First public release
This commit is contained in:
ben
262
src/randombytes.c
Normal file
262
src/randombytes.c
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// In the case that are compiling on linux, we need to define _GNU_SOURCE
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// *before* randombytes.h is included. Otherwise SYS_getrandom will not be
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// declared.
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#if defined(__linux__)
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# define _GNU_SOURCE
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#endif /* defined(__linux__) */
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#include "randombytes.h"
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#if defined(_WIN32)
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/* Windows */
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# include <windows.h>
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# include <wincrypt.h> /* CryptAcquireContext, CryptGenRandom */
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#endif /* defined(_WIN32) */
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#if defined(__linux__)
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/* Linux */
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// We would need to include <linux/random.h>, but not every target has access
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// to the linux headers. We only need RNDGETENTCNT, so we instead inline it.
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// RNDGETENTCNT is originally defined in `include/uapi/linux/random.h` in the
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// linux repo.
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# define RNDGETENTCNT 0x80045200
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# include <assert.h>
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# include <errno.h>
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# include <fcntl.h>
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# include <poll.h>
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# include <stdint.h>
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# include <sys/ioctl.h>
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# include <sys/stat.h>
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# include <sys/syscall.h>
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# include <sys/types.h>
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# include <unistd.h>
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// We need SSIZE_MAX as the maximum read len from /dev/urandom
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# if !defined(SSIZE_MAX)
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# define SSIZE_MAX (SIZE_MAX / 2 - 1)
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# endif /* defined(SSIZE_MAX) */
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#endif /* defined(__linux__) */
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#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
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/* Dragonfly, FreeBSD, NetBSD, OpenBSD (has arc4random) */
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# include <sys/param.h>
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# if defined(BSD)
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# include <stdlib.h>
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# endif
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#endif
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#if defined(__EMSCRIPTEN__)
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# include <assert.h>
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# include <emscripten.h>
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# include <errno.h>
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# include <stdbool.h>
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#endif /* defined(__EMSCRIPTEN__) */
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#if defined(_WIN32)
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static int randombytes_win32_randombytes(void* buf, const size_t n)
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{
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HCRYPTPROV ctx;
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BOOL tmp;
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tmp = CryptAcquireContext(&ctx, NULL, NULL, PROV_RSA_FULL,
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CRYPT_VERIFYCONTEXT);
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if (tmp == FALSE) return -1;
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tmp = CryptGenRandom(ctx, n, (BYTE*) buf);
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if (tmp == FALSE) return -1;
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tmp = CryptReleaseContext(ctx, 0);
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if (tmp == FALSE) return -1;
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return 0;
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}
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#endif /* defined(_WIN32) */
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#if defined(__linux__) && defined(SYS_getrandom)
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static int randombytes_linux_randombytes_getrandom(void *buf, size_t n)
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{
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/* I have thought about using a separate PRF, seeded by getrandom, but
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* it turns out that the performance of getrandom is good enough
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* (250 MB/s on my laptop).
