Поточный шифр [RC4,VMPC KSA3]

RC4 выдрано из rpcrt4.dll
VMPC немного переделанный исходник

#pragma pack(1)
// Состояние экземпляра RC4
typedef struct _RC4_INSTANCE_STATE {
  BYTE SBOX[256];   // S-блок 
  int i;           // Регистр RC4
  int j;     // Регистр RC4
}RC4_INSTANCE_STATE, *PRC4_INSTANCE_STATE;

typedef unsigned char u8;
typedef struct _VMPC_STATE {
u8 P[256];
u8 n;
u8 s;
} VMPC_STATE,*PVMPC_STATE;
#pragma pack()

// RC4 Key Scheduling Algorithm (KSA)
void rc4_key(PRC4_INSTANCE_STATE pRC4State, DWORD cbData, BYTE* pbData)
{
  BYTE t = 0;

  for (pRC4State->i = 0; pRC4State->i < 256; pRC4State->i++)
    pRC4State->SBOX[pRC4State->i] = pRC4State->i;

  pRC4State->j = 0;
  for (pRC4State->i = 0; pRC4State->i < 256; pRC4State->i++)
  {
    pRC4State->j = (
      pRC4State->j 
      + pRC4State->SBOX[pRC4State->i] 
      + (*(pbData + pRC4State->i))
    ) & 0x0FF;
  };

  t = pRC4State->SBOX[pRC4State->i];
  pRC4State->SBOX[pRC4State->i] = pRC4State->SBOX[pRC4State->j];  
  pRC4State->SBOX[pRC4State->j] = t;

};

// Классическая реализация алгоритма RC4
void rc4(PRC4_INSTANCE_STATE pRC4State, DWORD cbData, BYTE* pbData)
{
  BYTE t = 0;

  for (int p = 0; p < cbData; p++)
  {
    pRC4State->i = (pRC4State->i + 1) & 0x0FF; 
    pRC4State->j = (pRC4State->j + pRC4State->SBOX[pRC4State->i]) & 0x0FF;
    t = pRC4State->SBOX[pRC4State->i];
    pRC4State->SBOX[pRC4State->i] = pRC4State->SBOX[pRC4State->j];
    pRC4State->SBOX[pRC4State->j] = t;
    *(pbData + p) = 
      *(pbData + p) ^ pRC4State->SBOX[(pRC4State->SBOX[pRC4State->i] 
      + pRC4State->SBOX[pRC4State->j]) & 0xFF];
  }
  
}

void VMPC_init (PVMPC_STATE pVMPC,u8 * key, u8 * iv)
{
  long m, i;
  u8 temp;
  pVMPC->s = 0;

  for (i = 0; i != 256; i++)
    {
      pVMPC->P[i] = (u8) i;
    }

  for (m = 0; m != 768; m++)
    {
      pVMPC->s = pVMPC->P[(pVMPC->s + pVMPC->P[m & 0xff] + key[m % 64]) & 0xff];
      temp = pVMPC->P[m & 0xff];
      pVMPC->P[m & 0xff] = pVMPC->P[pVMPC->s & 0xff];
      pVMPC->P[pVMPC->s & 0xff] = temp;
    }

  for (m = 0; m < 768; m++)
    {
      pVMPC->s = pVMPC->P[(pVMPC->s + pVMPC->P[m & 0xff] + iv[m % 64]) & 0xff];
      temp = pVMPC->P[m & 0xff];
      pVMPC->P[m & 0xff] = pVMPC->P[pVMPC->s & 0xff];
      pVMPC->P[pVMPC->s & 0xff] = temp;
    }

  for (m = 0; m != 768; m++)
    {
      pVMPC->s = pVMPC->P[(pVMPC->s + pVMPC->P[m & 0xff] + key[m % 64]) & 0xff];
      temp = pVMPC->P[m & 0xff];
      pVMPC->P[m & 0xff] = pVMPC->P[pVMPC->s & 0xff];
      pVMPC->P[pVMPC->s & 0xff] = temp;
    }

  pVMPC->n = 0;
}

void VMPC_crypt (PVMPC_STATE pVMPC,u8 * input, u8 * output, long len)
{
  long i;
  u8 z, temp;
  for (i = 0; i != len; i++)
    {
      pVMPC->s = pVMPC->P[(pVMPC->s + pVMPC->P[pVMPC->n & 0xff]) & 0xff];
      z = pVMPC->P[(pVMPC->P[(pVMPC->P[pVMPC->s & 0xff]) & 0xff] + 1) & 0xff];
      temp = pVMPC->P[pVMPC->n & 0xff];
      pVMPC->P[pVMPC->n & 0xff] = pVMPC->P[pVMPC->s & 0xff];
      pVMPC->P[pVMPC->s & 0xff] = temp;
      pVMPC->n = (u8) ((pVMPC->n + 1) & 0xff);
      output[i] = (u8) (input[i] ^ z);
    }
}

Примерчик:

BOOL (__stdcall *SystemFunction036)(PVOID RandomBuffer, ULONG RandomBufferLength);

int main()
{
 char text[]="garik";
 RC4_INSTANCE_STATE rc4_st;
 BYTE key[256];

// генерим рандомный ключ в 2048 бит  8)
// [url]http://msdn.microsoft.com/en-us/library/aa387694(VS.85).aspx[/url] == RtlGenRandom
 SystemFunction036=(BOOL (__stdcall *)(PVOID, ULONG))GetProcAddress(GetModuleHandle("Advapi32.dll"), "SystemFunction036");
 SystemFunction036(key,256);

 // инициализируем RC4
 rc4_key(&rc4_st,256,key);

// шифруем
 rc4(&rc4_st,5,(BYTE *)text);
 
// SBOX то изменился поэтому инициализируем снова
 rc4_key(&rc4_st,256,key);

// расшифровываем
 rc4(&rc4_st,5,(BYTE *)text);

 return 0;
}