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ergo/vendor/github.com/xdg-go/scram/client.go
2021-07-30 12:20:13 -04:00

131 lines
3.8 KiB
Go

// Copyright 2018 by David A. Golden. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may
// not use this file except in compliance with the License. You may obtain
// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
package scram
import (
"sync"
"github.com/xdg-go/pbkdf2"
)
// Client implements the client side of SCRAM authentication. It holds
// configuration values needed to initialize new client-side conversations for
// a specific username, password and authorization ID tuple. Client caches
// the computationally-expensive parts of a SCRAM conversation as described in
// RFC-5802. If repeated authentication conversations may be required for a
// user (e.g. disconnect/reconnect), the user's Client should be preserved.
//
// For security reasons, Clients have a default minimum PBKDF2 iteration count
// of 4096. If a server requests a smaller iteration count, an authentication
// conversation will error.
//
// A Client can also be used by a server application to construct the hashed
// authentication values to be stored for a new user. See StoredCredentials()
// for more.
type Client struct {
sync.RWMutex
username string
password string
authzID string
minIters int
nonceGen NonceGeneratorFcn
hashGen HashGeneratorFcn
cache map[KeyFactors]derivedKeys
}
func newClient(username, password, authzID string, fcn HashGeneratorFcn) *Client {
return &Client{
username: username,
password: password,
authzID: authzID,
minIters: 4096,
nonceGen: defaultNonceGenerator,
hashGen: fcn,
cache: make(map[KeyFactors]derivedKeys),
}
}
// WithMinIterations changes minimum required PBKDF2 iteration count.
func (c *Client) WithMinIterations(n int) *Client {
c.Lock()
defer c.Unlock()
c.minIters = n
return c
}
// WithNonceGenerator replaces the default nonce generator (base64 encoding of
// 24 bytes from crypto/rand) with a custom generator. This is provided for
// testing or for users with custom nonce requirements.
func (c *Client) WithNonceGenerator(ng NonceGeneratorFcn) *Client {
c.Lock()
defer c.Unlock()
c.nonceGen = ng
return c
}
// NewConversation constructs a client-side authentication conversation.
// Conversations cannot be reused, so this must be called for each new
// authentication attempt.
func (c *Client) NewConversation() *ClientConversation {
c.RLock()
defer c.RUnlock()
return &ClientConversation{
client: c,
nonceGen: c.nonceGen,
hashGen: c.hashGen,
minIters: c.minIters,
}
}
func (c *Client) getDerivedKeys(kf KeyFactors) derivedKeys {
dk, ok := c.getCache(kf)
if !ok {
dk = c.computeKeys(kf)
c.setCache(kf, dk)
}
return dk
}
// GetStoredCredentials takes a salt and iteration count structure and
// provides the values that must be stored by a server to authentication a
// user. These values are what the Server credential lookup function must
// return for a given username.
func (c *Client) GetStoredCredentials(kf KeyFactors) StoredCredentials {
dk := c.getDerivedKeys(kf)
return StoredCredentials{
KeyFactors: kf,
StoredKey: dk.StoredKey,
ServerKey: dk.ServerKey,
}
}
func (c *Client) computeKeys(kf KeyFactors) derivedKeys {
h := c.hashGen()
saltedPassword := pbkdf2.Key([]byte(c.password), []byte(kf.Salt), kf.Iters, h.Size(), c.hashGen)
clientKey := computeHMAC(c.hashGen, saltedPassword, []byte("Client Key"))
return derivedKeys{
ClientKey: clientKey,
StoredKey: computeHash(c.hashGen, clientKey),
ServerKey: computeHMAC(c.hashGen, saltedPassword, []byte("Server Key")),
}
}
func (c *Client) getCache(kf KeyFactors) (derivedKeys, bool) {
c.RLock()
defer c.RUnlock()
dk, ok := c.cache[kf]
return dk, ok
}
func (c *Client) setCache(kf KeyFactors, dk derivedKeys) {
c.Lock()
defer c.Unlock()
c.cache[kf] = dk
return
}