Grid Computing

1. Visvesvaraya National Institute Of Technology
Computer Science And Engineering
Seminar Report
Grid Security
Presented By:
Mohit Modi
(BT08CSE043)
Project Supervisor:
O.G.Kakde

2. Abstract
A Computational Grid is a collection of heterogeneous computers and resources spread across multiple
administrative domains with the intent of providing users easy access to these resources. There are many
ways to access the resources of a Computational Grid, each with unique security requirements and
implications for both the resource user and the resource provider. A comprehensive set of Grid usage
scenarios is analyzed with regard to security requirements such as authentication, authorization,
integrity, and confidentiality. Here we examines the major security requirements of modern grids then
goes on to focus on the X.509 certificates used within it .The main value of these scenarios and the
associated security discussions is to provide a library of situations against which an application designer
can match, thereby facilitating security-aware application use and development from the initial stages of
the application design and invocation. A broader goal of these scenarios is to increase the awareness of
security issues in Grid Computing.
Introduction
A Grid is a system that:
1) Coordinates resources that are not subject to centralized control …
(A Grid integrates and coordinates resources and users that live within different control domains—for example,
the user’s desktop vs. central computing; different administrative units of the same company; or different
companies; and addresses the issues of security, policy, payment, membership, and so forth that arise in these
settings. Otherwise, we are dealing with a local management system.)
2) … using standard, open, general-purpose protocols and interfaces
(A Grid is built from multi-purpose protocols and interfaces that address such fundamental issues as
authentication, authorization, resource discovery, and resource access. As I discuss further below, it is important
that these protocols and interfaces be standard and open. Otherwise, we are dealing with an application specific
system.)
3) … to deliver nontrivial qualities of service.
(A Grid allows its constituent resources to be used in a coordinated fashion to deliver various qualities of service,
relating for example to response time, throughput, availability, and security, and/or co-allocation of multiple
resource types to meet complex user demands, so that the utility of the combined system is significantly greater
than that of the sum of its parts.)
So far the grid has lacked real standardization, many different companies are beginning to utilize grids, but run
into problems when trying to link these proprietary grids together.
General Model of Grid Security(Globus)
Public Key Cryptography
The most important thing to know about public key cryptography is that, unlike earlier cryptographic systems, it
relies not on a single key (a password or a secret "code"), but on two keys. These keys are numbers that are
mathematically related in such a way that if either key is used to encrypt a message, the other key must be used to
decrypt it. Also important is the fact that it is next to impossible (with our current knowledge of mathematics and
available computing power) to obtain the second key from the first one and/or any messages encoded with the first
key. By making one of the keys available publicly (a public key) and keeping the other key private , a person can
prove that he or she holds the private key simply by encrypting a message. If the message can be decrypted using
the public key, the person must have used the private key to encrypt the message.

3. Important: It is critical that private keys be kept private! Anyone who knows the private key can easily
impersonate the owner.
Digital Signatures
Using public key cryptography, it is possible to digitally "sign" a piece of information. Signing information
essentially means assuring a recipient of the information that the information hasn't been tampered with since it
left your hands.
To sign a piece of information, first compute a mathematical hash of the information. (A hash is a condensed
version of the information. The algorithm used to compute this hash must be known to the recipient of the
information, but it isn't a secret.) Using your private key, encrypt the hash, and attach it to the message. Make sure
that the recipient has your public key.
To verify that your signed message is authentic, the recipient of the message will compute the hash of the message
using the same hashing algorithm you used, and will then decrypt the encrypted hash that you attached to the
message. If the newly-computed hash and the decrypted hash match, then it proves that you signed the message
and that the message has not been changed since you signed it.
Certificates
A central concept in GSI(Grid Security Infrastructure) authentication is the certificate. Every user and service on
the Grid is identified via a certificate, which contains information vital to identifying and authenticating the user
or service.
A GSI certificate includes four primary pieces of information:
 A subject name, which identifies the person or object that the certificate represents.
 The public key belonging to the subject.
 The identity of a Certificate Authority (CA) that has signed the certificate to certify that the public key and
the identity both belong to the subject.
 The digital signature of the named CA.
Note that a third party (a CA) is used to certify the link between the public key and the subject in the certificate. In
order to trust the certificate and its contents, the CA's certificate must be trusted. The link between the CA and its
certificate must be established via some non-cryptographic means, or else the system is not trustworthy.
GSI certificates are encoded in the X.509 certificate format, a standard data format for certificates established by
the Internet Engineering Task Force (IETF). These certificates can be shared with other public key-based
software, including commercial web browsers from Microsoft and Netscape.
Mutual Authentication
If two parties have certificates, and if both parties trust the CAs that signed each other's certificates, then the two
parties can prove to each other that they are who they say they are. This is known as mutual authentication. The
GSI uses the Secure Sockets Layer (SSL) for its mutual authentication protocol, which is described below. (SSL is
also known by a new, IETF standard name: Transport Layer Security, or TLS.) Before mutual authentication can
occur, the parties involved must first trust the CAs that signed each other's certificates. In practice, this means that
they must have copies of the CAs' certificates--which contain the CAs' public keys--and that they must trust that
these certificates really belong to the CAs.
To mutually authenticate, the first person (A) establishes a connection to the second person (B). To start the
authentication process, A gives B his certificate. The certificate tells B who A is claiming to be (the identity), what
A's public key is, and what CA is being used to certify the certificate. B will first make sure that the certificate is
valid by checking the CA's digital signature to make sure that the CA actually signed the certificate and that the
certificate hasn't been tampered with. (This is where B must trust the CA that signed A's certificate.)

