Network Working Group P. Hallam-Baker Internet-Draft Comodo Group Inc. Intended status: Informational August 18, 2017 Expires: February 19, 2018 Mathematical Mesh: SSH Application draft-hallambaker-mesh-app-ssh-01 Abstract Mesh/SSH The use of the Mathematical Mesh to manage OpenSSH Keys is described. This document is also available online at http://prismproof.org/Documents/draft-hallambaker-mesh-app-ssh.html . Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on February 19, 2018. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Hallam-Baker Expires February 19, 2018 [Page 1] Internet-Draft Mathematical Mesh: SSH Application August 2017 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2.2. Related Specifications . . . . . . . . . . . . . . . . . 3 2.3. Defined Terms . . . . . . . . . . . . . . . . . . . . . . 3 2.4. Implementation Status . . . . . . . . . . . . . . . . . . 4 3. User Experience . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Initial profile creation . . . . . . . . . . . . . . . . 4 3.2. Configuring SSH for machine X . . . . . . . . . . . . . . 4 3.3. Configuring SSH for machine Y . . . . . . . . . . . . . . 4 3.4. Configuring SSH for machine Z . . . . . . . . . . . . . . 5 3.5. Deleting a Device . . . . . . . . . . . . . . . . . . . . 5 3.6. Future directions . . . . . . . . . . . . . . . . . . . . 5 3.6.1. Native Mesh support in SSH . . . . . . . . . . . . . 5 3.6.2. Update Daemon . . . . . . . . . . . . . . . . . . . . 5 3.6.3. Batched Connection Requests . . . . . . . . . . . . . 6 3.6.4. Enhanced administration . . . . . . . . . . . . . . . 6 4. Platform Bindings . . . . . . . . . . . . . . . . . . . . . . 6 4.1. OpenSSH Files . . . . . . . . . . . . . . . . . . . . . . 6 5. Application Profile . . . . . . . . . . . . . . . . . . . . . 6 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 9.2. Informative References . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction The Secure Shell (SSH) transport layer protocol [!RFC4253] is widely used as a mechanism for securing access to remote hosts. In addition to providing a terminal connection to a remote host, SSH also supports file transfer and remote access (VPN) functionality. It is also used to provide remote procedure call (RPC) capabilities in applications such as Git. While SSH permits a high level of security to be achieved, achieving a high security configuration requires a considerable degree of attention to detail. Numerous ?how to? guides found on the Internet advise the user to engage in many unsafe practices. These include: Hallam-Baker Expires February 19, 2018 [Page 2] Internet-Draft Mathematical Mesh: SSH Application August 2017 Using a single private key for authentication for every machine to be used as a client. Emailing a copy of the authentication key to yourself to transfer it to a new machine. (Alternatively use of insecure FTP, copying the data to /temp, etc.) Of equal concern was the fact that none of the guides mentioned any form of maintenance activity such as deleting authentication keys for a decommissioned device or performing a rekey operation in the case that a device is compromised. Configuring SSH securely is a non-trivial task because SSH is the tool through which the administrator will be connecting to secure their system. This is a bootstrap problem: It is easy to solve the problem of SSH configuration once we have SSH configured for use. To enable SSH access to a The Mathematical Mesh provides an infrastructure for single touch administration of all the devices a user has connected to their Mesh profile. Managing SSH configuration with the Mesh guides the user towards use of a maximally secure configuration. Once the configuration is achieved, it is maintained automatically. 2. Definitions This section presents the related specifications and standard, the terms that are used as terms of art within the documents and the terms used as requirements language. 2.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] [RFC2119] . 2.2. Related Specifications The related specifications are described in the Mesh Architecture specification [draft-hallambaker-mesh-architecture] [draft-hallambaker-mesh-architecture] 2.3. Defined Terms No terms of art are defined. Hallam-Baker Expires February 19, 2018 [Page 3] Internet-Draft Mathematical Mesh: SSH Application August 2017 2.4. Implementation Status The implementation status of the reference code base is described in the companion document [draft-hallambaker-mesh-developer] [draft-hallambaker-mesh-developer] . 3. User Experience Alice is a user of three machines, X, Y and Z. Machines X and Y are configured with monitors and keyboards enabling their use as an SSH client. Machine Z is to be configured as a headless machine (no monitor). When finished, Alice wants to be able to connect to machines X, Y or Z from machine X or Y. Since SSH is a tool principally used on UNIX based systems and machines configured to provide similar behavior, this guide assumes machines X, Y and Z are all UNIX systems when describing the files to be modified. When used on a Windows machine, the Mesh tools configure the equivalent Windows files. 