如何将加密数据发送到客户端?

时间:2016-08-17 15:06:56

标签: python sockets python-3.x encryption

这是我的客户代码。

import socket, pickle,time

from encryption import *

def Main():

    host = '127.0.0.1'
    port = 5006
    s = socket.socket()
    s.connect((host, port))
    m= encryption()
    pri_key,pub_key,n=m.generating_keys(1)
    filename = input("Filename? -> ")

    if filename != 'q':
        data=[filename,pub_key,n]
        msg=pickle.dumps(data)
        s.send(msg)
        data = s.recv(1024)
        data=data.decode('utf-8')
        if data == '1':
            size = s.recv(1024)
            size = int(size.decode('utf-8'))
            filesize = size
            message = input("File exists, " + str(filesize) +"Bytes, download? (Y/N)? -> ")
            if message == 'Y':
                s.send(b'1')
                count=0
                f = open('new_'+filename, 'wb')
                data = s.recv(1024)
                data=int.from_bytes(data,byteorder="little")
                msg=m.decrypt(data,pri_key,n)
                totalRecv = len(msg)
                f.write(msg)
                #count=0
                while totalRecv<filesize:
                    #time.sleep(.300)
                    decipher = s.recv(1024)
                    decipher=int.from_bytes(decipher,byteorder="little")
                    print(decipher)
                    if(decipher==0):
                        break
                    msg=m.decrypt(decipher,pri_key,n)
                    totalRecv += len(msg)
                    f.write(msg)
                    print ("{0:.2f}".format((totalRecv/float(filesize))*100)+ "% Done")
                print ("Download Complete!")
                f.close()
        else:
            print ("File Does Not Exist!")
    s.close() 
if __name__ == '__main__':

    Main()

这是我的服务器代码。

import socket,threading,os,pickle

from encryption import *

def RetrFile(name, sock):

    m=encryption()
    filename = sock.recv(1024)
    dat=pickle.loads(filename)
    if os.path.isfile(dat[0]):
        s='1'
        s=s.encode('utf-8')
        sock.send(s)
        k=str(os.path.getsize(dat[0]))
        k=k.encode('utf-8')
        sock.send(k)
        count=8
        userResponse = sock.recv(1024)
        if userResponse[:2] == (b'1'):
            with open(dat[0],'rb') as f:
                bytesToSend = f.read(1024)
                #print(type(bytesToSend))
                #print('1')
                #print(bytesToSend)
                msg= m.encrypt(bytesToSend,dat[1],dat[2])
                #print(msg)
                #print(1)
                k=msg.bit_length()
                if(k%8>=1):
                    k=k+1
                msg=msg.to_bytes(k,byteorder="little")
                #print (msg)
                #msg=msg.encode('utf-8')
                #print(msg)
                sock.send(msg)
                s=''
                s=s.encode('utf-8')
                while bytesToSend != s:

                    bytesToSend = f.read(1024)
                    msg= m.encrypt(bytesToSend,dat[1],dat[2])
                    k=msg.bit_length()
                    if(k%8>=1):
                        k=k//8+1
                    msg=msg.to_bytes(k,byteorder="little")
                    sock.send(msg)
                #count=count.to_bytes(1,byteorder="little")
                #sock.send(count)     
    else:
        sock.send(b'ERR')

    sock.close()

def Main():

    host = '127.0.0.1'
    port = 5006


    s = socket.socket()
    s.bind((host,port))

    s.listen(5)
    print ("Server Started.")
    while True:
        c, addr = s.accept()
        print ("client connedted ip:<" + str(addr) + ">")
        t = threading.Thread(target=RetrFile, args=("RetrThread", c))
        t.start()        
    s.close()
if __name__ == '__main__':

    Main()

现在我的问题是客户端的decipher.recv(1024)没有收到消息。我该怎么办。

2 个答案:

答案 0 :(得分:0)

在服务器端,将代码更改为:

while bytesToSend != s:
    bytesToSend = f.read(1024)
    length = len(bytesTosend) 
    leng = length.to_bytes(4, 'little')
    sock.sendall(leng)
    msg = m.encrypt(bytesToSend, dat[1], dat[2])
    k = msg.bit_length()
    if k % 8 >= 1 :
        k = k // 8 + 1
    else:
        k = k // 8
    msg = msg.to_bytes(k, byteorder='little')
    sock.sendall(msg)

