first draft

random.c

@@ -0,0 +1,81 @@
+/* rc4-based pseudo-random number generator for hping.
+ * Copyright (C) 2003 Salvatore Sanfilippo
+ * This software is released under the GPL license
+ * All rights reserved */
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/time.h>
+#include <time.h>
+
+u_int32_t hp_rand(void);
+
+/* The rc4 sbox */
+static unsigned char rc4_sbox[256];
+/* This flags is used to initialize the sbox the first time,
+ * without an explicit intialization step outside this file. */
+static int rc4_seedflag = 0;
+
+/* Initialize the sbox with pseudo random data */
+static void hp_rand_init(void)
+{
+	int i, fd;
+
+	/* Strong sbox initialization */
+	fd = open("/dev/urandom", O_RDONLY);
+	if (fd != -1) {
+		read(fd, rc4_sbox, 256);
+		close(fd);
+	}
+	/* Weaker sbox initialization */
+	for (i = 0; i < 256; i++) {
+		struct timeval tv;
+		gettimeofday(&tv, NULL);
+		if (i&1)
+			rc4_sbox[i] ^= (tv.tv_usec >> (i&0xF)) & 0xFF;
+		else
+			rc4_sbox[i] ^= (tv.tv_sec >> (i&0xF)) & 0xFF;
+	}
+	rc4_seedflag = 1;
+}
+
+#if 0
+/* Re-seed the generator with user-provided bytes. Not used for now. */
+static void hp_rand_seed(void *seed, size_t len)
+{
+	int i;
+
+	if (len > 256) len = 256;
+	memcpy(rc4_sbox, seed, len);
+	/* discard the first 256 bytes of output after the reseed */
+	for (i = 0; i < 32; i++)
+		(void) hp_rand();
+}
+#endif
+
+/* Generates a 32bit random number using an RC4-like algorithm */
+u_int32_t hp_rand(void)
+{
+	u_int32_t r = 0;
+	unsigned char *rc = (unsigned char*) &r;
+	static unsigned int i = 0, j = 0;
+	unsigned int si, sj, x;
+
+	/* initialization, only needed the first time */
+	if (!rc4_seedflag)
+		hp_rand_init();
+	/* generates 4 bytes of pseudo-random data using RC4 */
+	for (x = 0; x < 4; x++) {
+		i = (i+1) & 0xff;
+		si = rc4_sbox[i];
+		j = (j + si) & 0xff;
+		sj = rc4_sbox[j];
+		rc4_sbox[i] = sj;
+		rc4_sbox[j] = si;
+		*rc++ = rc4_sbox[(si+sj)&0xff];
+	}
+	return r;
+}
+