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29804cc1e0
systemd/src/journal/fsprg.c
Greg KH 29804cc1e0 use memzero(foo, length); for all memset(foo, 0, length); calls 
In trying to track down a stupid linker bug, I noticed a bunch of
memset() calls that should be using memzero() to make it more "obvious"
that the options are correct (i.e. 0 is not the length, but the data to
set).  So fix up all current calls to memset(foo, 0, length) to
memzero(foo, length).
2014-01-31 11:55:01 +01:00

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/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
/*
* fsprg v0.1 - (seekable) forward-secure pseudorandom generator
* Copyright (C) 2012 B. Poettering
* Contact: fsprg@point-at-infinity.org
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301 USA
*/
/*
* See "Practical Secure Logging: Seekable Sequential Key Generators"
* by G. A. Marson, B. Poettering for details:
*
* http://eprint.iacr.org/2013/397
*/
#include <gcrypt.h>
#include <string.h>
#include <assert.h>
#include "fsprg.h"
#define ISVALID_SECPAR(secpar) (((secpar) % 16 == 0) && ((secpar) >= 16) && ((secpar) <= 16384))
#define VALIDATE_SECPAR(secpar) assert(ISVALID_SECPAR(secpar));
#define RND_HASH GCRY_MD_SHA256
#define RND_GEN_P 0x01
#define RND_GEN_Q 0x02
#define RND_GEN_X 0x03
/******************************************************************************/
static void mpi_export(void *buf, size_t buflen, const gcry_mpi_t x) {
unsigned len;
size_t nwritten;
assert(gcry_mpi_cmp_ui(x, 0) >= 0);
len = (gcry_mpi_get_nbits(x) + 7) / 8;
assert(len <= buflen);
memzero(buf, buflen);
gcry_mpi_print(GCRYMPI_FMT_USG, buf + (buflen - len), len, &nwritten, x);
assert(nwritten == len);
}
static gcry_mpi_t mpi_import(const void *buf, size_t buflen) {
gcry_mpi_t h;
unsigned len;
gcry_mpi_scan(&h, GCRYMPI_FMT_USG, buf, buflen, NULL);
len = (gcry_mpi_get_nbits(h) + 7) / 8;
assert(len <= buflen);
assert(gcry_mpi_cmp_ui(h, 0) >= 0);
return h;
}
static void uint64_export(void *buf, size_t buflen, uint64_t x) {
assert(buflen == 8);
((uint8_t*) buf)[0] = (x >> 56) & 0xff;
((uint8_t*) buf)[1] = (x >> 48) & 0xff;
((uint8_t*) buf)[2] = (x >> 40) & 0xff;
((uint8_t*) buf)[3] = (x >> 32) & 0xff;
((uint8_t*) buf)[4] = (x >> 24) & 0xff;
((uint8_t*) buf)[5] = (x >> 16) & 0xff;
((uint8_t*) buf)[6] = (x >> 8) & 0xff;
((uint8_t*) buf)[7] = (x >> 0) & 0xff;
}
_pure_ static uint64_t uint64_import(const void *buf, size_t buflen) {
assert(buflen == 8);
return
(uint64_t)(((uint8_t*) buf)[0]) << 56 |
(uint64_t)(((uint8_t*) buf)[1]) << 48 |
(uint64_t)(((uint8_t*) buf)[2]) << 40 |
(uint64_t)(((uint8_t*) buf)[3]) << 32 |
(uint64_t)(((uint8_t*) buf)[4]) << 24 |
(uint64_t)(((uint8_t*) buf)[5]) << 16 |
