/
source_address_token.go
executable file
·76 lines (66 loc) · 1.67 KB
/
source_address_token.go
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package crypto
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"crypto/sha256"
"fmt"
"io"
"golang.org/x/crypto/hkdf"
)
// StkSource is used to create and verify source address tokens
type StkSource interface {
// NewToken creates a new token
NewToken([]byte) ([]byte, error)
// DecodeToken decodes a token
DecodeToken([]byte) ([]byte, error)
}
type stkSource struct {
aead cipher.AEAD
}
const stkKeySize = 16
// Chrome currently sets this to 12, but discusses changing it to 16. We start
// at 16 :)
const stkNonceSize = 16
// NewStkSource creates a source for source address tokens
func NewStkSource() (StkSource, error) {
secret := make([]byte, 32)
if _, err := rand.Read(secret); err != nil {
return nil, err
}
key, err := deriveKey(secret)
if err != nil {
return nil, err
}
c, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
aead, err := cipher.NewGCMWithNonceSize(c, stkNonceSize)
if err != nil {
return nil, err
}
return &stkSource{aead: aead}, nil
}
func (s *stkSource) NewToken(data []byte) ([]byte, error) {
nonce := make([]byte, stkNonceSize)
if _, err := rand.Read(nonce); err != nil {
return nil, err
}
return s.aead.Seal(nonce, nonce, data, nil), nil
}
func (s *stkSource) DecodeToken(p []byte) ([]byte, error) {
if len(p) < stkNonceSize {
return nil, fmt.Errorf("STK too short: %d", len(p))
}
nonce := p[:stkNonceSize]
return s.aead.Open(nil, nonce, p[stkNonceSize:], nil)
}
func deriveKey(secret []byte) ([]byte, error) {
r := hkdf.New(sha256.New, secret, nil, []byte("QUIC source address token key"))
key := make([]byte, stkKeySize)
if _, err := io.ReadFull(r, key); err != nil {
return nil, err
}
return key, nil
}