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package handshake
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"crypto/sha256"
"fmt"
"io"
"golang.org/x/crypto/hkdf"
)
// TokenProtectorKey is the key used to encrypt both Retry and session resumption tokens.
type TokenProtectorKey [32]byte
const tokenNonceSize = 32
// tokenProtector is used to create and verify a token
type tokenProtector struct {
key TokenProtectorKey
}
// newTokenProtector creates a source for source address tokens
func newTokenProtector(key TokenProtectorKey) *tokenProtector {
return &tokenProtector{key: key}
}
// NewToken encodes data into a new token.
func (s *tokenProtector) NewToken(data []byte) ([]byte, error) {
var nonce [tokenNonceSize]byte
if _, err := rand.Read(nonce[:]); err != nil {
return nil, err
}
aead, aeadNonce, err := s.createAEAD(nonce[:])
if err != nil {
return nil, err
}
return append(nonce[:], aead.Seal(nil, aeadNonce, data, nil)...), nil
}
// DecodeToken decodes a token.
func (s *tokenProtector) DecodeToken(p []byte) ([]byte, error) {
if len(p) < tokenNonceSize {
return nil, fmt.Errorf("token too short: %d", len(p))
}
nonce := p[:tokenNonceSize]
aead, aeadNonce, err := s.createAEAD(nonce)
if err != nil {
return nil, err
}
return aead.Open(nil, aeadNonce, p[tokenNonceSize:], nil)
}
func (s *tokenProtector) createAEAD(nonce []byte) (cipher.AEAD, []byte, error) {
h := hkdf.New(sha256.New, s.key[:], nonce, []byte("quic-go token source"))
key := make([]byte, 32) // use a 32 byte key, in order to select AES-256
if _, err := io.ReadFull(h, key); err != nil {
return nil, nil, err
}
aeadNonce := make([]byte, 12)
if _, err := io.ReadFull(h, aeadNonce); err != nil {
return nil, nil, err
}
c, err := aes.NewCipher(key)
if err != nil {
return nil, nil, err
}
aead, err := cipher.NewGCM(c)
if err != nil {
return nil, nil, err
}
return aead, aeadNonce, nil
}
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