20

Strictly speaking, all hash functions are compressing since the output can be smaller than the input, but I imagine you're asking about compressing data that can later be losslessly decompressed. This is impossible due to the pigeonhole principle. The fact that the fixed output space of a hash algorithm is smaller than the input space means that there will ...


10

There's simply no way to know. I find it very unlikely that AES will be vulnerable to a ciphertext-only attack in the next 20 years (remember, it has been around for over 20 years already and attacks haven't gotten very far). There's no reason to believe the same won't be true for ChaCha20. If you use a good cipher with 256-bit keys (to avoid potential ...


10

If the question was about (current form) Reversible cryptographic hash functions Then No! One-wayness property of the cryptographic secure hash functions will prevent that. Hash functions don't use keys. So if you can reverse, everybody will reverse and there will be no secure hash function at all. Besides, mathematically impossible, too; hash functions use ...


3

I know that theoretically, the security of the setup when used correctly is at least as secure as the most secure. That's true if they use independent keys. If they use the same key, the security of the cascaded cipher may be much worse. Consider the case where cipher B happens to be the exact inverse of cipher A with the same key. However, that doesn't ...


2

I'm not well versed in cryptography, but it seems like private set intersection may be what I'm looking for? Yes. In private set intersection (PSI) if we have elements from a universe $U$ (e.g. the set of 128 bit integers) and Alice has $N_A$ elements and Bob has $N_B$ elements, most good PSI protocols will try to give you $O(N_A+N_B)$ communication and ...


1

The blockchain network Nucypher offers something like that, through their cryptographic scheme, with a help of semi-trusted proxies. The scheme is secure as long as proxies don't cooperate, enough proxies don't reveal the secret and enough proxies stay online. They have papers on their website.


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