Unit 1: Protection and Security for Grid Computing

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Unit 1 Protection and Security for Grid
Computing
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Protection and security overview

• We will cover a lot of things, including
• Basic concepts of cryptography
• Authentication in context of Grid
• Authorization in context of Grid
• For both of these the focus is on what happens in
  a distributed environment, not on a particular OS
• We will not cover in lecture several things that
  are covered in the handouts
• read these for your own enrichment
• quizzes will emphasize the material covered in
  lecture be sure to read the assigned outside
  reading material!

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Some lecture slides in part from Cryptography and
Network Security

• Third Edition
• by William Stallings
• Lecture slides by Lawrie Brown
• Corresponds to handout Nutt, Chapter 14, section
  14.4

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Cryptography

• Basic idea convert clear text (also called
  plain text the original message) to ciphertext
  (the encrypted message)
• ciphertext encrypt(plaintext, KE)
• plaintext decrypt(ciphertext, KC)
• Can either make the encryption process hidden, so
  that an intruder cannot know it
• Or, can use a known technique and use a hidden
  key

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Secret-Key Cryptography

• traditional secret/single key cryptography uses
  one key
• shared by both sender and receiver
• if this key is disclosed communications are
  compromised
• also is symmetric, parties are equal
• hence does not protect sender from receiver
  forging a message claiming is sent by sender

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Simple Secret-Key Example

• P abra which has the binary representation
  0x61627261, or
• 01100001011000100011100101100001
• Choose a random string of bits as the key
• 10011101010010001111010101011100
• Can use a simple XOR of the binary to get C
• 11111100001010101000011100111101
• To get P back, use the same algorithm and key!
• The most popular secret key encryption today is
  DES.

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Public-Key Cryptography

• probably most significant advance in the 3000
  year history of cryptography
• uses two keys a public a private key
• asymmetric since parties are not equal
• uses clever application of number theoretic
  concepts to function
• complements rather than replaces secret key
  cryptography

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Public-Key Cryptography

• public-key/two-key/asymmetric cryptography
  involves the use of two keys
• a public-key, which may be known by anybody, and
  can be used to encrypt messages, and verify
  signatures
• a private-key, known only to the recipient, used
  to decrypt messages, and sign (create) signatures
• is asymmetric because
• those who encrypt messages or verify signatures
  cannot decrypt messages or create signatures

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Public-Key Cryptography
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Why Public-Key Cryptography?

• developed to address two key issues
• key distribution how to have secure
  communications in general without having to trust
  a KDC with your key
• digital signatures how to verify a message
  comes intact from the claimed sender
• public invention due to Whitfield Diffie Martin
  Hellman at Stanford Univ. in 1976
• known earlier in classified community

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Public-Key Characteristics

• Public-Key algorithms rely on two keys with the
  characteristics that it is
• computationally infeasible to find decryption key
  knowing only algorithm encryption key
• computationally easy to en/decrypt messages when
  the relevant (en/decrypt) key is known
• either of the two related keys can be used for
  encryption, with the other used for decryption
  (in some schemes)

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Sending a message with double encryption
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Public-Key Applications

• can classify uses into 3 categories
• encryption/decryption (provide secrecy)
• key exchange (of secret session keys)
• Session keys can be used in a session between a
  client and a server to encrypt network messages.
  
• They expire at the end of the session the short
  life span makes them difficult to break
• digital signatures (provide authentication)

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SSL An example of key exchange using
public/private keys

• SSL (Secure Socket Layer) and TLS (Transport
  Layer Security) use public/private keys to
  exchange a secret key used during a session
• The SSL handshake consists of several steps, as
  follows
• Step 1 The client contacts the server and sends
  SSL version number, a random number X, and some
  additional information

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SSL Handshake

• Step 2 The server sends the client the SSL
  version number, random number Y, and its public
  key (packaged into a certificate)
• Step 3 The client verifies that the server is
  who is says it is by examining the certificate
  (more on this in a bit)
• Step 4 The client creates a premaster secret
  using X, Y, and other information. It encrypts
  the secret using the servers public key.

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SSL Handshake

• Step 5 If the server has requested
  authentication, the client sends its own
  certificate and the premaster secret to the
  server
• Step 6 The server authenticates the client by
  examining the clients certificate, uses its
  private key to decrypt the premaster secret, then
  uses it to generate the master secret. The
  client also generates the master secret.

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SSL Handshake

• Step 7 Both the client and the server use the
  master secret to generate the session secret key
• Steps 8 (9) The client (server) sends a message
  to the server (client) telling it that it will
  use the secret key. It sends a second message
  encrypted with the secret key.

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SSL Handshake

• Step 10 The handshake is complete and the SSL
  session has begun.
• Read http//developer.netscape.com/docs/manuals/se
  curity/sslin/index.html
• for a description about the SSL handshake.

