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2

No, not if the messages $m_1$ and $m_2$ have an identical length. A one-time pad can produce any ciphertext from a message, so you wouldn't know which message was used. If the messages differ in length than you would know, because the resulting ciphertext from a one-time pad has the same length as the original message. This is of course assuming that you don'...


3

Stream cipher and CSPRNG aren't the same thing. CSPRNGs must handle initial seeding, post-compromise reseeding, back-tracing resistance among other things; stream ciphers only need to be able to output something indistinguishable from random. So can we turn a CSPRNG into a stream cipher? Possibly, if we make every generate requests to the CSPRNG idempotent, ...


1

There is a Berlekamp-Massey algorithm that constructs the shortest LFSR for a given binary sequence. For an LFSR of length $L$ given $2L$ output sequence from the LFSR, it is enough to construct the LFSR. To construct a 25-bit LSFR, 50 bits is enough. Note that, the algorithm doesn't need to know the taps. It just constructs the minimum LFSR that can produce ...


0

Ways to do this (for fun) depend on your requirements. If the passwords must be human readable then it makes things more difficult. I assume plaintexts match in size. If passwords need not be human readable then it is easily done with XOR. C1=Plaintext1 is XORed with a key. C2=Plaintext2 XOR C1. C2 is the final ciphertext. The two unreadable passwords ...


0

I've been thinking about this for a while and I can only think of one possible solution. If you want to share two different messages with the same cypher text then you might be able to use a "one-time pad" with multiple decryption possibilities, or rather multiple one-time pads for the same text. So if I were to have the following cypher text ...


12

The Insecurity of Proposed Scheme It is not as secure as it seems, in modern cryptography standards it is totally insecure. It is vulnerable to basic Known-Plaintext attacks (KPA) and in Modern Cryptography, we want a cipher secure against at least Chosen Plaintext Attack (CPA) or better Ind-CPA. Now take the idea $$K' = H(X\mathbin\|K) \mathbin\| H(H(X\...


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