---
title: "暗号署名"
version: 4.1
locale: ja
source: https://docs.djangoproject.com/ja/4.1/topics/signing/
canonical: https://djangodocs.dev/ja/4.1/topics/signing/
---
# 暗号署名

The golden rule of web application security is to never trust data from
untrusted sources. Sometimes it can be useful to pass data through an
untrusted medium. Cryptographically signed values can be passed through an
untrusted channel safe in the knowledge that any tampering will be detected.

Django provides both a low-level API for signing values and a high-level API
for setting and reading signed cookies, one of the most common uses of
signing in web applications.

以下のような便利な署名もあります。

- Generating "recover my account" URLs for sending to users who have
  lost their password.
- Ensuring data stored in hidden form fields has not been tampered with.
- Generating one-time secret URLs for allowing temporary access to a
  protected resource, for example a downloadable file that a user has
  paid for.

## Protecting `SECRET_KEY` and `SECRET_KEY_FALLBACKS`

[`startproject`](/ja/4.1/ref/django-admin/#django-admin-startproject) によって新しいプロジェクトを作る際、 `settings.py` が生成され、ランダムな [`SECRET_KEY`](/ja/4.1/ref/settings/#std-setting-SECRET_KEY) を得ます。この値が、署名されたデータを安全に保つ鍵になります。このキーを安全に保存するとこは極めて重要で、さもなければ攻撃を行うひとたちが彼らの署名を生成するのにも使えるからです。

[`SECRET_KEY_FALLBACKS`](/ja/4.1/ref/settings/#std-setting-SECRET_KEY_FALLBACKS) can be used to rotate secret keys. The
values will not be used to sign data, but if specified, they will be used to
validate signed data and must be kept secure.

> **Changed in Django 4.1**
>
> The `SECRET_KEY_FALLBACKS` setting was added.

## 低レベルの API を利用する

Django の署名用メソッドは `django.core.signing` モジュール内にあります。値に著名を行うには、はじめに、次のようにして `Signer` インスタンスを作成します。

```
>>> from django.core.signing import Signer
>>> signer = Signer()
>>> value = signer.sign('My string')
>>> value
'My string:GdMGD6HNQ_qdgxYP8yBZAdAIV1w'
```

署名が文字列の最後にコロンに続いて付加されます。元の値を取得するには、`unsign` メソッドを使用します。

```
>>> original = signer.unsign(value)
>>> original
'My string'
```

If you pass a non-string value to `sign`, the value will be forced to string
before being signed, and the `unsign` result will give you that string
value:

```
>>> signed = signer.sign(2.5)
>>> original = signer.unsign(signed)
>>> original
'2.5'
```

If you wish to protect a list, tuple, or dictionary you can do so using the
`sign_object()` and `unsign_object()` methods:

```
>>> signed_obj = signer.sign_object({'message': 'Hello!'})
>>> signed_obj
'eyJtZXNzYWdlIjoiSGVsbG8hIn0:Xdc-mOFDjs22KsQAqfVfi8PQSPdo3ckWJxPWwQOFhR4'
>>> obj = signer.unsign_object(signed_obj)
>>> obj
{'message': 'Hello!'}
```

See [Protecting complex data structures](#signing-complex-data) for more details.

何らかの理由により署名の値が書き換わってしまった場合、`django.core.signing.BadSignature` 例外が起こります。

```
>>> from django.core import signing
>>> value += 'm'
>>> try:
...    original = signer.unsign(value)
... except signing.BadSignature:
...    print("Tampering detected!")
```

デフォルトでは、`Signer` クラスは [`SECRET_KEY`](/ja/4.1/ref/settings/#std-setting-SECRET_KEY) 設定の値を署名生成に利用します。次のように `Signer` のコンストラクタに任意の値を渡すことで、異なる秘密鍵を使用することもできます。

```
>>> signer = Signer('my-other-secret')
>>> value = signer.sign('My string')
>>> value
'My string:EkfQJafvGyiofrdGnuthdxImIJw'
```

#### `class Signer(key=None, sep=':', salt=None, algorithm=None, fallback_keys=None)`

Returns a signer which uses `key` to generate signatures and `sep` to
separate values. `sep` cannot be in the [**URL safe base64 alphabet**](https://datatracker.ietf.org/doc/html/rfc4648.html#section-5). This alphabet contains alphanumeric characters, hyphens,
and underscores. `algorithm` must be an algorithm supported by
[`hashlib`](https://docs.python.org/3/library/hashlib.html#module-hashlib), it defaults to `'sha256'`. `fallback_keys` is a list
of additional values used to validate signed data, defaults to
[`SECRET_KEY_FALLBACKS`](/ja/4.1/ref/settings/#std-setting-SECRET_KEY_FALLBACKS).

> **Changed in Django 4.1**
>
> The `fallback_keys` argument was added.

