Cyberduck Mountain Duck CLI

#10404 closed feature (fixed)

Support for signed SSH certificates

Reported by: jshannon Owned by: dkocher
Priority: normal Milestone: 8.0
Component: sftp Version: 6.6.2
Severity: normal Keywords:
Cc: Architecture:


Please support ssh certs signed by a CA. See

This process produces a file which is signed by the CA and is presented to the server. I've tried selecting that file in CyberDuck and I get message that it's an invalid format.

Change History (4)

comment:1 Changed on Jul 23, 2018 at 9:55:15 AM by dkocher

  • Component changed from core to sftp
  • Owner set to dkocher
  • Summary changed from Support for signed ssh certificates to Support for signed SSH certificates
  • Type changed from enhancement to feature

comment:2 Changed on Aug 30, 2021 at 6:31:19 AM by dkocher

  • Milestone set to 8.0
  • Status changed from new to assigned

comment:3 Changed on Sep 1, 2021 at 10:00:47 AM by dkocher

  • Resolution set to fixed
  • Status changed from assigned to closed

In r51824.

comment:4 Changed on Sep 1, 2021 at 10:01:53 AM by dkocher

     ssh-keygen supports signing of keys to produce certificates that may be used for user or host authentication.  Certificates consist of a public key, some identity information, zero or more principal (user or host) names and a set of
     options that are signed by a Certification Authority (CA) key.  Clients or servers may then trust only the CA key and verify its signature on a certificate rather than trusting many user/host keys.  Note that OpenSSH certificates are a
     different, and much simpler, format to the X.509 certificates used in ssl(8).

     ssh-keygen supports two types of certificates: user and host.  User certificates authenticate users to servers, whereas host certificates authenticate server hosts to users.  To generate a user certificate:

           $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/

     The resultant certificate will be placed in /path/to/  A host certificate requires the -h option:

           $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/

     The host certificate will be output to /path/to/

     It is possible to sign using a CA key stored in a PKCS#11 token by providing the token library using -D and identifying the CA key by providing its public half as an argument to -s:

           $ ssh-keygen -s -D -I key_id

     Similarly, it is possible for the CA key to be hosted in a ssh-agent(1).  This is indicated by the -U flag and, again, the CA key must be identified by its public half.

           $ ssh-keygen -Us -I key_id

     In all cases, key_id is a "key identifier" that is logged by the server when the certificate is used for authentication.

     Certificates may be limited to be valid for a set of principal (user/host) names.  By default, generated certificates are valid for all users or hosts.  To generate a certificate for a specified set of principals:

           $ ssh-keygen -s ca_key -I key_id -n user1,user2
           $ ssh-keygen -s ca_key -I key_id -h -n host.domain

     Additional limitations on the validity and use of user certificates may be specified through certificate options.  A certificate option may disable features of the SSH session, may be valid only when presented from particular source
     addresses or may force the use of a specific command.  For a list of valid certificate options, see the documentation for the -O option above.

     Finally, certificates may be defined with a validity lifetime.  The -V option allows specification of certificate start and end times.  A certificate that is presented at a time outside this range will not be considered valid.  By
     default, certificates are valid from UNIX Epoch to the distant future.

     For certificates to be used for user or host authentication, the CA public key must be trusted by sshd(8) or ssh(1).  Please refer to those manual pages for details.

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