commit 3a45f6ffe95d4c51e4ad4e14f468feb3f4bd6b1e
Author: Nick Mathewson <nickm(a)torproject.org>
Date: Thu May 10 08:46:36 2018 -0400
Implementation for a simple order-preserving encryption scheme.
This is meant for use when encrypting the current time within the
period in order to get a monotonically increasing revision counter
without actually revealing our view of the time.
This scheme is far from the most state-of-the-art: don't use it for
anything else without careful analysis by somebody much smarter than
I am.
See ticket #25552 for some rationale for this logic.
---
src/lib/crypt_ops/crypto_ope.c | 179 +++++++++++++++++++++++++++++++++++++++++
src/lib/crypt_ops/crypto_ope.h | 35 ++++++++
src/lib/crypt_ops/include.am | 2 +
src/test/include.am | 1 +
src/test/ope_ref.py | 40 +++++++++
src/test/test.c | 1 +
src/test/test.h | 1 +
src/test/test_crypto_ope.c | 148 ++++++++++++++++++++++++++++++++++
8 files changed, 407 insertions(+)
diff --git a/src/lib/crypt_ops/crypto_ope.c b/src/lib/crypt_ops/crypto_ope.c
new file mode 100644
index 000000000..dd04ffbaa
--- /dev/null
+++ b/src/lib/crypt_ops/crypto_ope.c
@@ -0,0 +1,179 @@
+/* Copyright (c) 2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * A rudimentary order-preserving encryption scheme.
+ *
+ * To compute the encryption of N, this scheme uses an AES-CTR stream to
+ * generate M-byte values, and adds the first N of them together. (+1 each to
+ * insure that the ciphertexts are strictly decreasing.)
+ *
+ * We use this for generating onion service revision counters based on the
+ * current time, without leaking the amount of skew in our view of the current
+ * time. MUCH more analysis would be needed before using it for anything
+ * else!
+ */
+
+#include "orconfig.h"
+#include "crypto.h"
+
+#define CRYPTO_OPE_PRIVATE
+
+#include "crypto_ope.h"
+/**
+ * How infrequent should the precomputed values be for this encryption?
+ * The choice of this value creates a space/time tradeoff.
+ *
+ * Note that this value must be a multiple of 16; see
+ * ope_get_cipher()
+ */
+#define SAMPLE_INTERVAL 1024
+/** Number of precomputed samples to make for each OPE key. */
+#define N_SAMPLES (OPE_INPUT_MAX / SAMPLE_INTERVAL)
+
+struct crypto_ope_c {
+ /** An AES key for use with this object. */
+ uint8_t key[OPE_KEY_LEN];
+ /** Cached intermediate encryption values at SAMPLE_INTERVAL,
+ * SAMPLE_INTERVAL*2,...SAMPLE_INTERVAL*N_SAMPLES */
+ uint64_t samples[N_SAMPLES];
+};
+
+/** The type to add up in order to produce our OPE ciphertexts */
+typedef uint16_t ope_val_t;
+
+#ifdef WORDS_BIG_ENDIAN
+/** Convert an OPE value to little-endian */
+static inline ope_val_t
+ope_val_to_le(ope_val_t x)
+{
+ return
+ ((x) >> 8) |
+ (((x)&0xff) << 8);
+}
+#else
+#define ope_val_to_le(x) (x)
+#endif
+
+/**
+ * Return a new AES256-CTR stream cipher object for <b>ope</b>, ready to yield
+ * bytes from the stream at position <b>initial_idx</b>.
+ *
+ * Note that because the index is converted directly to an IV, it must be a
+ * multiple of the AES block size (16).
+ */
+STATIC crypto_cipher_t *
+ope_get_cipher(const crypto_ope_t *ope, uint32_t initial_idx)
+{
+ uint8_t iv[CIPHER_IV_LEN];
+ tor_assert((initial_idx & 0xf) == 0);
+ uint32_t n = htonl(initial_idx >> 4);
+ memset(iv, 0, sizeof(iv));
+ memcpy(iv + CIPHER_IV_LEN - sizeof(n), &n, sizeof(n));
+
+ return crypto_cipher_new_with_iv_and_bits(ope->key,
+ iv,
+ OPE_KEY_LEN * 8);
+}
+
+/**
+ * Retrieve and add the next <b>n</b> values from the stream cipher <b>c</b>,
+ * and return their sum.