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Digital Signatures

• Use a combination of a message digest (hash) and
  public key encryption to be able to guarantee
  that a message was sent by who claimed to send it
  
• Step 1 I create a message digest of the message
  
• Step 2 encrypt the message digest with my
  private key (that only I know). This is my
  digital signature

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Digital Signatures

• Step 3 Append the message with my digital
  signature and send the message in the open
  network
• Step 4 Anyone with my public key can decrypt
  the signature, apply the hash function to get the
  hash, then compare the hash with the decrypted
  signature to see if they are the same
• See http//www.youdzone.com/signature.html

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How secure is public key encryption?

• like private key schemes brute force exhaustive
  search attack is always theoretically possible
• but keys used are too large (gt512bits)
• security relies on a large enough difference in
  difficulty between easy (en/decrypt) and hard
  (cryptanalyse) problems
• more generally the hard problem is known, its
  just made too hard to do in practise
• requires the use of very large numbers
• hence is slow compared to private key schemes

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RSA the most commonly used Public Key
encryption algorithm

• by Rivest, Shamir Adleman of MIT in 1977
• best known widely used public-key scheme
• based on exponentiation in a finite (Galois)
  field over integers modulo a prime
• nb. exponentiation takes O((log n)3) operations
  (easy)
• uses large integers (eg. 1024 bits)
• security due to cost of factoring large numbers
• nb. factorization takes O(e log n log log n)
  operations (hard)

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Distribution of Public Keys

• Can be considered as using one of
• Public announcement
• Publicly available directory
• Public-key authority
• Public-key certificates

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Public Announcement a bad distribution
technique!

• users distribute public keys to recipients or
  broadcast to community at large
• eg. append PGP keys to email messages or post to
  news groups or email list
• major weakness is forgery
• Anyone can create a key claiming to be someone
  else and broadcast it
• Until forgery is discovered can masquerade as
  claimed user

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Recall the Digital Signature Application

• What if my enemy Doug wants to fool you into
  thinking that I sent a message?
• Doug might send you a public key that he claims
  is mine (and keep the matching private key to
  himself).
• If you believe that the public key Doug sent is
  mine, then Doug could sign a message with the
  private key and pretend to be me.
• How can you be sure that the public key you
  receive is mine?

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Public Key Distribution Using a Publicly
Available Directory

• can obtain greater security by registering keys
  with a public directory
• directory must be trusted with properties
• contains name,public-key entries
• participants register securely with directory
• participants can replace key at any time
• directory is periodically published
• directory can be accessed electronically
• still vulnerable to tampering or forgery

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Public Key Distribution Using a Public-Key
Authority

• improve security by tightening control over
  distribution of keys from directory
• has properties of directory
• and requires users to know public key for the
  directory
• then users interact with directory to obtain any
  desired public key securely
• does require real-time access to directory when
  keys are needed

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Public-Key Authority
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Public Key Distribution Using Public-Key
Certificates

• certificates allow key exchange without real-time
  access to public-key authority
• a certificate binds identity to public key
• usually with other info such as period of
  validity, rights of use etc
• with all contents signed by a trusted Public-Key
  or Certificate Authority (CA)
• can be verified by anyone who knows the
  public-key authoritys public-key

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Public-Key Certificates
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Public Key Certificates

• IF you trust the Certificate Authority
• AND you are confident that the KUauth key that
  you have is really the public key of the
  Certificate Authority
• THEN, you can decrypt the certificate with
  confidence to obtain the public key of the sender
• Read http//docs.sun.com/source/816-6154-10/conten
  ts.htm section starting with Certificates and
  Authentication

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Public Key Distribution Using Public-Key
Certificates

• The problem is really an authentication problem
  do you believe that the sender of the certificate
  is who it says it is?
• Next, a short diversion on authentication
  (section 14.1 and 14.2 from Nutt) and then we
  will talk about X.509, a standard for public-key
  certificates.

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Authentication and Authorization

• A user is authenticated when you are sure that
  the user is who he/she claims to be (e.g., that
  user logs in to an account with a password).
• A user is authorized to use a resource if he/she
  is allowed to have access to it.
• Authorization always implies authentication.
• Cryptography may be used to encode information so
  that only an authorized user can access it
• Authorized users may be given a key/password or
  other mechanism for accessing information

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Authentication and Authorization

• Many distributed systems do not separate the
  step of authentication and the step of
  authorization to use a resource if you can
  authenticate to a resource, then you can use it.
• Authentication, authorization, and cryptography
  are protection mechanisms
• A security policy is a specification that
  determines how the protection mechanism should be
  used.

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Authentication

• Authentication in the real world is hard because
  you have to trust the authenticator
• Most common approach is a userid and password
• A second common approach is certificate-based
  authentication

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Userids and password

• Consider a login prompt
• login gshrub
• There is no such user
• login
• A different login prompt behavior
• login gshrub
• password
• authentication failed
• login
• The second version is more secure because it
  reveals less information to a potential intruder
• FYI, see the distribution of passwords in Nutt,
  578

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Authentication in the Network

• Example of a program that executes without
  authenticating a worm
• Morriss Internet Worm is an infamous breach of
  security in the 1980s

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X.509 Certificates

• A standard for digital certificates developed by
  the International Telecommunications Union (ITU)
• Is used for SSL/TLS certificates