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// Copyright 2012 The Gorilla Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package securecookie
import (
"bytes"
"crypto/aes"
"crypto/cipher"
"crypto/hmac"
"crypto/rand"
"crypto/sha256"
"crypto/subtle"
"encoding/base64"
"encoding/gob"
"encoding/json"
"fmt"
"hash"
"io"
"strconv"
"strings"
"time"
)
// Error is the interface of all errors returned by functions in this library.
type Error interface {
error
// IsUsage returns true for errors indicating the client code probably
// uses this library incorrectly. For example, the client may have
// failed to provide a valid hash key, or may have failed to configure
// the Serializer adequately for encoding value.
IsUsage() bool
// IsDecode returns true for errors indicating that a cookie could not
// be decoded and validated. Since cookies are usually untrusted
// user-provided input, errors of this type should be expected.
// Usually, the proper action is simply to reject the request.
IsDecode() bool
// IsInternal returns true for unexpected errors occurring in the
// securecookie implementation.
IsInternal() bool
// Cause, if it returns a non-nil value, indicates that this error was
// propagated from some underlying library. If this method returns nil,
// this error was raised directly by this library.
//
// Cause is provided principally for debugging/logging purposes; it is
// rare that application logic should perform meaningfully different
// logic based on Cause. See, for example, the caveats described on
// (MultiError).Cause().
Cause() error
}
// errorType is a bitmask giving the error type(s) of an cookieError value.
type errorType int
const (
usageError = errorType(1 << iota)
decodeError
internalError
)
type cookieError struct {
typ errorType
msg string
cause error
}
func (e cookieError) IsUsage() bool { return (e.typ & usageError) != 0 }
func (e cookieError) IsDecode() bool { return (e.typ & decodeError) != 0 }
func (e cookieError) IsInternal() bool { return (e.typ & internalError) != 0 }
func (e cookieError) Cause() error { return e.cause }
func (e cookieError) Error() string {
parts := []string{"securecookie: "}
if e.msg == "" {
parts = append(parts, "error")
} else {
parts = append(parts, e.msg)
}
if c := e.Cause(); c != nil {
parts = append(parts, " - caused by: ", c.Error())
}
return strings.Join(parts, "")
}
var (
errGeneratingIV = cookieError{typ: internalError, msg: "failed to generate random iv"}
errNoCodecs = cookieError{typ: usageError, msg: "no codecs provided"}
errHashKeyNotSet = cookieError{typ: usageError, msg: "hash key is not set"}
errBlockKeyNotSet = cookieError{typ: usageError, msg: "block key is not set"}
errEncodedValueTooLong = cookieError{typ: usageError, msg: "the value is too long"}
errValueToDecodeTooLong = cookieError{typ: decodeError, msg: "the value is too long"}
errTimestampInvalid = cookieError{typ: decodeError, msg: "invalid timestamp"}
errTimestampTooNew = cookieError{typ: decodeError, msg: "timestamp is too new"}
errTimestampExpired = cookieError{typ: decodeError, msg: "expired timestamp"}
errDecryptionFailed = cookieError{typ: decodeError, msg: "the value could not be decrypted"}
errValueNotByte = cookieError{typ: decodeError, msg: "value not a []byte."}
errValueNotBytePtr = cookieError{typ: decodeError, msg: "value not a pointer to []byte."}
// ErrMacInvalid indicates that cookie decoding failed because the HMAC
// could not be extracted and verified. Direct use of this error
// variable is deprecated; it is public only for legacy compatibility,
// and may be privatized in the future, as it is rarely useful to
// distinguish between this error and other Error implementations.
ErrMacInvalid = cookieError{typ: decodeError, msg: "the value is not valid"}
)
// Codec defines an interface to encode and decode cookie values.
type Codec interface {
Encode(name string, value interface{}) (string, error)
Decode(name, value string, dst interface{}) error
}
// New returns a new SecureCookie.
//
// hashKey is required, used to authenticate values using HMAC. Create it using
// GenerateRandomKey(). It is recommended to use a key with 32 or 64 bytes.
