rc4.c

 
#include <winpr/assert.h>
#include <winpr/cast.h>
 
#include "rc4.h"
 
#define CTX_SIZE 256
 
struct winpr_int_rc4_ctx
{
  size_t i;
  size_t j;
  BYTE s[CTX_SIZE];
  BYTE t[CTX_SIZE];
};
 
static void swap(BYTE* p1, BYTE* p2)
{
  BYTE t = *p1;
  *p1 = *p2;
  *p2 = t;
}
 
winpr_int_RC4_CTX* winpr_int_rc4_new(const BYTE* key, size_t keylength)
{
  winpr_int_RC4_CTX* ctx = calloc(1, sizeof(winpr_int_RC4_CTX));
  if (!ctx)
    return NULL;
 
  for (size_t i = 0; i < CTX_SIZE; i++)
  {
    ctx->s[i] = WINPR_ASSERTING_INT_CAST(BYTE, i);
    ctx->t[i] = key[i % keylength];
  }
 
  size_t j = 0;
  for (size_t i = 0; i < CTX_SIZE; i++)
  {
    j = (j + ctx->s[i] + ctx->t[i]) % CTX_SIZE;
    swap(&ctx->s[i], &ctx->s[j]);
  }
  return ctx;
}
 
void winpr_int_rc4_free(winpr_int_RC4_CTX* ctx)
{
  free(ctx);
}
 
BOOL winpr_int_rc4_update(winpr_int_RC4_CTX* ctx, size_t length, const BYTE* input, BYTE* output)
{
  WINPR_ASSERT(ctx);
 
  size_t t1 = ctx->i;
  size_t t2 = ctx->j;
  for (size_t i = 0; i < length; i++)
  {
    t1 = (t1 + 1) % CTX_SIZE;
    t2 = (t2 + ctx->s[t1]) % CTX_SIZE;
    swap(&ctx->s[t1], &ctx->s[t2]);
 
    const size_t idx = ((size_t)ctx->s[t1] + ctx->s[t2]) % CTX_SIZE;
    const BYTE val = ctx->s[idx];
    const BYTE out = *input++ ^ val;
    *output++ = out;
  }
 
  ctx->i = t1;
  ctx->j = t2;
  return TRUE;
}