+ *
+ * Note that values are taken in little-endian order (for performance on
+ * prevalent hardware), and are mapped from range 0..2^n-1 to range 1..2^n (so
+ * that each input encrypts to a different output).
+ *
+ * NOTE: this function is not constant-time.
+ */
+STATIC uint64_t
+sum_values_from_cipher(crypto_cipher_t *c, size_t n)
+{
+#define BUFSZ 256
+ ope_val_t buf[BUFSZ];
+ uint64_t total = 0;
+ unsigned i;
+ while (n >= BUFSZ) {
+ memset(buf, 0, sizeof(buf));
+ crypto_cipher_crypt_inplace(c, (char*)buf, BUFSZ*sizeof(ope_val_t));
+
+ for (i = 0; i < BUFSZ; ++i) {
+ total += ope_val_to_le(buf[i]);
+ total += 1;
+ }
+ n -= BUFSZ;
+ }
+
+ memset(buf, 0, n*sizeof(ope_val_t));
+ crypto_cipher_crypt_inplace(c, (char*)buf, n*sizeof(ope_val_t));
+ for (i = 0; i < n; ++i) {
+ total += ope_val_to_le(buf[i]);
+ total += 1;
+ }
+
+ memset(buf, 0, sizeof(buf));
+ return total;
+}
+
+/**
+ * Return a new crypto_ope_t object, using the provided 256-bit key.
+ */
+crypto_ope_t *
+crypto_ope_new(const uint8_t *key)
+{
+ crypto_ope_t *ope = tor_malloc_zero(sizeof(crypto_ope_t));
+ memcpy(ope->key, key, OPE_KEY_LEN);
+
+ crypto_cipher_t *cipher = ope_get_cipher(ope, 0);
+
+ uint64_t v = 0;
+ int i;
+ for (i = 0; i < N_SAMPLES; ++i) {
+ v += sum_values_from_cipher(cipher, SAMPLE_INTERVAL);
+ ope->samples[i] = v;
+ }
+
+ crypto_cipher_free(cipher);
+ return ope;
+}
+
+/** Free all storage held in <>ope</b>. */
+void
+crypto_ope_free_(crypto_ope_t *ope)
+{
+ if (!ope)
+ return;
+ memwipe(ope, 0, sizeof(*ope));
+ tor_free(ope);
+}
+
+/**
+ * Return the encrypted value corresponding to <b>input</b>. The input value
+ * must be in range 1..OPE_INPUT_MAX. Returns UINT64_MAX on an invalid input.
+ *
+ * NOTE: this function is not constant-time.
+ */
+uint64_t
+crypto_ope_encrypt(const crypto_ope_t *ope, int plaintext)
+{
+ if (plaintext <= 0 || plaintext > OPE_INPUT_MAX)
+ return UINT64_MAX;
+
+ const int sample_idx = (plaintext / SAMPLE_INTERVAL);
+ const int starting_iv = sample_idx * SAMPLE_INTERVAL;
+ const int remaining_values = plaintext - starting_iv;
+ uint64_t v;
+ if (sample_idx == 0) {
+ v = 0;
+ } else {
+ v = ope->samples[sample_idx - 1];
+ }
+ crypto_cipher_t *cipher = ope_get_cipher(ope, starting_iv*sizeof(ope_val_t));
+
+ v += sum_values_from_cipher(cipher, remaining_values);
+
+ crypto_cipher_free(cipher);
+
+ return v;
+}
+
diff --git a/src/lib/crypt_ops/crypto_ope.h b/src/lib/crypt_ops/crypto_ope.h
new file mode 100644
index 000000000..885ce84b2
--- /dev/null
+++ b/src/lib/crypt_ops/crypto_ope.h
@@ -0,0 +1,35 @@
+/* Copyright (c) 2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#ifndef CRYPTO_OPE_H