//
// blockKey is optional, used to encrypt values. Create it using
// GenerateRandomKey(). The key length must correspond to the block size
// of the encryption algorithm. For AES, used by default, valid lengths are
// 16, 24, or 32 bytes to select AES-128, AES-192, or AES-256.
// The default encoder used for cookie serialization is encoding/gob.
//
// Note that keys created using GenerateRandomKey() are not automatically
// persisted. New keys will be created when the application is restarted, and
// previously issued cookies will not be able to be decoded.
func New(hashKey, blockKey []byte) *SecureCookie {
s := &SecureCookie{
hashKey: hashKey,
blockKey: blockKey,
hashFunc: sha256.New,
maxAge: 86400 * 30,
maxLength: 4096,
sz: GobEncoder{},
}
if hashKey == nil {
s.err = errHashKeyNotSet
}
if blockKey != nil {
s.BlockFunc(aes.NewCipher)
}
return s
}
// SecureCookie encodes and decodes authenticated and optionally encrypted
// cookie values.
type SecureCookie struct {
hashKey []byte
hashFunc func() hash.Hash
blockKey []byte
block cipher.Block
maxLength int
maxAge int64
minAge int64
err error
sz Serializer
// For testing purposes, the function that returns the current timestamp.
// If not set, it will use time.Now().UTC().Unix().
timeFunc func() int64
}
// Serializer provides an interface for providing custom serializers for cookie
// values.
type Serializer interface {
Serialize(src interface{}) ([]byte, error)
Deserialize(src []byte, dst interface{}) error
}
// GobEncoder encodes cookie values using encoding/gob. This is the simplest
// encoder and can handle complex types via gob.Register.
type GobEncoder struct{}
// JSONEncoder encodes cookie values using encoding/json. Users who wish to
// encode complex types need to satisfy the json.Marshaller and
// json.Unmarshaller interfaces.
type JSONEncoder struct{}
// NopEncoder does not encode cookie values, and instead simply accepts a []byte
// (as an interface{}) and returns a []byte. This is particularly useful when
// you encoding an object upstream and do not wish to re-encode it.
type NopEncoder struct{}
// MaxLength restricts the maximum length, in bytes, for the cookie value.
//
// Default is 4096, which is the maximum value accepted by Internet Explorer.
func (s *SecureCookie) MaxLength(value int) *SecureCookie {
s.maxLength = value
return s
}
// MaxAge restricts the maximum age, in seconds, for the cookie value.
//
// Default is 86400 * 30. Set it to 0 for no restriction.
func (s *SecureCookie) MaxAge(value int) *SecureCookie {
s.maxAge = int64(value)
return s
}
// MinAge restricts the minimum age, in seconds, for the cookie value.
//
// Default is 0 (no restriction).
func (s *SecureCookie) MinAge(value int) *SecureCookie {
s.minAge = int64(value)
return s
}
// HashFunc sets the hash function used to create HMAC.
//
// Default is crypto/sha256.New.
func (s *SecureCookie) HashFunc(f func() hash.Hash) *SecureCookie {
s.hashFunc = f
return s
}
// BlockFunc sets the encryption function used to create a cipher.Block.
//
// Default is crypto/aes.New.
func (s *SecureCookie) BlockFunc(f func([]byte) (cipher.Block, error)) *SecureCookie {
if s.blockKey == nil {
s.err = errBlockKeyNotSet
} else if block, err := f(s.blockKey); err == nil {
s.block = block
} else {
s.err = cookieError{cause: err, typ: usageError}
}
return s
}
// Encoding sets the encoding/serialization method for cookies.
//
// Default is encoding/gob. To encode special structures using encoding/gob,
// they must be registered first using gob.Register().
func (s *SecureCookie) SetSerializer(sz Serializer) *SecureCookie {
s.sz = sz
return s
}
// Encode encodes a cookie value.
//
// It serializes, optionally encrypts, signs with a message authentication code,
// and finally encodes the value.
//
// The name argument is the cookie name. It is stored with the encoded value.
