Don Newton | 379ae25 | 2019-04-01 12:17:06 -0400 | [diff] [blame^] | 1 | // Copyright 2018 by David A. Golden. All rights reserved. |
| 2 | // |
| 3 | // Licensed under the Apache License, Version 2.0 (the "License"); you may |
| 4 | // not use this file except in compliance with the License. You may obtain |
| 5 | // a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 |
| 6 | |
| 7 | package scram |
| 8 | |
| 9 | import ( |
| 10 | "sync" |
| 11 | |
| 12 | "golang.org/x/crypto/pbkdf2" |
| 13 | ) |
| 14 | |
| 15 | // Client implements the client side of SCRAM authentication. It holds |
| 16 | // configuration values needed to initialize new client-side conversations for |
| 17 | // a specific username, password and authorization ID tuple. Client caches |
| 18 | // the computationally-expensive parts of a SCRAM conversation as described in |
| 19 | // RFC-5802. If repeated authentication conversations may be required for a |
| 20 | // user (e.g. disconnect/reconnect), the user's Client should be preserved. |
| 21 | // |
| 22 | // For security reasons, Clients have a default minimum PBKDF2 iteration count |
| 23 | // of 4096. If a server requests a smaller iteration count, an authentication |
| 24 | // conversation will error. |
| 25 | // |
| 26 | // A Client can also be used by a server application to construct the hashed |
| 27 | // authentication values to be stored for a new user. See StoredCredentials() |
| 28 | // for more. |
| 29 | type Client struct { |
| 30 | sync.RWMutex |
| 31 | username string |
| 32 | password string |
| 33 | authzID string |
| 34 | minIters int |
| 35 | nonceGen NonceGeneratorFcn |
| 36 | hashGen HashGeneratorFcn |
| 37 | cache map[KeyFactors]derivedKeys |
| 38 | } |
| 39 | |
| 40 | func newClient(username, password, authzID string, fcn HashGeneratorFcn) *Client { |
| 41 | return &Client{ |
| 42 | username: username, |
| 43 | password: password, |
| 44 | authzID: authzID, |
| 45 | minIters: 4096, |
| 46 | nonceGen: defaultNonceGenerator, |
| 47 | hashGen: fcn, |
| 48 | cache: make(map[KeyFactors]derivedKeys), |
| 49 | } |
| 50 | } |
| 51 | |
| 52 | // WithMinIterations changes minimum required PBKDF2 iteration count. |
| 53 | func (c *Client) WithMinIterations(n int) *Client { |
| 54 | c.Lock() |
| 55 | defer c.Unlock() |
| 56 | c.minIters = n |
| 57 | return c |
| 58 | } |
| 59 | |
| 60 | // WithNonceGenerator replaces the default nonce generator (base64 encoding of |
| 61 | // 24 bytes from crypto/rand) with a custom generator. This is provided for |
| 62 | // testing or for users with custom nonce requirements. |
| 63 | func (c *Client) WithNonceGenerator(ng NonceGeneratorFcn) *Client { |
| 64 | c.Lock() |
| 65 | defer c.Unlock() |
| 66 | c.nonceGen = ng |
| 67 | return c |
| 68 | } |
| 69 | |
| 70 | // NewConversation constructs a client-side authentication conversation. |
| 71 | // Conversations cannot be reused, so this must be called for each new |
| 72 | // authentication attempt. |
| 73 | func (c *Client) NewConversation() *ClientConversation { |
| 74 | c.RLock() |
| 75 | defer c.RUnlock() |
| 76 | return &ClientConversation{ |
| 77 | client: c, |
| 78 | nonceGen: c.nonceGen, |
| 79 | hashGen: c.hashGen, |
| 80 | minIters: c.minIters, |
| 81 | } |
| 82 | } |
| 83 | |
| 84 | func (c *Client) getDerivedKeys(kf KeyFactors) derivedKeys { |
| 85 | dk, ok := c.getCache(kf) |
| 86 | if !ok { |
| 87 | dk = c.computeKeys(kf) |
| 88 | c.setCache(kf, dk) |
| 89 | } |
| 90 | return dk |
| 91 | } |
| 92 | |
| 93 | // GetStoredCredentials takes a salt and iteration count structure and |
| 94 | // provides the values that must be stored by a server to authentication a |
| 95 | // user. These values are what the Server credential lookup function must |
| 96 | // return for a given username. |
| 97 | func (c *Client) GetStoredCredentials(kf KeyFactors) StoredCredentials { |
| 98 | dk := c.getDerivedKeys(kf) |
| 99 | return StoredCredentials{ |
| 100 | KeyFactors: kf, |
| 101 | StoredKey: dk.StoredKey, |
| 102 | ServerKey: dk.ServerKey, |
| 103 | } |
| 104 | } |
| 105 | |
| 106 | func (c *Client) computeKeys(kf KeyFactors) derivedKeys { |
| 107 | h := c.hashGen() |
| 108 | saltedPassword := pbkdf2.Key([]byte(c.password), []byte(kf.Salt), kf.Iters, h.Size(), c.hashGen) |
| 109 | clientKey := computeHMAC(c.hashGen, saltedPassword, []byte("Client Key")) |
| 110 | |
| 111 | return derivedKeys{ |
| 112 | ClientKey: clientKey, |
| 113 | StoredKey: computeHash(c.hashGen, clientKey), |
| 114 | ServerKey: computeHMAC(c.hashGen, saltedPassword, []byte("Server Key")), |
| 115 | } |
| 116 | } |
| 117 | |
| 118 | func (c *Client) getCache(kf KeyFactors) (derivedKeys, bool) { |
| 119 | c.RLock() |
| 120 | defer c.RUnlock() |
| 121 | dk, ok := c.cache[kf] |
| 122 | return dk, ok |
| 123 | } |
| 124 | |
| 125 | func (c *Client) setCache(kf KeyFactors, dk derivedKeys) { |
| 126 | c.Lock() |
| 127 | defer c.Unlock() |
| 128 | c.cache[kf] = dk |
| 129 | return |
| 130 | } |