Add google-endpoints to third_party/.

third_party/google-endpoints/rsa/pkcs1.py

+# -*- coding: utf-8 -*-
+#
+#  Copyright 2011 Sybren A. Stüvel <sybren@stuvel.eu>
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+"""Functions for PKCS#1 version 1.5 encryption and signing
+
+This module implements certain functionality from PKCS#1 version 1.5. For a
+very clear example, read http://www.di-mgt.com.au/rsa_alg.html#pkcs1schemes
+
+At least 8 bytes of random padding is used when encrypting a message. This makes
+these methods much more secure than the ones in the ``rsa`` module.
+
+WARNING: this module leaks information when decryption fails. The exceptions
+that are raised contain the Python traceback information, which can be used to
+deduce where in the process the failure occurred. DO NOT PASS SUCH INFORMATION
+to your users.
+"""
+
+import hashlib
+import os
+
+from rsa._compat import b
+from rsa import common, transform, core
+
+# ASN.1 codes that describe the hash algorithm used.
+HASH_ASN1 = {
+    'MD5': b('\x30\x20\x30\x0c\x06\x08\x2a\x86\x48\x86\xf7\x0d\x02\x05\x05\x00\x04\x10'),
+    'SHA-1': b('\x30\x21\x30\x09\x06\x05\x2b\x0e\x03\x02\x1a\x05\x00\x04\x14'),
+    'SHA-256': b('\x30\x31\x30\x0d\x06\x09\x60\x86\x48\x01\x65\x03\x04\x02\x01\x05\x00\x04\x20'),
+    'SHA-384': b('\x30\x41\x30\x0d\x06\x09\x60\x86\x48\x01\x65\x03\x04\x02\x02\x05\x00\x04\x30'),
+    'SHA-512': b('\x30\x51\x30\x0d\x06\x09\x60\x86\x48\x01\x65\x03\x04\x02\x03\x05\x00\x04\x40'),
+}
+
+HASH_METHODS = {
+    'MD5': hashlib.md5,
+    'SHA-1': hashlib.sha1,
+    'SHA-256': hashlib.sha256,
+    'SHA-384': hashlib.sha384,
+    'SHA-512': hashlib.sha512,
+}
+
+
+class CryptoError(Exception):
+    """Base class for all exceptions in this module."""
+
+
+class DecryptionError(CryptoError):
+    """Raised when decryption fails."""
+
+
+class VerificationError(CryptoError):
+    """Raised when verification fails."""
+
+
+def _pad_for_encryption(message, target_length):
+    r"""Pads the message for encryption, returning the padded message.
+
+    :return: 00 02 RANDOM_DATA 00 MESSAGE
+
+    >>> block = _pad_for_encryption(b'hello', 16)
+    >>> len(block)
+    16
+    >>> block[0:2]
+    b'\x00\x02'
+    >>> block[-6:]
+    b'\x00hello'
+
+    """
+
+    max_msglength = target_length - 11
+    msglength = len(message)
+
+    if msglength > max_msglength:
+        raise OverflowError('%i bytes needed for message, but there is only'
+                            ' space for %i' % (msglength, max_msglength))
+
+    # Get random padding
+    padding = b('')
+    padding_length = target_length - msglength - 3
+
+    # We remove 0-bytes, so we'll end up with less padding than we've asked for,
+    # so keep adding data until we're at the correct length.
+    while len(padding) < padding_length:
+        needed_bytes = padding_length - len(padding)
+
+        # Always read at least 8 bytes more than we need, and trim off the rest
+        # after removing the 0-bytes. This increases the chance of getting
+        # enough bytes, especially when needed_bytes is small
+        new_padding = os.urandom(needed_bytes + 5)
+        new_padding = new_padding.replace(b('\x00'), b(''))
+        padding = padding + new_padding[:needed_bytes]
+
+    assert len(padding) == padding_length
+
+    return b('').join([b('\x00\x02'),
+                       padding,
+                       b('\x00'),
+                       message])
+
+
+def _pad_for_signing(message, target_length):
+    r"""Pads the message for signing, returning the padded message.
+
+    The padding is always a repetition of FF bytes.
