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5

So is there any method of doing this properly? Here's the most obvious method: Iterate through the lower 14 bits of $y$, that is, you'll perform the below steps for each of the 16384 possible settings of the lower bits of $y$ Compute what the lower 14 bits of $x$ are, using $x = A - y$ (because the subtraction is modulo $2^{64}$, we can ignore everything ...

1

One of the issue in sending out the XORed value is to disclose the PSK length This is only an issue if you consider the length of the PSK to be a secret and not just the value. In that case you probably should redesign your system to not depend on the length of the PSK being secret, e.g. by always sending an upper-length PSK and also sending the amount of ...

2

First, there's no issue with modern stream cipher constructions - either using an AEAD block cipher mode of operation such as GCM, or the combination of ChaCha20-Poly1305 as Google had experimented and subsequently formalized in the form of Internet RFC documents. Stream ciphers are basically reduced-capability one-time-pads as one may infer: stream cipher ...

3

In implementing crypto, it is essential to distinguish strings (of characters) from byte vectors, also known as bytestrings or byte arrays. In most computer languages, strings store characters, not bytes, and are not adequate for (un-encoded) intermediary values, ciphertext, keys, Initialization Vectors.. even when and if adequate for plaintext. In C, ...

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