 1 {
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connection.SetHostname(utils.GetTorV3Hostname(remoteAuthMessage.LongTermPublicKey))
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connection.SetCapability(AuthCapability)
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} else {
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log.Errorf("Failed Decrypt Challenge: [%x] [%x]\n", remoteChallenge, challengeBytes)
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connection.Close()
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}
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}
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