在客户端:

while True:
    length = s.recv(4)
    length = int.from_bytes(length, byteorder='little')
    decipher = s.recv(leng)
    decipher = int.from_bytes(decipher, byteorder='little')
    if not decipher:
        break
    msg = m.decrypt(decipher, pri_key, n)
    f.write(msg)
f.close()

答案 1 :(得分:0)

如果没有看到代码中引用的encryption模块,则很难检查代码。由于缺少这样的功能,测试以找出问题的位置变得不可能。因此,提供以下程序以及另一个加密模块的实现。

服务器应该从命令行运行,并且需要在执行时提供端口号和密码。使用的唯一形式的身份验证或授权是对客户端的正确理解。客户端必须使用相同的密码才能被服务器理解。

服务器

#! /usr/bin/env python3
import argparse
import pathlib
import pickle
import pickletools
import random
import socket
import socketserver
import zlib


import encryption
BYTES_USED = bytes(range(1 << 8))
CHAIN_SIZE = 1 << 8


def main():
    """Start a file server and serve clients forever."""
    parser = argparse.ArgumentParser(description='Execute a file server demo.')
    parser.add_argument('port', type=int, help='location where server listens')
    parser.add_argument('password', type=str, help='key to use on secure line')
    arguments = parser.parse_args()
    server_address = socket.gethostbyname(socket.gethostname()), arguments.port
    server = CustomServer(server_address, CustomHandler, arguments.password)
    server.serve_forever()


class CustomServer(socketserver.ThreadingTCPServer):

    """Provide server support for the management of encrypted data."""

    def __init__(self, server_address, request_handler_class, password):
        """Initialize the server and keep a set of security credentials."""
        super().__init__(server_address, request_handler_class, True)
        self.key = encryption.Key.new_client_random(
            BYTES_USED,
            CHAIN_SIZE,
            random.Random(password)
        )
        self.primer = encryption.Primer.new_client_random(
            self.key,
            random.Random(password)
        )


class CustomHandler(socketserver.StreamRequestHandler):

    """Allow forwarding of data to all connected clients."""

    def __init__(self, request, client_address, server):
        """Initialize the handler with security translators."""
        self.decoder = encryption.Decrypter(server.key, server.primer)
        self.encoder = encryption.Encrypter(server.key, server.primer)
        super().__init__(request, client_address, server)

    def handle(self):
        """Run the code to handle clients while dealing with errors."""
        try:
            self.process_file_request()
        except (ConnectionResetError, EOFError):
            pass

    def process_file_request(self):
        """Deal with clients that wish to download a file."""
        segment = self.load()
        path = pathlib.Path(segment)
        if path.is_file():
            size = path.stat().st_size
            self.dump(size)
            accepted = self.load()
            if accepted:
                with path.open('rb') as file:
                    while True:
                        buffer = file.read(1 << 15)
                        self.dump(buffer)
                        if not buffer:
                            break
        else:
            error = 'The given path does not specify a file.'
            self.dump(error)

    def load(self):
        """Read the client's connection with blocking."""
        data = self.decoder.load_16bit_frame(self.rfile)
        bytes_object = zlib.decompress(data)
        return pickle.loads(bytes_object)

    def dump(self, obj):
        """Send an object securely over to the client if possible."""
        pickle_string = pickle.dumps(obj, pickle.HIGHEST_PROTOCOL)
        bytes_object = pickletools.optimize(pickle_string)
        data = zlib.compress(bytes_object, zlib.Z_BEST_COMPRESSION)
        self.encoder.dump_16bit_frame(data, self.wfile)


if __name__ == '__main__':
    main()

客户端也应该从命令行运行,并且需要服务器的主机名,端口号和密码。通信使用密码加密,如果不同则无法正确解密。请注意,两个程序中几乎没有检查错误。

<强>客户端

#! /usr/bin/env python3
import argparse
import pathlib
import pickle
import pickletools
import random
import socket
import zlib


import encryption
BYTES_USED = bytes(range(1 << 8))
CHAIN_SIZE = 1 << 8


# These are possible answers accepted for yes/no style questions.
POSITIVE = tuple(map(str.casefold, ('yes', 'true', '1')))
NEGATIVE = tuple(map(str.casefold, ('no', 'false', '0')))