+#define CRYPTO_OPE_H
+
+#include "orconfig.h"
+#include "crypto.h"
+#include "crypto_util.h"
+
+#include "crypto_ope.h"
+
+/** Length of OPE key, in bytes. */
+#define OPE_KEY_LEN 32
+
+/** Largest value that can be passed to crypto_ope_encrypt() */
+#define OPE_INPUT_MAX 131072
+
+typedef struct crypto_ope_c crypto_ope_t;
+
+crypto_ope_t *crypto_ope_new(const uint8_t *key);
+void crypto_ope_free_(crypto_ope_t *ope);
+#define crypto_ope_free(ope) \
+ FREE_AND_NULL(crypto_ope_t, crypto_ope_free_, (ope))
+
+uint64_t crypto_ope_encrypt(const crypto_ope_t *ope, int plaintext);
+
+#ifdef CRYPTO_OPE_PRIVATE
+STATIC crypto_cipher_t *ope_get_cipher(const crypto_ope_t *ope,
+ uint32_t initial_idx);
+STATIC uint64_t sum_values_from_cipher(crypto_cipher_t *c, size_t n);
+#endif
+
+#endif
+
diff --git a/src/lib/crypt_ops/include.am b/src/lib/crypt_ops/include.am
index b881c689d..6b0b0d200 100644
--- a/src/lib/crypt_ops/include.am
+++ b/src/lib/crypt_ops/include.am
@@ -14,6 +14,7 @@ src_lib_libtor_crypt_ops_a_SOURCES = \
src/lib/crypt_ops/crypto_ed25519.c \
src/lib/crypt_ops/crypto_format.c \
src/lib/crypt_ops/crypto_hkdf.c \
+ src/lib/crypt_ops/crypto_ope.c \
src/lib/crypt_ops/crypto_openssl_mgt.c \
src/lib/crypt_ops/crypto_pwbox.c \
src/lib/crypt_ops/crypto_rand.c \
@@ -37,6 +38,7 @@ noinst_HEADERS += \
src/lib/crypt_ops/crypto.h \
src/lib/crypt_ops/crypto_hkdf.h \
src/lib/crypt_ops/crypto_openssl_mgt.h \
+ src/lib/crypt_ops/crypto_ope.h \
src/lib/crypt_ops/crypto_pwbox.h \
src/lib/crypt_ops/crypto_rand.h \
src/lib/crypt_ops/crypto_rsa.h \
diff --git a/src/test/include.am b/src/test/include.am
index 7e5ad4611..390c84ebe 100644
--- a/src/test/include.am
+++ b/src/test/include.am
@@ -117,6 +117,7 @@ src_test_test_SOURCES += \
src/test/test_controller.c \
src/test/test_controller_events.c \
src/test/test_crypto.c \
+ src/test/test_crypto_ope.c \
src/test/test_crypto_openssl.c \
src/test/test_data.c \
src/test/test_dir.c \
diff --git a/src/test/ope_ref.py b/src/test/ope_ref.py
new file mode 100644
index 000000000..3677e57a6
--- /dev/null
+++ b/src/test/ope_ref.py
@@ -0,0 +1,40 @@
+#!/usr/bin/python3
+# Copyright 2018, The Tor Project, Inc. See LICENSE for licensing info.
+
+# Reference implementation for our rudimentary OPE code, used to
+# generate test vectors. See crypto_ope.c for more details.
+
+from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+from cryptography.hazmat.primitives.ciphers.algorithms import AES
+from cryptography.hazmat.backends import default_backend
+
+from binascii import a2b_hex
+
+#randomly generated and values.
