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71 lines
2.1 KiB
Go
71 lines
2.1 KiB
Go
// Copyright (c) 2018 Shivaram Lingamneni <slingamn@cs.stanford.edu>
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// released under the MIT license
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package utils
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import (
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"crypto/rand"
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"crypto/subtle"
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"encoding/base32"
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"encoding/base64"
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)
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var (
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// slingamn's own private b32 alphabet, removing 1, l, o, and 0
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B32Encoder = base32.NewEncoding("abcdefghijkmnpqrstuvwxyz23456789").WithPadding(base32.NoPadding)
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)
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const (
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SecretTokenLength = 26
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)
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// generate a secret token that cannot be brute-forced via online attacks
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func GenerateSecretToken() string {
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// 128 bits of entropy are enough to resist any online attack:
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var buf [16]byte
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rand.Read(buf[:])
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// 26 ASCII characters, should be fine for most purposes
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return B32Encoder.EncodeToString(buf[:])
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}
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// "munge" a secret token to a new value. requirements:
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// 1. MUST be roughly as unlikely to collide with `GenerateSecretToken` outputs
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// as those outputs are with each other
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// 2. SHOULD be deterministic (motivation: if a JOIN line has msgid x,
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// create a deterministic msgid y for the fake HistServ PRIVMSG that "replays" it)
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// 3. SHOULD be in the same "namespace" as `GenerateSecretToken` outputs
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// (same length and character set)
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func MungeSecretToken(token string) (result string) {
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bytes, err := B32Encoder.DecodeString(token)
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if err != nil {
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// this should never happen
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return GenerateSecretToken()
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}
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// add 1 with carrying
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for i := len(bytes) - 1; 0 <= i; i -= 1 {
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bytes[i] += 1
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if bytes[i] != 0 {
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break
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} // else: overflow, carry to the next place
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}
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return B32Encoder.EncodeToString(bytes)
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}
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// securely check if a supplied token matches a stored token
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func SecretTokensMatch(storedToken string, suppliedToken string) bool {
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// XXX fix a potential gotcha: if the stored token is uninitialized,
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// then nothing should match it, not even supplying an empty token.
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if len(storedToken) == 0 {
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return false
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}
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return subtle.ConstantTimeCompare([]byte(storedToken), []byte(suppliedToken)) == 1
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}
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// generate a 256-bit secret key that can be written into a config file
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func GenerateSecretKey() string {
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var buf [32]byte
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rand.Read(buf[:])
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return base64.RawURLEncoding.EncodeToString(buf[:])
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}
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