76 lines
1.7 KiB
Go
76 lines
1.7 KiB
Go
package crypto
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import (
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"crypto/aes"
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"crypto/cipher"
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"crypto/rand"
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"crypto/sha256"
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"fmt"
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"io"
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"golang.org/x/crypto/hkdf"
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)
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// StkSource is used to create and verify source address tokens
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type StkSource interface {
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// NewToken creates a new token
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NewToken([]byte) ([]byte, error)
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// DecodeToken decodes a token
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DecodeToken([]byte) ([]byte, error)
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}
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type stkSource struct {
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aead cipher.AEAD
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}
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const stkKeySize = 16
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// Chrome currently sets this to 12, but discusses changing it to 16. We start
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// at 16 :)
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const stkNonceSize = 16
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// NewStkSource creates a source for source address tokens
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func NewStkSource() (StkSource, error) {
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secret := make([]byte, 32)
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if _, err := rand.Read(secret); err != nil {
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return nil, err
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}
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key, err := deriveKey(secret)
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if err != nil {
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return nil, err
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}
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c, err := aes.NewCipher(key)
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if err != nil {
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return nil, err
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}
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aead, err := cipher.NewGCMWithNonceSize(c, stkNonceSize)
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if err != nil {
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return nil, err
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}
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return &stkSource{aead: aead}, nil
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}
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func (s *stkSource) NewToken(data []byte) ([]byte, error) {
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nonce := make([]byte, stkNonceSize)
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if _, err := rand.Read(nonce); err != nil {
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return nil, err
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}
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return s.aead.Seal(nonce, nonce, data, nil), nil
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}
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func (s *stkSource) DecodeToken(p []byte) ([]byte, error) {
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if len(p) < stkNonceSize {
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return nil, fmt.Errorf("STK too short: %d", len(p))
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}
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nonce := p[:stkNonceSize]
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return s.aead.Open(nil, nonce, p[stkNonceSize:], nil)
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}
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func deriveKey(secret []byte) ([]byte, error) {
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r := hkdf.New(sha256.New, secret, nil, []byte("QUIC source address token key"))
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key := make([]byte, stkKeySize)
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if _, err := io.ReadFull(r, key); err != nil {
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return nil, err
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}
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return key, nil
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}
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