### Using the `salt` argument

If you do not wish for every occurrence of a particular string to have the same
signature hash, you can use the optional `salt` argument to the `Signer`
class. Using a salt will seed the signing hash function with both the salt and
your [`SECRET_KEY`](/ja/4.1/ref/settings/#std-setting-SECRET_KEY):

```
>>> signer = Signer()
>>> signer.sign('My string')
'My string:GdMGD6HNQ_qdgxYP8yBZAdAIV1w'
>>> signer.sign_object({'message': 'Hello!'})
'eyJtZXNzYWdlIjoiSGVsbG8hIn0:Xdc-mOFDjs22KsQAqfVfi8PQSPdo3ckWJxPWwQOFhR4'
>>> signer = Signer(salt='extra')
>>> signer.sign('My string')
'My string:Ee7vGi-ING6n02gkcJ-QLHg6vFw'
>>> signer.unsign('My string:Ee7vGi-ING6n02gkcJ-QLHg6vFw')
'My string'
>>> signer.sign_object({'message': 'Hello!'})
'eyJtZXNzYWdlIjoiSGVsbG8hIn0:-UWSLCE-oUAHzhkHviYz3SOZYBjFKllEOyVZNuUtM-I'
>>> signer.unsign_object('eyJtZXNzYWdlIjoiSGVsbG8hIn0:-UWSLCE-oUAHzhkHviYz3SOZYBjFKllEOyVZNuUtM-I')
{'message': 'Hello!'}
```

Using salt in this way puts the different signatures into different
namespaces.  A signature that comes from one namespace (a particular salt
value) cannot be used to validate the same plaintext string in a different
namespace that is using a different salt setting. The result is to prevent an
attacker from using a signed string generated in one place in the code as input
to another piece of code that is generating (and verifying) signatures using a
different salt.

Unlike your [`SECRET_KEY`](/ja/4.1/ref/settings/#std-setting-SECRET_KEY), your salt argument does not need to stay
secret.

### Verifying timestamped values

`TimestampSigner` is a subclass of [`Signer`](#django.core.signing.Signer) that appends a signed
timestamp to the value. This allows you to confirm that a signed value was
created within a specified period of time:

```
>>> from datetime import timedelta
>>> from django.core.signing import TimestampSigner
>>> signer = TimestampSigner()
>>> value = signer.sign('hello')
>>> value
'hello:1NMg5H:oPVuCqlJWmChm1rA2lyTUtelC-c'
>>> signer.unsign(value)
'hello'
>>> signer.unsign(value, max_age=10)
...
SignatureExpired: Signature age 15.5289158821 > 10 seconds
>>> signer.unsign(value, max_age=20)
'hello'
>>> signer.unsign(value, max_age=timedelta(seconds=20))
'hello'
```

#### `class TimestampSigner(key=None, sep=':', salt=None, algorithm='sha256')`

#### `sign(value)`

Sign `value` and append current timestamp to it.

#### `unsign(value, max_age=None)`

Checks if `value` was signed less than `max_age` seconds ago,
otherwise raises `SignatureExpired`. The `max_age` parameter can
accept an integer or a [`datetime.timedelta`](https://docs.python.org/3/library/datetime.html#datetime.timedelta) object.

#### `sign_object(obj, serializer=JSONSerializer, compress=False)`

Encode, optionally compress, append current timestamp, and sign complex
data structure (e.g. list, tuple, or dictionary).

#### `unsign_object(signed_obj, serializer=JSONSerializer, max_age=None)`

Checks if `signed_obj` was signed less than `max_age` seconds ago,
otherwise raises `SignatureExpired`. The `max_age` parameter can
accept an integer or a [`datetime.timedelta`](https://docs.python.org/3/library/datetime.html#datetime.timedelta) object.

### Protecting complex data structures

If you wish to protect a list, tuple or dictionary you can do so using the
`Signer.sign_object()` and `unsign_object()` methods, or signing module's
`dumps()` or `loads()` functions (which are shortcuts for
`TimestampSigner(salt='django.core.signing').sign_object()/unsign_object()`).
These use JSON serialization under the hood. JSON ensures that even if your
[`SECRET_KEY`](/ja/4.1/ref/settings/#std-setting-SECRET_KEY) is stolen an attacker will not be able to execute
arbitrary commands by exploiting the pickle format:

```
>>> from django.core import signing
>>> signer = signing.TimestampSigner()
>>> value = signer.sign_object({'foo': 'bar'})
>>> value
'eyJmb28iOiJiYXIifQ:1kx6R3:D4qGKiptAqo5QW9iv4eNLc6xl4RwiFfes6oOcYhkYnc'
>>> signer.unsign_object(value)
{'foo': 'bar'}
>>> value = signing.dumps({'foo': 'bar'})
>>> value
'eyJmb28iOiJiYXIifQ:1kx6Rf:LBB39RQmME-SRvilheUe5EmPYRbuDBgQp2tCAi7KGLk'
>>> signing.loads(value)
{'foo': 'bar'}
```

Because of the nature of JSON (there is no native distinction between lists
and tuples) if you pass in a tuple, you will get a list from
`signing.loads(object)`:

```
>>> from django.core import signing
>>> value = signing.dumps(('a','b','c'))
>>> signing.loads(value)
['a', 'b', 'c']
```

#### `dumps(obj, key=None, salt='django.core.signing', serializer=JSONSerializer, compress=False)`

Returns URL-safe, signed base64 compressed JSON string. Serialized object
is signed using [`TimestampSigner`](#django.core.signing.TimestampSigner).

#### `loads(string, key=None, salt='django.core.signing', serializer=JSONSerializer, max_age=None, fallback_keys=None)`

Reverse of `dumps()`, raises `BadSignature` if signature fails.
Checks `max_age` (in seconds) if given.

> **Changed in Django 4.1**
>
> The `fallback_keys` argument was added.