Tokyo Westerns CTF 2017 – Palindromes Pairs (Challenge Phase)

This challenge was a follow-up to an earlier challenge, titled "Palindromes Pairs - Coding Phase". In that earlier warmup ppc challenge, the goal was to write an algorithm to solve the following problem: given up to 1000 strings $latex s_i$, each of length at most 1000, count the number of pairs $latex (i, j)$ such… Continue reading Tokyo Westerns CTF 2017 – Palindromes Pairs (Challenge Phase)

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Tokyo Westerns CTF 2017 – Liar’s Trap

On the surface, this challenge appears to be about secret sharing. The setup is simple: the flag is divided into $latex N=100$ pieces using Shamir's secret sharing scheme so that it can be recovered given any $latex K=25$ of these pieces (but is impossible to recover with any fewer). The server provides you with all… Continue reading Tokyo Westerns CTF 2017 – Liar’s Trap