81 lines
1.6 KiB
Python
81 lines
1.6 KiB
Python
from __future__ import annotations
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from dataclasses import dataclass
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from random import Random
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from tea3.tea3 import Tea3
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def rand_key(rng: Random) -> list[int]:
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return [rng.getrandbits(8) for _ in range(10)]
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def rand_frame_number(rng: Random) -> int:
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return rng.getrandbits(32)
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@dataclass
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class BiasResult:
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samples: int
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matches: int
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p_match: float
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bias: float
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estimated_needed_samples: float
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def estimate_black_box_output_bias(
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*,
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key: list[int],
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output_byte_index: int = 0,
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output_bit: int = 0,
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samples: int = 10000,
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seed: int = 1,
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) -> BiasResult:
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rng = Random(seed)
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matches = 0
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for _ in range(samples):
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frame_number = rand_frame_number(rng)
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tea = Tea3(frame_number, key)
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for _ in range(output_byte_index + 1):
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tea.next_byte()
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out_byte = tea.iv_view() >> 56
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bit = (out_byte >> output_bit) & 1
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if bit == 0:
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matches += 1
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p_match = matches / samples
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bias = abs(p_match - 0.5)
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needed = float("inf") if bias == 0 else 1.0 / (bias * bias)
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return BiasResult(
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samples=samples,
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matches=matches,
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p_match=p_match,
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bias=bias,
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estimated_needed_samples=needed,
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)
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def main():
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rng = Random(123)
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key = rand_key(rng)
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res = estimate_black_box_output_bias(
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key=key,
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output_byte_index=0,
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output_bit=0,
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samples=20000,
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seed=123,
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)
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print("black-box output bias")
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print("expected non-biased p_match: 1/2")
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print(res)
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if __name__ == "__main__":
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main()
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