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Mjiig/rc4.cpp

Created June 8, 2012 21:17
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rc4 cipher for MagPi
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rc4.cpp
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <cstring>
class State
{
unsigned char s[256];
int i, j;
void swap(int a, int b);
public:
unsigned char getbyte(void);
State(unsigned char key[], int length );
};
State::State(unsigned char key[], int length)
{
for(int k=0; k<256; k++)
{
s[k]=k;
}
j=0;
for(i=0; i<256 ; i++)
{
j=(j + s[i] + key[i % length]) % 256;
swap(i, j);
}
i=j=0;
}
void State::swap(int a, int b)
{
unsigned char temp=s[i];
s[i]=s[j];
s[j]=temp;
}
unsigned char State::getbyte(void)
{
i=(i+1)%256;
j=(j+s[i])%256;
swap(i, j);
int index=(s[i]+s[j])%256;
return s[index];
}
void parseargs(int argc, char ** argv, std::string & key, std::string & file)
{
bool readkey = false;
bool readfile = false;
bool toomanyargs =false;
for( int i=1 ; i<argc ; i++ )
{
std::string arg = argv[i];
if(!readkey)
{
key=arg;
readkey=true;
}
else if(!readfile)
{
file=arg;
readfile=true;
}
else
{
toomanyargs=true;
}
}
if(toomanyargs || !readfile || !readkey)
{
std::cout << "Usage is: " << argv[0] << " key file" << std::endl;
exit(EXIT_FAILURE);
}
return;
}
int gettextkey(unsigned char data[], std::string key)
{
if(key.length() > 256)
{
std::cout << "ASCII key must be 256 characters or less" <<std::endl;
exit(EXIT_FAILURE);
}
size_t i;
for(i=0; i<key.length(); i++)
{
data[i]=key[i];
}
return i;
}
void outfilename(std::string &file)
{
if(file.find(".rc4", file.length()-4) != std::string::npos) //ie, if file ends with ".rc4"
{
file.erase(file.length()-4);
}
else
{
file.append(".rc4");
}
}
void openfiles(std::fstream & infile, std::fstream & outfile, std::string & filename)
{
infile.open(filename.c_str(), std::ios::in | std::ios::binary);
if(!infile.is_open())
{
std::cout << filename << " does not exist" << std::endl;
exit(EXIT_FAILURE);
}
outfilename(filename);
outfile.open(filename.c_str(), std::ios::in);
if(outfile.is_open()) //file we are going to write exists!
{
std::cout << filename << " already exists, aborting to preserve it" <<std::endl;
exit(EXIT_FAILURE);
}
outfile.close();
outfile.open(filename.c_str(), std::ios::out | std::ios::binary);
if(!outfile.is_open())
{
std::cout << filename << " could not be opened for writing" << std::endl;
exit(EXIT_FAILURE);
}
}
int main(int argc, char **argv)
{
std::string key, file;
parseargs(argc, argv, key, file);
int len=0;
unsigned char keydata[256];
len=gettextkey(keydata, key);
State bytestream (keydata, len);
std::fstream infile;
std::fstream outfile;
openfiles(infile, outfile, file);
char inbyte;
char outbyte;
unsigned char streambyte;
infile.get(inbyte);
while(!infile.eof())
{
streambyte=bytestream.getbyte();
outbyte=inbyte ^ streambyte;
outfile.put(outbyte);
infile.get(inbyte);
}
outfile.close();
infile.close();
std::cout << "Encryption finished, output to " << file << std::endl;
return 0;
}
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