RAND_load_file, RAND_write_file, RAND_file_name - PRNG seed file
#include <openssl/rand.h> int RAND_load_file(const char *filename, long max_bytes); int RAND_write_file(const char *filename); const char *RAND_file_name(char *buf, size_t num);
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 max_bytes are read; if max_bytes is -1, the complete file is read. Do not load the same file multiple times unless its contents have been updated by RAND_write_file() between reads. Also, note that filename should be adequately protected so that an attacker cannot replace or examine the contents.
RAND_write_file() writes a number of random bytes (currently 128) to file filename which can be used to initialize the PRNG by calling RAND_load_file() in a later session.
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.
On all systems, if the environment variable RANDFILE is set, its value will be used as the seed file name. Otherwise, the file is called
.rnd, found in platform dependent locations:
- On Windows (in order of preference)
%HOME%, %USERPROFILE%, %SYSTEMROOT%, C:\
- On VMS
- On all other systems
$HOME (on non-Windows and non-VMS system) is not set either, or num is too small for the path name, an error occurs.
RAND_load_file() returns the number of bytes read or -1 on error.
RAND_write_file() returns the number of bytes written, or -1 if the bytes written were generated without appropriate seeding.
RAND_file_name() returns a pointer to buf on success, and NULL on error.
A comment in the source since at least OpenSSL 1.0.2 said that RAND_load_file() and RAND_write_file() were only intended for regular files, and not really device special files such as
/dev/random. This was poorly enforced before OpenSSL 1.1.1.
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