Date: Thu, 29 May 2014 19:54:21 -0700 From: Adrian Chadd <adrian@freebsd.org> To: Ted Unangst <tedu@tedunangst.com> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: switch arc4random to chacha Message-ID: <CAJ-Vmo=xbVnb7ExGaa-utM1FLe_Z7T6JzCR6TeE=_i-pqfFR%2Bg@mail.gmail.com> In-Reply-To: <f0b9ae8e7b2a40a9ab253438261c2c75@tedunangst.com> References: <f0b9ae8e7b2a40a9ab253438261c2c75@tedunangst.com>
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Hi!
How about running this via the security team here?
Start with Mark Murray (markm@freebsd.org)
I'm sure they'll at least want you to fire this up in a VM and test. :P
-a
On 29 May 2014 18:04, Ted Unangst <tedu@tedunangst.com> wrote:
> This syncs libc arc4random.c with OpenBSD, mostly to change the
> implementation to ChaCha20.
>
> I removed the more complicated seed fetching code and changed it to
> just sysctl(). A quick check revealed that the FreeBSD kernel supports
> this for at least five years now. It's much simpler to use code that
> always works instead of a series of untested fallbacks that are even
> less likely to work.
>
> Also removes the addrandom interface as a useless complication. If the
> kernel is incapable of properly seeding arc4random, application code
> can't do any better.
>
> Unfortunately, I don't have any FreeBSD systems running at the moment,
> so I can't make any promises that this will even compile, but it
> passed the eyeball test.
>
> --- arc4random.c.orig Thu May 29 20:28:49 2014
> +++ arc4random.c Thu May 29 20:51:59 2014
> @@ -1,8 +1,9 @@
> -/* $OpenBSD: arc4random.c,v 1.22 2010/12/22 08:23:42 otto Exp $ */
> +/* $OpenBSD: arc4random.c,v 1.30 2014/05/06 16:06:33 tedu 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
> @@ -18,15 +19,7 @@
> */
>
> /*
> - * 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 <sys/cdefs.h>
> @@ -40,28 +33,24 @@
> #include <sys/types.h>
> #include <sys/param.h>
> #include <sys/sysctl.h>
> +#include <sys/mman.h>
> #include <sys/time.h>
> #include <pthread.h>
>
> #include "libc_private.h"
> #include "un-namespace.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];
> -};
> -
> static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER;
>
> -#define RANDOMDEV "/dev/random"
> -#define KEYSIZE 128
> #define _ARC4_LOCK() \
> do { \
> if (__isthreaded) \
> @@ -74,187 +63,149 @@
> _pthread_mutex_unlock(&arc4random_mtx); \
> } while (0)
>
> +#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 pid_t rs_stir_pid;
> +static chacha_ctx *rs; /* chacha context for random keystream */
> +static u_char *rs_buf; /* 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 _rs_rekey(u_char *dat, size_t datlen);
> +
> extern int __sysctl(int *name, u_int namelen, void *oldp, size_t *oldlenp,
> void *newp, size_t newlen);
>
> -static inline u_int8_t arc4_getbyte(void);
> -static void arc4_stir(void);
> -
> static inline void
> -arc4_init(void)
> +_rs_init(u_char *buf, size_t n)
> {
> - int n;
> + if (n < KEYSZ + IVSZ)
> + return;
>
> - for (n = 0; n < 256; n++)
> - rs.s[n] = n;
> - rs.i = 0;
> - rs.j = 0;
> -}
> + if (rs == NULL && (rs = mmap(NULL, sizeof(*rs), PROT_READ|PROT_WRITE,
> + MAP_ANON, -1, 0)) == MAP_FAILED)
> + abort();
> + if (rs_buf == NULL && (rs_buf = mmap(NULL, RSBUFSZ, PROT_READ|PROT_WRITE,
> + MAP_ANON, -1, 0)) == MAP_FAILED)
> + abort();
>
> -static inline void
> -arc4_addrandom(u_char *dat, int datlen)
> -{
> - 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;
> + chacha_keysetup(rs, buf, KEYSZ * 8, 0);
> + chacha_ivsetup(rs, buf + KEYSZ);
> }
>
> -static size_t
> -arc4_sysctl(u_char *buf, size_t size)
> +static void
> +_rs_stir(void)
> {
> - int mib[2];
> - size_t len, done;
> + int mib[2];
> + size_t len;
> + u_char rnd[KEYSZ + IVSZ];
>
> mib[0] = CTL_KERN;
> mib[1] = KERN_ARND;
> - done = 0;
>
> - do {
> - len = size;
> - if (__sysctl(mib, 2, buf, &len, NULL, 0) == -1)
> - return (done);
> - done += len;
> - buf += len;