4. Once B has checked out A's certificate, B must make sure that A really is the person identified in the certificate. B
generates a random message and sends it to A, asking A to encrypt it. A encrypts the message using his private key,
and sends it back to B. B decrypts the message using A's public key. If this results in the original random message,
then B knows that A is who he says he is.
Now that B trusts A's identity, the same operation must happen in reverse. B sends A her certificate, A validates
the certificate and sends a challenge message to be encrypted. B encrypts the message and sends it back to A, and A
decrypts it and compares it with the original. If it matches, then A knows that B is who she says she is.
At this point, A and B have established a connection to each other and are certain that they know each others'
identities.
Confidential Communication
By default, the GSI does not establish confidential (encrypted) communication between parties. Once mutual
authentication is performed, the GSI gets out of the way so that communication can occur without the overhead of
constant encryption and decryption.
The GSI can easily be used to establish a shared key for encryption if confidential communication is desired.
Recently relaxed United States export laws now allow us to include encrypted communication as a standard
optional feature of the GSI.
A related security feature is communication integrity. Integrity means that an eavesdropper may be able to read
communication between two parties but is not able to modify the communication in any way. The GSI provides
communication integrity by default. (It can be turned off if desired). Communication integrity introduces some
overhead in communication, but not as large an overhead as encryption.
Securing Private Keys
The core GSI software provided by the Globus Toolkit expects the user's private key to be stored in a file in the
local computer's storage. To prevent other users of the computer from stealing the private key, the file that
contains the key is encrypted via a password (also known as a pass phrase). To use the GSI, the user must enter the
pass phrase required to decrypt the file containing their private key. We have also prototyped the use of
cryptographic smartcards in conjunction with the GSI. This allows users to store their private key on a smartcard
rather than in a filesystem, making it still more difficult for others to gain access to the key.
Delegation and Single Sign-On
The GSI provides a delegation capability: an extension of the standard SSL protocol which reduces the number of
times the user must enter his pass phrase. If a Grid computation requires that several Grid resources be used (each
requiring mutual authentication), or if there is a need to have agents (local or remote) requesting services on behalf
of a user, the need to re-enter the user's pass phrase can be avoided by creating a proxy.
A proxy consists of a new certificate (with a new public key in it) and a new private key. The new certificate
contains the owner's identity, modified slightly to indicate that it is a proxy. The new certificate is signed by the
owner, rather than a CA. (See diagram below.) The certificate also includes a time notation after which the proxy
should no longer be accepted by others. Proxies have limited lifetimes.
The proxy's private key must be kept secure, but because the proxy isn't valid for very long, it doesn't have to kept
quite as secure as the owner's private key. It is thus possible to store the proxy's private key in a local storage
system without being encrypted, as long as the permissions on the file prevent anyone else from looking at them
easily. Once a proxy is created and stored, the user can use the proxy certificate and private key for mutual
authentication without entering a password.

5. When proxies are used, the mutual authentication process differs slightly. The remote party receives not only the
proxy's certificate (signed by the owner), but also the owner's certificate. During mutual authentication, the
owner's public key (obtained from her certificate) is used to validate the signature on the proxy certificate. The
CA's public key is then used to validate the signature on the owner's certificate. This establishes a chain of trust
from the CA to the proxy through the owner.
Note that the GSI and software based on it (notably the Globus Toolkit, GSI-SSH, and GridFTP) is currently the
only software which supports the delegation extensions to TLS (a.k.a. SSL). The Globus Project is actively working
with the Grid Forum and the IETF to establish proxies as a standard extension to TLS so that GSI proxies may be
used with other TLS software.
Problems with Globus security
Scalability
The Globus Security Infrastructure (GSI) makes extensive use of X.509 certificates, they have been found to be
sufficiently secure for the small scale implementations so far. However the scalability of such a system is very poor
for the receiving machine. The current grid authorization mechanisms is almost wholly concentrated on the use of
Access Control Lists (ACL’s) holding details of every individual who is authorized to use a system.
CA Trust
Very careful consideration has to be given to which CA to sign up with and which to accept certificates from. If
your computer knows to trust a certain CA it will trust all the certificates that are issued from it that turn out
valid. Globus runs its own test CA for use in development of the toolkit. There are however many reasons why this
CA is not suitable for use in real business. The Globus test CA merely checks that the certificate requests domain
matches that of the email the request was sent from. It also checks the presence of any existing certificates for that
machine. This level of security would be extremely inadequate for most types of grid system.
Proxy Certificates
When a proxy certificate is generated the PEM phrase authorizes a certificate generator to sign a new temporary
certificate (self certified) which uses the original certificate as verification. ie you can prove the original certificates
owner signed the proxy by entering the PEM phrase. This leaves a dilemma, a new public / private key set is
generated for use while the proxy is active. The new private key cannot be secured by a user PEM phrase because
that was the whole point of the proxy in the first place! Globus will not secure proxy certificates by itself. By this it
is meant that the private key used is not encrypted. The machine it resides on represents the main line of defence
against them being altered or stolen by outside forces. The reasoning behind this being that the certificate itself is
only temporary and uses a different private key from the original permanent certificate anyway; however the risk
is not necessarily negligible as a user can make a proxy certificate valid for as long as they wish.

