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-rw-r--r--src/journal/fsprg.c389
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diff --git a/src/journal/fsprg.c b/src/journal/fsprg.c
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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 "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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