DH attack
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`Hardness of computing the most significant bits of secret keys in Diffie-Hellman and related schemes <https://crypto.stanford.edu/~dabo/pubs/abstracts/dhmsb.html>`_

`Merkle–Hellman knapsack cryptosystem <https://en.wikipedia.org/wiki/Merkle%E2%80%93Hellman_knapsack_cryptosystem>`_
已被攻破，使用贪心算法。