Shevek's crypto stuff
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  • Side-channel attack to modular inversion

    Modular inversion is a common mathematical operation that is given within cryptographic algorithms based on finite groups generated by a prime number. Mainly, these algorithms are related to public key cryptographic, specially, to Elliptic Curve Cryptography (ECC). The way to compute a modular inverse is always hard; at least, it is roughly 100 times harder than the opposite operation, the modular product.

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  • The maths of Secret Santa

    Secret Santa is a way to share gifts among work mates, family, etc. It is organized in such a way that every person is commited to gift secretly to another, and the latter does not know who is the gifter. In Spanish this game is called amigo invisible (invisible friend).

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  • RC4 as pencil & paper cipher

    RC4 is a well-known stream cipher, extremely simple ā€”Iā€™d say minimalistā€” and strong enough to be still used, spite of some documented weaknesses which, mostly, fall on the key schedule.

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