// The value argument is the value to be encoded. It can be any value that can
// be encoded using the currently selected serializer; see SetSerializer().
//
// It is the client's responsibility to ensure that value, when encoded using
// the current serialization/encryption settings on s and then base64-encoded,
// is shorter than the maximum permissible length.
func (s *SecureCookie) Encode(name string, value interface{}) (string, error) {
if s.err != nil {
return "", s.err
}
if s.hashKey == nil {
s.err = errHashKeyNotSet
return "", s.err
}
var err error
var b []byte
// 1. Serialize.
if b, err = s.sz.Serialize(value); err != nil {
return "", cookieError{cause: err, typ: usageError}
}
// 2. Encrypt (optional).
if s.block != nil {
if b, err = encrypt(s.block, b); err != nil {
return "", cookieError{cause: err, typ: usageError}
}
}
b = encode(b)
// 3. Create MAC for "name|date|value". Extra pipe to be used later.
b = []byte(fmt.Sprintf("%s|%d|%s|", name, s.timestamp(), b))
mac := createMac(hmac.New(s.hashFunc, s.hashKey), b[:len(b)-1])
// Append mac, remove name.
b = append(b, mac...)[len(name)+1:]
// 4. Encode to base64.
b = encode(b)
// 5. Check length.
if s.maxLength != 0 && len(b) > s.maxLength {
return "", errEncodedValueTooLong
}
// Done.
return string(b), nil
}
// Decode decodes a cookie value.
//
// It decodes, verifies a message authentication code, optionally decrypts and
// finally deserializes the value.
//
// The name argument is the cookie name. It must be the same name used when
// it was stored. The value argument is the encoded cookie value. The dst
// argument is where the cookie will be decoded. It must be a pointer.
func (s *SecureCookie) Decode(name, value string, dst interface{}) error {
if s.err != nil {
return s.err
}
if s.hashKey == nil {
s.err = errHashKeyNotSet
return s.err
}
// 1. Check length.
if s.maxLength != 0 && len(value) > s.maxLength {
return errValueToDecodeTooLong
}
// 2. Decode from base64.
b, err := decode([]byte(value))
if err != nil {
return err
}
// 3. Verify MAC. Value is "date|value|mac".
parts := bytes.SplitN(b, []byte("|"), 3)
if len(parts) != 3 {
return ErrMacInvalid
}
h := hmac.New(s.hashFunc, s.hashKey)
b = append([]byte(name+"|"), b[:len(b)-len(parts[2])-1]...)
if err = verifyMac(h, b, parts[2]); err != nil {
return err
}
// 4. Verify date ranges.
var t1 int64
if t1, err = strconv.ParseInt(string(parts[0]), 10, 64); err != nil {
return errTimestampInvalid
}
t2 := s.timestamp()
if s.minAge != 0 && t1 > t2-s.minAge {
return errTimestampTooNew
}
if s.maxAge != 0 && t1 < t2-s.maxAge {
return errTimestampExpired
}
// 5. Decrypt (optional).
b, err = decode(parts[1])
if err != nil {
return err
}
if s.block != nil {
if b, err = decrypt(s.block, b); err != nil {
return err
}
}
// 6. Deserialize.
if err = s.sz.Deserialize(b, dst); err != nil {
return cookieError{cause: err, typ: decodeError}
}
// Done.
return nil
}
// timestamp returns the current timestamp, in seconds.
//
// For testing purposes, the function that generates the timestamp can be
// overridden. If not set, it will return time.Now().UTC().Unix().
func (s *SecureCookie) timestamp() int64 {
if s.timeFunc == nil {
return time.Now().UTC().Unix()
}
return s.timeFunc()
}
// Authentication -------------------------------------------------------------
// createMac creates a message authentication code (MAC).
func createMac(h hash.Hash, value []byte) []byte {
h.Write(value)
return h.Sum(nil)
}
// verifyMac verifies that a message authentication code (MAC) is valid.
func verifyMac(h hash.Hash, value []byte, mac []byte) error {
mac2 := createMac(h, value)
// Check that both MACs are of equal length, as subtle.ConstantTimeCompare
// does not do this prior to Go 1.4.
if len(mac) == len(mac2) && subtle.ConstantTimeCompare(mac, mac2) == 1 {
return nil
}
return ErrMacInvalid
}
// Encryption -----------------------------------------------------------------
// encrypt encrypts a value using the given block in counter mode.
