upstream: When signing certificates with an RSA key, default to

using the rsa-sha2-512 signature algorithm. Certificates signed by RSA keys
will therefore be incompatible with OpenSSH < 7.2 unless the default is
overridden.

Document the ability of the ssh-keygen -t flag to override the
signature algorithm when signing certificates, and the new default.

ok deraadt@

OpenBSD-Commit-ID: 400c9c15013978204c2cb80f294b03ae4cfc8b95

1 files changed, 11 insertions, 2 deletions

diff --git a/ssh-keygen.1 b/ssh-keygen.1
index f29774249..673bf6e2f 100644
--- a/ssh-keygen.1
+++ b/ssh-keygen.1
@@ -1,4 +1,4 @@
-.\"     $OpenBSD: ssh-keygen.1,v 1.158 2019/04/19 05:47:44 dtucker Exp $
+.\"     $OpenBSD: ssh-keygen.1,v 1.159 2019/05/20 00:20:35 djm 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 19 2019 $
+.Dd $Mdocdate: May 20 2019 $
 .Dt SSH-KEYGEN 1
 .Os
 .Sh NAME
@@ -577,6 +577,15 @@ The possible values are
 .Dq ed25519 ,
 or
 .Dq rsa .
+.Pp
+This flag may also be used to specify the desired signature type when
+signing certificates using a RSA CA key.
+The available RSA signature variants are
+.Dq ssh-rsa
+(SHA1 signatures, not recommended),
+.Dq rsa-sha2-256
+.Dq rsa-sha2-512
+(the default).
 .It Fl U
 When used in combination with
 .Fl s ,