Question

List the primitive operations used in the RC4 stream cipher algorithm for

A) Key Stream Generation

B) Bit Stream Encryption

Answer 1

A)RC4 is a stream cipher and variable length key algorithm. This calculation encodes each byte in turn (or bigger units on a period). A key information is pseudorandom bit generator that creates a stream 8-bit number that is erratic without information on input key, The yield of the generator is called key-stream, is joined each byte in turn with the plaintext stream cipher utilizing X-OR activity.

Example:

RC4 Encryption

10011000 ? 01010000=11001000

RC4 Decryption

11001000 ? 01010000=10011000

11001000 ? 01010000 = 10011000

Key-Generation Algorithm –A variable-length key from 1 to 256 byte is utilized to introduce a 256-byte state vector S, with components S[0] to S[255]. For encryption and unscrambling, a byte k is produced from S by choosing one of the 255 entries in a methodical manner, at that point the sections in S are permuted once more.

Key-Scheduling Algorithm:

Iinitialization: The sections of S are set equivalent to the qualities from 0 to 255 in climbing request, a transitory vector T, is made.

On the off chance that the length of the key k is 256 bytes, at that point k is allocated to T. Something else, for a key with length(k-len) bytes, the main k-len components of T as replicated from K and afterward K is rehashed the same number of times as important to fill T. The thought is represented as follow:

for
   i = 0 to 255 do S[i] = i;
T[i] = K[i mod k - len];

we use T to produce the initial permutation of S. Starting with S[0] to S[255], and for each S[i] algorithm swap it with another byte in S according to a scheme dictated by T[i], but S will still contain values from 0 to 255 :j = 0;
for
   i = 0 to 255 do
   {
       j = (j + S[i] + T[i])mod 256;
       Swap(S[i], S[j]);
   }
Pseudo random generation algorithm (Stream Generation):
When the vector S is introduced, the info key won't be utilized. In this progression, for each S[i] calculation trade it with another byte in S as indicated by a plan directed by the current arrangement of S. In the wake of coming to S[255] the procedure keeps, beginning from S[0] once more

i, j = 0;
while (true)
   i = (i + 1)mod 256;
j = (j + S[i])mod 256;
Swap(S[i], S[j]);
t = (S[i] + S[j])mod 256;
k = S[t];
BIT STREAM Encrypt using X-Or():XOR Encryption is an encryption technique used to scramble information and is difficult to break by animal power strategy, i.e creating arbitrary encryption keys to coordinate with the right one.

void encryptDecrypt(char inpString[])
{
   // Define XOR key
   // Any character value will work
   char xorKey = 'P';

   // calculate length of input string
   int len = strlen(inpString);

   // perform XOR operation of key
   // with every caracter in string
   for (int i = 0; i < len; i++)
   {
       inpString[i] = inpString[i] ^ xorKey;
       printf("%c",inpString[i]);
   }
}

// Driver program to test above function
int main()
{
   char sampleString[] = "GeeksforGeeks";

   // Encrypt the string
   printf("Encrypted String: ");
   encryptDecrypt(sampleString);
   printf("\n");

   // Decrypt the string
   printf("Decrypted String: ");
   encryptDecrypt(sampleString);

   return 0;
}