| 1 | #include <errno.h> |
| 2 | #include <fcntl.h> |
| 3 | #include <limits.h> |
| 4 | #include <stdint.h> |
| 5 | #include <unistd.h> |
| 6 | |
| 7 | #include "warnp.h" |
| 8 | |
| 9 | #include "entropy.h" |
| 10 | |
| 11 | /** |
| 12 | * XXX Portability |
| 13 | * XXX We obtain random bytes from the operating system by opening |
| 14 | * XXX /dev/urandom and reading them from that device; this works on |
| 15 | * XXX modern UNIX-like operating systems but not on systems like |
| 16 | * XXX win32 where there is no concept of /dev/urandom. |
| 17 | */ |
| 18 | |
| 19 | /** |
| 20 | * entropy_read(buf, buflen): |
| 21 | * Fill the given buffer with random bytes provided by the operating system. |
| 22 | */ |
| 23 | int |
| 24 | entropy_read(uint8_t * buf, size_t buflen) |
| 25 | { |
| 26 | int fd; |
| 27 | ssize_t lenread; |
| 28 | |
| 29 | /* Sanity-check the buffer size. */ |
| 30 | if (buflen > SSIZE_MAX) { |
| 31 | warn0("Programmer error: " |
| 32 | "Trying to read insane amount of random data: %zu", |
| 33 | buflen); |
| 34 | goto err0; |
| 35 | } |
| 36 | |
| 37 | /* Open /dev/urandom. */ |
| 38 | if ((fd = open("/dev/urandom", O_RDONLY)) == -1) { |
| 39 | warnp("open(/dev/urandom)"); |
| 40 | goto err0; |
| 41 | } |
| 42 | |
| 43 | /* Read bytes until we have filled the buffer. */ |
| 44 | while (buflen > 0) { |
| 45 | if ((lenread = read(fd, buf, buflen)) == -1) { |
| 46 | warnp("read(/dev/urandom)"); |
| 47 | goto err1; |
| 48 | } |
| 49 | |
| 50 | /* The random device should never EOF. */ |
| 51 | if (lenread == 0) { |
| 52 | warn0("EOF on /dev/urandom?"); |
| 53 | goto err1; |
| 54 | } |
| 55 | |
| 56 | /* We've filled a portion of the buffer. */ |
| 57 | buf += (size_t)lenread; |
| 58 | buflen -= (size_t)lenread; |
| 59 | } |
| 60 | |
| 61 | /* Close the device. */ |
| 62 | while (close(fd) == -1) { |
| 63 | if (errno != EINTR) { |
| 64 | warnp("close(/dev/urandom)"); |
| 65 | goto err0; |
| 66 | } |
| 67 | } |
| 68 | |
| 69 | /* Success! */ |
| 70 | return (0); |
| 71 | |
| 72 | err1: |
| 73 | close(fd); |
| 74 | err0: |
| 75 | /* Failure! */ |
| 76 | return (-1); |
| 77 | } |