provided code

src/tests/arc4.c

@@ -0,0 +1,53 @@
+#include <stdint.h>
+#include "tests/arc4.h"
+
+/* Swap bytes. */
+static inline void
+swap_byte (uint8_t *a, uint8_t *b)
+{
+  uint8_t t = *a;
+  *a = *b;
+  *b = t;
+}
+
+void
+arc4_init (struct arc4 *arc4, const void *key_, size_t size)
+{
+  const uint8_t *key = key_;
+  size_t key_idx;
+  uint8_t *s;
+  int i, j;
+
+  s = arc4->s;
+  arc4->i = arc4->j = 0;
+  for (i = 0; i < 256; i++)
+    s[i] = (uint8_t) i;
+  for (key_idx = 0, i = j = 0; i < 256; i++)
+    {
+      j = (j + s[i] + key[key_idx]) & 255;
+      swap_byte (s + i, s + j);
+      if (++key_idx >= size)
+        key_idx = 0;
+    }
+}
+
+void
+arc4_crypt (struct arc4 *arc4, void *buf_, size_t size)
+{
+  uint8_t *buf = buf_;
+  uint8_t *s;
+  uint8_t i, j;
+
+  s = arc4->s;
+  i = arc4->i;
+  j = arc4->j;
+  while (size-- > 0)
+    {
+      i = (uint8_t) (i + 1);
+      j = (uint8_t) (j + s[i]);
+      swap_byte (s + i, s + j);
+      *buf++ ^= s[(s[i] + s[j]) & 255];
+    }
+  arc4->i = i;
+  arc4->j = j;
+}