> - size -= len;
> - } while (size > 0);
> + len = sizeof(rnd);
> + __sysctl(mib, 2, rnd, &len, NULL, 0);
>
> - return (done);
> -}
> -
> -static void
> -arc4_stir(void)
> -{
> - int done, fd, i;
> - struct {
> - struct timeval tv;
> - pid_t pid;
> - u_char rnd[KEYSIZE];
> - } rdat;
> -
> if (!rs_initialized) {
> - arc4_init();
> rs_initialized = 1;
> - }
> - done = 0;
> - if (arc4_sysctl((u_char *)&rdat, KEYSIZE) == KEYSIZE)
> - done = 1;
> - if (!done) {
> - fd = _open(RANDOMDEV, O_RDONLY | O_CLOEXEC, 0);
> - if (fd >= 0) {
> - if (_read(fd, &rdat, KEYSIZE) == KEYSIZE)
> - done = 1;
> - (void)_close(fd);
> - }
> - }
> - if (!done) {
> - (void)gettimeofday(&rdat.tv, NULL);
> - rdat.pid = getpid();
> - /* We'll just take whatever was on the stack too... */
> - }
> + _rs_init(rnd, sizeof(rnd));
> + } else
> + _rs_rekey(rnd, sizeof(rnd));
> + bzero(rnd, sizeof(rnd)); /* explicit_bzero */
>
> - arc4_addrandom((u_char *)&rdat, KEYSIZE);
> + /* invalidate rs_buf */
> + rs_have = 0;
> + memset(rs_buf, 0, RSBUFSZ);
>
> - /*
> - * Discard early keystream, as per recommendations in:
> - * "(Not So) Random Shuffles of RC4" by Ilya Mironov.
> - */
> - for (i = 0; i < 1024; i++)
> - (void)arc4_getbyte();
> - arc4_count = 1600000;
> + 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 u_int8_t
> -arc4_getbyte(void)
> +static inline void
> +_rs_rekey(u_char *dat, size_t datlen)
> {
> - u_int8_t si, sj;
> +#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;
>
> - 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]);
> + 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_int32_t
> -arc4_getword(void)
> +static inline void
> +_rs_random_buf(void *_buf, size_t n)
> {
> - u_int32_t val;
> - val = arc4_getbyte() << 24;
> - val |= arc4_getbyte() << 16;
> - val |= arc4_getbyte() << 8;
> - val |= arc4_getbyte();
> - return val;
> -}
> + u_char *buf = (u_char *)_buf;
> + size_t m;
>
> -void
> -arc4random_stir(void)
> -{
> - _ARC4_LOCK();
> - arc4_stir();
> - _ARC4_UNLOCK();
> + _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);
> + }
> }
>
> -void
> -arc4random_addrandom(u_char *dat, int datlen)
> +static inline void
> +_rs_random_u32(u_int32_t *val)
> {
> - _ARC4_LOCK();
> - if (!rs_initialized)
> - arc4_stir();
> - arc4_addrandom(dat, datlen);
> - _ARC4_UNLOCK();
> + _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;
> }
>
> 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();
> }
>
> @@ -276,17 +227,8 @@
> if (upper_bound < 2)
> return 0;
>
> -#if (ULONG_MAX > 0xffffffffUL)
> - min = 0x100000000UL % upper_bound;
> -#else
> - /* Calculate (2**32 % upper_bound) avoiding 64-bit math */
> - if (upper_bound > 0x80000000)
> - min = 1 + ~upper_bound; /* 2**32 - upper_bound */
> - else {
> - /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
> - min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
> - }
> -#endif
> + /* 2**32 % x == (2**32 - x) % x */
> + min = -upper_bound % upper_bound;
>
> /*
> * This could theoretically loop forever but each retry has
> @@ -302,24 +244,3 @@
>
> return r % upper_bound;
> }
> -
> -#if 0
> -/*-------- Test code for i386 --------*/
> -#include <stdio.h>
> -#include <machine/pctr.h>
> -int
> -main(int argc, char **argv)
> -{
> - const int iter = 1000000;
> - int i;
> - pctrval v;
> -
> - v = rdtsc();
> - for (i = 0; i < iter; i++)
> - arc4random();
> - v = rdtsc() - v;
> - v /= iter;
> -
> - printf("%qd cycles\n", v);
> -}
> -#endif
> --- /dev/null Thu May 29 20:52:04 2014
> +++ chacha_private.h Thu May 29 20:40:54 2014
> @@ -0,0 +1,222 @@
> +/*
> +chacha-merged.c version 20080118
> +D. J. Bernstein
> +Public domain.
> +*/
> +
> +/* $OpenBSD: chacha_private.h,v 1.2 2013/10/04 07:02:27 djm Exp $ */
> +
> +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 = NULL;
> + u8 tmp[64];
> + u_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
> + }
> +}
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