+KEY = a2b_hex(
+ "19e05891d55232c08c2cad91d612fdb9cbd6691949a0742434a76c80bc6992fe")
+PTS = [ 121132, 82283, 72661, 72941, 123122, 12154, 121574, 11391, 65845,
+ 86301, 61284, 70505, 30438, 60150, 114800, 109403, 21893, 123569,
+ 95617, 48561, 53334, 92746, 7110, 9612, 106958, 46889, 87790, 68878,
+ 47917, 121128, 108602, 28217, 69498, 63870, 57542, 122148, 46254,
+ 42850, 92661, 57720]
+
+IV = b'\x00' * 16
+
+backend = default_backend()
+
+def words():
+ cipher = Cipher(algorithms.AES(KEY), modes.CTR(IV), backend=backend)
+ e = cipher.encryptor()
+ while True:
+ v = e.update(b'\x00\x00')
+ yield v[0] + 256 * v[1] + 1
+
+def encrypt(n):
+ return sum(w for w, _ in zip(words(), range(n)))
+
+def example(n):
+ return ' {{ {}, UINT64_C({}) }},'.format(n, encrypt(n))
+
+for v in PTS:
+ print(example(v))
diff --git a/src/test/test.c b/src/test/test.c
index 1a3f4f8eb..baf9e05be 100644
--- a/src/test/test.c
+++ b/src/test/test.c
@@ -861,6 +861,7 @@ struct testgroup_t testgroups[] = {
{ "control/", controller_tests },
{ "control/event/", controller_event_tests },
{ "crypto/", crypto_tests },
+ { "crypto/ope/", crypto_ope_tests },
{ "crypto/openssl/", crypto_openssl_tests },
{ "dir/", dir_tests },
{ "dir_handle_get/", dir_handle_get_tests },
diff --git a/src/test/test.h b/src/test/test.h
index 9abd46008..b24163ed3 100644
--- a/src/test/test.h
+++ b/src/test/test.h
@@ -212,6 +212,7 @@ extern struct testcase_t container_tests[];
extern struct testcase_t controller_tests[];
extern struct testcase_t controller_event_tests[];
extern struct testcase_t crypto_tests[];
+extern struct testcase_t crypto_ope_tests[];
extern struct testcase_t crypto_openssl_tests[];
extern struct testcase_t dir_tests[];
extern struct testcase_t dir_handle_get_tests[];
diff --git a/src/test/test_crypto_ope.c b/src/test/test_crypto_ope.c
new file mode 100644
index 000000000..1b93e6981
--- /dev/null
+++ b/src/test/test_crypto_ope.c
@@ -0,0 +1,148 @@
+/* Copyright (c) 2001-2004, Roger Dingledine.
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2017, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#include "orconfig.h"
+
+#define CRYPTO_OPE_PRIVATE
+
+#include "lib/crypt_ops/crypto_ope.h"
+#include "common/util_format.h"
+#include "test/test.h"
+
+static void
+test_crypto_ope_consistency(void *arg)
+{
+ (void)arg;
+
+ crypto_ope_t *ope = NULL;
+ crypto_cipher_t *aes = NULL;
+ const int TEST_VALS[] = { 5, 500, 1023, 1024, 1025, 2046, 2047, 2048, 2049,
+ 10000, OPE_INPUT_MAX };
+ unsigned i;
+ const uint8_t key[32] = "A fixed key, chosen arbitrarily.";
+
+ ope = crypto_ope_new(key);
+ tt_assert(ope);
+
+ uint64_t last_val = 0;
+ for (i = 0; i < ARRAY_LENGTH(TEST_VALS); ++i) {
+ aes = ope_get_cipher(ope, 0);
+ int val = TEST_VALS[i];
+ uint64_t v1 = crypto_ope_encrypt(ope, val);
+ uint64_t v2 = sum_values_from_cipher(aes, val);
+ tt_u64_op(v1, OP_EQ, v2);
+ tt_u64_op(v2, OP_GT, last_val);
+ last_val = v2;
+ crypto_cipher_free(aes);
+ }
+
+ done:
+ crypto_cipher_free(aes);
+ crypto_ope_free(ope);
+}
+
+static void
+test_crypto_ope_oob(void *arg)
+{
+ (void)arg;
+
+ crypto_ope_t *ope = NULL;
