1RAND_set_rand_method(3)             OpenSSL            RAND_set_rand_method(3)
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NAME

6       RAND_set_rand_method, RAND_get_rand_method, RAND_SSLeay - select RAND
7       method
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SYNOPSIS

10        #include <openssl/rand.h>
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12        void RAND_set_rand_method(const RAND_METHOD *meth);
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14        const RAND_METHOD *RAND_get_rand_method(void);
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16        RAND_METHOD *RAND_SSLeay(void);
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DESCRIPTION

19       A RAND_METHOD specifies the functions that OpenSSL uses for random
20       number generation. By modifying the method, alternative implementations
21       such as hardware RNGs may be used. IMPORTANT: See the NOTES section for
22       important information about how these RAND API functions are affected
23       by the use of ENGINE API calls.
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25       Initially, the default RAND_METHOD is the OpenSSL internal
26       implementation, as returned by RAND_SSLeay().
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28       RAND_set_default_method() makes meth the method for PRNG use. NB: This
29       is true only whilst no ENGINE has been set as a default for RAND, so
30       this function is no longer recommended.
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32       RAND_get_default_method() returns a pointer to the current RAND_METHOD.
33       However, the meaningfulness of this result is dependent on whether the
34       ENGINE API is being used, so this function is no longer recommended.
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THE RAND_METHOD STRUCTURE

37        typedef struct rand_meth_st
38        {
39               void (*seed)(const void *buf, int num);
40               int (*bytes)(unsigned char *buf, int num);
41               void (*cleanup)(void);
42               void (*add)(const void *buf, int num, int entropy);
43               int (*pseudorand)(unsigned char *buf, int num);
44               int (*status)(void);
45        } RAND_METHOD;
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47       The components point to the implementation of RAND_seed(),
48       RAND_bytes(), RAND_cleanup(), RAND_add(), RAND_pseudo_rand() and
49       RAND_status().  Each component may be NULL if the function is not
50       implemented.
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RETURN VALUES

53       RAND_set_rand_method() returns no value. RAND_get_rand_method() and
54       RAND_SSLeay() return pointers to the respective methods.
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NOTES

57       As of version 0.9.7, RAND_METHOD implementations are grouped together
58       with other algorithmic APIs (eg. RSA_METHOD, EVP_CIPHER, etc) in ENGINE
59       modules. If a default ENGINE is specified for RAND functionality using
60       an ENGINE API function, that will override any RAND defaults set using
61       the RAND API (ie.  RAND_set_rand_method()). For this reason, the ENGINE
62       API is the recommended way to control default implementations for use
63       in RAND and other cryptographic algorithms.
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SEE ALSO

66       rand(3), engine(3)
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HISTORY

69       RAND_set_rand_method(), RAND_get_rand_method() and RAND_SSLeay() are
70       available in all versions of OpenSSL.
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72       In the engine version of version 0.9.6, RAND_set_rand_method() was
73       altered to take an ENGINE pointer as its argument. As of version 0.9.7,
74       that has been reverted as the ENGINE API transparently overrides RAND
75       defaults if used, otherwise RAND API functions work as before.
76       RAND_set_rand_engine() was also introduced in version 0.9.7.
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801.0.2o                            2020-01-28           RAND_set_rand_method(3)
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