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package mint
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"crypto/sha256"
"fmt"
"io"
"golang.org/x/crypto/hkdf"
)
// CookieProtector is used to create and verify a cookie
type CookieProtector interface {
// NewToken creates a new token
NewToken([]byte) ([]byte, error)
// DecodeToken decodes a token
DecodeToken([]byte) ([]byte, error)
}
const cookieSecretSize = 32
const cookieNonceSize = 32
// The DefaultCookieProtector is a simple implementation for the CookieProtector.
type DefaultCookieProtector struct {
secret []byte
}
var _ CookieProtector = &DefaultCookieProtector{}
// NewDefaultCookieProtector creates a source for source address tokens
func NewDefaultCookieProtector() (CookieProtector, error) {
secret := make([]byte, cookieSecretSize)
if _, err := rand.Read(secret); err != nil {
return nil, err
}
return &DefaultCookieProtector{secret: secret}, nil
}
// NewToken encodes data into a new token.
func (s *DefaultCookieProtector) NewToken(data []byte) ([]byte, error) {
nonce := make([]byte, cookieNonceSize)
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 *DefaultCookieProtector) DecodeToken(p []byte) ([]byte, error) {
if len(p) < cookieNonceSize {
return nil, fmt.Errorf("Token too short: %d", len(p))
}
nonce := p[:cookieNonceSize]
aead, aeadNonce, err := s.createAEAD(nonce)
if err != nil {
return nil, err
}
return aead.Open(nil, aeadNonce, p[cookieNonceSize:], nil)
}
func (s *DefaultCookieProtector) createAEAD(nonce []byte) (cipher.AEAD, []byte, error) {
h := hkdf.New(sha256.New, s.secret, nonce, []byte("mint cookie 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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