(uint64_t)(((uint8_t*) buf)[6]) << 8 |
(uint64_t)(((uint8_t*) buf)[7]) << 0;
}
/* deterministically generate from seed/idx a string of buflen pseudorandom bytes */
static void det_randomize(void *buf, size_t buflen, const void *seed, size_t seedlen, uint32_t idx) {
gcry_md_hd_t hd, hd2;
size_t olen, cpylen;
uint32_t ctr;
olen = gcry_md_get_algo_dlen(RND_HASH);
gcry_md_open(&hd, RND_HASH, 0);
gcry_md_write(hd, seed, seedlen);
gcry_md_putc(hd, (idx >> 24) & 0xff);
gcry_md_putc(hd, (idx >> 16) & 0xff);
gcry_md_putc(hd, (idx >> 8) & 0xff);
gcry_md_putc(hd, (idx >> 0) & 0xff);
for (ctr = 0; buflen; ctr++) {
gcry_md_copy(&hd2, hd);
gcry_md_putc(hd2, (ctr >> 24) & 0xff);
gcry_md_putc(hd2, (ctr >> 16) & 0xff);
gcry_md_putc(hd2, (ctr >> 8) & 0xff);
gcry_md_putc(hd2, (ctr >> 0) & 0xff);
gcry_md_final(hd2);
cpylen = (buflen < olen) ? buflen : olen;
memcpy(buf, gcry_md_read(hd2, RND_HASH), cpylen);
gcry_md_close(hd2);
buf += cpylen;
buflen -= cpylen;
}
gcry_md_close(hd);
}
/* deterministically generate from seed/idx a prime of length `bits' that is 3 (mod 4) */
static gcry_mpi_t genprime3mod4(int bits, const void *seed, size_t seedlen, uint32_t idx) {
size_t buflen = bits / 8;
uint8_t buf[buflen];
gcry_mpi_t p;
assert(bits % 8 == 0);
assert(buflen > 0);
det_randomize(buf, buflen, seed, seedlen, idx);
buf[0] |= 0xc0; /* set upper two bits, so that n=pq has maximum size */
buf[buflen - 1] |= 0x03; /* set lower two bits, to have result 3 (mod 4) */
p = mpi_import(buf, buflen);
while (gcry_prime_check(p, 0))
gcry_mpi_add_ui(p, p, 4);
return p;
}
/* deterministically generate from seed/idx a quadratic residue (mod n) */
static gcry_mpi_t gensquare(const gcry_mpi_t n, const void *seed, size_t seedlen, uint32_t idx, unsigned secpar) {
size_t buflen = secpar / 8;
uint8_t buf[buflen];
gcry_mpi_t x;
det_randomize(buf, buflen, seed, seedlen, idx);
buf[0] &= 0x7f; /* clear upper bit, so that we have x < n */
x = mpi_import(buf, buflen);
assert(gcry_mpi_cmp(x, n) < 0);
gcry_mpi_mulm(x, x, x, n);
return x;
}
/* compute 2^m (mod phi(p)), for a prime p */
static gcry_mpi_t twopowmodphi(uint64_t m, const gcry_mpi_t p) {
gcry_mpi_t phi, r;
int n;
phi = gcry_mpi_new(0);
gcry_mpi_sub_ui(phi, p, 1);
/* count number of used bits in m */
for (n = 0; (1ULL << n) <= m; n++)
;
r = gcry_mpi_new(0);
gcry_mpi_set_ui(r, 1);
while (n) { /* square and multiply algorithm for fast exponentiation */
n--;
gcry_mpi_mulm(r, r, r, phi);
if (m & ((uint64_t)1 << n)) {
gcry_mpi_add(r, r, r);
if (gcry_mpi_cmp(r, phi) >= 0)
gcry_mpi_sub(r, r, phi);
}
}
gcry_mpi_release(phi);
return r;
}
/* Decompose $x \in Z_n$ into $(xp,xq) \in Z_p \times Z_q$ using Chinese Remainder Theorem */