+ const uint8_t key[32] = "A fixed key, chosen arbitrarily.";
+ ope = crypto_ope_new(key);
+
+ tt_u64_op(UINT64_MAX, OP_EQ, crypto_ope_encrypt(ope,INT_MIN));
+ tt_u64_op(UINT64_MAX, OP_EQ, crypto_ope_encrypt(ope,-100));
+ tt_u64_op(UINT64_MAX, OP_EQ, crypto_ope_encrypt(ope,0));
+ tt_u64_op(UINT64_MAX, OP_NE, crypto_ope_encrypt(ope,1));
+ tt_u64_op(UINT64_MAX, OP_NE, crypto_ope_encrypt(ope,7000));
+ tt_u64_op(UINT64_MAX, OP_NE, crypto_ope_encrypt(ope,OPE_INPUT_MAX));
+ tt_u64_op(UINT64_MAX, OP_EQ, crypto_ope_encrypt(ope,OPE_INPUT_MAX+1));
+ tt_u64_op(UINT64_MAX, OP_EQ, crypto_ope_encrypt(ope,INT_MAX));
+ done:
+ crypto_ope_free(ope);
+}
+
+static const char OPE_TEST_KEY[] =
+ "19e05891d55232c08c2cad91d612fdb9cbd6691949a0742434a76c80bc6992fe";
+
+/* generated by a separate python implementation. */
+static const struct {
+ int v;
+ uint64_t r;
+} OPE_TEST_VECTORS[] = {
+ { 121132, UINT64_C(3971694514) },
+ { 82283, UINT64_C(2695743564) },
+ { 72661, UINT64_C(2381548866) },
+ { 72941, UINT64_C(2390408421) },
+ { 123122, UINT64_C(4036781069) },
+ { 12154, UINT64_C(402067100) },
+ { 121574, UINT64_C(3986197593) },
+ { 11391, UINT64_C(376696838) },
+ { 65845, UINT64_C(2161801517) },
+ { 86301, UINT64_C(2828270975) },
+ { 61284, UINT64_C(2013616892) },
+ { 70505, UINT64_C(2313368870) },
+ { 30438, UINT64_C(1001394664) },
+ { 60150, UINT64_C(1977329668) },
+ { 114800, UINT64_C(3764946628) },
+ { 109403, UINT64_C(3585352477) },
+ { 21893, UINT64_C(721388468) },
+ { 123569, UINT64_C(4051780471) },
+ { 95617, UINT64_C(3134921876) },
+ { 48561, UINT64_C(1597596985) },
+ { 53334, UINT64_C(1753691710) },
+ { 92746, UINT64_C(3040874493) },
+ { 7110, UINT64_C(234966492) },
+ { 9612, UINT64_C(318326551) },
+ { 106958, UINT64_C(3506124249) },
+ { 46889, UINT64_C(1542219146) },
+ { 87790, UINT64_C(2877361609) },
+ { 68878, UINT64_C(2260369112) },
+ { 47917, UINT64_C(1576681737) },
+ { 121128, UINT64_C(3971553290) },
+ { 108602, UINT64_C(3559176081) },
+ { 28217, UINT64_C(929692460) },
+ { 69498, UINT64_C(2280554161) },
+ { 63870, UINT64_C(2098322675) },
+ { 57542, UINT64_C(1891698992) },
+ { 122148, UINT64_C(4004515805) },
+ { 46254, UINT64_C(1521227949) },
+ { 42850, UINT64_C(1408996941) },
+ { 92661, UINT64_C(3037901517) },
+ { 57720, UINT64_C(1897369989) },
+};
+
+static void
+test_crypto_ope_vectors(void *arg)
+{
+ (void)arg;
+ uint8_t key[32];
+ crypto_ope_t *ope = NULL, *ope2 = NULL;
+
+ base16_decode((char*)key, 32, OPE_TEST_KEY, strlen(OPE_TEST_KEY));
+
+ ope = crypto_ope_new(key);
+ key[8] += 1;
+ ope2 = crypto_ope_new(key);
+ unsigned i;
+ for (i = 0; i < ARRAY_LENGTH(OPE_TEST_VECTORS); ++i) {
+ int val = OPE_TEST_VECTORS[i].v;
+ uint64_t res = OPE_TEST_VECTORS[i].r;
+
+ tt_u64_op(crypto_ope_encrypt(ope, val), OP_EQ, res);
+ tt_u64_op(crypto_ope_encrypt(ope2, val), OP_NE, res);
+ }
+ done:
+ crypto_ope_free(ope);
+ crypto_ope_free(ope2);
+}
+
+struct testcase_t crypto_ope_tests[] = {
+ { "consistency", test_crypto_ope_consistency, 0, NULL, NULL },
+ { "oob", test_crypto_ope_oob, 0, NULL, NULL },
+ { "vectors", test_crypto_ope_vectors, 0, NULL, NULL },
+ END_OF_TESTCASES
+};
+
