104 lines
2.5 KiB
C++
104 lines
2.5 KiB
C++
#include <iostream>
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#include <sstream>
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#include <array>
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#include <bitset>
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#define BLOCK_SIZE 16
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#define FEISTELBLOCK_SIZE (BLOCK_SIZE / 2)
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#define N_ROUNDS 8
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typedef std::bitset<BLOCK_SIZE> Block;
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typedef std::bitset<FEISTELBLOCK_SIZE> Feistelblock;
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// Split a data block into two feistel blocks (into L and R)
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std::pair<Feistelblock, Feistelblock> FeistelSplit(const Block& block);
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// Combine two feistel blocks (L and R) into a regular data block
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Block FeistelCombine(const Feistelblock& l, const Feistelblock& r);
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// Feistel-cipher
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Block Feistel(const Block& data, const std::array<Feistelblock, 8>& keys, bool reverseKeyOrder = false);
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// Arbitrary cipher function
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Feistelblock F(Feistelblock m, const Feistelblock& key);
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int main()
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{
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Block message = 0b1010101010101010;
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const std::array<Feistelblock, N_ROUNDS> keys = {
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0b11101101,
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0b01110101,
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0b10111101,
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0b00010110,
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0b00000011,
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0b10110011,
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0b11011101,
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0b00111101
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};
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std::cout << "Input: " << message << std::endl;
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Block ciphertext = Feistel(message, keys);
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std::cout << "Ciphertext: " << ciphertext << std::endl;
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Block decrypted = Feistel(ciphertext, keys, true);
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std::cout << "Decrypted: " << decrypted << std::endl;
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return 0;
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}
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Block Feistel(const Block& data, const std::array<Feistelblock, 8>& keys, bool reverseKeyOrder)
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{
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const auto splitData = FeistelSplit(data);
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Feistelblock l = splitData.first;
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Feistelblock r = splitData.second;
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Feistelblock tmp;
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for (std::size_t i = 0; i < N_ROUNDS; i++)
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{
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// Calculate key index
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std::size_t keyIndex;
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if (reverseKeyOrder)
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keyIndex = N_ROUNDS - i - 1;
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else
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keyIndex = i;
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// Do a feistel round
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tmp = r;
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r = l ^ F(r, keys[keyIndex]);
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l = tmp;
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}
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return FeistelCombine(r, l);
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}
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Feistelblock F(Feistelblock m, const Feistelblock& key)
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{
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// Made-up F function
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// Shift 5 to the left
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m <<= 5;
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// Xor with key
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return m ^ key;
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}
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std::pair<Feistelblock, Feistelblock> FeistelSplit(const Block& block)
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{
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const std::string bits = block.to_string();
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Feistelblock l(bits.substr(0, bits.size() / 2));
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Feistelblock r(bits.substr(bits.size() / 2));
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return std::make_pair(l, r);
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}
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Block FeistelCombine(const Feistelblock& l, const Feistelblock& r)
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{
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return Block(l.to_string() + r.to_string());
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}
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