//
// A random initialization vector (http://goo.gl/zF67k) with the length of the
// block size is prepended to the resulting ciphertext.
func encrypt(block cipher.Block, value []byte) ([]byte, error) {
iv := GenerateRandomKey(block.BlockSize())
if iv == nil {
return nil, errGeneratingIV
}
// Encrypt it.
stream := cipher.NewCTR(block, iv)
stream.XORKeyStream(value, value)
// Return iv + ciphertext.
return append(iv, value...), nil
}
// decrypt decrypts a value using the given block in counter mode.
//
// The value to be decrypted must be prepended by a initialization vector
// (http://goo.gl/zF67k) with the length of the block size.
func decrypt(block cipher.Block, value []byte) ([]byte, error) {
size := block.BlockSize()
if len(value) > size {
// Extract iv.
iv := value[:size]
// Extract ciphertext.
value = value[size:]
// Decrypt it.
stream := cipher.NewCTR(block, iv)
stream.XORKeyStream(value, value)
return value, nil
}
return nil, errDecryptionFailed
}
// Serialization --------------------------------------------------------------
// Serialize encodes a value using gob.
func (e GobEncoder) Serialize(src interface{}) ([]byte, error) {
buf := new(bytes.Buffer)
enc := gob.NewEncoder(buf)
if err := enc.Encode(src); err != nil {
return nil, cookieError{cause: err, typ: usageError}
}
return buf.Bytes(), nil
}
// Deserialize decodes a value using gob.
func (e GobEncoder) Deserialize(src []byte, dst interface{}) error {
dec := gob.NewDecoder(bytes.NewBuffer(src))
if err := dec.Decode(dst); err != nil {
return cookieError{cause: err, typ: decodeError}
}
return nil
}
// Serialize encodes a value using encoding/json.
func (e JSONEncoder) Serialize(src interface{}) ([]byte, error) {
buf := new(bytes.Buffer)
enc := json.NewEncoder(buf)
if err := enc.Encode(src); err != nil {
return nil, cookieError{cause: err, typ: usageError}
}
return buf.Bytes(), nil
}
// Deserialize decodes a value using encoding/json.
func (e JSONEncoder) Deserialize(src []byte, dst interface{}) error {
dec := json.NewDecoder(bytes.NewReader(src))
if err := dec.Decode(dst); err != nil {
return cookieError{cause: err, typ: decodeError}
}
return nil
}
// Serialize passes a []byte through as-is.
func (e NopEncoder) Serialize(src interface{}) ([]byte, error) {
if b, ok := src.([]byte); ok {
return b, nil
}
return nil, errValueNotByte
}
// Deserialize passes a []byte through as-is.
func (e NopEncoder) Deserialize(src []byte, dst interface{}) error {
if dat, ok := dst.(*[]byte); ok {
*dat = src
return nil
}
return errValueNotBytePtr
}
// Encoding -------------------------------------------------------------------
// encode encodes a value using base64.
func encode(value []byte) []byte {
encoded := make([]byte, base64.URLEncoding.EncodedLen(len(value)))
base64.URLEncoding.Encode(encoded, value)
return encoded
}
// decode decodes a cookie using base64.
func decode(value []byte) ([]byte, error) {
decoded := make([]byte, base64.URLEncoding.DecodedLen(len(value)))
b, err := base64.URLEncoding.Decode(decoded, value)
if err != nil {
return nil, cookieError{cause: err, typ: decodeError, msg: "base64 decode failed"}
}
return decoded[:b], nil
}
// Helpers --------------------------------------------------------------------
// GenerateRandomKey creates a random key with the given length in bytes.
