upstream: Add default for number of rounds (-a). ok djm@

OpenBSD-Commit-ID: cb7e9aa04ace01a98e63e4bd77f34a42ab169b15

ssh-keygen.1

@@ -1,4 +1,4 @@
-.\"	$OpenBSD: ssh-keygen.1,v 1.203 2020/04/03 02:26:56 djm Exp $
+.\"	$OpenBSD: ssh-keygen.1,v 1.204 2020/07/15 04:27:34 dtucker Exp $
 .\"
 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -35,7 +35,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: April 3 2020 $
+.Dd $Mdocdate: July 15 2020 $
 .Dt SSH-KEYGEN 1
 .Os
 .Sh NAME
@@ -270,6 +270,7 @@ When saving a private key, this option specifies the number of KDF
 (key derivation function) rounds used.
 Higher numbers result in slower passphrase verification and increased
 resistance to brute-force password cracking (should the keys be stolen).
+The default is 16 rounds.
 .It Fl B
 Show the bubblebabble digest of specified private or public key file.
 .It Fl b Ar bits