4

That is not practical since either you keep a sequence of the bits of the $\pi$ or regenerate them every time. You may need to store 64GB sequence if you want to encrypt such files. Then you need to multiply it with the 128-bit number. That is not practical, consider multiplication of 64GB number with a random 128-bit number. OTP needs true random bit ...


3

I'm going to treat this question as a strict one time pad one. With a key k of sufficient length, say 128 bits, is it possible to use kth multiple of π as a one-time pad? That's 107 characters of description plus 128 bits of secrecy (plus $\pi$ which is a known constant). Your Kolmogorov complexity cannot exceed 200 characters if you consider that:- $$\pi =...


3

Take the output $H$ of $\operatorname{SHA-256(M)}$ or any other hash of $b$ bits. Count the number $u$ of bits set in $H$ and output $u\bmod3$. This is optimally close to unbiased in $\{0,1,2\}$, for an ideal hash and the requirement to deterministically output a value for any $M$. Counting the number of bits set can be fast. Sometimes there's even an ...


3

Bug 1: You're not substituting the letters, frequency analysis breaks it horribly. Bug 2: You're noting down the coordinates, it's not clear whether it's supposed to be used as the key or ciphertext. Bug 3: Your scheme has no key, which is a violation of Kerckhoffs's principle. That's it if you want to learn some basics about cryptography. There's plenty of ...


3

Generally speaking, more than 128 bit security is not required - except maybe for protection against multi-target attacks where large amounts of ciphertext become available to the adversary. The reason for this is that no system will be able to perform $2^{128}$ operations. So if there is an analysis that threatens the structure or number of rounds used, ...


2

Unless otherwise noted, I assume adversaries know the genuine QR-code, and can alter it and submit it for decryption. I posit the design requirements are: Confidentiality of $\text{seed}$, to as high a level as the passphrase + key stretching of Argon2 allows. Integrity of $\text{seed}$, to 64-bit security level [ample in the context, where we want to catch ...


1

Are there any cryptographic primitives/protocols allowing the sender to signal to the recipient faster that the message is intended for them, yet not reveal the true recipient to everyone else and allow them to quickly skip trying to decrypt the message? It doesn't appear that the problem of recognizing the message (without leaking who the message is for) ...


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