security mechanisms the european datagrid project team

Security Mechanisms

The European DataGrid Project Team

http://www.eu-datagrid.org

Security Tutorial - n° 2Torino, 5-6/12/02

Contents

Concepts of Cryptography

Digital Certificates

Security problems (and solution) of the Grid

EDG user authentication (practical guide)

EDG authorization (overview)


Security Needs

Authentication establish the identity of an entity (user, process, host,

service, ...)

Confidentiality a third party cannot understand the communication

Integrity data is not modified during communication

Non-repudiation the sender cannot claim he didn’t send the data

Authorization establish the rights of the entity


Cryptography

Mathematical tool that provides some important building blocks for the implementation of a security infrastructure

Terminology

Plaintext: M

Cyphertext: C

Encryption with key K1 : E K1(M) = C

Decryption with key K2 : D K2(C) = M

Algorithms

Symmetric: K1 = K2

Public Key (asymmetric): K1 ≠ K2

K2K1

EncryptionEncryption DecryptionDecryptionM C M


Symmetric Algoritms

The same key is used for encryption and decryption

fast how to distribute the keys? the number of keys is O(n2)

Examples: DES 3DES Rijndael (AES) Blowfish

A B

ciao

3$r ciao

A B

ciao

3$r ciao

3$r

3$r


Public Key Algorithms Every user has two keys: one

private and one public: it is practically impossible to

derive the private key from the public one;

a message encrypted by one key can be decripted only by the other one.

No exchange of secrets is necessary

the sender cyphers using the public key of the receiver;

the receiver decripts using his private key;

the number of keys is O(n).

Examples: Diffie-Helmann (1977) RSA (1978)

B’s keys

public private

A’s keys

public private

A B

ciao

3$r ciao

A B

ciao

cy7 ciao

3$r

cy7


One-Way Hash Functions

Functions (H) that given as input a variable-length message (M) produce as output a string of fixed length (h) the length of h must be at least 128 bits (to avoid birthday

attacks)

1. given M, it must be easy to calculate H(M) = h

2. given h, it must be difficult to calculateM = H-1(h)

3. given M, it must be difficult to find M’ such that H(M) = H(M’)

Examples: SNEFRU: hash of 128 or 256 bits; MD4/MD5: hash of 128 bits; SHA (Standard FIPS): hash of 160 bits.


Digital Signature A calculates the hash of the

message and he encrypts it using his private key: the encrypted hash is the digital signature.

A sends the signed message to B.

B calculates the hash of the message and verifies it with the one received by A and decyphered with A’s pubblic key.

If the thwo hashes are equal, the message wasn’t modified and A cannot repudiate it.

A’s keys

public private

B

hash (B)

hash (A)

= ?

ciao

A

ciao ciaohash (A)


Digital Certificates

A’s digital signature is safe if:

1. A’s private key is not compromised

2. B knows A’s public key

How can B be sure that A’s public key is really A’s public key and not someone else’s? A third party guarantees the correspondence between public

key and owner’s identity, by signing a document which contains the owner’s identity and his public key (Digital Certificate)

Both A and B must trust this third party

Two models: X.509: hierarchical organization; PGP: “web of trust”.


PGP “web of trust”

A

B

C

D

E

F

F knows D and E, who knows A and C, who knows A and B.

F is reasonably sure that the key from A is really from A.


X.509 Certificates

The “third party” is called Certification Authority (CA).

An X.509 Certificate contains: identity of the owner; time of validity; owner’s public key; info on the Certification Authority; digital signature of the Certification Authority.

Certificates are published in a directory (e.g. LDAP or WWW) managed by the CA

CA’s periodically publish a list of compromised certificates

Certificate Revocation Lists (CRL) Online Certificate Status Protocol (OCSP).


Certificate Chains

Per: INFN CA

Firma: INFN CA

Per: Verisign

Firma: Verisign

Per: AltraCA

Firma: Verisign

Per:Leo

Firma:AltraCA

Per:Silvia

Firma:AltraCA

Per:Carlo

Firma:INFNCA

CA’s have their own certificates, too.

A CA can guarantee for other CA’s by signing their certificates

At the top there is a self-signed certificate (root certificate).

CA certificate are widely publicized and so difficult to forge.


The problems of grid security The user population is large and dynamic

the same user will have different credentials and accounts at different sites;

the same user may have a regular account at some site, while at others a dynamically assigned one

Users want to authenticate themselves to the Grid only once (single sign-on)

The resources being used may be valuable.

The data to process may be sensitive (e.g. medical data).

The set of resources required by a process may be large, dynamic, and unpredictable.

Resources may belong to different administrative domains, each with its own specific policies.

Security mechanisms must not override local policies.


Grid Security Infrastructure (GSI)

Based on an X.509 PKI: every user/host/service has an X.509 certificate; certificates are signed by trusted (by the local sites) CA’s; every Grid transaction is mutually authenticated:

1. user sends his certificate;

2. other end sends user a challenge string;

3. user encodes the challenge string with his private key;

4. the public key is used to decode the challenge.

Private keys must be stored only in protected places, and only in encrypted form.


