98 lines
2.9 KiB
Go
98 lines
2.9 KiB
Go
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// 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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"crypto/rand"
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"encoding/base64"
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"strings"
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)
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// NonceGeneratorFcn defines a function that returns a string of high-quality
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// random printable ASCII characters EXCLUDING the comma (',') character. The
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// default nonce generator provides Base64 encoding of 24 bytes from
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// crypto/rand.
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type NonceGeneratorFcn func() string
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// derivedKeys collects the three cryptographically derived values
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// into one struct for caching.
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type derivedKeys struct {
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ClientKey []byte
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StoredKey []byte
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ServerKey []byte
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}
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// KeyFactors represent the two server-provided factors needed to compute
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// client credentials for authentication. Salt is decoded bytes (i.e. not
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// base64), but in string form so that KeyFactors can be used as a map key for
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// cached credentials.
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type KeyFactors struct {
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Salt string
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Iters int
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}
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// StoredCredentials are the values that a server must store for a given
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// username to allow authentication. They include the salt and iteration
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// count, plus the derived values to authenticate a client and for the server
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// to authenticate itself back to the client.
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//
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// NOTE: these are specific to a given hash function. To allow a user to
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// authenticate with either SCRAM-SHA-1 or SCRAM-SHA-256, two sets of
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// StoredCredentials must be created and stored, one for each hash function.
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type StoredCredentials struct {
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KeyFactors
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StoredKey []byte
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ServerKey []byte
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}
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// CredentialLookup is a callback to provide StoredCredentials for a given
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// username. This is used to configure Server objects.
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//
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// NOTE: these are specific to a given hash function. The callback provided
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// to a Server with a given hash function must provide the corresponding
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// StoredCredentials.
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type CredentialLookup func(string) (StoredCredentials, error)
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func defaultNonceGenerator() string {
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raw := make([]byte, 24)
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nonce := make([]byte, base64.StdEncoding.EncodedLen(len(raw)))
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rand.Read(raw)
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base64.StdEncoding.Encode(nonce, raw)
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return string(nonce)
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}
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func encodeName(s string) string {
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return strings.Replace(strings.Replace(s, "=", "=3D", -1), ",", "=2C", -1)
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}
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func decodeName(s string) (string, error) {
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// TODO Check for = not followed by 2C or 3D
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return strings.Replace(strings.Replace(s, "=2C", ",", -1), "=3D", "=", -1), nil
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}
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func computeHash(hg HashGeneratorFcn, b []byte) []byte {
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h := hg()
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h.Write(b)
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return h.Sum(nil)
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}
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func computeHMAC(hg HashGeneratorFcn, key, data []byte) []byte {
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mac := hmac.New(hg, key)
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mac.Write(data)
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return mac.Sum(nil)
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}
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func xorBytes(a, b []byte) []byte {
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// TODO check a & b are same length, or just xor to smallest
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xor := make([]byte, len(a))
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for i := range a {
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xor[i] = a[i] ^ b[i]
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}
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return xor
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}
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