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*/
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size_t offset = 0, chunk;
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int ret;
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while (n > 0) {
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/* getrandom does not allow chunks larger than 33554431 */
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chunk = n <= 33554431 ? n : 33554431;
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do {
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ret = syscall(SYS_getrandom, (char *)buf + offset, chunk, 0);
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} while (ret == -1 && errno == EINTR);
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if (ret < 0) return ret;
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offset += ret;
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n -= ret;
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}
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assert(n == 0);
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return 0;
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}
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#endif /* defined(__linux__) && defined(SYS_getrandom) */
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#if defined(__linux__) && !defined(SYS_getrandom)
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static int randombytes_linux_wait_for_entropy(int device)
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{
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/* We will block on /dev/random, because any increase in the OS' entropy
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* level will unblock the request. I use poll here (as does libsodium),
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* because we don't *actually* want to read from the device. */
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const int bits = 128;
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struct pollfd pfd;
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int fd;
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int retcode, retcode_error = 0; // Used as return codes throughout this function
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int entropy = 0;
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/* If the device has enough entropy already, we will want to return early */
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retcode = ioctl(device, RNDGETENTCNT, &entropy);
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if (retcode != 0) {
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// Unrecoverable ioctl error
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// TODO(dsprenkels) Use `/proc/sys/kernel/random/entropy_avail`
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return retcode;
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}
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if (entropy >= bits) {
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return 0;
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}
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do {
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fd = open("/dev/random", O_RDONLY);
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} while (fd == -1 && errno == EINTR); /* EAGAIN will not occur */
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if (fd == -1) {
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/* Unrecoverable IO error */
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return -1;
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}
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pfd.fd = fd;
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pfd.events = POLLIN;
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for (;;) {
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retcode = poll(&pfd, 1, -1);
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if (retcode == -1 && (errno == EINTR || errno == EAGAIN)) {
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continue;
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} else if (retcode == 1) {
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retcode = ioctl(device, RNDGETENTCNT, &entropy);
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if (retcode != 0) {
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// Unrecoverable ioctl error
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retcode_error = retcode;
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break;
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}
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if (entropy >= bits) {
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break;
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}
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} else {
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// Unreachable: poll() can should only return -1 or 1
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retcode_error = -1;
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break;
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}
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}
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do {
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retcode = close(fd);
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} while (retcode == -1 && errno == EINTR);
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if (retcode_error != 0) {
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return retcode_error;
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}
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return retcode;
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}
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static int randombytes_linux_randombytes_urandom(void *buf, size_t n)
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{
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int fd;
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size_t offset = 0, count;
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ssize_t tmp;
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do {
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fd = open("/dev/urandom", O_RDONLY);
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} while (fd == -1 && errno == EINTR);
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if (fd == -1) return -1;
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if (randombytes_linux_wait_for_entropy(fd) == -1) return -1;
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while (n > 0) {
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count = n <= SSIZE_MAX ? n : SSIZE_MAX;
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tmp = read(fd, (char *)buf + offset, count);
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if (tmp == -1 && (errno == EAGAIN || errno == EINTR)) {
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continue;
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}
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if (tmp == -1) return -1; /* Unrecoverable IO error */
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offset += tmp;
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n -= tmp;
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}
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assert(n == 0);
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return 0;
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}
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#endif /* defined(__linux__) && !defined(SYS_getrandom) */
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#if defined(BSD)
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static int randombytes_bsd_randombytes(void *buf, size_t n)
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{
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arc4random_buf(buf, n);
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return 0;
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}
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#endif /* defined(BSD) */
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#if defined(__EMSCRIPTEN__)
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static int randombytes_js_randombytes_nodejs(void *buf, size_t n) {
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const int ret = EM_ASM_INT({
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var crypto;
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try {
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crypto = require('crypto');
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} catch (error) {
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return -2;
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}
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try {
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writeArrayToMemory(crypto.randomBytes($1), $0);
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return 0;
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} catch (error) {
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return -1;
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}
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}, buf, n);
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switch (ret) {
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case 0:
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return 0;
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case -1:
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errno = EINVAL;
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return -1;
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case -2:
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errno = ENOSYS;
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return -1;
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}
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assert(false); // Unreachable
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}
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#endif /* defined(__EMSCRIPTEN__) */
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int randombytes(void *buf, size_t n)
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{
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#if defined(__EMSCRIPTEN__)
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# pragma message("Using crypto api from NodeJS")
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return randombytes_js_randombytes_nodejs(buf, n);
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#elif defined(__linux__)
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# if defined(SYS_getrandom)
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# pragma message("Using getrandom system call")
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/* Use getrandom system call */
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return randombytes_linux_randombytes_getrandom(buf, n);
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# else
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# pragma message("Using /dev/urandom device")
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/* When we have enough entropy, we can read from /dev/urandom */
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return randombytes_linux_randombytes_urandom(buf, n);
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# endif
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#elif defined(BSD)
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# pragma message("Using arc4random system call")
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/* Use arc4random system call */
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return randombytes_bsd_randombytes(buf, n);
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#elif defined(_WIN32)
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# pragma message("Using Windows cryptographic API")
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/* Use windows API */
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return randombytes_win32_randombytes(buf, n);
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#else
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# error "randombytes(...) is not supported on this platform"
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#endif
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}
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