def main():
    """Connect a file client to a server and process incoming commands."""
    parser = argparse.ArgumentParser(description='Execute a file client demo.')
    parser.add_argument('host', type=str, help='name of server on the network')
    parser.add_argument('port', type=int, help='location where server listens')
    parser.add_argument('password', type=str, help='key to use on secure line')
    arguments = parser.parse_args()
    connection = socket.create_connection((arguments.host, arguments.port))
    try:
        talk_to_server(*make_dump_and_load(connection, arguments.password))
    finally:
        connection.shutdown(socket.SHUT_RDWR)
        connection.close()


def make_dump_and_load(connection, password):
    """Create objects to help with the encrypted communications."""
    reader = connection.makefile('rb', -1)
    writer = connection.makefile('wb', 0)
    chaos = random.Random(password)
    key = encryption.Key.new_client_random(BYTES_USED, CHAIN_SIZE, chaos)
    chaos = random.Random(password)
    primer = encryption.Primer.new_client_random(key, chaos)
    decoder = encryption.Decrypter(key, primer)
    encoder = encryption.Encrypter(key, primer)

    def dump(obj):
        """Write an object to the writer file in an encoded form."""
        pickle_string = pickle.dumps(obj, pickle.HIGHEST_PROTOCOL)
        bytes_object = pickletools.optimize(pickle_string)
        data = zlib.compress(bytes_object, zlib.Z_BEST_COMPRESSION)
        encoder.dump_16bit_frame(data, writer)

    def load():
        """Read an object from the reader file and decode the results."""
        data = decoder.load_16bit_frame(reader)
        bytes_object = zlib.decompress(data)
        return pickle.loads(bytes_object)

    return dump, load


def talk_to_server(dump, load):
    """Converse with the serve while trying to get a file."""
    segment = input('Filename: ')
    dump(segment)
    size = load()
    if isinstance(size, int):
        print('File exists and takes', size, 'bytes to download.')
        response = get_response('Continue? ')
        dump(response)
        if response:
            location = input('Where should the new file be created? ')
            with pathlib.Path(location).open('wb') as file:
                written = 0
                while True:
                    buffer = load()
                    if not buffer:
                        break
                    written += file.write(buffer)
                    print('Progress: {:.1%}'.format(written / size))
            print('Download complete!')
    else:
        print(size)


def get_response(query):
    """Ask the user yes/no style questions and return the results."""
    while True:
        answer = input(query).casefold()
        if answer:
            if any(option.startswith(answer) for option in POSITIVE):
                return True
            if any(option.startswith(answer) for option in NEGATIVE):
                return False
        print('Please provide a positive or negative answer.')


if __name__ == '__main__':
    main()

由于未提供对encryption模块的访问,因此下面列出了替代实现。不保证其在任何容量或任何目的的适用性。它可能有点慢,因为当前配置了软件,但如果需要混淆则效果很好。

<强>加密

"""Provide an implementation of Markov Encryption for simplified use.

This module exposes primitives useful for executing Markov Encryption
processes. ME was inspired by a combination of Markov chains with the
puzzles of Sudoku. This implementation has undergone numerous changes
and optimizations since its original design. Please see documentation."""

###############################################################################

# Import several functions needed later in the code.

from collections import deque
from math import ceil
from random import Random, SystemRandom
from struct import calcsize, pack, unpack
from inspect import currentframe

__author__ = 'Stephen "Zero" Chappell <Noctis.Skytower@gmail.com>'
__date__ = '18 August 2016'
__version__ = 2, 0, 8

###############################################################################

# Create some tools to use in the classes down below.

_CHAOS = SystemRandom()


def slots(names=''):
    """Set the __slots__ variable in the calling context with private names.

    This function allows a convenient syntax when specifying the slots
    used in a class. Simply call it in a class definition context with
    the needed names. Locals are modified with private slot names."""
    currentframe().f_back.f_locals['__slots__'] = \
        tuple('__' + name for name in names.replace(',', ' ').split())

###############################################################################

# Implement a Key primitive data type for Markov Encryption.


class Key:

    """Key(data) -> Key instance

    This class represents a Markov Encryption Key primitive. It allows for
    easy key creation, checks for proper data construction, and helps with
    encoding and decoding indexes based on cached internal tables."""

    slots('data dimensions base size encoder axes order decoder')

    @classmethod
    def new(cls, bytes_used, chain_size):
        """Return a Key instance created from bytes_used and chain_size.