3.1. Initial profile creation If this is the first time Alice has used the Mesh, she creates a personal profile for herself on machine X: X> meshman /personal alice@mesh.prismproof.org 3.2. Configuring SSH for machine X To configure SSH on machine X, Alice adds it to her profile. X> meshman /ssh Note that the meshman tool only performs the At this point, Alice has a new private key that is unique to machine X and the corresponding public key has been added to her profile 3.3. Configuring SSH for machine Y To configure the second machine, Alice first requests adding it to her profile: Y> This request must be accepted on machine X: X> Hallam-Baker Expires February 19, 2018 [Page 4] Internet-Draft Mathematical Mesh: SSH Application August 2017 Alice now adds the SSH profile to machine Y: Y> meshman /ssh At this point machines X and Y both have a unique private key and both the corresponding public keys have been added to the authorized key files on Y. The authorized key file on X will be updated by a mesh profile manager running periodically. 3.4. Configuring SSH for machine Z Configuration of machine Z begins in exactly the same way as for machine Y. The only difference is that when she creates the SSH profile for the device, she requests it be a host only profile: Z> meshman /ssh /host 3.5. Deleting a Device 3.6. Future directions 3.6.1. Native Mesh support in SSH The chief weakness in this user experience is that the machines cannot update themselves automatically or even know when an update is required. The only approach that is available is for the host devices to periodically poll the Mesh portal and request updates for the registered profiles. This delay can be avoided if the SSH protocol and implementations were updated to support direct use of Mesh profiles. This allows a client to push the updated profile data to the server when making the connection attempt. 3.6.2. Update Daemon Native support allows the process of adding devices to be automated but does not guarantee timely processing of deletion requests. It also requires action by third parties who may not be interested in providing Mesh support. A better approach would be to run a daemon on each machine that could receive update notifications from the portal whenever a significant event (profile addition/deletion) had occurred. Hallam-Baker Expires February 19, 2018 [Page 5] Internet-Draft Mathematical Mesh: SSH Application August 2017 3.6.3. Batched Connection Requests The existing management tools require a device to be connected to a profile before use of applications are enabled on the device. 3.6.4. Enhanced administration While this approach is functional, it does not meet the requirement for complete mediation of the log in request. While the system administrator has the ability to permit or deny remote access capabilities to a user, these are the only options that the administration tools currently supported by most SSH configurations provide. The administrator cannot control the types of credentials used by specific users. The Mesh could be employed to permit a closer level of control. Storing the user?s profile fingerprint in the password database (/etc/passwd or /etc/shadow) would allow every application and system utility to refer to a single root of trust for authenticating every credential presented by a user. 4. Platform Bindings Since SSH is an application program 4.1. OpenSSH Files Contains a list of all the keys that are authorized to access the corresponding account. This is a list of Mesh SSH per device application keys. Default name for the user?s RSA public key Default name for the user?s RSA private key List of host keys known to this user. 5. Application Profile 6. Acknowledgements 7. Security Considerations [This is just a sketch for the present.] Hallam-Baker Expires February 19, 2018 [Page 6] Internet-Draft Mathematical Mesh: SSH Application August 2017 8. IANA Considerations [TBS list out all the code points that require an IANA registration] 9. References 9.1. Normative References [draft-hallambaker-mesh-architecture] Hallam-Baker, P., "Mathematical Mesh: Architecture", draft-hallambaker-mesh-architecture-03 (work in progress), May 2017. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. 9.2. Informative References [draft-hallambaker-mesh-developer] Hallam-Baker, P., "Mathematical Mesh: Developer's Guide", draft-hallambaker-mesh-developer-02 (work in progress), September 2016. Author's Address Phillip Hallam-Baker Comodo Group Inc. Email: philliph@comodo.com Hallam-Baker Expires February 19, 2018 [Page 7]