+
+    :return: 00 01 PADDING 00 MESSAGE
+
+    >>> block = _pad_for_signing(b'hello', 16)
+    >>> len(block)
+    16
+    >>> block[0:2]
+    b'\x00\x01'
+    >>> block[-6:]
+    b'\x00hello'
+    >>> block[2:-6]
+    b'\xff\xff\xff\xff\xff\xff\xff\xff'
+
+    """
+
+    max_msglength = target_length - 11
+    msglength = len(message)
+
+    if msglength > max_msglength:
+        raise OverflowError('%i bytes needed for message, but there is only'
+                            ' space for %i' % (msglength, max_msglength))
+
+    padding_length = target_length - msglength - 3
+
+    return b('').join([b('\x00\x01'),
+                       padding_length * b('\xff'),
+                       b('\x00'),
+                       message])
+
+
+def encrypt(message, pub_key):
+    """Encrypts the given message using PKCS#1 v1.5
+
+    :param message: the message to encrypt. Must be a byte string no longer than
+        ``k-11`` bytes, where ``k`` is the number of bytes needed to encode
+        the ``n`` component of the public key.
+    :param pub_key: the :py:class:`rsa.PublicKey` to encrypt with.
+    :raise OverflowError: when the message is too large to fit in the padded
+        block.
+
+    >>> from rsa import key, common
+    >>> (pub_key, priv_key) = key.newkeys(256)
+    >>> message = b'hello'
+    >>> crypto = encrypt(message, pub_key)
+
+    The crypto text should be just as long as the public key 'n' component:
+
+    >>> len(crypto) == common.byte_size(pub_key.n)
+    True
+
+    """
+
+    keylength = common.byte_size(pub_key.n)
+    padded = _pad_for_encryption(message, keylength)
+
+    payload = transform.bytes2int(padded)
+    encrypted = core.encrypt_int(payload, pub_key.e, pub_key.n)
+    block = transform.int2bytes(encrypted, keylength)
+
+    return block
+
+
+def decrypt(crypto, priv_key):
+    r"""Decrypts the given message using PKCS#1 v1.5
+
+    The decryption is considered 'failed' when the resulting cleartext doesn't
+    start with the bytes 00 02, or when the 00 byte between the padding and
+    the message cannot be found.
+
+    :param crypto: the crypto text as returned by :py:func:`rsa.encrypt`
+    :param priv_key: the :py:class:`rsa.PrivateKey` to decrypt with.
+    :raise DecryptionError: when the decryption fails. No details are given as
+        to why the code thinks the decryption fails, as this would leak
+        information about the private key.
+
+
+    >>> import rsa
+    >>> (pub_key, priv_key) = rsa.newkeys(256)
+
+    It works with strings:
+
+    >>> crypto = encrypt(b'hello', pub_key)
+    >>> decrypt(crypto, priv_key)
+    b'hello'
+
+    And with binary data:
+
+    >>> crypto = encrypt(b'\x00\x00\x00\x00\x01', pub_key)
+    >>> decrypt(crypto, priv_key)
+    b'\x00\x00\x00\x00\x01'
+
+    Altering the encrypted information will *likely* cause a
+    :py:class:`rsa.pkcs1.DecryptionError`. If you want to be *sure*, use
+    :py:func:`rsa.sign`.
+
+
+    .. warning::
+
+        Never display the stack trace of a
+        :py:class:`rsa.pkcs1.DecryptionError` exception. It shows where in the
+        code the exception occurred, and thus leaks information about the key.
+        It's only a tiny bit of information, but every bit makes cracking the
+        keys easier.
+
+    >>> crypto = encrypt(b'hello', pub_key)
+    >>> crypto = crypto[0:5] + b'X' + crypto[6:] # change a byte
+    >>> decrypt(crypto, priv_key)
+    Traceback (most recent call last):
+    ...
+    rsa.pkcs1.DecryptionError: Decryption failed
+
+    """
+
+    blocksize = common.byte_size(priv_key.n)
+    encrypted = transform.bytes2int(crypto)
+    decrypted = priv_key.blinded_decrypt(encrypted)
+    cleartext = transform.int2bytes(decrypted, blocksize)
+
+    # If we can't find the cleartext marker, decryption failed.
+    if cleartext[0:2] != b('\x00\x02'):
+        raise DecryptionError('Decryption failed')
+
+    # Find the 00 separator between the padding and the message
+    try:
+        sep_idx = cleartext.index(b('\x00'), 2)
+    except ValueError:
+        raise DecryptionError('Decryption failed')
+
+    return cleartext[sep_idx + 1:]
+
+
+def sign(message, priv_key, hash):
+    """Signs the message with the private key.
