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

feedback and ok djm@

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

src/lib/libc/crypt/chacha_private.h

@@ -0,0 +1,220 @@
+/*
+chacha-merged.c version 20080118
+D. J. Bernstein
+Public domain.
+*/
+
+typedef unsigned char u8;
+typedef unsigned int u32;
+
+typedef struct
+{
+  u32 input[16]; /* could be compressed */
+} chacha_ctx;
+
+#define U8C(v) (v##U)
+#define U32C(v) (v##U)
+
+#define U8V(v) ((u8)(v) & U8C(0xFF))
+#define U32V(v) ((u32)(v) & U32C(0xFFFFFFFF))
+
+#define ROTL32(v, n) \
+  (U32V((v) << (n)) | ((v) >> (32 - (n))))
+
+#define U8TO32_LITTLE(p) \
+  (((u32)((p)[0])      ) | \
+   ((u32)((p)[1]) <<  8) | \
+   ((u32)((p)[2]) << 16) | \
+   ((u32)((p)[3]) << 24))
+
+#define U32TO8_LITTLE(p, v) \
+  do { \
+    (p)[0] = U8V((v)      ); \
+    (p)[1] = U8V((v) >>  8); \
+    (p)[2] = U8V((v) >> 16); \
+    (p)[3] = U8V((v) >> 24); \
+  } while (0)
+
+#define ROTATE(v,c) (ROTL32(v,c))
+#define XOR(v,w) ((v) ^ (w))
+#define PLUS(v,w) (U32V((v) + (w)))
+#define PLUSONE(v) (PLUS((v),1))
+
+#define QUARTERROUND(a,b,c,d) \
+  a = PLUS(a,b); d = ROTATE(XOR(d,a),16); \
+  c = PLUS(c,d); b = ROTATE(XOR(b,c),12); \
+  a = PLUS(a,b); d = ROTATE(XOR(d,a), 8); \
+  c = PLUS(c,d); b = ROTATE(XOR(b,c), 7);
+
+static const char sigma[16] = "expand 32-byte k";
+static const char tau[16] = "expand 16-byte k";
+
+static void
+chacha_keysetup(chacha_ctx *x,const u8 *k,u32 kbits,u32 ivbits)
+{
+  const char *constants;
+
+  x->input[4] = U8TO32_LITTLE(k + 0);
+  x->input[5] = U8TO32_LITTLE(k + 4);
+  x->input[6] = U8TO32_LITTLE(k + 8);
+  x->input[7] = U8TO32_LITTLE(k + 12);
+  if (kbits == 256) { /* recommended */
+    k += 16;
+    constants = sigma;
+  } else { /* kbits == 128 */
+    constants = tau;
+  }
+  x->input[8] = U8TO32_LITTLE(k + 0);
+  x->input[9] = U8TO32_LITTLE(k + 4);
+  x->input[10] = U8TO32_LITTLE(k + 8);
+  x->input[11] = U8TO32_LITTLE(k + 12);
+  x->input[0] = U8TO32_LITTLE(constants + 0);
+  x->input[1] = U8TO32_LITTLE(constants + 4);
+  x->input[2] = U8TO32_LITTLE(constants + 8);
+  x->input[3] = U8TO32_LITTLE(constants + 12);
+}
+
+static void
+chacha_ivsetup(chacha_ctx *x,const u8 *iv)
+{
+  x->input[12] = 0;
+  x->input[13] = 0;
+  x->input[14] = U8TO32_LITTLE(iv + 0);
+  x->input[15] = U8TO32_LITTLE(iv + 4);
+}
+
+static void
+chacha_encrypt_bytes(chacha_ctx *x,const u8 *m,u8 *c,u32 bytes)
+{
+  u32 x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15;
+  u32 j0, j1, j2, j3, j4, j5, j6, j7, j8, j9, j10, j11, j12, j13, j14, j15;
+  u8 *ctarget;
+  u8 tmp[64];
+  int i;
+
+  if (!bytes) return;
+
+  j0 = x->input[0];
+  j1 = x->input[1];
+  j2 = x->input[2];
+  j3 = x->input[3];
+  j4 = x->input[4];
+  j5 = x->input[5];
+  j6 = x->input[6];
+  j7 = x->input[7];
+  j8 = x->input[8];
+  j9 = x->input[9];
+  j10 = x->input[10];
