def _mgf1(hash_algorithm, seed, mask_length):
    """
    The PKCS#1 MGF1 mask generation algorithm

    :param hash_algorithm:
        The string name of the hash algorithm to use: "sha1", "sha224",
        "sha256", "sha384", "sha512"

    :param seed:
        A byte string to use as the seed for the mask

    :param mask_length:
        The desired mask length, as an integer

    :return:
        A byte string of the mask
    """

    if not isinstance(seed, byte_cls):
        raise TypeError(pretty_message(
            '''
            seed must be a byte string, not %s
            ''',
            type_name(seed)
        ))

    if not isinstance(mask_length, int_types):
        raise TypeError(pretty_message(
            '''
            mask_length must be an integer, not %s
            ''',
            type_name(mask_length)
        ))

    if mask_length < 1:
        raise ValueError(pretty_message(
            '''
            mask_length must be greater than 0 - is %s
            ''',
            repr(mask_length)
        ))

    if hash_algorithm not in set(['sha1', 'sha224', 'sha256', 'sha384', 'sha512']):
        raise ValueError(pretty_message(
            '''
            hash_algorithm must be one of "sha1", "sha224", "sha256", "sha384",
            "sha512", not %s
            ''',
            repr(hash_algorithm)
        ))

    output = b''

    hash_length = {
        'sha1': 20,
        'sha224': 28,
        'sha256': 32,
        'sha384': 48,
        'sha512': 64
    }[hash_algorithm]

    iterations = int(math.ceil(mask_length / hash_length))

    pack = struct.Struct(b'>I').pack
    hash_func = getattr(hashlib, hash_algorithm)

    for counter in range(0, iterations):
        b = pack(counter)
        output += hash_func(seed + b).digest()

    return output[0:mask_length]
def _mgf1(hash_algorithm, seed, mask_length):
    

    if not isinstance(seed, byte_cls):
        raise TypeError(pretty_message(
            ,
            type_name(seed)
        ))

    if not isinstance(mask_length, int_types):
        raise TypeError(pretty_message(
            ,
            type_name(mask_length)
        ))

    if mask_length < 1:
        raise ValueError(pretty_message(
            ,
            repr(mask_length)
        ))

    if hash_algorithm not in set(['sha1', 'sha224', 'sha256', 'sha384', 'sha512']):
        raise ValueError(pretty_message(
            ,
            repr(hash_algorithm)
        ))

    output = b''

    hash_length = {
        'sha1': 20,
        'sha224': 28,
        'sha256': 32,
        'sha384': 48,
        'sha512': 64
    }[hash_algorithm]

    iterations = int(math.ceil(mask_length / hash_length))

    pack = struct.Struct(b'>I').pack
    hash_func = getattr(hashlib, hash_algorithm)

    for counter in range(0, iterations):
        b = pack(counter)
        output += hash_func(seed + b).digest()

    return output[0:mask_length]
def _mgf1 ( hash_algorithm , seed , mask_length ) : if not isinstance ( seed , byte_cls ) : raise TypeError ( pretty_message ( '''
            seed must be a byte string, not %s
            ''' , type_name ( seed ) ) ) if not isinstance ( mask_length , int_types ) : raise TypeError ( pretty_message ( '''
            mask_length must be an integer, not %s
            ''' , type_name ( mask_length ) ) ) if mask_length < 1 : raise ValueError ( pretty_message ( '''
            mask_length must be greater than 0 - is %s
            ''' , repr ( mask_length ) ) ) if hash_algorithm not in set ( [ 'sha1' , 'sha224' , 'sha256' , 'sha384' , 'sha512' ] ) : raise ValueError ( pretty_message ( '''
            hash_algorithm must be one of "sha1", "sha224", "sha256", "sha384",
            "sha512", not %s
            ''' , repr ( hash_algorithm ) ) ) output = b'' hash_length = { 'sha1' : 20 , 'sha224' : 28 , 'sha256' : 32 , 'sha384' : 48 , 'sha512' : 64 } [ hash_algorithm ] iterations = int ( math . ceil ( mask_length / hash_length ) ) pack = struct . Struct ( b'>I' ) . pack hash_func = getattr ( hashlib , hash_algorithm ) for counter in range ( 0 , iterations ) : b = pack ( counter ) output += hash_func ( seed + b ) . digest ( ) return output [ 0 : mask_length ]
The PKCS#1 MGF1 mask generation algorithm

    :param hash_algorithm:
        The string name of the hash algorithm to use: "sha1", "sha224",
        "sha256", "sha384", "sha512"

    :param seed:
        A byte string to use as the seed for the mask

    :param mask_length:
        The desired mask length, as an integer

    :return:
        A byte string of the mask
The PKCS#1 MGF1 mask generation algorithm