static void CRT_decompose(gcry_mpi_t *xp, gcry_mpi_t *xq, const gcry_mpi_t x, const gcry_mpi_t p, const gcry_mpi_t q) {
*xp = gcry_mpi_new(0);
*xq = gcry_mpi_new(0);
gcry_mpi_mod(*xp, x, p);
gcry_mpi_mod(*xq, x, q);
}
/* Compose $(xp,xq) \in Z_p \times Z_q$ into $x \in Z_n$ using Chinese Remainder Theorem */
static void CRT_compose(gcry_mpi_t *x, const gcry_mpi_t xp, const gcry_mpi_t xq, const gcry_mpi_t p, const gcry_mpi_t q) {
gcry_mpi_t a, u;
a = gcry_mpi_new(0);
u = gcry_mpi_new(0);
*x = gcry_mpi_new(0);
gcry_mpi_subm(a, xq, xp, q);
gcry_mpi_invm(u, p, q);
gcry_mpi_mulm(a, a, u, q); /* a = (xq - xp) / p (mod q) */
gcry_mpi_mul(*x, p, a);
gcry_mpi_add(*x, *x, xp); /* x = p * ((xq - xp) / p mod q) + xp */
gcry_mpi_release(a);
gcry_mpi_release(u);
}
static void initialize_libgcrypt(void) {
const char *p;
if (gcry_control(GCRYCTL_INITIALIZATION_FINISHED_P))
return;
p = gcry_check_version("1.4.5");
assert(p);
/* Turn off "secmem". Clients which whish to make use of this
* feature should initialize the library manually */
gcry_control(GCRYCTL_DISABLE_SECMEM);
gcry_control(GCRYCTL_INITIALIZATION_FINISHED, 0);
}
/******************************************************************************/
size_t FSPRG_mskinbytes(unsigned _secpar) {
VALIDATE_SECPAR(_secpar);
return 2 + 2 * (_secpar / 2) / 8; /* to store header,p,q */
}
size_t FSPRG_mpkinbytes(unsigned _secpar) {
VALIDATE_SECPAR(_secpar);
return 2 + _secpar / 8; /* to store header,n */
}
size_t FSPRG_stateinbytes(unsigned _secpar) {
VALIDATE_SECPAR(_secpar);
return 2 + 2 * _secpar / 8 + 8; /* to store header,n,x,epoch */
}
static void store_secpar(void *buf, uint16_t secpar) {
secpar = secpar / 16 - 1;
((uint8_t*) buf)[0] = (secpar >> 8) & 0xff;
((uint8_t*) buf)[1] = (secpar >> 0) & 0xff;
}
static uint16_t read_secpar(const void *buf) {
uint16_t secpar;
secpar =
(uint16_t)(((uint8_t*) buf)[0]) << 8 |
(uint16_t)(((uint8_t*) buf)[1]) << 0;
return 16 * (secpar + 1);
}
void FSPRG_GenMK(void *msk, void *mpk, const void *seed, size_t seedlen, unsigned _secpar) {
uint8_t iseed[FSPRG_RECOMMENDED_SEEDLEN];
gcry_mpi_t n, p, q;
uint16_t secpar;
VALIDATE_SECPAR(_secpar);
secpar = _secpar;
initialize_libgcrypt();
if (!seed) {
gcry_randomize(iseed, FSPRG_RECOMMENDED_SEEDLEN, GCRY_STRONG_RANDOM);
seed = iseed;
seedlen = FSPRG_RECOMMENDED_SEEDLEN;
}
p = genprime3mod4(secpar / 2, seed, seedlen, RND_GEN_P);
q = genprime3mod4(secpar / 2, seed, seedlen, RND_GEN_Q);
if (msk) {
store_secpar(msk + 0, secpar);
mpi_export(msk + 2 + 0 * (secpar / 2) / 8, (secpar / 2) / 8, p);
mpi_export(msk + 2 + 1 * (secpar / 2) / 8, (secpar / 2) / 8, q);
}
if (mpk) {
n = gcry_mpi_new(0);
gcry_mpi_mul(n, p, q);
assert(gcry_mpi_get_nbits(n) == secpar);
store_secpar(mpk + 0, secpar);
