[Pgi-wg] OGF PGI - Security Model

[Etienne URBAH]

To All,


In order to handle X509 proxies, we regrettably have to take into 
account both the OpenSSL and GSI implementations of TLS, which are 
incompatible.


So I have updated my 'PGI Security Model' below and at
http://forge.gridforum.org/sf/go/doc15584?nav=1


OGF PGI - Security Model
========================


Current Established Base
========================
Chapters 1, 2 and 3 below describe the current security model of 
Computing Grid Infrastructures.


1) Grid Users and Certificate Authorities
-----------------------------------------
1.1)  Each grid User is authenticated by a legal body (recognized by a 
government).

1.2)  This legal body uses a Certificate Authority to grant a (long 
lived) X509 certificate to the grid User.

1.3)  Each Certificate Authority is itself or is authenticated by a 
self-signed Root Certificate Authority.

1.4)  All such Root Certificate Authorities trust each other and 
cooperate within APGridPMA, EUGridPMA or TAGPMA (Policy Management 
Authorities).

1.5)  These 3 Policy Management Authorities trust each other and 
cooperate within IGTF.

1.6)  IGTF distributes the list of CA Certificates to be trusted.

1.7)  Each grid Site providing grid Services to grid Users installs the 
CA Certificates it deems necessary.  In general, there is no requirement 
to keep them up-to-date, but typically it is considered a security 
update and as such is strongly recommended to apply.  Some 
infrastructures issue warnings for sites with outdated CA certs, but 
normally it does not impede operations.

1.8)  Using its X509 certificate, each grid User can create at any time 
a (usually short lived) X509 proxy with permits impersonation / 
delegation during a (usually short) period.


2)  Virtual Organizations
-------------------------
2.1)  A Virtual Organization (VO) groups grid Users (usually with common 
goals).  A Virtual Organization may be a legal body, and may be a 
Certificate Authority which can issue X509 certificates, but most are NOT.

2.2)  Inside DEISA, a Virtual Community also groups grid Users with 
common goals.  {{{The relationships between Virtual Communities and 
Virtual Organizations have to be explained by Morris RIEDEL}}}

2.3)  Each grid User belongs to 1 or more VO (Virtual Organization), 
which grants him access rights to grid Storage and Computing Resources.

2.4)  Access rights are granted by VOs to grid Users through either :
       2.4.1)  VOMS extensions of X509 proxies (this makes a VOMS proxy)
       2.4.2)  SAML assertions


3)  Grid Services :  Information, AUTHN, AUTHZ
----------------------------------------------
3.1)  Some grid Infrastructures provide an Information Service with 
describes the Infrastructure, for example according to the 'GLUE 1.3' 
schema.

3.2)  If this Information Service exists, then each grid User can query 
it in order to discover the list, requirements and capabilities of grid 
Services.

3.3)  Each grid User can directly access data hosted by grid Storage 
Services.  For Authentication, the grid User can present the public part 
of his X509 certificate or X509 proxy.  For Authorization, the grid User 
has to present either (depending on the Infrastructure) :
       3.3.1)  the public part of his X509 certificate, or
       3.3.2)  the public part of his X509 proxy (without VOMS 
extensions), or
       3.3.3)  the public part of his VOMS proxy, or
       3.3.4)  a bag of SAML assertions.
       In order to handle X509 proxies, both the OpenSSL and GSI 
implementations of TLS are widely used, but they are INCOMPATIBLE.
       If the grid User accesses data through a interface requiring 
delegation, then the next subchapter applies.

3.4)  Each grid User can submit Jobs to grid Computing Services.  If 
such a Job needs access to data hosted by grid Storage Services, then 
the grid User must provide a delegation token.  This delegation token is 
either (depending on the Infrastructure) :
       3.4.1)  an X509 proxy, or
       3.4.2)  a VOMS proxy, or
       3.4.3)  a bag of SAML assertions.  {{{Morris RIEDEL has to 
explain if and how delegation of SAML assertions work}}}

3.5)  Each grid Site providing grid Services to grid Users has installed 
Authorization Files (such as 'gridmap' files) describing VOMS 
authorizations, other authorizations, and mapping of grid credentials to 
local credentials.   Grid Sites try to keep those Authorization Files up 
to date.
       There is a trend to replace these static 'gridmap' files by a 
robust Authorization Service (SCAS by EGEE, GUMS by OSG).



