Security

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Security
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Secure Connections

• Secure connections are needed in many computer
  related activities, including e-business and grid
  computing.

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Key requirements for ensuring a secure connection

• Data Confidentiality - information exchange needs
  to protected against eavesdroppers.
• Authentication - access needs to be restricted to
  those (humans or systems) that can provide proof
  of identity.
• Data Integrity - need to assure that message was
  not modified in transit (intentionally or by
  accident).
• Non-repudiation - guarantees that sender cannot
  deny that he/she sent message. Similarly receiver
  not deny receiving message.

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Additional Factors

• Authorization - The process of deciding whether a
  particular identity can access a particular
  resource.
• Access control - broader aspect of authorization
  and controlling specific types of access.

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AuthenticationPassword-Based

• User enters a user name and password.
• User name and password sent through network to
  server.
• Server validates name and password and responds.

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Name 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
• Second version a little more secure because it
  reveals less information to a potential intruder,
  but ...

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Name and Password

• Since name and password sent in plain text,
  vulnerable to interference and being stolen.
• Need a system in which in one can be sure of
  sender.

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• Two aspects
• Send information in an encrypted form.
• Have a trusted third party or some sure way of
  proving identity.

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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)
• plaintext decrypt(ciphertext)
• Can either make 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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Cryptography algorithms with keys

• Converts data into scrambled binary patterns,
  using a large binary number called a key.
• A key is also used to convert the scrambled
  patterns back to the original data.
• Algorithms are well-known - it is a specific key
  that must be kept secure.

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Secret Key Cryptography

• Sender and receiver has a same secret key in
  their possession.
• Sender uses secret key to encrypt data.
• Receiver uses same key to decrypt data.
• Known as symmetric cryptography. Key is called a
  symmetric key.

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Encryption and Decryption
Hello. This is my message that must be kept secret
Hello. This is my message that must be kept secret
12gajey ck027jcLsajckjyfrasbiioppa2354mghdas
Original data
Cipher data
Original data
Same key
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Simple Secret-Key Example

• Data abra which has the binary
  representation
• 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!
• Practical algorithm usually much more complex.

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Common Symmetric Key Cryptography Systems

• Data Encryption Standard (DES) 56-bit key plus 8
  parity bits - IBM 1970s.
• Triple-DES 112 bit key plus 16 parity bits or
  168-bit plus 24 parity bits.
• RC2 and RC4 variable sized key, often 40 to 128
  bits.

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Problemswith Symmetric key Cryptography

• Need a way of both sender and receiver to obtain
  secret key without anyone else knowing the key.
• Need a different key for each receiver that a
  sender may communicate with.

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Advantagesof Symmetric Key Cryptography

• Fast encryption/decryption (compared to
  asymmetric key cryptography (see next).
• Used because of speed in conjunction with
  asymmetric key cryptography.

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Public-Key Cryptography

• Public invention due to Whitfield Diffie Martin
  Hellman at Stanford Univ. in 1976
• known earlier in classified community
• Probably most significant advance in the 3000
  year history of cryptography
• Uses clever application of number theoretic
  concepts of functions
• Complements rather than replaces secret key
  cryptography

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Public Key Cryptography(Asymmetric key pair)

• Two keys are formed
• a public key to encrypt the transmission, and
• a private key to decrypt the transmission
• (or vice versa).

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Encryption and Decryption
Hello. This is my message that must be kept secret
Hello. This is my message that must be kept secret
12gajey ck027jcLsajckjyfrasbiioppa2354mghdas
Public key
Private Key
Original data
Cipher data
Original data
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Public Key and Private Key

• Public and private keys are pairs such that a
  message encrypted with the public key can only be
  decrypted with the private key (and vice versa).
• Public key, as the name suggests, is available to
  all.
• Private key is only known by its owner.
• It is not possible to find the private key from
  the public key for all practical purposes.

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Public-Key Cryptography
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Non-repudiation

• Public key cryptography can provide for
  non-repudiation - a sender cannot deny they sent
  out a message if encrypted with their private
  key. Can be read with their public key.

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How secure is public key encryption?

• like private key schemes, brute force exhaustive
  search attack is always theoretically possible
• but
• requires the use of very large numbers
• hence is slow compared to private key schemes

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Aside

• One of the assignments we have considered is
  breaking codes by exhausive search.

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Sequential Search
This figure does come from my own book Parallel
Programming Techniques and Application Using
Networked Workstations and Parallel Computers 2nd
edition, by Barry Wilkinson and Michael Allen,
Prentice Hall Inc., 2004.
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Using Multiple Identical Grid Services
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Public Key Cryptography Example

• Rivest, Shanir, and Adleman (RSA) variable sized
  key, usually between 512 - 2048 bits

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Problem with Public Key Cryptography

• Slow
• Cannot be sure that a sender is sending the
  message encrypted with the public key as everyone
  knows this key

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Digital Signatures

• A way of achieving authentication and data
  integrity.
• Uses a hash function to create a message digest,
  a footprint of the message which is encrypted
  with senders private key to create a digital
  signature.