mpi_export(mpk + 2, secpar / 8, n);
gcry_mpi_release(n);
}
gcry_mpi_release(p);
gcry_mpi_release(q);
}
void FSPRG_GenState0(void *state, const void *mpk, const void *seed, size_t seedlen) {
gcry_mpi_t n, x;
uint16_t secpar;
initialize_libgcrypt();
secpar = read_secpar(mpk + 0);
n = mpi_import(mpk + 2, secpar / 8);
x = gensquare(n, seed, seedlen, RND_GEN_X, secpar);
memcpy(state, mpk, 2 + secpar / 8);
mpi_export(state + 2 + 1 * secpar / 8, secpar / 8, x);
memzero(state + 2 + 2 * secpar / 8, 8);
gcry_mpi_release(n);
gcry_mpi_release(x);
}
void FSPRG_Evolve(void *state) {
gcry_mpi_t n, x;
uint16_t secpar;
uint64_t epoch;
initialize_libgcrypt();
secpar = read_secpar(state + 0);
n = mpi_import(state + 2 + 0 * secpar / 8, secpar / 8);
x = mpi_import(state + 2 + 1 * secpar / 8, secpar / 8);
epoch = uint64_import(state + 2 + 2 * secpar / 8, 8);
gcry_mpi_mulm(x, x, x, n);
epoch++;
mpi_export(state + 2 + 1 * secpar / 8, secpar / 8, x);
uint64_export(state + 2 + 2 * secpar / 8, 8, epoch);
gcry_mpi_release(n);
gcry_mpi_release(x);
}
uint64_t FSPRG_GetEpoch(const void *state) {
uint16_t secpar;
secpar = read_secpar(state + 0);
return uint64_import(state + 2 + 2 * secpar / 8, 8);
}
void FSPRG_Seek(void *state, uint64_t epoch, const void *msk, const void *seed, size_t seedlen) {
gcry_mpi_t p, q, n, x, xp, xq, kp, kq, xm;
uint16_t secpar;
initialize_libgcrypt();
secpar = read_secpar(msk + 0);
p = mpi_import(msk + 2 + 0 * (secpar / 2) / 8, (secpar / 2) / 8);
q = mpi_import(msk + 2 + 1 * (secpar / 2) / 8, (secpar / 2) / 8);
n = gcry_mpi_new(0);
gcry_mpi_mul(n, p, q);
x = gensquare(n, seed, seedlen, RND_GEN_X, secpar);
CRT_decompose(&xp, &xq, x, p, q); /* split (mod n) into (mod p) and (mod q) using CRT */
kp = twopowmodphi(epoch, p); /* compute 2^epoch (mod phi(p)) */
kq = twopowmodphi(epoch, q); /* compute 2^epoch (mod phi(q)) */
gcry_mpi_powm(xp, xp, kp, p); /* compute x^(2^epoch) (mod p) */
gcry_mpi_powm(xq, xq, kq, q); /* compute x^(2^epoch) (mod q) */
CRT_compose(&xm, xp, xq, p, q); /* combine (mod p) and (mod q) to (mod n) using CRT */
store_secpar(state + 0, secpar);
mpi_export(state + 2 + 0 * secpar / 8, secpar / 8, n);
mpi_export(state + 2 + 1 * secpar / 8, secpar / 8, xm);
uint64_export(state + 2 + 2 * secpar / 8, 8, epoch);
gcry_mpi_release(p);
gcry_mpi_release(q);
gcry_mpi_release(n);
gcry_mpi_release(x);
gcry_mpi_release(xp);
gcry_mpi_release(xq);
gcry_mpi_release(kp);
gcry_mpi_release(kq);
gcry_mpi_release(xm);
}
void FSPRG_GetKey(const void *state, void *key, size_t keylen, uint32_t idx) {
uint16_t secpar;
initialize_libgcrypt();
secpar = read_secpar(state + 0);
det_randomize(key, keylen, state + 2, 2 * secpar / 8 + 8, idx);
}
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