        Creating a new key is easy with this method. Call this class method
        with the bytes you want the key to recognize along with the size of
        the chains you want the encryption/decryption processes to use."""
        selection, blocks = list(set(bytes_used)), []
        for _ in range(chain_size):
            _CHAOS.shuffle(selection)
            blocks.append(bytes(selection))
        return cls(tuple(blocks))

    @classmethod
    def new_deterministic(cls, bytes_used, chain_size):
        """Automatically create a key with the information provided."""
        selection, blocks, chaos = list(set(bytes_used)), [], Random()
        chaos.seed(chain_size.to_bytes(ceil(
            chain_size.bit_length() / 8), 'big') + bytes(range(256)))
        for _ in range(chain_size):
            chaos.shuffle(selection)
            blocks.append(bytes(selection))
        return cls(tuple(blocks))

    @classmethod
    def new_client_random(cls, bytes_used, chain_size, chaos):
        """Create a key using chaos as the key's source of randomness."""
        selection, blocks = list(set(bytes_used)), []
        for _ in range(chain_size):
            chaos.shuffle(selection)
            blocks.append(bytes(selection))
        return cls(tuple(blocks))

    def __init__(self, data):
        """Initialize the Key instance's variables after testing the data.

        Keys are created with tuples of carefully constructed bytes arrays.
        This method tests the given data before going on to build internal
        tables for efficient encoding and decoding methods later on."""
        self.__test_data(data)
        self.__make_vars(data)

    @staticmethod
    def __test_data(data):
        """Test the data for correctness in its construction.

        The data must be a tuple of at least two byte arrays. Each byte
        array must have at least two bytes, all of which must be unique.
        Furthermore, all arrays should share the exact same byte set."""
        if not isinstance(data, tuple):
            raise TypeError('Data must be a tuple object!')
        if len(data) < 2:
            raise ValueError('Data must contain at least two items!')
        item = data[0]
        if not isinstance(item, bytes):
            raise TypeError('Data items must be bytes objects!')
        length = len(item)
        if length < 2:
            raise ValueError('Data items must contain at least two bytes!')
        unique = set(item)
        if len(unique) != length:
            raise ValueError('Data items must contain unique byte sets!')
        for item in data[1:]:
            if not isinstance(item, bytes):
                raise TypeError('Data items must be bytes objects!')
            next_length = len(item)
            if next_length != length:
                raise ValueError('All data items must have the same size!')
            next_unique = set(item)
            if len(next_unique) != next_length:
                raise ValueError('Data items must contain unique byte sets!')
            if next_unique ^ unique:
                raise ValueError('All data items must use the same byte set!')

    def __make_vars(self, data):
        """Build various internal tables for optimized calculations.

        Encoding and decoding rely on complex relationships with the given
        data. This method caches several of these key relationships for use
        when the encryption and decryption processes are being executed."""
        self.__data = data
        self.__dimensions = len(data)
        base, *mutations = data
        self.__base = base = tuple(base)
        self.__size = size = len(base)
        offset = -sum(base.index(block[0]) for block in mutations[:-1]) % size
        self.__encoder = base[offset:] + base[:offset]
        self.__axes = tuple(reversed([tuple(base.index(byte) for byte in block)
                                      for block in mutations]))
        self.__order = key = tuple(sorted(base))
        grid = []
        for rotation in range(size):
            block, row = base[rotation:] + base[:rotation], [None] * size
            for byte, value in zip(block, key):
                row[key.index(byte)] = value
            grid.append(tuple(row))
        self.__decoder = tuple(grid[offset:] + grid[:offset])

    def test_primer(self, primer):
        """Raise an error if the primer is not compatible with this key.

        Key and primers have a certain relationship that must be maintained
        in order for them to work together. Since the primer understands
        the requirements, it is asked to check this key for compatibility."""
        primer.test_key(self)

    def encode(self, index):
        """Encode index based on internal tables and return byte code.

        An index probes into the various axes of the multidimensional,
        virtual grid that a key represents. The index is evaluated, and
        the value at its coordinates is returned by running this method."""
        assert len(index) == self.__dimensions, \
            'Index size is not compatible with key dimensions!'
        *probes, current = index
        return self.__encoder[(sum(
            table[probe] for table, probe in zip(self.__axes, probes)
        ) + current) % self.__size]

    def decode(self, index):
        """Decode index based on internal tables and return byte code.

