DOC: Extend the description of EVP_PKEY_CTX_new_from_name()

This adds text the should lead the user to documentation on different
KEYMGMT implementations.

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/11220)

1 files changed, 27 insertions, 5 deletions

diff --git a/doc/man3/EVP_PKEY_CTX_new.pod b/doc/man3/EVP_PKEY_CTX_new.pod
index 5f8a01242d..327d09f348 100644
--- a/doc/man3/EVP_PKEY_CTX_new.pod
+++ b/doc/man3/EVP_PKEY_CTX_new.pod
@@ -32,7 +32,8 @@ The EVP_PKEY_CTX_new_from_name() function allocates a public key algorithm
 context using the library context I<libctx> (see L<OPENSSL_CTX(3)>), the
 key type specified by I<name> and the property query I<propquery>.  None
 of the arguments are duplicated, so they  must remain unchanged for the
-lifetime of the returned B<EVP_PKEY_CTX> or of any of its duplicates.
+lifetime of the returned B<EVP_PKEY_CTX> or of any of its duplicates.  Read
+further about the possible names in L</NOTES> below.
 
 The EVP_PKEY_CTX_new_from_pkey() function allocates a public key algorithm
 context using the library context I<libctx> (see L<OPENSSL_CTX(3)>) and the
@@ -52,16 +53,14 @@ If I<ctx> is NULL, nothing is done.
 
 =head1 NOTES
 
-=over 4
-
-=item 1.
+=head2 On B<EVP_PKEY_CTX>
 
 The B<EVP_PKEY_CTX> structure is an opaque public key algorithm context used
 by the OpenSSL high level public key API. Contexts B<MUST NOT> be shared between
 threads: that is it is not permissible to use the same context simultaneously
 in two threads.
 
-=item 2.
+=head2 On Key Types
 
 We mention "key type" in this manual, which is the same
 as "algorithm" in most cases, allowing either term to be used
@@ -69,6 +68,29 @@ interchangeably.  There are algorithms where the I<key type> and the
 I<algorithm> of the operations that use the keys are not the same,
 such as EC keys being used for ECDSA and ECDH operations.
 
+Key types are given in two different manners:
+
+=over 4
+
+=item Legacy NID or EVP_PKEY type
+
+This is the I<id> used with EVP_PKEY_CTX_new_id().
+
+These are B<EVP_PKEY_RSA>, B<EVP_PKEY_RSA_PSS>, B<EVP_PKEY_DSA>,
+B<EVP_PKEY_DH>, B<EVP_PKEY_EC>, B<EVP_PKEY_SM2>, B<EVP_PKEY_X25519>,
+B<EVP_PKEY_X448>, and are used by legacy methods.
+
+=item Name strings
+
+This is the I<name> used with EVP_PKEY_CTX_new_from_name().
+
+These are names like "RSA", "DSA", and what's available depends on what
+providers are currently accessible.
+
+The OpenSSL providers offer a set of key types available this way, please
+see L<OSSL_PROVIDER-FIPS(7)> and L<OSSL_PROVIDER-default(7)> and related
+documentation for more information.
+
 =back
 
 =head1 RETURN VALUES