replace rc4 with ChaCha20; inspired by Nick Mathewson's work on libottery;

feedback and ok djm@

1 files changed, 106 insertions, 98 deletions

diff --git a/src/lib/libc/crypt/arc4random.c b/src/lib/libc/crypt/arc4random.c
index f00f5ee9f1..356e231815 100644
--- a/src/lib/libc/crypt/arc4random.c
+++ b/src/lib/libc/crypt/arc4random.c
@@ -1,8 +1,9 @@
-/*      $OpenBSD: arc4random.c,v 1.24 2013/06/11 16:59:50 deraadt Exp $ */
+/*      $OpenBSD: arc4random.c,v 1.25 2013/10/01 18:34:57 markus Exp $  */
 
 /*
  * Copyright (c) 1996, David Mazieres <dm@uun.org>
  * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
+ * Copyright (c) 2013, Markus Friedl <markus@openbsd.org>
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -18,20 +19,13 @@
  */
 
 /*
- * Arc4 random number generator for OpenBSD.
- *
- * This code is derived from section 17.1 of Applied Cryptography,
- * second edition, which describes a stream cipher allegedly
- * compatible with RSA Labs "RC4" cipher (the actual description of
- * which is a trade secret).  The same algorithm is used as a stream
- * cipher called "arcfour" in Tatu Ylonen's ssh package.
- *
- * RC4 is a registered trademark of RSA Laboratories.
+ * ChaCha based random number generator for OpenBSD.
  */
 
 #include <fcntl.h>
 #include <limits.h>
 #include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 #include <sys/types.h>
 #include <sys/param.h>
@@ -39,64 +33,43 @@
 #include <sys/sysctl.h>
 #include "thread_private.h"
 
+#define KEYSTREAM_ONLY
+#include "chacha_private.h"
+
 #ifdef __GNUC__
 #define inline __inline
 #else                           /* !__GNUC__ */
 #define inline
 #endif                          /* !__GNUC__ */
 
-struct arc4_stream {
-        u_int8_t i;
-        u_int8_t j;
-        u_int8_t s[256];
-};
-
+#define KEYSZ   32
+#define IVSZ    8
+#define BLOCKSZ 64
+#define RSBUFSZ (16*BLOCKSZ)
 static int rs_initialized;
-static struct arc4_stream rs;
-static pid_t arc4_stir_pid;
-static int arc4_count;
-
-static inline u_int8_t arc4_getbyte(void);
+static pid_t rs_stir_pid;
+static chacha_ctx rs;           /* chacha context for random keystream */
+static u_char rs_buf[RSBUFSZ];  /* keystream blocks */
+static size_t rs_have;          /* valid bytes at end of rs_buf */
+static size_t rs_count;         /* bytes till reseed */
 
-static inline void
-arc4_init(void)
-{
-        int     n;
-
-        for (n = 0; n < 256; n++)
-                rs.s[n] = n;
-        rs.i = 0;
-        rs.j = 0;
-}
+static inline void _rs_rekey(u_char *dat, size_t datlen);
 
 static inline void
-arc4_addrandom(u_char *dat, int datlen)
+_rs_init(u_char *buf, size_t n)
 {
-        int     n;
-        u_int8_t si;
-
-        rs.i--;
-        for (n = 0; n < 256; n++) {
-                rs.i = (rs.i + 1);
-                si = rs.s[rs.i];
-                rs.j = (rs.j + si + dat[n % datlen]);
-                rs.s[rs.i] = rs.s[rs.j];
-                rs.s[rs.j] = si;
-        }
-        rs.j = rs.i;
+        if (n < KEYSZ + IVSZ)
+                return;
+        chacha_keysetup(&rs, buf, KEYSZ * 8, 0);
+        chacha_ivsetup(&rs, buf + KEYSZ);
 }
 
 static void
-arc4_stir(void)
+_rs_stir(void)
 {
-        int     i, mib[2];
+        int     mib[2];
         size_t  len;
-        u_char rnd[128];
-
-        if (!rs_initialized) {
-                arc4_init();
-                rs_initialized = 1;
-        }
+        u_char rnd[KEYSZ + IVSZ];
 
         mib[0] = CTL_KERN;
         mib[1] = KERN_ARND;
@@ -104,68 +77,109 @@ arc4_stir(void)
         len = sizeof(rnd);
         sysctl(mib, 2, rnd, &len, NULL, 0);
 
-        arc4_addrandom(rnd, sizeof(rnd));
+        if (!rs_initialized) {
+                rs_initialized = 1;
+                _rs_init(rnd, sizeof(rnd));
+        } else
+                _rs_rekey(rnd, sizeof(rnd));
+        memset(rnd, 0, sizeof(rnd));
 
-        /*
-         * Discard early keystream, as per recommendations in:
-         * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
-         */
-        for (i = 0; i < 256; i++)
-                (void)arc4_getbyte();
-        arc4_count = 1600000;
+        /* invalidate rs_buf */
+        rs_have = 0;
+        memset(rs_buf, 0, RSBUFSZ);
+
+        rs_count = 1600000;
 }
 
