SEE-GRID tutorial, Istanbul, 09-10.12.2004
Security on Grid
Roberto Barbera
Univ. of Catania and INFN
Overview
• Glossary
• Encryption
•
•
Symmetric algorithms
Asymmetric algorithms: PKI
• Certificates
•
•
Digital Signatures
X509 certificates
• Grid Security
•
•
•
•
Basic concepts
Grid Security Infrastructure
Proxy certificates
Command line interfaces
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 2
Overview
• Glossary
• Encryption
•
•
Symmetric algorithms
Asymmetric algorithms: PKI
• Certificates
•
•
Digital Signatures
X509 certificates
• Grid Security
•
•
•
•
Basic concepts
Grid Security Infrastructure
Proxy certificates
Command line interfaces
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 3
Glossary
• Principal
•
An entity: a user, a program, or a machine
• Credentials
•
Some data providing a proof of identity
• Authentication
•
Verify the identity of the principal
• Authorization
•
Map an entity to some set of privileges
• Confidentiality
•
Encrypt the message so that only the recipient can understand it
• Integrity
•
Ensure that the message has not been altered in the transmission
• Non-repudiation
•
Impossibility of denying the authenticity of a digital signature
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 4
Overview
• Glossary
• Encryption
•
•
Symmetric algorithms
Asymmetric algorithms: PKI
• Certificates
•
•
Digital Signatures
X509 certificates
• Grid Security
•
•
•
•
Basic concepts
Grid Security Infrastructure
Proxy certificates
Command line interfaces
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 5
Cryptography
K1
Encryption
M
K2
C
Decryption
M
•
Mathematical algorithm that provides important building blocks for the
implementation of a security infrastructure
•
Symbology
•
•
Plaintext: M
•
Cyphertext: C
•
Encryption with key K1 : E K1(M) = C
•
Decryption with key K2 : D K2(C) = M
Algorithms
•
Symmetric: K1 = K2
•
Asymmetric: K1 ≠ K2
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 6
Symmetric Algoritms
• The same key is used for
encryption and decryption
• Advantages:
•
A
ciao
B
3$r
3$r
ciao
Fast
• Disadvantages:
•
•
how to distribute the keys?
the number of keys is O(n2)
• Examples:
•
•
•
•
•
A
ciao
B
3$r
3$r
ciao
DES
3DES
Rijndael (AES)
Blowfish
Kerberos
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 8
Public Key Algorithms
•
Every user has two keys: one
private and one public:
•
•
•
No exchange of secrets is
necessary
•
•
•
•
it is impossible to derive the
private key from the public one;
a message encrypted by one
key can be decripted only by the
other one.
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:
•
•
A
ciao
B
3$r
A
ciao
3$r
ciao
B
cy7
cy7
A’s keys
B’s keys
public private
public private
ciao
Diffie-Helmann (1977)
RSA (1978)
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 9
Overview
• Glossary
• Encryption
•
•
Symmetric algorithms
Asymmetric algorithms: PKI
• Certificates
•
•
Digital Signatures
X509 certificates
• Grid Security
•
•
•
•
Basic concepts
Grid Security Infrastructure
Proxy certificates
Command line interfaces
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 10
One-Way Hash Functions
• Functions (H) that given as input a variable-length
message (M) produce as output a string of fixed length (h)
•
1.
2.
3.
the length of h must be at least 128 bits (to avoid birthday attacks)
given M, it must be easy to calculate H(M) = h
given h, it must be difficult to calculate
M = H-1(h)
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.
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 11
Digital Signature
• A calculates the hash of the
message
• A encrypts the hash 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 public key.
• If the two hashes are equal, the
message wasn’t modified and A
cannot repudiate it.
A’s keys
A
This is some
Hash(A)
message
Digital Signature
message
Digital Signature
B
Hash(B)
=?
Hash(A)
public
This is some
This is some
message
Digital Signature
private
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 12
Digital Certificates
• A’s digital signature is safe if:
1.
2.
•
A’s private key is not compromised
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”.