+  j11 = x->input[11];
+  j12 = x->input[12];
+  j13 = x->input[13];
+  j14 = x->input[14];
+  j15 = x->input[15];
+
+  for (;;) {
+    if (bytes < 64) {
+      for (i = 0;i < bytes;++i) tmp[i] = m[i];
+      m = tmp;
+      ctarget = c;
+      c = tmp;
+    }
+    x0 = j0;
+    x1 = j1;
+    x2 = j2;
+    x3 = j3;
+    x4 = j4;
+    x5 = j5;
+    x6 = j6;
+    x7 = j7;
+    x8 = j8;
+    x9 = j9;
+    x10 = j10;
+    x11 = j11;
+    x12 = j12;
+    x13 = j13;
+    x14 = j14;
+    x15 = j15;
+    for (i = 20;i > 0;i -= 2) {
+      QUARTERROUND( x0, x4, x8,x12)
+      QUARTERROUND( x1, x5, x9,x13)
+      QUARTERROUND( x2, x6,x10,x14)
+      QUARTERROUND( x3, x7,x11,x15)
+      QUARTERROUND( x0, x5,x10,x15)
+      QUARTERROUND( x1, x6,x11,x12)
+      QUARTERROUND( x2, x7, x8,x13)
+      QUARTERROUND( x3, x4, x9,x14)
+    }
+    x0 = PLUS(x0,j0);
+    x1 = PLUS(x1,j1);
+    x2 = PLUS(x2,j2);
+    x3 = PLUS(x3,j3);
+    x4 = PLUS(x4,j4);
+    x5 = PLUS(x5,j5);
+    x6 = PLUS(x6,j6);
+    x7 = PLUS(x7,j7);
+    x8 = PLUS(x8,j8);
+    x9 = PLUS(x9,j9);
+    x10 = PLUS(x10,j10);
+    x11 = PLUS(x11,j11);
+    x12 = PLUS(x12,j12);
+    x13 = PLUS(x13,j13);
+    x14 = PLUS(x14,j14);
+    x15 = PLUS(x15,j15);
+
+#ifndef KEYSTREAM_ONLY
+    x0 = XOR(x0,U8TO32_LITTLE(m + 0));
+    x1 = XOR(x1,U8TO32_LITTLE(m + 4));
+    x2 = XOR(x2,U8TO32_LITTLE(m + 8));
+    x3 = XOR(x3,U8TO32_LITTLE(m + 12));
+    x4 = XOR(x4,U8TO32_LITTLE(m + 16));
+    x5 = XOR(x5,U8TO32_LITTLE(m + 20));
+    x6 = XOR(x6,U8TO32_LITTLE(m + 24));
+    x7 = XOR(x7,U8TO32_LITTLE(m + 28));
+    x8 = XOR(x8,U8TO32_LITTLE(m + 32));
+    x9 = XOR(x9,U8TO32_LITTLE(m + 36));
+    x10 = XOR(x10,U8TO32_LITTLE(m + 40));
+    x11 = XOR(x11,U8TO32_LITTLE(m + 44));
+    x12 = XOR(x12,U8TO32_LITTLE(m + 48));
+    x13 = XOR(x13,U8TO32_LITTLE(m + 52));
+    x14 = XOR(x14,U8TO32_LITTLE(m + 56));
+    x15 = XOR(x15,U8TO32_LITTLE(m + 60));
+#endif
+
+    j12 = PLUSONE(j12);
+    if (!j12) {
+      j13 = PLUSONE(j13);
+      /* stopping at 2^70 bytes per nonce is user's responsibility */
+    }
+
+    U32TO8_LITTLE(c + 0,x0);
+    U32TO8_LITTLE(c + 4,x1);
+    U32TO8_LITTLE(c + 8,x2);
+    U32TO8_LITTLE(c + 12,x3);
+    U32TO8_LITTLE(c + 16,x4);
+    U32TO8_LITTLE(c + 20,x5);
+    U32TO8_LITTLE(c + 24,x6);
+    U32TO8_LITTLE(c + 28,x7);
+    U32TO8_LITTLE(c + 32,x8);
+    U32TO8_LITTLE(c + 36,x9);
+    U32TO8_LITTLE(c + 40,x10);
+    U32TO8_LITTLE(c + 44,x11);
+    U32TO8_LITTLE(c + 48,x12);
+    U32TO8_LITTLE(c + 52,x13);
+    U32TO8_LITTLE(c + 56,x14);
+    U32TO8_LITTLE(c + 60,x15);
+
+    if (bytes <= 64) {
+      if (bytes < 64) {
+        for (i = 0;i < bytes;++i) ctarget[i] = c[i];
+      }
+      x->input[12] = j12;
+      x->input[13] = j13;
+      return;
+    }
+    bytes -= 64;
+    c += 64;
+#ifndef KEYSTREAM_ONLY
+    m += 64;
+#endif
+  }
+}