        Decoding does the exact same thing as encoding, but it indexes
        into a virtual grid that represents the inverse of the encoding
        grid. Tables are used to make the process fast and efficient."""
        assert len(index) == self.__dimensions, \
            'Index size is not compatible with key dimensions!'
        *probes, current = index
        return self.__decoder[sum(
            table[probe] for table, probe in zip(self.__axes, probes)
        ) % self.__size][current]

    @property
    def data(self):
        """Data that the instance was initialized with.

        This is the tuple of byte arrays used to create this key and can
        be used to create an exact copy of this key at some later time."""
        return self.__data

    @property
    def dimensions(self):
        """Dimensions that the internal, virtual grid contains.

        The virtual grid has a number of axes that can be referenced when
        indexing into it, and this number is the count of its dimensions."""
        return self.__dimensions

    @property
    def base(self):
        """Base value that the internal grid is built from.

        The Sudoku nature of the grid comes from rotating this value by
        offsets, keeping values unique along any axis while traveling."""
        return self.__base

    @property
    def order(self):
        """Order of base after its values have been sorted.

        A sorted base is important when constructing inverse rows and when
        encoding raw bytes for use in updating an encode/decode index."""
        return self.__order

###############################################################################

# Implement a Primer primitive data type for Markov Encryption.


class Primer:

    """Primer(data) -> Primer instance

    This class represents a Markov Encryption Primer primitive. It is very
    important for starting both the encryption and decryption processes. A
    method is provided for their easy creation with a related key."""

    slots('data')

    @classmethod
    def new(cls, key):
        """Return a Primer instance from a parent Key.

        Primers must be compatible with the keys they are used with. This
        method takes a key and constructs a cryptographically sound primer
        that is ready to use in the beginning stages of encryption."""
        base = key.base
        return cls(bytes(_CHAOS.choice(base)
                         for _ in range(key.dimensions - 1)))

    @classmethod
    def new_deterministic(cls, key):
        """Automatically create a primer with the information provided."""
        base, chain_size, chaos = key.base, key.dimensions, Random()
        chaos.seed(chain_size.to_bytes(ceil(
            chain_size.bit_length() / 8), 'big') + bytes(range(256)))
        return cls(bytes(chaos.choice(base) for _ in range(chain_size - 1)))

    @classmethod
    def new_client_random(cls, key, chaos):
        """Create a primer using chaos as the primer's source of randomness."""
        base = key.base
        return cls(
            bytes(chaos.choice(base) for _ in range(key.dimensions - 1))
        )

    def __init__(self, data):
        """Initialize the Primer instance after testing validity of data.

        Though not as complicated in its requirements as keys, primers do
        need some simple structure in the data they are given. A checking
        method is run before saving the data to the instance's attribute."""
        self.__test_data(data)
        self.__data = data

    @staticmethod
    def __test_data(data):
        """Test the data for correctness and test the data.

        In order for the primer to be compatible with the nature of the
        Markov Encryption processes, the data must be an array of bytes;
        and to act as a primer, it must contain at least some information."""
        if not isinstance(data, bytes):
            raise TypeError('Data must be a bytes object!')
        if not data:
            raise ValueError('Data must contain at least one byte!')

    def test_key(self, key):
        """Raise an error if the key is not compatible with this primer.

        Primers provide needed data to start encryption and decryption. For
        it be compatible with a key, it must contain one byte less than the
        key's dimensions and must be a subset of the base in the key."""
        if len(self.__data) != key.dimensions - 1:
            raise ValueError('Key size must be one more than the primer size!')
        if not set(self.__data).issubset(key.base):
            raise ValueError('Key data must be a superset of primer data!')

    @property
    def data(self):
        """Data that the instance was initialized with.

        This is the byte array used to create this primer and can be used
        if desired to create an copy of this primer at some later time."""
        return self.__data

###############################################################################

# Create an abstract processing class for use in encryption and decryption.


class _Processor:

    """_Processor(key, primer) -> NotImplementedError exception

    This class acts as a base for the encryption and decryption processes.
    The given key is saved, and several tables are created along with an
    index. Since it is abstract, calling the class will raise an exception."""

    slots('key into index from')

    def __init__(self, key, primer):
        """Initialize the _Processor instance if it is from a child class.

