# All Questions

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### Any weakness when sha256'ing output of sha256, repeatedly?

Is it significantly easier to reverse a sha256 hash if you know that the input was a 32 byte output of sha256? I assume for most outputs of sha256 there will be zero, one or two possible 32 byte ...
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### Hierarchical Encryption

Is there a way to setup a hierarchical encryption using public key encryption? Let's say a higher level user can decrypt messages encrypted by lower level users. Is that possible? I guess it is only ...
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### Homomorphic encryption based on XOR

Consider the values a and b are encrypted as c1=(a XOR D )and c2=(b XOR D), my question is that can we derive b+a from any combination of c1 and c2 ? Note: (1) I admit that the D should have not been ...
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