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 13
PGP “web of trust”
D
B
F
C
E
A
• 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.
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X.509
The “third party” is called Certification Authority (CA).
• Issue certificates for users, programs and machines
• Check the identity and the personal data of the requestor
•
Registration Authorities (RAs) do the actual validation
• CA’s periodically publish a list of compromised certificates
•
Certificate Revocation Lists (CRL)
• They contain all the revoked certificates yet to expire
•
Online Certificate Status Protocol (OCSP).
• CA certificates are self-signed
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 15
X.509 Certificates
• An X.509 Certificate contains:
Structure of a X.509 certificate
•
owner’s public key;
•
identity of the owner;
Subject:C=CH, O=CERN,
OU=GRID, CN=Andrea Sciaba
8968
•
info on the CA;
Issuer: C=CH, O=CERN,
OU=GRID, CN=CERN CA
time of validity;
Expiration date: Aug 26 08:08:14
2005 GMT
•
Public key
Serial number: 625 (0x271)
•
Serial number;
CA Digital signature
•
digital signature of the CA
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 16
Overview
• Glossary
• Encryption
•
•
Symmetric algorithms
Asymmetric algorithms: PKI
• Certificates
•
•
Digital Signatures
X509 certificates
• Grid Security
•
•
•
•
Basic concepts
Grid Security Infrastructure
Proxy certificates
Command line interfaces
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 17
GRID Security: the players
Users
• Large and dynamic population
•Different accounts at different sites
•Personal and confidential data
•Heterogeneous privileges (roles)
•Desire Single Sign-On
“Groups”
• “Group” data
• Access Patterns
• Membership
Grid
Sites
• Heterogeneous Resources
• Access Patterns
• Local policies
• Membership
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The Risks
• Launch attacks to other sites
•
Large distributed farms of machines
• Illegal or inappropriate data distribution and access
sensitive information
•
Massive distributed storage capacity
• Disruption by exploiting security holes
•
Complex, heterogeneous and dynamic environment
• Damage caused by viruses, worms etc.
•
Highly connected and novel infrastructure
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 19
The Grid Security Infrastructure (GSI)
B
A
Based on X.509 PKI:
A’s certificate
•
•
•
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:
VERY IMPORTANT Verify CA signature
Random phrase
Private keys must be stored only:
1. A sends his certificate;
Encrypt with A’ s private key
in protected places
2. B verifies signature in A’s certificate;
3. B sends to A a challenge string;
Encrypted phrase
AND
4. A encrypts the challenge string with his
5.
6.
7.
8.
private key;
A sends encrypted challenge to B
B uses A’s public key to decrypt the
challenge.
B compares the decrypted string with the
original challenge
If they match, B verified A’s identity and A
can not repudiate it.
Decrypt with A’ s public key
in encrypted form
Compare with original phrase
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 20
Certificate request … more details
• Egee/LCG recognizes a given set of CAs
•
https://lcg-registrar.cern.ch/pki_certificates.html
• How do you request a certificate depends on your CA
• The certificate request is created together with the
certificate private key (encrypted by a pass phrase)
• For GILDA, have a look at the Demo Video:
•
•
https://gilda.ct.infn.it/video/Certification/Allproxy.html
(Flash)
https://gilda.ct.infn.it/video/Certification/AllCertproxy.ram (Real)
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 21
Certificate Request
User generates
public/private
key pair.
CA confirms identity,
signs certificate and
sends back to user.
Cert
Request
Public Key
Cert
ID
Private Key
encrypted on
local disk
User send public key to
CA along with proof of
identity.
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 22
Certificate Information
• To get cert information run grid-cert-info
[scampana@grid019:~]$ grid-cert-info -subject
/C=CH/O=CERN/OU=GRID/CN=Simone Campana 7461
• Options for printing cert information
-all
-subject
-issuer
-startdate
-enddate
-help
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 23
X.509 Proxy Certificate
•
GSI extension to X.509 Identity Certificates
•
•
•
Enables single sign-on
Support some important features
•
•
•
•
signed by the normal end entity cert (or by another proxy).
