1 files changed, 262 insertions, 0 deletions
diff --git a/src/randombytes.c b/src/randombytes.c
new file mode 100644
index 0000000..105aa58
--- /dev/null
+++ b/src/randombytes.c
@@ -0,0 +1,262 @@
+// In the case that are compiling on linux, we need to define _GNU_SOURCE
+// *before* randombytes.h is included. Otherwise SYS_getrandom will not be
+// declared.
+#if defined(__linux__)
+# define _GNU_SOURCE
+#endif /* defined(__linux__) */
+
+#include "randombytes.h"
+
+#if defined(_WIN32)
+/* Windows */
+# include <windows.h>
+# include <wincrypt.h> /* CryptAcquireContext, CryptGenRandom */
+#endif /* defined(_WIN32) */
+
+
+#if defined(__linux__)
+/* Linux */
+// We would need to include <linux/random.h>, but not every target has access
+// to the linux headers. We only need RNDGETENTCNT, so we instead inline it.
+// RNDGETENTCNT is originally defined in `include/uapi/linux/random.h` in the
+// linux repo.
+# define RNDGETENTCNT 0x80045200
+
+# include <assert.h>
+# include <errno.h>
+# include <fcntl.h>
+# include <poll.h>
+# include <stdint.h>
+# include <sys/ioctl.h>
+# include <sys/stat.h>
+# include <sys/syscall.h>
+# include <sys/types.h>
+# include <unistd.h>
+
+// We need SSIZE_MAX as the maximum read len from /dev/urandom
+# if !defined(SSIZE_MAX)
+#  define SSIZE_MAX (SIZE_MAX / 2 - 1)
+# endif /* defined(SSIZE_MAX) */
+
+#endif /* defined(__linux__) */
+
+
+#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
+/* Dragonfly, FreeBSD, NetBSD, OpenBSD (has arc4random) */
+# include <sys/param.h>
+# if defined(BSD)
+#  include <stdlib.h>
+# endif
+#endif
+
+#if defined(__EMSCRIPTEN__)
+# include <assert.h>
+# include <emscripten.h>
+# include <errno.h>
+# include <stdbool.h>
+#endif /* defined(__EMSCRIPTEN__) */
+
+
+#if defined(_WIN32)
+static int randombytes_win32_randombytes(void* buf, const size_t n)
+{
+	HCRYPTPROV ctx;
+	BOOL tmp;
+
+	tmp = CryptAcquireContext(&ctx, NULL, NULL, PROV_RSA_FULL,
+	                          CRYPT_VERIFYCONTEXT);
+	if (tmp == FALSE) return -1;
+
+	tmp = CryptGenRandom(ctx, n, (BYTE*) buf);
+	if (tmp == FALSE) return -1;
+
+	tmp = CryptReleaseContext(ctx, 0);
+	if (tmp == FALSE) return -1;
+
+	return 0;
+}
+#endif /* defined(_WIN32) */
+
+
+#if defined(__linux__) && defined(SYS_getrandom)
+static int randombytes_linux_randombytes_getrandom(void *buf, size_t n)
+{
+	/* I have thought about using a separate PRF, seeded by getrandom, but
+	 * it turns out that the performance of getrandom is good enough
+	 * (250 MB/s on my laptop).