Where we propose to go
======================
Chapters 4, 5, 6 and 7 below describe a security model for short term 
Interoperability between Computing Grid Infrastructures.


4)  Operational Robustness of Security
--------------------------------------
4.1)  The number of Certificate Authorities for grid Infrastructures 
SHOULD be kept as low as possible.


5)  Interoperability between X509 certificates and X509 proxies for 
Authentication
----------------------------------------------------------------------------------
5.1)  For this short term Security Profile aimed at short term 
Interoperability, we accept Shibboleth as an option, but knowingly 
exclude Shibboleth from any requirement.

5.2)  X509 proxies MUST fully comply either to RFC 3820 or to GSI.

5.3)  VOMS services, which deliver X509 proxies with VOMS extensions, 
MUST fully comply either to RFC 3820 or to GSI.

5.4)  The authentication library used by grid Services MUST fully comply 
either to RFC 3820 or to GSI.


6)  Information Service describing the Infrastructure according the the 
GLUE2 schema
------------------------------------------------------------------------------------
6.1)  Each grid Infrastructure MUST provide an Information Service, 
which describes the Infrastructure according the the GLUE2 schema.

6.2)  If access to the Information Service is restricted, the grid 
Infrastructure MUST provide a Bootstrap Information Service, with 
describes the security requirements for access to the full Information 
Service according the the GLUE2 schema.


7)  Interoperable Grid Services :  Information, AUTHN, AUTHZ
------------------------------------------------------------
7.1)  The semantics of Authorization tokens MUST be the same for all 
grid Infrastructures.
       Examples of Authorization tokens are :
       7.1.1)  DN of the X509 certificate or proxy
       7.1.2)  VOMS-style Attribute Certificates
       7.1.3)  Restriction attributes
       7.1.4)  Shibboleth

7.2)  The Information Service of each grid Infrastructure MUST describe, 
for each grid Service, the security requirements for access to the grid 
Service, and which Authorization Tokens this Service expects 
(potentially several).

7.3)  The Information Service of each grid Infrastructure MUST describe 
the transport method that the grid Service expects (potentially several).
       In order to handle X509 proxies, we regrettably have to take into 
account both the OpenSSL and GSI implementations of TLS, which are 
incompatible.

7.4)  Each grid Site providing grid Services to grid Users MUST install 
and keep up to date a robust Authorization Service enforcing VOMS 
authorizations, other authorizations, and mapping of grid credentials to 
local credentials.

7.5)  Each grid Service MUST accept at least :
       7.5.1)  One of the following Authorization Tokens :
               -  DN of the X509 certificate or proxy
               -  X509 VOMS-style Attribute Certificates (VOMS extensions)
                  They are defined in 'VOMS Attribute Certificate 
Format' at http://forge.gridforum.org/sf/go/doc13797?nav=1
               -  X509 restriction attributes
                  {{{Please give the reference of a description document}}}
               -  SAML assertions
                  {{{Please give the reference of a description document}}}
       7.5.2)  One of the following transport methods :
               -  OpenSSL (compliant to RFC 3820) for attributes of X509 
proxies
               -  GSI for attributes of X509 proxies
               -  SOAP header for SAML assertions

7.6)  As long as it satisfies subchapter 7.5, each grid Service MAY also 
accept Authentication and Authorization methods based on Shibboleth.

7.7)  In order to ease the development and deployment of grid Clients, 
each grid Service SHOULD accept following types of Authorization Tokens :
       7.7.1)  X509 VOMS-style Attribute Certificates (VOMS extensions)
       7.7.2)  X509 restriction attributes.
               In the 2 previous cases, the grid Service SHOULD accept 
that they are transported through OpenSSL (compliant to RFC 3820).
               Transport through GSI is explicitly DEPRECATED.
       7.7.3)  SAML assertions.
               In that case, the grid Service SHOULD accept that they 
are transported inside SOAP headers.

7.8)  In order to keep middleware complexity and bandwidth usage as low 
as possible, grid Services should NOT send their full description of 
their security interface inside each message, but only when specifically 
requested (for example by the Information Service).

To be thoroughly criticized ...


Best regards.

----------------------------------
Etienne URBAH          IN2P3 - LAL
Bat 200     91898 ORSAY     France
Tel: +33 1 64 46 84 87
Mob: +33 6 22 30 53 27
Skype: etienne.urbah
mailto:urbah at lal.in2p3.fr
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