148 lines
4.2 KiB
C
148 lines
4.2 KiB
C
/* Statistical tests for arc4random-related functions.
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Copyright (C) 2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <array_length.h>
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#include <stdbool.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <string.h>
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#include <support/check.h>
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enum
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{
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arc4random_key_size = 32
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};
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struct key
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{
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unsigned char data[arc4random_key_size];
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};
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/* With 12,000 keys, the probability that a byte in a predetermined
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position does not have a predetermined value in all generated keys
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is about 4e-21. The probability that this happens with any of the
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16 * 256 possible byte position/values is 1.6e-17. This results in
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an acceptably low false-positive rate. */
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enum { key_count = 12000 };
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static struct key keys[key_count];
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/* Used to perform the distribution check. */
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static int byte_counts[arc4random_key_size][256];
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/* Bail out after this many failures. */
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enum { failure_limit = 100 };
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static void
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find_stuck_bytes (bool (*func) (unsigned char *key))
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{
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memset (&keys, 0xcc, sizeof (keys));
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int failures = 0;
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for (int key = 0; key < key_count; ++key)
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{
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while (true)
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{
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if (func (keys[key].data))
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break;
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++failures;
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if (failures >= failure_limit)
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{
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printf ("warning: bailing out after %d failures\n", failures);
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return;
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}
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}
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}
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printf ("info: key generation finished with %d failures\n", failures);
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memset (&byte_counts, 0, sizeof (byte_counts));
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for (int key = 0; key < key_count; ++key)
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for (int pos = 0; pos < arc4random_key_size; ++pos)
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++byte_counts[pos][keys[key].data[pos]];
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for (int pos = 0; pos < arc4random_key_size; ++pos)
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for (int byte = 0; byte < 256; ++byte)
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if (byte_counts[pos][byte] == 0)
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{
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support_record_failure ();
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printf ("error: byte %d never appeared at position %d\n", byte, pos);
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}
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}
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/* Test adapter for arc4random. */
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static bool
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generate_arc4random (unsigned char *key)
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{
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uint32_t words[arc4random_key_size / 4];
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_Static_assert (sizeof (words) == arc4random_key_size, "sizeof (words)");
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for (int i = 0; i < array_length (words); ++i)
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words[i] = arc4random ();
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memcpy (key, &words, arc4random_key_size);
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return true;
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}
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/* Test adapter for arc4random_buf. */
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static bool
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generate_arc4random_buf (unsigned char *key)
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{
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arc4random_buf (key, arc4random_key_size);
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return true;
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}
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/* Test adapter for arc4random_uniform. */
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static bool
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generate_arc4random_uniform (unsigned char *key)
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{
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for (int i = 0; i < arc4random_key_size; ++i)
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key[i] = arc4random_uniform (256);
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return true;
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}
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/* Test adapter for arc4random_uniform with argument 257. This means
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that byte 0 happens more often, but we do not perform such a
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statistcal check, so the test will still pass */
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static bool
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generate_arc4random_uniform_257 (unsigned char *key)
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{
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for (int i = 0; i < arc4random_key_size; ++i)
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key[i] = arc4random_uniform (257);
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return true;
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}
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static int
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do_test (void)
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{
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puts ("info: arc4random implementation test");
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find_stuck_bytes (generate_arc4random);
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puts ("info: arc4random_buf implementation test");
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find_stuck_bytes (generate_arc4random_buf);
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puts ("info: arc4random_uniform implementation test");
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find_stuck_bytes (generate_arc4random_uniform);
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puts ("info: arc4random_uniform implementation test (257 variant)");
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find_stuck_bytes (generate_arc4random_uniform_257);
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return 0;
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}
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#include <support/test-driver.c>
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