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5

XSalsa20 uses the same cryptographic core as Salsa20 and comes with a security proof that it's secure if Salsa20 is secure. It doesn't use the core of ChaCha and thus has worse diffusion. The way XSalsa20 works is that it hashes its 256 bit key and the first 128 bits of the nonce using HSalsa down to a 256 bit key and then uses that key together with the ...


3

Compared to fixed rotations, data-dependent rotations improve resistance to differential and linear cryptanalysis. A fixed rotation has no effect (beyond helping with diffusion) in the probability of a (xor-)differential characteristic, whereas a data-dependent rotation also introduces differences in the rotation amounts, which brings probabilities down. ...


2

It depends on the exact Merkle-Damgaard hash. MD5 will literally take an arbitrary length; that's because the value placed in the padding is actually computed modulo $2^{64}$. For SHA-1 and the SHA-2 hashes, yes, you are correct; there is an upper bound on the length of the preimages that could potentially be hashed; for SHA-1, SHA-224 and SHA-256, it's ...


1

I suggest Vigenère cipher, it is fun on paper and also you can be creative in using key. you can use your phone number as key or your entire family phone number in age order. Key: ABCDABCDABCDABCDABCDABCDABCD Plaintext: CRYPTOISSHORTFORCRYPTOGRAPHY Ciphertext: CSASTPKVSIQUTGQUCSASTPIUAQJB http://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher


1

For confidentiality purposes? one time pad (when possible) rc4 (because you can by hand)


1

Normally, questions like this are considered off-topic; however, in this case, I can give a quick answer -- it's RC4



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