91 lines
1.9 KiB
Go
91 lines
1.9 KiB
Go
// Copyright 2015 The Chihaya Authors. All rights reserved.
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// Use of this source code is governed by the BSD 2-Clause license,
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// which can be found in the LICENSE file.
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package udp
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import (
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"bytes"
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"crypto/aes"
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"crypto/cipher"
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"crypto/rand"
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"net"
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)
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// ConnectionIDGenerator represents the logic to generate 64-bit UDP
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// connection IDs from peer IP addresses.
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type ConnectionIDGenerator struct {
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iv, iv2 []byte
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block cipher.Block
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}
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// NewConnectionIDGenerator creates a ConnectionIDGenerator and generates its
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// AES key and first initialization vector.
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func NewConnectionIDGenerator() (gen *ConnectionIDGenerator, err error) {
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gen = &ConnectionIDGenerator{}
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key := make([]byte, 16)
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_, err = rand.Read(key)
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if err != nil {
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return
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}
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gen.block, err = aes.NewCipher(key)
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if err != nil {
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return
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}
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err = gen.NewIV()
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return
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}
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// Generate returns the 64-bit connection ID for an IP
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func (g *ConnectionIDGenerator) Generate(ip net.IP) []byte {
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return g.generate(ip, g.iv)
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}
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func (g *ConnectionIDGenerator) generate(ip net.IP, iv []byte) []byte {
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for len(ip) < 8 {
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ip = append(ip, ip...) // Not enough bits in output.
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}
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ct := make([]byte, 16)
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stream := cipher.NewCFBDecrypter(g.block, iv)
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stream.XORKeyStream(ct, ip)
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for i := len(ip) - 1; i >= 8; i-- {
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ct[i-8] ^= ct[i]
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}
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return ct[:8]
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}
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// Matches checks if the given connection ID matches an IP with the current or
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// previous initialization vectors.
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func (g *ConnectionIDGenerator) Matches(id []byte, ip net.IP) bool {
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if expected := g.generate(ip, g.iv); bytes.Equal(id, expected) {
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return true
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}
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if iv2 := g.iv2; iv2 != nil {
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if expected := g.generate(ip, iv2); bytes.Equal(id, expected) {
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return true
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}
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}
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return false
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}
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// NewIV generates a new initialization vector and rotates the current one.
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func (g *ConnectionIDGenerator) NewIV() error {
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newiv := make([]byte, 16)
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if _, err := rand.Read(newiv); err != nil {
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return err
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}
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g.iv2 = g.iv
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g.iv = newiv
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return nil
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}
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