X.509 Proxy Certificate

A Proxy is a special type of X.509 certificate, signed by the normal end entity cert (or by another proxy).

It allows process to act on behalf of user, supporting single sign-on and delegation

if there is a need to have agents requesting services on behalf of the user, avoids the need to re-enter the user's pass phrase

the Subject of the proxy contains the Subject of the signing cert

It reduces exposure of user’s private key

It is created by the grid-proxy-init command

The private key of the Proxy is not encrypted: stored in local file protected by file system security: must be

readable only by the owner; proxy lifetime is short (typically 12 h) to minimize security

risks.


Delegation Proxy creation can be recursive

each time a new private key and new X.509 proxy certificate, signed by the original key

Allows remote process to act on behalf of the user

Avoids sending passwords or private keys across the network

The proxy may be a “Restricted Proxy”: a proxy with a reduced set of privileges (e.g. cannot submit jobs).


Site A(Kerberos)

Site A(Kerberos)

Site B (Unix)

Site B (Unix)

GSI interface GSI interface

Remote processcreation

requests*

* with mutual authentication

Site C(Kerberos)

Site C(Kerberos)

User

Single sign-on& generation of proxy cred. User Proxy

Proxycredential

Storagesystem

Communication*

GSI-enabledFTP server

AuthorizeMap to local idAccess file

Remote fileaccess

request*

Process

Kerberosticket

Restrictedproxy

Process

Restrictedproxy

Local id

Local id

AuthorizeMap to local idCreate processGenerate credentials

AuthorizeMap to local idCreate process

Generate credentials

Job Execution

from The Globus Toolkit™:Security Services, http://www.globus.org/

from The Globus Toolkit™:Security Services, http://www.globus.org/

Or: retrieval of proxy cred.

from online repository


Authentication/Authorization

Authentication 16 national certification authorities

+ CrossGrid CA’s policies & procedures mutual trust users identified by certificates

Authorization Based on Virtual Organizations (VO). Management tools for

VO membership lists. 10+2 Virtual Organizations

VO’s

ALICE Earth Obs.

ATLAS Biomedical

BaBar D0

Genomics

Medical Im.

CMS Testbed

LHCb Tutorial

CA’s

CERN

CESNET

CNRS (3)

GermanGrid

Grid-Ireland

INFN

NIKHEF

NorduGrid

LIP

Russian DataGrid

DATAGRID-ES

GridPP (UK)

US–DOE Root CA

US-DOE Sub CA

CrossGrid (*)


EDG AA Overview

User requests a certificate from his CA [yearly]

User registers himself in the EDG LDAP-VO [once]

User generates a proxy certificate (short lifetime) [daily]

Host/service requests a certificate [yearly]

Local site retrieves the trusted CA’s certificates [periodically] and their CRL’s [daily]

Local site generates a gridmap-file from the LDAP database for authorization and mapping [daily]

User contacts a service: they exchange their certificates to authenticate each other; the service bases its authorization decision on the gridmap-file


Requesting a certificate (batch)

grid-cert-requestA certificate request and private key is being created.[...]Using configuration from /usr/local/grid/globus/etc/globus-user-ssleay.confGenerating a 1024 bit RSA private key[...]A private key and a certificate request has been generated with the subject:/O=Grid/O=CERN/OU=cern.ch/CN=Akos Frohner[...]Your private key is stored in .../.globus/userkey.pemYour request is stored in .../.globus/usercert_request.pemPlease e-mail the certificate request to the CERN CA

cat .../.globus/usercert_request.pem | mail [email protected]

Your certificate will be mailed to you within two working days.


Requesting a certificate (online)

Online procedure: donwload your CA certificate; fill the online request form; wait for the identity check by the CA; download the certificate.

Protect the certificate.

Export the certificate and make a backup copy.


Download the INFN CA cert 1/2

http://security.fi.infn.it/CA/

Click on Certificato INFN CA

ignore warning messages about connecting to an unknow site...

Click on Scarica Certificato


Download the INFN CA cert 2/2

Netscape: select all the three

options

Explorer: save with

extension .der double-click on the file

name and click on Installa certificato

choose the default answer in all the following questions

Verify that the certificate is among the “root certificates”

Explore

r

Netscap

e


Fill the online request form

http://security.fi.infn.it/CA/

Click on Richiesta certificati

Fill the details of the owner: Nome sezione; Nome e Cognome; E-mail, it must be the official

one, [email protected].

Click on Sottometti Richiesta.

After the identity checks, you’ll receive an e-mail with the instructions for the download.


Download the certificate

Open the URL in the mail from INFN-CA with the same browser used to submit the request

Verify that the certificate appears in the browser DB

Netscape


Protect the certificate

Your certificate must be password protected to avoid unauthorized use

Netscape


Export the certificate

Export the certificate (extension .p12) and save a copy on a floppy (two is better...).The copy can be imported in another browser.

