path: root/jwt/__init__.py

""" JSON Web Token implementation

Minimum implementation based on this spec:
http://self-issued.info/docs/draft-jones-json-web-token-01.html
"""
from __future__ import unicode_literals
import base64
import binascii
import hashlib
import hmac
import sys

from datetime import datetime
from calendar import timegm
from collections import Mapping

try:
    import json
except ImportError:
    import simplejson as json


if sys.version_info >= (3, 0, 0):
    unicode = str
    basestring = str


__version__ = '0.2.3'
__all__ = ['encode', 'decode', 'DecodeError']


class DecodeError(Exception):
    pass


class ExpiredSignature(Exception):
    pass


signing_methods = {
    'HS256': lambda msg, key: hmac.new(key, msg, hashlib.sha256).digest(),
    'HS384': lambda msg, key: hmac.new(key, msg, hashlib.sha384).digest(),
    'HS512': lambda msg, key: hmac.new(key, msg, hashlib.sha512).digest()
}

verify_methods = {
    'HS256': lambda msg, key: hmac.new(key, msg, hashlib.sha256).digest(),
    'HS384': lambda msg, key: hmac.new(key, msg, hashlib.sha384).digest(),
    'HS512': lambda msg, key: hmac.new(key, msg, hashlib.sha512).digest()
}


def prepare_HS_key(key):
    if not isinstance(key, basestring) and not isinstance(key, bytes):
        raise TypeError('Expecting a string- or bytes-formatted key.')

    if isinstance(key, unicode):
        key = key.encode('utf-8')

    return key

prepare_key_methods = {
    'HS256': prepare_HS_key,
    'HS384': prepare_HS_key,
    'HS512': prepare_HS_key
}

try:
    from Crypto.Signature import PKCS1_v1_5
    from Crypto.Hash import SHA256
    from Crypto.Hash import SHA384
    from Crypto.Hash import SHA512
    from Crypto.PublicKey import RSA

    signing_methods.update({
        'RS256': lambda msg, key: PKCS1_v1_5.new(key).sign(SHA256.new(msg)),
        'RS384': lambda msg, key: PKCS1_v1_5.new(key).sign(SHA384.new(msg)),
        'RS512': lambda msg, key: PKCS1_v1_5.new(key).sign(SHA512.new(msg))
    })

    verify_methods.update({
        'RS256': lambda msg, key, sig: PKCS1_v1_5.new(key).verify(SHA256.new(msg), sig),
        'RS384': lambda msg, key, sig: PKCS1_v1_5.new(key).verify(SHA384.new(msg), sig),
        'RS512': lambda msg, key, sig: PKCS1_v1_5.new(key).verify(SHA512.new(msg), sig)
    })

    def prepare_RS_key(key):
        if isinstance(key, basestring):
            if isinstance(key, unicode):
                key = key.encode('utf-8')

            key = RSA.importKey(key)
        elif isinstance(key, RSA._RSAobj):
            pass
        else:
            raise TypeError('Expecting a PEM- or RSA-formatted key.')

        return key

    prepare_key_methods.update({
        'RS256': prepare_RS_key,
        'RS384': prepare_RS_key,
        'RS512': prepare_RS_key
    })

except ImportError:
    pass


def constant_time_compare(val1, val2):
    """
    Returns True if the two strings are equal, False otherwise.

    The time taken is independent of the number of characters that match.
    """
    if len(val1) != len(val2):
        return False

    result = 0

    if sys.version_info >= (3, 0, 0):
        # Bytes are numbers
        for x, y in zip(val1, val2):
            result |= x ^ y
    else:
        for x, y in zip(val1, val2):
            result |= ord(x) ^ ord(y)

    return result == 0


def base64url_decode(input):
    rem = len(input) % 4

    if rem > 0:
        input += b'=' * (4 - rem)

    return base64.urlsafe_b64decode(input)


def base64url_encode(input):
    return base64.urlsafe_b64encode(input).replace(b'=', b'')


def header(jwt):
    header_segment = jwt.split(b'.', 1)[0]
    try:
        header_data = base64url_decode(header_segment).decode('utf-8')
        return json.loads(header_data)
    except (ValueError, TypeError):
        raise DecodeError('Invalid header encoding')


def encode(payload, key, algorithm='HS256', headers=None):
    segments = []

    # Check that we get a mapping
    if not isinstance(payload, Mapping):
        raise TypeError('Expecting a mapping object, as json web token only'
                        'support json objects.')

    # Header
    header = {'typ': 'JWT', 'alg': algorithm}
    if headers:
        header.update(headers)

    json_header = json.dumps(header, separators=(',', ':')).encode('utf-8')
    segments.append(base64url_encode(json_header))

    # Payload
    for time_claim in ['exp', 'iat', 'nbf']:
        # Convert datetime to a intDate value in known time-format claims
        if isinstance(payload.get(time_claim), datetime):
            payload[time_claim] = timegm(payload[time_claim].utctimetuple())

    json_payload = json.dumps(payload, separators=(',', ':')).encode('utf-8')
    segments.append(base64url_encode(json_payload))

    # Segments
    signing_input = b'.'.join(segments)
    try:
        key = prepare_key_methods[algorithm](key)
        signature = signing_methods[algorithm](signing_input, key)
    except KeyError:
        raise NotImplementedError('Algorithm not supported')

    segments.append(base64url_encode(signature))

    return b'.'.join(segments)


def decode(jwt, key='', verify=True, verify_expiration=True, leeway=0):
    payload, signing_input, header, signature = load(jwt)

    if verify:
        verify_signature(payload, signing_input, header, signature, key,
                         verify_expiration, leeway)

    return payload


def load(jwt):
    if isinstance(jwt, unicode):
        jwt = jwt.encode('utf-8')
    try:
        signing_input, crypto_segment = jwt.rsplit(b'.', 1)
        header_segment, payload_segment = signing_input.split(b'.', 1)
    except ValueError:
        raise DecodeError('Not enough segments')

    try:
        header_data = base64url_decode(header_segment)
    except (TypeError, binascii.Error):
        raise DecodeError('Invalid header padding')
    try:
        header = json.loads(header_data.decode('utf-8'))
    except ValueError as e:
        raise DecodeError('Invalid header string: %s' % e)

    try:
        payload_data = base64url_decode(payload_segment)
    except (TypeError, binascii.Error):
        raise DecodeError('Invalid payload padding')
    try:
        payload = json.loads(payload_data.decode('utf-8'))
    except ValueError as e:
        raise DecodeError('Invalid payload string: %s' % e)

    try:
        signature = base64url_decode(crypto_segment)
    except (TypeError, binascii.Error):
        raise DecodeError('Invalid crypto padding')

    return (payload, signing_input, header, signature)


def verify_signature(payload, signing_input, header, signature, key='',
                     verify_expiration=True, leeway=0):
    try:
        algorithm = header['alg'].upper()
        key = prepare_key_methods[algorithm](key)

        if algorithm.startswith('HS'):
            expected = verify_methods[algorithm](signing_input, key)

            if not constant_time_compare(signature, expected):
                raise DecodeError('Signature verification failed')
        else:
            if not verify_methods[algorithm](signing_input, key, signature):
                raise DecodeError('Signature verification failed')
    except KeyError:
        raise DecodeError('Algorithm not supported')

    if 'exp' in payload and verify_expiration:
        utc_timestamp = timegm(datetime.utcnow().utctimetuple())

        if payload['exp'] < (utc_timestamp - leeway):
            raise ExpiredSignature('Signature has expired')