+
+    Hashes the message, then signs the hash with the given key. This is known
+    as a "detached signature", because the message itself isn't altered.
+
+    :param message: the message to sign. Can be an 8-bit string or a file-like
+        object. If ``message`` has a ``read()`` method, it is assumed to be a
+        file-like object.
+    :param priv_key: the :py:class:`rsa.PrivateKey` to sign with
+    :param hash: the hash method used on the message. Use 'MD5', 'SHA-1',
+        'SHA-256', 'SHA-384' or 'SHA-512'.
+    :return: a message signature block.
+    :raise OverflowError: if the private key is too small to contain the
+        requested hash.
+
+    """
+
+    # Get the ASN1 code for this hash method
+    if hash not in HASH_ASN1:
+        raise ValueError('Invalid hash method: %s' % hash)
+    asn1code = HASH_ASN1[hash]
+
+    # Calculate the hash
+    hash = _hash(message, hash)
+
+    # Encrypt the hash with the private key
+    cleartext = asn1code + hash
+    keylength = common.byte_size(priv_key.n)
+    padded = _pad_for_signing(cleartext, keylength)
+
+    payload = transform.bytes2int(padded)
+    encrypted = priv_key.blinded_encrypt(payload)
+    block = transform.int2bytes(encrypted, keylength)
+
+    return block
+
+
+def verify(message, signature, pub_key):
+    """Verifies that the signature matches the message.
+
+    The hash method is detected automatically from the signature.
+
+    :param message: the signed message. Can be an 8-bit string or a file-like
+        object. If ``message`` has a ``read()`` method, it is assumed to be a
+        file-like object.
+    :param signature: the signature block, as created with :py:func:`rsa.sign`.
+    :param pub_key: the :py:class:`rsa.PublicKey` of the person signing the message.
+    :raise VerificationError: when the signature doesn't match the message.
+
+    """
+
+    keylength = common.byte_size(pub_key.n)
+    encrypted = transform.bytes2int(signature)
+    decrypted = core.decrypt_int(encrypted, pub_key.e, pub_key.n)
+    clearsig = transform.int2bytes(decrypted, keylength)
+
+    # Get the hash method
+    method_name = _find_method_hash(clearsig)
+    message_hash = _hash(message, method_name)
+
+    # Reconstruct the expected padded hash
+    cleartext = HASH_ASN1[method_name] + message_hash
+    expected = _pad_for_signing(cleartext, keylength)
+
+    # Compare with the signed one
+    if expected != clearsig:
+        raise VerificationError('Verification failed')
+
+    return True
+
+
+def _hash(message, method_name):
+    """Returns the message digest.
+
+    :param message: the signed message. Can be an 8-bit string or a file-like
+        object. If ``message`` has a ``read()`` method, it is assumed to be a
+        file-like object.
+    :param method_name: the hash method, must be a key of
+        :py:const:`HASH_METHODS`.
+
+    """
+
+    if method_name not in HASH_METHODS:
+        raise ValueError('Invalid hash method: %s' % method_name)
+
+    method = HASH_METHODS[method_name]
+    hasher = method()
+
+    if hasattr(message, 'read') and hasattr(message.read, '__call__'):
+        # Late import to prevent DeprecationWarnings.
+        from . import varblock
+
+        # read as 1K blocks
+        for block in varblock.yield_fixedblocks(message, 1024):
+            hasher.update(block)
+    else:
+        # hash the message object itself.
+        hasher.update(message)
+
+    return hasher.digest()
+
+
+def _find_method_hash(clearsig):
+    """Finds the hash method.
+
+    :param clearsig: full padded ASN1 and hash.
+    :return: the used hash method.
+    :raise VerificationFailed: when the hash method cannot be found
+    """
+
+    for (hashname, asn1code) in HASH_ASN1.items():
+        if asn1code in clearsig:
+            return hashname
+
+    raise VerificationError('Verification failed')
+
+
+__all__ = ['encrypt', 'decrypt', 'sign', 'verify',
+           'DecryptionError', 'VerificationError', 'CryptoError']
+
+if __name__ == '__main__':
+    print('Running doctests 1000x or until failure')
+    import doctest
+
+    for count in range(1000):
+        (failures, tests) = doctest.testmod()
+        if failures:
+            break
+
+        if count and count % 100 == 0:
+            print('%i times' % count)
+
+    print('Doctests done')