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#include <stdio.h>
#include <openssl/bio.h>
#include <openssl/rand.h>
int rand_test()
{
char buf[20];
const char* p;
unsigned char outBuf[20];
char file[50];
int ret,len;
BIO *bio_stdout;
//① 方式1
//int RAND_pseudo_bytes(unsigned char *buf, int num);
//RAND_pseudo_bytes() puts num pseudo-random bytes into buf
unsigned char rkey[16];
RAND_pseudo_bytes(rkey, sizeof rkey);
//② 方式2, 最终调用的RAND_bytes产生的随机数。
RAND_screen(); //以屏幕内容作为"seed"产生随机数
strcpy(buf,"");
RAND_add(buf,20,strlen(buf));
strcpy(buf,"23424d");
RAND_seed(buf,20);
while(1)
{
ret=RAND_status();
if(ret==1)
{
printf("seeded enough!\n");
break;
}
else
{
printf("not enough sedded!\n");
RAND_poll();
}
}
/*
RAND_file_name() generates a default path for the random seed file. buf
points to a buffer of size num in which to store the filename. The seed
file is $RANDFILE if that environment variable is set, $HOME/.rnd
otherwise. If $HOME is not set either, or num is too small for the path
name, an error occurs.
*/
p=RAND_file_name(file, sizeof(file));
if(p==NULL)
{
printf("can not get rand file\n");
return -1;
}
/*
RAND_write_file() writes a number of random bytes (currently 1024) to
file filename which can be used to initialize the PRNG by calling
RAND_load_file() in a later session.
*/
ret=RAND_write_file(p);
//PRNG 伪随机数发生器(PRNG)是一个软件，其产生一个被叫做基于一些算法的随机数。
//实际上它不是一个实际的随机数字而是一个伪随机数。最后伪随机数保持对一个度或另一个是可预言的。这个随机数产生器是一个伪随机数产生器。
/*
RAND_load_file() reads a number of bytes from file filename and adds
them to the PRNG. If max_bytes is non-negative, up to to max_bytes are
read; starting with OpenSSL 0.9.5, if max_bytes is -1, the complete
file is read.
*/
len=RAND_load_file(p,1024);
ret=RAND_bytes(outBuf, 20);
if(ret!=1)
{
printf("err.\n");
return -1;
}
bio_stdout=BIO_new(BIO_s_file());
BIO_set_fp(bio_stdout,stdout,BIO_NOCLOSE);
BIO_write(bio_stdout,outBuf,20);
BIO_write(bio_stdout,"\n",2);
BIO_free(bio_stdout);
RAND_cleanup();
return 0;
}
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