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https://github.com/samba-team/samba.git
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dbdd6952b6
Signed-off-by: Jennifer Sutton <jennifersutton@catalyst.net.nz> Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz> Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
104 lines
3.1 KiB
Python
104 lines
3.1 KiB
Python
# Unix SMB/CIFS implementation.
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# Copyright (C) Catalyst.Net Ltd 2025
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#
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <https://www.gnu.org/licenses/>.
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#
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"""ASN.1 module"""
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import math
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from typing import Optional
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class Asn1Error(Exception):
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pass
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def length_in_bytes(value: int) -> int:
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"""Return the length in bytes of an integer once it is encoded as
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bytes."""
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if value < 0:
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raise Asn1Error("value must be positive")
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if not isinstance(value, int):
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raise Asn1Error("value must be an integer")
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length_in_bits = max(1, math.log2(value + 1))
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length_in_bytes = math.ceil(length_in_bits / 8)
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return length_in_bytes
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def bytes_from_int(value: int, *, length: Optional[int] = None) -> bytes:
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"""Return an integer encoded big-endian into bytes of an optionally
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specified length.
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"""
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if length is None:
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length = length_in_bytes(value)
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return value.to_bytes(length, "big")
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def int_from_bytes(data: bytes) -> int:
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"""Return an integer decoded from bytes in big-endian format."""
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return int.from_bytes(data, "big")
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def int_from_bit_string(string: str) -> int:
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"""Return an integer decoded from a bitstring."""
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return int(string, base=2)
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def bit_string_from_int(value: int) -> str:
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"""Return a bitstring encoding of an integer."""
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string = f"{value:b}"
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# The bitstring must be padded to a multiple of 8 bits in length, or
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# pyasn1 will interpret it incorrectly (as if the padding bits were
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# present, but on the wrong end).
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length = len(string)
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padding_len = math.ceil(length / 8) * 8 - length
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return "0" * padding_len + string
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def bit_string_from_bytes(data: bytes) -> str:
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"""Return a bitstring encoding of bytes in big-endian format."""
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value = int_from_bytes(data)
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return bit_string_from_int(value)
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def bytes_from_bit_string(string: str) -> bytes:
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"""Return big-endian format bytes encoded from a bitstring."""
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value = int_from_bit_string(string)
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length = math.ceil(len(string) / 8)
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return value.to_bytes(length, "big")
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def asn1_length(data: bytes) -> bytes:
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"""Return the ASN.1 encoding of the length of some data."""
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length = len(data)
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if length <= 0:
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raise Asn1Error("length must be greater than zero")
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if length < 0x80:
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return bytes([length])
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encoding_len = length_in_bytes(length)
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if encoding_len >= 0x80:
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raise Asn1Error("item is too long to be ASN.1 encoded")
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data = bytes_from_int(length, length=encoding_len)
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return bytes([0x80 | encoding_len]) + data
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