        After passing several tests for creating a valid processing object,
        the key is saved, and the primer is used to start an index. Tables
        are also formed for converting byte values between systems."""
        if type(self) is _Processor:
            raise NotImplementedError('This is an abstract class!')
        key.test_primer(primer)
        self.__key = key
        self.__into = table = dict(map(reversed, enumerate(key.order)))
        self.__index = deque(map(table.__getitem__, primer.data),
                             key.dimensions)
        self.__from = dict(map(reversed, table.items()))

    def process(self, data):
        """Process the data and return its transformed state.

        A cache for the data transformation is created and an internal
        method is run to quickly encode or decode the given bytes. The
        cache is finally converted to immutable bytes when returned."""
        cache = bytearray()
        self._run(data, cache.append, self.__key, self.__into, self.__index)
        return bytes(cache)

    @staticmethod
    def _run(data, cache_append, key, table, index):
        """Run the processing algorithm in an overloaded method.

        Since this is only an abstract base class for encoding/decoding,
        this method will raise an exception when run. Inheriting classes
        should implement whatever is appropriate for the intended function."""
        raise NotImplementedError('This is an abstract method!')

    @property
    def primer(self):
        """Primer representing the state of the internal index.

        The index can be retrieved as a primer, useful for initializing
        another processor in the same starting state as the current one."""
        index = self.__index
        index.append(None)
        index.pop()
        return Primer(bytes(map(self.__from.__getitem__, index)))

###############################################################################

# Inherit from _Processor and implement the ME encoding algorithm.


class Encrypter(_Processor):

    """Encrypter(key, primer) -> Encrypter instance

    This class represents a state-aware encryption engine that can be fed
    data and will return a stream of coherent cipher-text. An index is
    maintained, and a state-continuation primer can be retrieved at will."""

    slots()

    @staticmethod
    def _run(data, cache_append, key, table, index):
        """Encrypt the data with the given arguments.

        To run the encryption process as fast as possible, methods are
        cached as names. As the algorithm operates, only recognized bytes
        are encoded while running through the selective processing loop."""
        encode, index_append = key.encode, index.append
        for byte in data:
            if byte in table:
                index_append(table[byte])
                cache_append(encode(index))
            else:
                cache_append(byte)

    def dump_16bit_frame(self, data, file):
        """Write the data to the file using a guaranteed frame size."""
        size = len(data)
        if not 1 <= size <= 1 << 16:
            raise ValueError('data has an unsupported length')
        packed = self.process(pack('<H{}s'.format(size), size - 1, data))
        if file.write(packed) != len(packed):
            raise IOError('frame was not properly written to file')

###############################################################################

# Inherit from _Processor and implement the ME decoding algorithm.


class Decrypter(_Processor):

    """Decrypter(key, primer) -> Decrypter instance

    This class represents a state-aware decryption engine that can be fed
    data and will return a stream of coherent plain-text. An index is
    maintained, and a state-continuation primer can be retrieved at will."""

    slots()

    SIZE = '<H'
    DATA = '{}s'

    @staticmethod
    def _run(data, cache_append, key, table, index):
        """Decrypt the data with the given arguments.

        To run the decryption process as fast as possible, methods are
        cached as names. As the algorithm operates, only recognized bytes
        are decoded while running through the selective processing loop."""
        decode, index_append = key.decode, index.append
        for byte in data:
            if byte in table:
                index_append(table[byte])
                value = decode(index)
                cache_append(value)
                index[-1] = table[value]
            else:
                cache_append(byte)

    def load_16bit_frame(self, file):
        """Read some data from the file using a guaranteed frame size."""
        size = unpack(self.SIZE, self.process(self.read_all(
            file,
            calcsize(self.SIZE)
        )))[0] + 1
        return unpack(self.DATA.format(size), self.process(self.read_all(
            file,
            size
        )))[0]

    @staticmethod
    def read_all(file, size):
        """Get all the data that has been requested from the file."""
        if not 1 <= size <= 1 << 16:
            raise ValueError('size has an unsupported value')
        buffer = bytearray()
        while size > 0:
            data = file.read(size)
            if not data:
                raise EOFError('file has unexpectedly reached the end')
            buffer.extend(data)
            size -= len(data)
        if size < 0:
            raise IOError('more data was read than was required')
        return bytes(buffer)