+	 */
+	size_t offset = 0, chunk;
+	int ret;
+	while (n > 0) {
+		/* getrandom does not allow chunks larger than 33554431 */
+		chunk = n <= 33554431 ? n : 33554431;
+		do {
+			ret = syscall(SYS_getrandom, (char *)buf + offset, chunk, 0);
+		} while (ret == -1 && errno == EINTR);
+		if (ret < 0) return ret;
+		offset += ret;
+		n -= ret;
+	}
+	assert(n == 0);
+	return 0;
+}
+#endif /* defined(__linux__) && defined(SYS_getrandom) */
+
+
+#if defined(__linux__) && !defined(SYS_getrandom)
+static int randombytes_linux_wait_for_entropy(int device)
+{
+	/* We will block on /dev/random, because any increase in the OS' entropy
+	 * level will unblock the request. I use poll here (as does libsodium),
+	 * because we don't *actually* want to read from the device. */
+	const int bits = 128;
+	struct pollfd pfd;
+	int fd;
+	int retcode, retcode_error = 0; // Used as return codes throughout this function
+	int entropy = 0;
+
+	/* If the device has enough entropy already, we will want to return early */
+	retcode = ioctl(device, RNDGETENTCNT, &entropy);
+	if (retcode != 0) {
+		// Unrecoverable ioctl error
+		// TODO(dsprenkels) Use `/proc/sys/kernel/random/entropy_avail`
+		return retcode;
+	}
+	if (entropy >= bits) {
+		return 0;
+	}
+
+	do {
+		fd = open("/dev/random", O_RDONLY);
+	} while (fd == -1 && errno == EINTR); /* EAGAIN will not occur */
+	if (fd == -1) {
+		/* Unrecoverable IO error */
+		return -1;
+	}
+
+	pfd.fd = fd;
+	pfd.events = POLLIN;
+	for (;;) {
+		retcode = poll(&pfd, 1, -1);
+		if (retcode == -1 && (errno == EINTR || errno == EAGAIN)) {
+			continue;
+		} else if (retcode == 1) {
+			retcode = ioctl(device, RNDGETENTCNT, &entropy);
+			if (retcode != 0) {
+				// Unrecoverable ioctl error
+				retcode_error = retcode;
+				break;
+			}
+			if (entropy >= bits) {
+				break;
+			}		
+		} else {
+			// Unreachable: poll() can should only return -1 or 1
+			retcode_error = -1;
+			break;
+		}
+	}
+	do {
+		retcode = close(fd);
+	} while (retcode == -1 && errno == EINTR);
+	if (retcode_error != 0) {
+		return retcode_error;
+	}
+	return retcode;
+}
+
+
+static int randombytes_linux_randombytes_urandom(void *buf, size_t n)
+{
+	int fd;
+	size_t offset = 0, count;
+	ssize_t tmp;
+	do {
+		fd = open("/dev/urandom", O_RDONLY);
+	} while (fd == -1 && errno == EINTR);
+	if (fd == -1) return -1;
+	if (randombytes_linux_wait_for_entropy(fd) == -1) return -1;
+
+	while (n > 0) {
+		count = n <= SSIZE_MAX ? n : SSIZE_MAX;
+		tmp = read(fd, (char *)buf + offset, count);
+		if (tmp == -1 && (errno == EAGAIN || errno == EINTR)) {
+			continue;
+		}
+		if (tmp == -1) return -1; /* Unrecoverable IO error */
+		offset += tmp;
+		n -= tmp;
+	}
+	assert(n == 0);
+	return 0;
+}
+#endif /* defined(__linux__) && !defined(SYS_getrandom) */
+
+
+#if defined(BSD)
+static int randombytes_bsd_randombytes(void *buf, size_t n)
+{
+	arc4random_buf(buf, n);
+	return 0;
+}
+#endif /* defined(BSD) */
+
+
+#if defined(__EMSCRIPTEN__)
+static int randombytes_js_randombytes_nodejs(void *buf, size_t n) {
+	const int ret = EM_ASM_INT({
+		var crypto;
+		try {
+			crypto = require('crypto');
+		} catch (error) {
+			return -2;
+		}
+		try {
+			writeArrayToMemory(crypto.randomBytes($1), $0);
+			return 0;
+		} catch (error) {
+			return -1;
+		}
+	}, buf, n);
+	switch (ret) {
+	case 0:
+		return 0;
+	case -1:
+		errno = EINVAL;
+		return -1;
+	case -2:
+		errno = ENOSYS;
+		return -1;
+	}
+	assert(false); // Unreachable
+}
+#endif /* defined(__EMSCRIPTEN__) */
+
+
+int randombytes(void *buf, size_t n)
+{
+#if defined(__EMSCRIPTEN__)
+# pragma message("Using crypto api from NodeJS")
+	return randombytes_js_randombytes_nodejs(buf, n);
+#elif defined(__linux__)
+# if defined(SYS_getrandom)
+#  pragma message("Using getrandom system call")
+	/* Use getrandom system call */
+	return randombytes_linux_randombytes_getrandom(buf, n);
+# else
+#  pragma message("Using /dev/urandom device")
+	/* When we have enough entropy, we can read from /dev/urandom */
+	return randombytes_linux_randombytes_urandom(buf, n);
+# endif
+#elif defined(BSD)
+# pragma message("Using arc4random system call")
+	/* Use arc4random system call */
+	return randombytes_bsd_randombytes(buf, n);
+#elif defined(_WIN32)
+# pragma message("Using Windows cryptographic API")
+	/* Use windows API */
+	return randombytes_win32_randombytes(buf, n);
+#else
+# error "randombytes(...) is not supported on this platform"
+#endif
+}