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# Unix SMB/CIFS implementation.
# Copyright (C) Catalyst.Net Ltd 2025
#
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <https://www.gnu.org/licenses/>.
#
"""ASN.1 module"""
import math
from typing import Optional
class Asn1Error(Exception):
pass
def length_in_bytes(value: int) -> int:
"""Return the length in bytes of an integer once it is encoded as
bytes."""
if value < 0:
raise Asn1Error("value must be positive")
if not isinstance(value, int):
raise Asn1Error("value must be an integer")
length_in_bits = max(1, math.log2(value + 1))
length_in_bytes = math.ceil(length_in_bits / 8)
return length_in_bytes
def bytes_from_int(value: int, *, length: Optional[int] = None) -> bytes:
"""Return an integer encoded big-endian into bytes of an optionally
specified length.
"""
if length is None:
length = length_in_bytes(value)
return value.to_bytes(length, "big")
def int_from_bytes(data: bytes) -> int:
"""Return an integer decoded from bytes in big-endian format."""
return int.from_bytes(data, "big")
def int_from_bit_string(string: str) -> int:
"""Return an integer decoded from a bitstring."""
return int(string, base=2)
def bit_string_from_int(value: int) -> str:
"""Return a bitstring encoding of an integer."""
string = f"{value:b}"
# The bitstring must be padded to a multiple of 8 bits in length, or
# pyasn1 will interpret it incorrectly (as if the padding bits were
# present, but on the wrong end).
length = len(string)
padding_len = math.ceil(length / 8) * 8 - length
return "0" * padding_len + string
def bit_string_from_bytes(data: bytes) -> str:
"""Return a bitstring encoding of bytes in big-endian format."""
value = int_from_bytes(data)
return bit_string_from_int(value)
def bytes_from_bit_string(string: str) -> bytes:
"""Return big-endian format bytes encoded from a bitstring."""
value = int_from_bit_string(string)
length = math.ceil(len(string) / 8)
return value.to_bytes(length, "big")
def asn1_length(data: bytes) -> bytes:
"""Return the ASN.1 encoding of the length of some data."""
length = len(data)
if length <= 0:
raise Asn1Error("length must be greater than zero")
if length < 0x80:
return bytes([length])
encoding_len = length_in_bytes(length)
if encoding_len >= 0x80:
raise Asn1Error("item is too long to be ASN.1 encoded")
data = bytes_from_int(length, length=encoding_len)
return bytes([0x80 | encoding_len]) + data
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