问题描述
我想用的/ dev /随机或的/ dev / urandom的在C.我怎样才能做到这一点？我不知道我该怎么处理它们在C，如果有人知道请告诉我如何。谢谢。
I want to use /dev/random or /dev/urandom in C. How can I do it? I don't know how can I handle them in C, if someone knows please tell me how. Thank you.
推荐答案
在一般情况下，这是一个更好的主意，以避免打开文件获得随机的数据，因为失败的多少分有在程序中。
In general, it's a better idea to avoid opening files to get random data, because of how many points of failure there are in the procedure.
在最近的Linux发行版中，系统调用可用来获取加密安全随机数字，就不能不如果 GRND_RANDOM 是的不是的指定为标志和读取量为至多256个字节。
On recent Linux distributions, the getrandom system call can be used to get crypto-secure random numbers, and it cannot fail if GRND_RANDOM is not specified as a flag and the read amount is at most 256 bytes.
在OpenBSD系统中，<一个href=\"http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man3/arc4random.3?query=arc4random&sec=3\"><$c$c>arc4random家人返回加密安全随机数字，不能失败。不幸的是，很多有一个 arc4random 实现不循经而仍然使用RC4等系统;不要指望加密安全性是跨平台的，请检查您的联机手册。
On OpenBSD, the arc4random family returns crypto-secure random numbers and can't fail. Unfortunately, a lot of other systems that have an arc4random implementation didn't follow through and still use RC4; don't expect the crypto-secure properties to be cross-platform, check your manpages.
否则，您可以使用随机的设备，如果他们的文件。您可以从他们读，你会得到随机数据。我使用打开 / 读在这里，但的fopen / FREAD 将工作一样好。
Otherwise, you can use the random devices as if they were files. You read from them and you get random data. I'm using open/read here, but fopen/fread would work just as well.
int randomData = open("/dev/random", O_RDONLY);
char myRandomData[50];
size_t randomDataLen = 0;
while (randomDataLen < sizeof myRandomData)
{
ssize_t result = read(randomData, myRandomData + randomDataLen, (sizeof myRandomData) - randomDataLen);
if (result < 0)
{
// error, unable to read /dev/random
}
randomDataLen += result;
}
close(randomData);
您可以关闭文件描述符前阅读更多的随机字节，但的/ dev /随机将最终耗尽。一旦这样做，将中止读操作和读将返回多少字节被成功读取。 的/ dev / urandom的不会阻塞或耗尽。 （的/ dev / urandom的也将永远给你你要的字节数，这样你就不会需要大约读循环。）
You may read many more random bytes before closing the file descriptor, although /dev/random will eventually deplete. Once it does, it will abort the reading operation and read will return how many bytes were successfully read. /dev/urandom will never block or deplete. (/dev/urandom will also always give you the number of bytes you asked for, so you wouldn't need the loop around the read.)
与的/ dev /随机和的/ dev / urandom的是 /的区别开发/随机使用从设备驱动程序收集创建随机数的环境噪音。 的/ dev / urandom的返回随机数的根据的关于的/ dev /随机，但它也背后都有一个RNG算法来掩饰在没有熵位都可以从的/ dev /随机。它仍然被认为密码安全，所以一般是用比的/ dev /随机。
The difference between /dev/random and /dev/urandom is that /dev/random uses environmental noise gathered from device drivers to create random numbers. /dev/urandom returns random numbers based on /dev/random, but it also has a RNG algorithm behind it to cover up for when no entropy bits are available from /dev/random. It is still considered cryptographically-secure, and so in general it's a better idea to use it than /dev/random.
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