/* Encryption RC4 Rivest Cipher 4, is a symmetrical encryption technique. This encryption method is no longer considered secure for TLS(https) but is still a beautiful algorithm to study and maybe even still use in some situations. It uses a key that can have various length of up to 256 bytes. The key is then used to shape the T temporary box and indirectly also shaping the S box via the T box. The S box contains all numbers from 0 to 255, thus is an array of 256 in length. The S box will have multiple permutations based on how th T box was filled (which in turn depends on the key). Once the S box is setup, we can use it to drive a byte stream generator. The generator uses a pseudo random generator algorithm to stream a byte value on command, a byte that will be used to cipher each byte coming from the message stream. This was a very fun algorithm to implement. Very simple and I just love when I can plug in a generator somewhere in a code. revised : may 21 2022 */ #include #include #include #include using uc = unsigned char; using namespace std; vectorget_S(vectorkey){ vectorS(256); vectorT(256); for(unsigned i=0,ks=key.size();i<=255;i++){ S[i]=i; T[i]=key[i%ks]; } for(int i=0,j=0;i<=255;i++){ j=(j+S[i]+T[i])%256; swap(S[i],S[j]); } return S; } vectorget_key(){ srand(time(0)); size_t length=rand()%256+1; vectorkey(length); for(auto & b:key){ b=(rand()%256); } return key; } functionPRG(vectorS){ int i=0, j=0; return [=]() mutable{ i = (i+1)%256; j = (j+S[i]) %256; swap(S[i], S[j]); int t = (S[i]+S[j])% 256; return S[t]; }; } vectorrc4(vectormsg,vectorkey){ vectorresult{}; auto S=get_S(key); auto generator=PRG(S); for(auto b:msg) result.push_back(generator()^b); return result; } int main() { string m="hello world"; unsigned drop=0; for(unsigned i=0;imsg{m.begin(),m.end()}; vectorkey{0x63,0x72, 0x79,0x70, 0x74,0x69, 0x69}; vectorencrypted{rc4(msg,key)}; vectordecrypted{rc4(encrypted,key)}; cout<<"original: "<

RC4 - Rivest Cipher 4