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    To store N bits of information, and the information does not contain noise (unneeded bits) or equivocation (bits that change together), you need N physical bits of storage. This is basic to information theory. Commented Feb 26, 2021 at 19:10
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    True, all hashes have collisions, but cryptographic hashes have collision resistance. If you have a cryptographically sound hash, the only way to create a plaintext that matches the hash is via brute force. With MD5, there are shortcuts that allow you to create it systematically and in less time, making collision attacks not just possible but feasible. Commented Feb 26, 2021 at 19:35
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    I don't understand what you just said. Commented Feb 26, 2021 at 20:02
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    You are looking for a proof of the pigeon hole principle?Here is one at math.stackexchange Commented Feb 27, 2021 at 9:33
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    It is not possible to store an independent value in a set of 16-combinations within 3 bits. It may however be possible to store multiple values in a set of 16-combinations in less than 4 bits in average. If it wouldn't, there would be no compression. Commented Feb 27, 2021 at 12:55