RSA: add simple getters for commonly used struct members

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6290)

doc/man3/RSA_get0_key.pod

diff --git a/doc/man3/RSA_get0_key.pod b/doc/man3/RSA_get0_key.pod
index 6e6576e..ba25f32 100644
--- a/doc/man3/RSA_get0_key.pod
+++ b/doc/man3/RSA_get0_key.pod
@@ -3,7 +3,10 @@
 =head1 NAME
 
 RSA_set0_key, RSA_set0_factors, RSA_set0_crt_params, RSA_get0_key,
-RSA_get0_factors, RSA_get0_crt_params, RSA_clear_flags,
+RSA_get0_factors, RSA_get0_crt_params,
+RSA_get0_n, RSA_get0_e, RSA_get0_d, RSA_get0_p, RSA_get0_q,
+RSA_get0_dmp1, RSA_get0_dmq1, RSA_get0_iqmp,
+RSA_clear_flags,
 RSA_test_flags, RSA_set_flags, RSA_get0_engine, RSA_get_multi_prime_extra_count,
 RSA_get0_multi_prime_factors, RSA_get0_multi_prime_crt_params,
 RSA_set0_multi_prime_params, RSA_get_version
@@ -22,6 +25,14 @@
  void RSA_get0_crt_params(const RSA *r,
                           const BIGNUM **dmp1, const BIGNUM **dmq1,
                           const BIGNUM **iqmp);
+ const BIGNUM *RSA_get0_n(const RSA *d);
+ const BIGNUM *RSA_get0_e(const RSA *d);
+ const BIGNUM *RSA_get0_d(const RSA *d);
+ const BIGNUM *RSA_get0_p(const RSA *d);
+ const BIGNUM *RSA_get0_q(const RSA *d);
+ const BIGNUM *RSA_get0_dmp1(const RSA *r);
+ const BIGNUM *RSA_get0_dmq1(const RSA *r);
+ const BIGNUM *RSA_get0_iqmp(const RSA *r);
  void RSA_clear_flags(RSA *r, int flags);
  int RSA_test_flags(const RSA *r, int flags);
  void RSA_set_flags(RSA *r, int flags);
@@ -82,6 +93,11 @@
 sets a collect of multi-prime 'triplet' members (prime, exponent and coefficient)
 into an RSA object.
 
+Any of the values B<n>, B<e>, B<d>, B<p>, B<q>, B<dmp1>, B<dmq1>, and B<iqmp> can also be
+retrieved separately by the corresponding function
+RSA_get0_n(), RSA_get0_e(), RSA_get0_d(), RSA_get0_p(), RSA_get0_q(),
+RSA_get0_dmp1(), RSA_get0_dmq1(), and RSA_get0_iqmp(), respectively.
+
 RSA_set_flags() sets the flags in the B<flags> parameter on the RSA
 object. Multiple flags can be passed in one go (bitwise ORed together).
 Any flags that are already set are left set. RSA_test_flags() tests to
@@ -116,6 +132,10 @@
 RSA_set0_key(), RSA_set0_factors(), RSA_set0_crt_params() and
 RSA_set0_multi_prime_params() return 1 on success or 0 on failure.
 
+RSA_get0_n(), RSA_get0_e(), RSA_get0_d(), RSA_get0_p(), RSA_get0_q(),
+RSA_get0_dmp1(), RSA_get0_dmq1(), and RSA_get0_iqmp()
+return the respective value.
+
 RSA_get0_multi_prime_factors() and RSA_get0_multi_prime_crt_params() return
 1 on success or 0 on failure.