Protect the copy with a good password (it will be asked during the export procedure)

Convert the certificatefor use by the globus toolkit: openssl pkcs12 -nocerts\ –in user.p12 \ –out ~/.globus/userkey.pem openssl pkcs12 –clcerts \ -nokeys \ –out ~/.globus/usercert.pem

Netscap

e

Explore

r


Registration Users must accept the EDG

usage guidelines and be registered in an EDG VO

If you don’t have your certificate in a browser:

convert the certificateopenssl pkcs12 –export \ –in ~/.globus/usercert.pem \ –inkey ~/.globus/userkey.pem \ –out user.p12 –name ’M. Rossi’

import your certificate in your browser

Sign the usage guidelines open the following URL

and click on “Accept”: https://marianne.in2p3.fr/cgi-bin/datagrid/register/account.pl

Ask an account from your VO administrator.


Starting a grid session „login”:grid-proxy-initYour identity: /C=IT/O=INFN/CN=M.Rossi/[email protected] GRID pass phrase for this identity: *********Creating proxy ........................................ DoneYour proxy is valid until Fri Nov 29 02:44:51 2002

the proxy is stored in /tmp/x509up_uxxx

You can now use use the grid services.

„logout”:grid-proxy-destroy


Proxy certificate structure

openssl x509 -text -noout -in /tmp/x509up_u504 Data: Version: 3 (0x2) Serial Number: 981 (0x3d5) Signature Algorithm: md5WithRSAEncryption Issuer: C=IT,O=INFN,CN=M.Rossi/[email protected] Validity Not Before: Nov 28 14:14:57 2002 GMT Not After : Nov 29 02:19:57 2002 GMT Subject: C=IT,O=INFN,CN=M.Rossi/[email protected], CN=proxy Subject Public Key Info: Public Key Algorithm: rsaEncryption RSA Public Key: (512 bit) Modulus (512 bit): ...................................... Exponent: 65537 (0x10001) Signature Algorithm: md5WithRSAEncryption ......................................


Authorization: the present Based on VO LDAP servers

Each VO manages an LDAP Directory Only groups provided, no roles Secure web interface for EDG AUP signing

Mapping X509 credentials user at local site Each site periodically generates (mkgridmap) a “grid-

mapfile” (mapping DN username). Dynamic mapping available (gridmapdir). Mapping customizable by the local site managers.


grid-mapfile generationo=testbed,dc=eu-datagrid, dc=org

CN=Franz Elmer

ou=People

CN=John Smith

mkgridmap

grid-mapfile

VOVODirectoryDirectory

““AuthorizatioAuthorizationn

Directory”Directory”

CN=Mario Rossi

o=xyz,dc=eu-datagrid, dc=org

CN=Franz ElmerCN=John Smith

Authentication Certificate



ou=People

ou=Testbed1

ou=???

local users ban list


Authorization: the future Virtual Organization Membership Service (VOMS)

Grants authorization data to users at VO level Each VO has its own VOMS

Local Centre Authorization Service (LCAS) Handles authorization requests to local fabric

Local Credential Mapping Service (LCMAPS) Provides local credentials needed for jobs in fabric

Grid ACL (GACL) library Provides DN based ACL’s


VOMS Operations

Authentication

Request

AuthDB

C=IT/O=INFN /L=CNAF/CN=Pinco Palla/CN=proxy

User’sattribu

tes

User’sattribut

es

1. Mutual authentication Client-Server

2. Client sends request to Server

3. Server checks correctness of request

4. Server sends back the required info, signed by itself

5. Client repeats process for other VOMS’s

6. Client creates a proxy certificate containing all the info received into a (non critical) extension


LCAS / LCMAPS LCAS

Handles authorization requests to local fabric Authorization decisions based on proxy user certificate and

job specification Supports gridmap-file mechanism Plug-in framework (hooks for external authorization plug-ins)

LCMAPS Provides local credentials needed for jobs in fabric

Accepts requests validated by LCAS Returns, if any, local credentials already assigned to user or

generates new ones.

Replaces gridmap(dir), but keeps functionality


EDG gatekeeper

TLS auth

LCAS (so)

assist_gridmap

Jobmanager-*

Gatekeeper

TLS auth

LCAS client

apply creds *

Jobmanager-*

Gatekeeper LCAS

ACL

timeslot

gridmap

config

LCMAPS clntLCMAPS

role2uid

role2afs

config

* And store in job repository

Id

Yes/no

Id

credlist

NOW EDG1.4, EDG2.x

By Martijn Steenbakkers (EDG WP4)


Further Information

Grid

EDG CAs: http://marianne.in2p3.fr/datagrid/ca

EDG Security Requirements: http://edms.cern.ch/document/340234

GGF Security Area: http://www.gridforum.org/security/

Grid Security Infrastructure (GSI): http://www.globus.org/security/

Background

Bruce Schneier,Applied Cryptography: Protocols, Algorithms and Source Code in C, John Wiley & Sons.

Generic Security Services Application Programming Interface (GSSAPI): http://www.faqs.org/faqs/kerberos-faq/general/section-84.html

S. Tuecke et al., Internet X.509 Public Key Infrastructure Proxy Certificate Profile, draft-ietf-pkix-proxy-03.

security mechanisms the european datagrid project team

Documents