mirror of
https://github.com/ergochat/ergo.git
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150 lines
4.0 KiB
Go
150 lines
4.0 KiB
Go
// Copyright 2018 by David A. Golden. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may
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// not use this file except in compliance with the License. You may obtain
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// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
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package scram
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import (
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"crypto/hmac"
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"encoding/base64"
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"errors"
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"fmt"
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"strings"
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)
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type clientState int
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const (
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clientStarting clientState = iota
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clientFirst
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clientFinal
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clientDone
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)
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// ClientConversation implements the client-side of an authentication
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// conversation with a server. A new conversation must be created for
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// each authentication attempt.
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type ClientConversation struct {
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client *Client
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nonceGen NonceGeneratorFcn
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hashGen HashGeneratorFcn
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minIters int
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state clientState
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valid bool
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gs2 string
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nonce string
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c1b string
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serveSig []byte
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}
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// Step takes a string provided from a server (or just an empty string for the
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// very first conversation step) and attempts to move the authentication
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// conversation forward. It returns a string to be sent to the server or an
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// error if the server message is invalid. Calling Step after a conversation
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// completes is also an error.
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func (cc *ClientConversation) Step(challenge string) (response string, err error) {
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switch cc.state {
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case clientStarting:
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cc.state = clientFirst
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response, err = cc.firstMsg()
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case clientFirst:
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cc.state = clientFinal
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response, err = cc.finalMsg(challenge)
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case clientFinal:
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cc.state = clientDone
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response, err = cc.validateServer(challenge)
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default:
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response, err = "", errors.New("Conversation already completed")
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}
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return
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}
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// Done returns true if the conversation is completed or has errored.
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func (cc *ClientConversation) Done() bool {
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return cc.state == clientDone
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}
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// Valid returns true if the conversation successfully authenticated with the
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// server, including counter-validation that the server actually has the
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// user's stored credentials.
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func (cc *ClientConversation) Valid() bool {
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return cc.valid
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}
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func (cc *ClientConversation) firstMsg() (string, error) {
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// Values are cached for use in final message parameters
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cc.gs2 = cc.gs2Header()
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cc.nonce = cc.client.nonceGen()
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cc.c1b = fmt.Sprintf("n=%s,r=%s", encodeName(cc.client.username), cc.nonce)
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return cc.gs2 + cc.c1b, nil
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}
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func (cc *ClientConversation) finalMsg(s1 string) (string, error) {
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msg, err := parseServerFirst(s1)
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if err != nil {
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return "", err
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}
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// Check nonce prefix and update
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if !strings.HasPrefix(msg.nonce, cc.nonce) {
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return "", errors.New("server nonce did not extend client nonce")
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}
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cc.nonce = msg.nonce
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// Check iteration count vs minimum
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if msg.iters < cc.minIters {
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return "", fmt.Errorf("server requested too few iterations (%d)", msg.iters)
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}
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// Create client-final-message-without-proof
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c2wop := fmt.Sprintf(
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"c=%s,r=%s",
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base64.StdEncoding.EncodeToString([]byte(cc.gs2)),
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cc.nonce,
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)
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// Create auth message
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authMsg := cc.c1b + "," + s1 + "," + c2wop
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// Get derived keys from client cache
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dk := cc.client.getDerivedKeys(KeyFactors{Salt: string(msg.salt), Iters: msg.iters})
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// Create proof as clientkey XOR clientsignature
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clientSignature := computeHMAC(cc.hashGen, dk.StoredKey, []byte(authMsg))
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clientProof := xorBytes(dk.ClientKey, clientSignature)
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proof := base64.StdEncoding.EncodeToString(clientProof)
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// Cache ServerSignature for later validation
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cc.serveSig = computeHMAC(cc.hashGen, dk.ServerKey, []byte(authMsg))
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return fmt.Sprintf("%s,p=%s", c2wop, proof), nil
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}
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func (cc *ClientConversation) validateServer(s2 string) (string, error) {
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msg, err := parseServerFinal(s2)
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if err != nil {
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return "", err
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}
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if len(msg.err) > 0 {
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return "", fmt.Errorf("server error: %s", msg.err)
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}
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if !hmac.Equal(msg.verifier, cc.serveSig) {
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return "", errors.New("server validation failed")
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}
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cc.valid = true
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return "", nil
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}
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func (cc *ClientConversation) gs2Header() string {
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if cc.client.authzID == "" {
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return "n,,"
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}
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return fmt.Sprintf("n,%s,", encodeName(cc.client.authzID))
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}
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