6. Extended Security Model For Grid
Assumptions:
� Widespread grid adoption within companies of large / medium size.
� Business outsourcing of tasks to specialist companies to simplify increasing maintenance and running costs. eg:
Storage ,Software Access ,Dataset Access ,Hardware Access
� The majority of business grid users will utilize such services, but will be largely unaware of their own company
utilizing excess cycles on their office machines to cut costs; effectively hosting some services of its own (potentially
for export as services themselves).
Once those assumptions have been taken into account it is possible to see how the grid might look if it were to
continue using its current security model in the future. One of the biggest problems is that of scalability. Now we
show first attempt to control the scalability problem and then a generally workable approach. We assumes that the
existing mechanisms of public key infrastructures and X.509 certificates will continue to remain the core of the
model. One solution to this task would be to introduce the concept of group certificates, where everyone in the
company used the same certificate. This method would at first look quite workable; unfortunately problems
emerge when one considers the security implications of such a development. It weakens the PKI because it is by its
very design a one to one mechanism. Issues with stolen copies, revocation of existing copies etc make this approach
infeasible.
A possible solution
What is really needed is to reduce the amount of work the service has to do to establish authorization, without
doing so by looking up the actual person However the traditional view of people being given roles does not work
very well in the grid either. The main issues are that it is very difficult to give people meaningful roles, and people
understand different things by those roles. These systems also tend to lose the security granularity to the stage
where it is difficult to determine who uses a system if you need to. They do however make authorization much
simpler as you are only checking whether a certain role can use a service. Therefore what is actually needed is the
flexibility of a role based system, but with the potential to hold the same amount of information as the current
systems. This is a somewhat daunting task as at first it would appear that the two methods are in direct opposition
to each other. However it is possible to augment the two successfully, as described below:
Role Augmented X.509 Authorization (RAXA)
In order to make this security model as simple as possible. Basically Globus(general grid infrastructure(model))
uses X.509 certificates for authentication and authorization purposes. One of the problems with this approach is
related to the way in which authorization occurs. The existing Globus security model only authorizes individuals to
use machines, rather than groups of people. As the X.509 protocol is virtually standardized and well accepted this
document wisely does not alter its operation in any way. It does however add to the authentication and
authorization process an extra piece of evidence besides the X.509 certificate itself. This evidence is held within a
separate file that accompanies the certificate. This approach avoids the need to re-engineer the existing X.509
format to add any extra fields. This proposal assumes a user may wish to have more than one “role” relating to
them in the file. In its present form this information cannot be used as a validation mechanism due to its lack of
credibility. Meaning anybody could write the entire accompanying file or alter it, or lie about their role in the
company; therefore it is clear that individual users could not be trusted to write their own entries for security
reasons. Thus a user could request an entry from a trusted centralized authority at each company / VO, which
could in turn write the entry itself and send it to the user (after checking on the users request). However this still
poses the problem that the user could change the entry when they receive it. In order to secure the individual
entries from tampering and to prove who created them a type of digital signature can be created.
**Role entry consists of Name of organization, Unique identifier from X.509 certificate, Date Issued, Date of
Expiry

9. Conclusion
In conclusion it is easy to see that the requirements of grid computing are complex, and in order to encompass new
abilities and even a new interface paradigm, a number of changes are inevitable. This report highlights in
particular issues relating to Globus, and the use of the X.509 certificate model for authentication purposes. This
report also put forward a new form of Role based Action Control (RBAC)in the form of the RAXA extension
proposal. Given the complexities of grid computing it is possible that RBAC mechanisms may play a part in the
future of grid computing in order to streamline access rights. However a considerable amount of work would be
required in the area to determine what level of integration with existing mechanisms is feasible.