rc5.cpp

RC5 encryption algorithm

#include <stdio.h>
#include <iostream.h>
#define r 12 // number of rounds
#define t (2*r+2) // number of sub-keys needed
unsigned long S[t]; // array used for key expansion
#define b 16 // number of bytes in key
#define c 1 // number of words in key
unsigned long Pw = 0xb7e15163; // constant used for key expansion
unsigned long Qw = 0x9e3779b9; // constant used for key expansion
#define max(i,j) (i>=j?i:j)
class int_record
{
public:
unsigned long data0;
unsigned long data1;
};
// left rotate function, rotates LE by RE bits.
unsigned long left_rotate( unsigned long LE, unsigned long RE)
{
return ((LE << (RE & (32-1))) | (LE >> (32 -(RE & (32-1)))));
}
// right rotate function, rotates LE by RE bits.
unsigned long right_rotate( unsigned long LE, unsigned long RE)
{
return ((LE >> (RE & (32-1))) | (LE << (32 -(RE & (32-1)))));
}
/*The encryption process encrypts a given plaintext to a
ciphertext by using the expanded array key, S, of length 2r + 2.
Returns the ciphertext*/
int_record * encryption(int_record &inputs)
{
unsigned long i, LE, RE;
int_record * val = new int_record();
LE = inputs.data0 + S[0];
/* Initial value of first data block added to S[0] subkey */
RE = inputs.data1 + S[1];
/* Initial value of second data block added to S[1] subkey*/
i=1;
/* The ecryption rounds which generate the final ciphertext,r=12 */
while ( i <= r )
{
LE = left_rotate(LE^RE, RE) + S[2 * i];
RE = left_rotate(RE^LE, LE) + S[2 * i + 1];
i++;
}
// Final value of ciphertext blocks
val->data0 = LE;
val->data1 = RE;
return val;
}
/*Decrypts a given ciphertext to the original plaintext
using the same expanded array key, S, of length 2r + 2.
The decryption is the inverse of the encryption process
Returns Plaintext*/
int_record * decryption(int_record * crypted_data)
{
unsigned long i, LD, RD;
int_record * val = new int_record();
RD = crypted_data->data1; //First ciphertext block
LD = crypted_data->data0; //Second ciphertext block
// The Decryption rounds , r=12
for (i = r; i > 0; i--)
{
RD = right_rotate(RD - S[2*i+1], LD) ^ LD;
LD = right_rotate(LD - S[2*i], RD) ^ RD;
}
val->data0 = LD - S[0];/*First block of final decrypted plaintext
value */
val->data1 = RD - S[1];/* Second block of final decrypted plaintext
value */
return val;
}
//Key Expansion process has two parts
// Array initialization
// Key mixing
void key_expansion(unsigned char *key)
{
unsigned long w, i, j, key_round, X, Y, L[c];
//Initialization of L array
for (i=0; i<c; i++)
L[i] = 0;
//Convertion of b byte key array to c word L array
for (i=0; i<b; i++) {
w = i/c;
L[w] = L[w] << 8;
L[w] = L[w] | key[i];
}
S[0] = Pw;
//Initialization of S Array with constant Pw and Qw
for (i = 1; i < t; i++)
S[i] = S[i - 1] + Qw;
/* The mixing of the S array and L array to produce the final S array
of subkeys */
i = j = X = Y = 0;
for (key_round = 0; key_round < 3 * max(t,c) ; key_round++)
{
S[i] = left_rotate(S[i] + X + Y, 3);
X = S[i];
i = (i + 1) % t;
L[j] = left_rotate(L[j] + X + Y, X + Y);
Y = L[j];
j = (j + 1) % c;
}
}
/* Function to check that decrypted plaintext matches original
plaintext */
void check_data_validity(int_record &inputs, int_record * decrypted)
{
if (inputs.data0 != decrypted->data0 || inputs.data1 !=
decrypted->data1)
cout << "ERROR in algorithm, data differ" << endl;
}
//Function to input the two blocks of plaintext to be encrypted
int get_inputs( int_record &inputs)
{
cout << "Input first data block, zero to terminate: ";
cin >> inputs.data0;
if (inputs.data0 == 0)
return 0;
cout << "Input second data block: ";
cin >> inputs.data1;
return inputs.data0;
}
int main()
{
int_record inputs;
int_record *encrypted;
int_record *decrypted;
unsigned long random = 292; /* Random number used to generate
initial
key */
while (get_inputs(inputs)) {
unsigned long i;
unsigned char key[b];
// Creation of b byte key array
for (i = 0; i < b; i++)
key[i] = (unsigned char) (random ^ i);
key_expansion(key);
encrypted = encryption(inputs);
decrypted = decryption(encrypted);
printf("The generated cipher text is: %.8lX %.8lX",
encrypted->data0, encrypted->data1);
cout << endl;
check_data_validity(inputs, decrypted);
cout << "The first data block after decryption is: " <<
decrypted->data0 << endl;
cout << "The second data block after decryption is: " <<
decrypted->data1 << endl;
cout << "The final expanded key used for encryption was: " << endl;
for (i = 0; i < b; i++)
printf("%.2X ", key[i]);
cout << endl;
delete(decrypted);
delete(encrypted);
}
return 0;
}