-static void
-arc4_stir_if_needed(void)
+static inline void
+_rs_stir_if_needed(size_t len)
 {
         pid_t pid = getpid();
 
-        if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid) {
-                arc4_stir_pid = pid;
-                arc4_stir();
+        if (rs_count <= len || !rs_initialized || rs_stir_pid != pid) {
+                rs_stir_pid = pid;
+                _rs_stir();
+        } else
+                rs_count -= len;
+}
+
+static inline void
+_rs_rekey(u_char *dat, size_t datlen)
+{
+#ifndef KEYSTREAM_ONLY
+        memset(rs_buf, 0,RSBUFSZ);
+#endif
+        /* fill rs_buf with the keystream */
+        chacha_encrypt_bytes(&rs, rs_buf, rs_buf, RSBUFSZ);
+        /* mix in optional user provided data */
+        if (dat) {
+                size_t i, m;
+
+                m = MIN(datlen, KEYSZ + IVSZ);
+                for (i = 0; i < m; i++)
+                        rs_buf[i] ^= dat[i];
         }
+        /* immediately reinit for backtracking resistance */
+        _rs_init(rs_buf, KEYSZ + IVSZ);
+        memset(rs_buf, 0, KEYSZ + IVSZ);
+        rs_have = RSBUFSZ - KEYSZ - IVSZ;
 }
 
-static inline u_int8_t
-arc4_getbyte(void)
+static inline void
+_rs_random_buf(void *_buf, size_t n)
 {
-        u_int8_t si, sj;
-
-        rs.i = (rs.i + 1);
-        si = rs.s[rs.i];
-        rs.j = (rs.j + si);
-        sj = rs.s[rs.j];
-        rs.s[rs.i] = sj;
-        rs.s[rs.j] = si;
-        return (rs.s[(si + sj) & 0xff]);
+        u_char *buf = (u_char *)_buf;
+        size_t m;
+
+        _rs_stir_if_needed(n);
+        while (n > 0) {
+                if (rs_have > 0) {
+                        m = MIN(n, rs_have);
+                        memcpy(buf, rs_buf + RSBUFSZ - rs_have, m);
+                        memset(rs_buf + RSBUFSZ - rs_have, 0, m);
+                        buf += m;
+                        n -= m;
+                        rs_have -= m;
+                }
+                if (rs_have == 0)
+                        _rs_rekey(NULL, 0);
+        }
 }
 
-static inline u_int32_t
-arc4_getword(void)
+static inline void
+_rs_random_u32(u_int32_t *val)
 {
-        u_int32_t val;
-        val = arc4_getbyte() << 24;
-        val |= arc4_getbyte() << 16;
-        val |= arc4_getbyte() << 8;
-        val |= arc4_getbyte();
-        return val;
+        _rs_stir_if_needed(sizeof(*val));
+        if (rs_have < sizeof(*val))
+                _rs_rekey(NULL, 0);
+        memcpy(val, rs_buf + RSBUFSZ - rs_have, sizeof(*val));
+        memset(rs_buf + RSBUFSZ - rs_have, 0, sizeof(*val));
+        rs_have -= sizeof(*val);
+        return;
 }
 
 void
 arc4random_stir(void)
 {
         _ARC4_LOCK();
-        arc4_stir();
+        _rs_stir();
         _ARC4_UNLOCK();
 }
 
 void
 arc4random_addrandom(u_char *dat, int datlen)
 {
+        int m;
+
         _ARC4_LOCK();
         if (!rs_initialized)
-                arc4_stir();
-        arc4_addrandom(dat, datlen);
+                _rs_stir();
+        while (datlen > 0) {
+                m = MIN(datlen, KEYSZ + IVSZ);
+                _rs_rekey(dat, m);
+                dat += m;
+                datlen -= m;
+        }
         _ARC4_UNLOCK();
 }
 
@@ -173,25 +187,18 @@ u_int32_t
 arc4random(void)
 {
         u_int32_t val;
+
         _ARC4_LOCK();
-        arc4_count -= 4;
-        arc4_stir_if_needed();
-        val = arc4_getword();
+        _rs_random_u32(&val);
         _ARC4_UNLOCK();
         return val;
 }
 
 void
-arc4random_buf(void *_buf, size_t n)
+arc4random_buf(void *buf, size_t n)
 {
-        u_char *buf = (u_char *)_buf;
         _ARC4_LOCK();
-        arc4_stir_if_needed();
-        while (n--) {
-                if (--arc4_count <= 0)
-                        arc4_stir();
-                buf[n] = arc4_getbyte();
-        }
+        _rs_random_buf(buf, n);
         _ARC4_UNLOCK();
 }
 
@@ -249,5 +256,6 @@ main(int argc, char **argv)
         v /= iter;
 
         printf("%qd cycles\n", v);
+        exit(0);
 }
 #endif