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#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <stdint.h>
#include <stdlib.h>
#ifdef _MSC_VER
#include <windows.h>
#include <wincrypt.h>
#else
#include <fcntl.h>
#include <unistd.h>
#endif
#include "warnp.h"
#include "entropy.h"
/**
* XXX Portability
* XXX We obtain random bytes from the operating system by opening
* XXX /dev/urandom and reading them from that device; this works on
* XXX modern UNIX-like operating systems but not on systems like
* XXX win32 where there is no concept of /dev/urandom.
*/
/**
* Entropy reader state. This structure holds OS-dependent state:
* - On Unix: a file descriptor for /dev/urandom
* - On Windows: a cryptographic provider handle
*/
struct entropy_read_cookie {
#ifdef _MSC_VER
HCRYPTPROV hCryptProv;
#else
int fd;
#endif
};
/**
* entropy_read_init(void):
* Initialize the ability to produce random bytes from the operating system,
* and return a cookie.
*/
struct entropy_read_cookie *
entropy_read_init(void)
{
struct entropy_read_cookie * er;
/* Allocate cookie. */
if ((er = malloc(sizeof(struct entropy_read_cookie))) == NULL) {
warnp("malloc");
goto err0;
}
#ifdef _MSC_VER
/* Acquire a cryptographic provider context handle. */
if (!CryptAcquireContext(&er->hCryptProv, NULL, NULL,
PROV_RSA_FULL, CRYPT_VERIFYCONTEXT)) {
warnp("CryptAcquireContext");
goto err1;
}
#else
/* Open /dev/urandom. */
if ((er->fd = open("/dev/urandom", O_RDONLY)) == -1) {
warnp("open(/dev/urandom)");
goto err1;
}
#endif
/* Success! */
return (er);
err1:
free(er);
err0:
/* Failure! */
return (NULL);
}
/**
* entropy_read_fill(er, buf, buflen):
* Fill the given buffer with random bytes provided by the operating system
* using the resources in ${er}.
*/
int
entropy_read_fill(struct entropy_read_cookie * er, uint8_t * buf,
size_t buflen)
{
/* Sanity checks. */
assert(er != NULL);
assert(buflen <= SSIZE_MAX);
#ifdef _MSC_VER
/* Use Windows CryptoAPI to generate random bytes */
if (!CryptGenRandom(er->hCryptProv, (DWORD)buflen, buf)) {
warnp("CryptGenRandom");
goto err0;
}
#else
ssize_t lenread;
/* Read bytes until we have filled the buffer. */
while (buflen > 0) {
if ((lenread = read(er->fd, buf, buflen)) == -1) {
warnp("read(/dev/urandom)");
goto err0;
}
/* The random device should never EOF. */
if (lenread == 0) {
warn0("EOF on /dev/urandom?");
goto err0;
}
/* We've filled a portion of the buffer. */
buf += (size_t)lenread;
buflen -= (size_t)lenread;
}
#endif
/* Success! */
return (0);
err0:
/* Failure! */
return (-1);
}
/**
* entropy_read_done(er):
* Release any resources used by ${er}.
*/
int
entropy_read_done(struct entropy_read_cookie * er)
{
/* Sanity check. */
assert(er != NULL);
#ifdef _MSC_VER
/* Release the cryptographic provider context */
if (!CryptReleaseContext(er->hCryptProv, 0)) {
warnp("CryptReleaseContext");
goto err1;
}
#else
/* Close the device. */
while (close(er->fd) == -1) {
if (errno != EINTR) {
warnp("close(/dev/urandom)");
goto err1;
}
}
#endif
/* Clean up. */
free(er);
/* Success! */
return (0);
err1:
free(er);
/* Failure! */
return (-1);
}
/**
* entropy_read(buf, buflen):
* Fill the given buffer with random bytes provided by the operating system.
*/
int
entropy_read(uint8_t * buf, size_t buflen)
{
struct entropy_read_cookie * er;
/* Sanity-check the buffer size. */
assert(buflen <= SSIZE_MAX);
/* Open /dev/urandom. */
if ((er = entropy_read_init()) == NULL) {
warn0("entropy_read_init");
goto err0;
}
/* Read bytes until we have filled the buffer. */
if (entropy_read_fill(er, buf, buflen)) {
warn0("entropy_read_fill");
goto err1;
}
/* Close the device. */
if (entropy_read_done(er)) {
warn0("entropy_read_done");
goto err0;
}
/* Success! */
return (0);
err1:
entropy_read_done(er);
err0:
/* Failure! */
return (-1);
}
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