openssl-pkeyutl.pod.in: add that -sign is default op, update claim on…

… hash needed for -sign/-verify, etc.

Reviewed-by: Tomas Mraz <[email protected]>
Reviewed-by: Viktor Dukhovni <[email protected]>
(Merged from openssl#25831)

doc/man1/openssl-pkeyutl.pod.in

@@ -48,6 +48,8 @@ B<openssl> B<pkeyutl>
 This command can be used to perform low-level public key
 operations using any supported algorithm.
 
+By default the signing operation (see B<-sign> option) is assumed.
+
 =head1 OPTIONS
 
 =over 4
@@ -75,8 +77,10 @@ signing or verifying it with the input key. This option could be omitted if the
 signature algorithm does not require one (for instance, EdDSA). If this option
 is omitted but the signature algorithm requires one, a default value will be
 used. For signature algorithms like RSA, DSA and ECDSA, SHA-256 will be the
-default digest algorithm. For SM2, it will be SM3. If this option is present,
-then the B<-rawin> option must be also specified.
+default digest algorithm. For SM2, it will be SM3.
+If this option is present, then the B<-rawin> option must be also specified.
+At this time, HashEdDSA (the ph or "prehash" variant of EdDSA) is not supported,
+so the B<-digest> option cannot be used with EdDSA.
 
 =item B<-out> I<filename>
 
@@ -127,21 +131,26 @@ The input is a certificate containing a public key.
 =item B<-rev>
 
 Reverse the order of the input buffer. This is useful for some libraries
-(such as CryptoAPI) which represent the buffer in little endian format.
+(such as CryptoAPI) which represent the buffer in little-endian format.
+This cannot be used in conjunction with B<-rawin>.
 
 =item B<-sign>
 
-Sign the input data (which must be a hash) and output the signed result. This
-requires a private key.
+Sign the input data and output the signed result. This requires a private key.
+The input data given with the B<-in> option should be a hash value
+unless the use of a message digest operation is implied,
 
 =item B<-verify>
 
-Verify the input data (which must be a hash) against the signature file and
-indicate if the verification succeeded or failed.
+Verify the input data against the signature given with the B<-sigfile> option
+and indicate if the verification succeeded or failed.
+The input data given with the B<-in> option should be a hash value
+unless the use of a message digest operation is implied,
 
 =item B<-verifyrecover>
 
-Verify the input data (which must be a hash) and output the recovered data.
+Verify the input data and output the recovered data.
+The input data given with the B<-in> option should be a hash value.
 
 =item B<-encrypt>