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You're missing that using a KEM for hybrid is not encrypting random garbage. Say you have a chain of ciphertexts $C_1||C_2||\dots|| C_n$, where $C_1 = \mathsf{Enc}_K(k)$, where $k$ is an AES key, and $C_2||\dots||C_n$ is the result of encrypting some stream of plaintexts under the AES key $k$ in some mode of operation. If we can compute $k = \mathsf{Dec}_K(...


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What does "cryptobox" mean in Libsodium and NaCl? In general, and in specific case, what does "box" do? cryptobox or correctly crypto_box is just box. box_easy calls secretbox with the shared key between the sender and receiver, unique per direction. box_seal calls box_easy with a random sender secret key and prepends the ciphertext with its corresponding ...


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means that $X$ and $X'$ have $\ell$ bits[...]? Yes. means that [...] $\Delta X=X-X'$[...]? Yes and no. Fundamentally what $x-y$ means is $x+(-y)$, but for bit-strings over $\mathbb F_2$ this becomes $x+(-y)\bmod 2$ for each bit, and $-y\equiv y\pmod 2$, i.e. $y$ and $-y$ behave the same. As this means that addition is just XOR, we write $x\oplus y$ to ...


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