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Hash Function

• Applying hash function to data will create a
  small fixed sized block of data called in this in
  text a message digest
• Cannot obtain original data from the digest -
  hence one-way.
• Changes to the data will usually alter the
  message digest.

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Digital Signature
Hello. This is my message that must be kept secret
asthwsf
129345
Hash function
Data
Digital Signature
Senders Private Key
Message Digest
Attach digital signature to message (data)
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Checking digital signature

• Receiver can do the following
• 1. Create a message digest from message using
  same hash function.
• 2. Decrypt message digest with senders public
  key.
• 3. Compare two message digests - if same message
  should be from sender and not altered.

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Checking digital signature
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• Digital signature alone not sufficient to ensure
  data not altered and is from the sender -
  possible that public key is a fake. Still could
  get matching digital signatures.

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Certificates

• A digital document belonging to the End-Entity
  listing its specific public key.
• A trusted party (a certificate authority, CA)
  certifies that the public key does in fact belong
  to the end-entity on the certificate.
• Certificate comparable to a Drivers license or
  passport.

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Certificate
Certificate This certificate belongs to Barry
Wilkinson Public key of certificate owner
Signature of Certificate Authority MyCA
Other information also on certificate, see later.
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Certificate Authority

• Certificate Authority has to first create its
  own certificate to identify itself (keeping its
  private key protected).
• End-Entities submit their details to CA for CA to
  issue a certificate back to End-Entity.

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Types of Certificates

• X.509 most widely used.
• Defined by International Telecommunications Union
  (ITU)
• Version 1 defined in 1988
• Version 2 , Version 3 (1996) adds fields, see
  next slide.

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X.509 Format (version 3)

• Certificate version
• Certificate serial number
• Issuer signature algorithm ID
• Issuer X-500 name
• Validity period
• Subject X-500 name
• Subject public key information Algorithm ID
  Public key value
• Issuer unique ID
• Subject unique ID
• Extensions
• Issuer digital signature

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Public Key Certificates

• IF you trust the Certificate Authority
• AND you are confident that the 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/conte
  nts.htm, section starting with Certificates and
  Authentication

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SSL (Secure Socket Layer) Protocol

• Uses public/private keys.
• Introduced by Netscape and widely adopted.
• Supported by both Netscape and Microsoft Internet
  Explorer browser.
• TLS (Transport Layer Security) newer but similar.

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• Requires several message to be exchanged between
  client and server
• .
• Described here in four phases.

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Phase I

• Client starts handshake and sends
• a random number, X.
• list of supported ciphers and compression
  algorithms

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Phase II

• Server selects cipher and compression algorithm,
  and notifies client. Then it sends
• another random number, Y.
• a server certificate which includes public key

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Phase III

• Client sends
• a premaster secret encrypting it with server
  public key
• possibly a client certificate

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Phase IV

• Handshake finished. Message sent to inform
  client..
• Server and client each generate a master secret
  by combining random numbers X and Y, and the
  premaster secret.
• Several secret keys are generated from the master
  secret, one to encrypt the data.
• Encrypted data then sent to client.

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SSL

• Ensures
• Authentication (by verifying certificates)
• Confidentiality ((by encrypting data with secret
  key)
• Integrity (by digesting data)
• Non-repudiation not ensured because Message
  Authentication Code (MAC) of transmitted data
  calculated with common secret key.

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Globus Grid Security Infrastructure(GSI)

• Uses public key cryptography
• Secure communication for authentication etc.
• Task communication can be encrypted with shared
  key if required
• Security across organizational boundaries (how?)
• Proxies provide single sign-on

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Certificates

• Every user and service on grid identified with a
  certificate
• X.509 format
• Certified by a Certificate Authority - Globus
  provides one, Simple CA.

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Getting certificate from Simple CA

• Run
• GLOBUS_LOCATION/bin/grid-cert-request
• Certificate request stored in
• HOME/.globus/usercert_request.pem
• Email this request to certificate authority given
  in request.

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Single sign-on

• to enable user and its agents to acquire
  additional resources without repeated
  authentication (passwords)
• Achieved with proxies

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Proxy

• Consists of a new certificate with new public,
  private keys, and owners identify (/CNproxy
  added to name).
• Certificate signed by owner (not CA)
• Proxy given limited lifetimes
• Proxys private key does not need to be kept as
  secure as owners private key - setting file
  permissions usually sufficient

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Additional Proxies
From Overview of the Grid Security
Infrastructure http//www.globus.org/security/ove
rview.htm
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Mutual Authentication with Proxies

• Remote party receives owners certificate and
  owners proxy certificate.
• Chain of trust
• Owners public key from owners certificate used
  to validate proxy signature on proxy certificate
• Certificate authority (CA) public key used to
  validate owners signature on owners certificate

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More InformationOn-line

• Deploying a Public Key Infrastucture, IBM
  Redbooks, www.redbooks.ibm.com, 2000,
  SG24-5512-00.
• For SSL protocol http//developer.netscape.com/do
  cs/manuals/security/sslin/index.html
• Digital signatures
• http//www.youdzone.com/signature.html

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Books

• Cryptography and Network Security 3rd edition, by
  William Stalling.