Document RAND library.

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diff --git a/doc/crypto/RAND_set_rand_method.pod b/doc/crypto/RAND_set_rand_method.pod
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+=pod
+
+=head1 NAME
+
+RAND_set_rand_method, RAND_get_rand_method, RAND_SSLeay - Select RAND method
+
+=head1 SYNOPSIS
+
+ #include <openssl/rand.h>
+
+ void RAND_set_rand_method(RAND_METHOD *meth);
+
+ RAND_METHOD *RAND_get_rand_method(void);
+
+ RAND_METHOD *RAND_SSLeay(void);
+
+=head1 DESCRIPTION
+
+A B<RAND_METHOD> specifies the functions that OpenSSL uses for random
+number generation. By modifying the method, alternative
+implementations such as hardware RNGs may be used.  Initially, the
+default is to use the OpenSSL internal implementation. RAND_SSLeay()
+returns a pointer to that method.
+
+RAND_set_rand_method() sets the RAND method to B<meth>.
+RAND_get_rand_method() returns a pointer to the current method.
+
+=head1 THE RAND_METHOD STUCTURE
+
+ typedef struct rand_meth_st
+ {
+        void (*seed)(const void *buf, int num);
+        int (*bytes)(unsigned char *buf, int num);
+        void (*cleanup)(void);
+        void (*add)(const void *buf, int num, int entropy);
+        int (*pseudorand)(unsigned char *buf, int num);
+ } RAND_METHOD;
+
+The components point to the implementation of RAND_seed(),
+RAND_bytes(), RAND_cleanup(), RAND_add() and RAND_pseudo_rand().
+Each component may be NULL if the function is not implemented.
+
+=head1 RETURN VALUES
+
+RAND_set_rand_method() returns no value. RAND_get_rand_method() and
+RAND_SSLeay() return pointers to the respective methods.
+
+=head1 SEE ALSO
+
+rand(3)
+
+=head1 HISTORY
+
+RAND_set_rand_method(), RAND_get_rand_method() and RAND_SSLeay() are
+available in all versions of OpenSSL.
+
+=cut