Delegation
Mutual authentication
Has a limited lifetime (minimized risk of “compromised credentials”)
It is created by the grid-proxy-init command:
% grid-proxy-init
Enter PEM pass phrase: ******
•
Options for grid-proxy-init:
•
•
•
-hours <lifetime of credential>
-bits <length of key>
-help
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 24
grid-proxy-init
• User enters pass phrase, which is used to decrypt private key.
• Private key is used to sign a proxy certificate with its own, new
public/private key pair.
•
User’s private key not exposed after proxy has been signed
User
certificate file
Pass
Phrase
Private Key
(Encrypted)
User Proxy
certificate file
• Proxy placed in /tmp, read-only by user
•
the private key of the Proxy is not encrypted:
• stored in local file: must be readable only by the owner;
• proxy lifetime is short (typically 12 h) to minimize security risks.
• NOTE: No network traffic!
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 25
Proxy again …
• grid-proxy-init ≡ “login to the Grid”
• To “logout” you have to destroy your proxy:
• grid-proxy-destroy
•
•
•
This does NOT destroy any proxies that were delegated from this
proxy.
You cannot revoke a remote proxy
Usually create proxies with short lifetimes
• To gather information about your proxy:
• grid-proxy-info
•
Options for printing proxy information
-subject
-type
-strength
-issuer
-timeleft
-help
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 26
Delegation and limited proxy
• Delegation = remote creation of a (second level) proxy credential
•
New key pair generated remotely on server
• Clients signs proxy cert and returns it
• Allows remote process to authenticate on behalf of the user
•
Remote process “impersonates” the user
• The client can elect to delegate a “limited proxy”
•
Each service decides whether it will allow authentication with a limited proxy
• Job manager service requires a full proxy
• GridFTP server allows either full or limited proxy to be used
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 27
Long term proxy
• Proxy has limited lifetime (default is 12 h)
•
Bad idea to have longer proxy
• However, a grid task might need to use a proxy for a much longer time
•
Grid jobs in HEP Data Challenges on LCG last up to 2 days
• myproxy server:
•
•
Allows to create and store a long term proxy certificate:
myproxy-init -s <host_name> -d -n
• -s: <host_name> specifies the hostname of the myproxy server
• -d: server to use the subject of the certificate as the default username
• -n: avoids the use of a passphrase to access to the long-term proxy
– so the WMS can perform the renewals automatically.
•
myproxy-get-delegation -s <host_name>
• Get a new proxy from the MyProxy server
•
myproxy-destroy
• A dedicated service on the RB can renews automatically the proxy
•
contacts the myproxy server
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 28
GSI environment variables
•
User certificate files:
•
•
•
•
Host certificate files:
•
•
•
Certificate: X509_USER_CERT (default: $HOME/.globus/usercert.pem)
Private key: X509_USER_KEY
(default: $HOME/.globus/userkey.pem)
Proxy:
X509_USER_PROXY (default: /tmp/x509up_u<id>)
Certificate: X509_USER_CERT
Private key: X509_USER_KEY
(default: /etc/grid-security/hostcert.pem)
(default: /etc/grid-security/hostkey.pem)
Trusted certification authority certificates:
•
X509_CERT_DIR
(default: /etc/grid-security/certificates)
SEE-GRID tutorial, Istanbul, 09-10.12.2004 - 29
Further Information
Grid
• LCG Security: http://proj-lcg-security.web.cern.ch/proj-lcg-security/
• LCG Registration: http://lcg-registrar.cern.ch/
• Globus Security: http://www.globus.org/security/
Background
• GGF Security: http://www.gridforum.org/security/
• GSS-API: http://www.faqs.org/faqs/kerberos-faq/general/section-84.html
• GSS-API: http://docsun.cites.uiuc.edu/sun_docs/C/solaris_9/
SUNWdev/GSSAPIPG/toc.html
• IETF PKIX charter: http://www.ietf.org/html.charters/pkix-charter.html
• PKCS: http://www.rsasecurity.com/rsalabs/pkcs/index.html
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