// On failure, returns nil.
//
// Callers should explicitly check for the possibility of a nil return, treat
// it as a failure of the system random number generator, and not continue.
func GenerateRandomKey(length int) []byte {
k := make([]byte, length)
if _, err := io.ReadFull(rand.Reader, k); err != nil {
return nil
}
return k
}
// CodecsFromPairs returns a slice of SecureCookie instances.
//
// It is a convenience function to create a list of codecs for key rotation. Note
// that the generated Codecs will have the default options applied: callers
// should iterate over each Codec and type-assert the underlying *SecureCookie to
// change these.
//
// Example:
//
// codecs := securecookie.CodecsFromPairs(
// []byte("new-hash-key"),
// []byte("new-block-key"),
// []byte("old-hash-key"),
// []byte("old-block-key"),
// )
//
// // Modify each instance.
// for _, s := range codecs {
// if cookie, ok := s.(*securecookie.SecureCookie); ok {
// cookie.MaxAge(86400 * 7)
// cookie.SetSerializer(securecookie.JSONEncoder{})
// cookie.HashFunc(sha512.New512_256)
// }
// }
//
func CodecsFromPairs(keyPairs ...[]byte) []Codec {
codecs := make([]Codec, len(keyPairs)/2+len(keyPairs)%2)
for i := 0; i < len(keyPairs); i += 2 {
var blockKey []byte
if i+1 < len(keyPairs) {
blockKey = keyPairs[i+1]
}
codecs[i/2] = New(keyPairs[i], blockKey)
}
return codecs
}
// EncodeMulti encodes a cookie value using a group of codecs.
//
// The codecs are tried in order. Multiple codecs are accepted to allow
// key rotation.
//
// On error, may return a MultiError.
func EncodeMulti(name string, value interface{}, codecs ...Codec) (string, error) {
if len(codecs) == 0 {
return "", errNoCodecs
}
var errors MultiError
for _, codec := range codecs {
encoded, err := codec.Encode(name, value)
if err == nil {
return encoded, nil
}
errors = append(errors, err)
}
return "", errors
}
// DecodeMulti decodes a cookie value using a group of codecs.
//
// The codecs are tried in order. Multiple codecs are accepted to allow
// key rotation.
//
// On error, may return a MultiError.
func DecodeMulti(name string, value string, dst interface{}, codecs ...Codec) error {
if len(codecs) == 0 {
return errNoCodecs
}
var errors MultiError
for _, codec := range codecs {
err := codec.Decode(name, value, dst)
if err == nil {
return nil
}
errors = append(errors, err)
}
return errors
}
// MultiError groups multiple errors.
type MultiError []error
func (m MultiError) IsUsage() bool { return m.any(func(e Error) bool { return e.IsUsage() }) }
func (m MultiError) IsDecode() bool { return m.any(func(e Error) bool { return e.IsDecode() }) }
func (m MultiError) IsInternal() bool { return m.any(func(e Error) bool { return e.IsInternal() }) }
// Cause returns nil for MultiError; there is no unique underlying cause in the
// general case.
//
// Note: we could conceivably return a non-nil Cause only when there is exactly
// one child error with a Cause. However, it would be brittle for client code
// to rely on the arity of causes inside a MultiError, so we have opted not to
// provide this functionality. Clients which really wish to access the Causes
// of the underlying errors are free to iterate through the errors themselves.
func (m MultiError) Cause() error { return nil }
func (m MultiError) Error() string {
s, n := "", 0
for _, e := range m {
if e != nil {
if n == 0 {
s = e.Error()
}
n++
}
}
switch n {
case 0:
return "(0 errors)"
case 1:
return s
case 2:
return s + " (and 1 other error)"
}
return fmt.Sprintf("%s (and %d other errors)", s, n-1)
}
// any returns true if any element of m is an Error for which pred returns true.
func (m MultiError) any(pred func(Error) bool) bool {
for _, e := range m {
if ourErr, ok := e.(Error); ok && pred(ourErr) {
return true
}
}
return false
}