GS: Chapter 3 Encryption, Authentication and Java Cryptography

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GS Chapter 3Encryption, Authentication and
Java Cryptography
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Cryptography Java

1. Encryption
2. Authentication
3. Java Cryptography

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Encryption

• Encryption Basics
• An algorithm (or cipher) and a key are required
  in order to encrypt or decrypt messages.
• Example the Caesar cipher (p.34)
• A symmetric, stream cipher
• Exercise Encrypt DDAY using Caesar cipher (5).
• Answer IIFD.
• Q What is the algorithm?
• Q What is the key?
• Q How would the cipher be decrypted?

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Encryption

• Symmetric Encryptions
• Both the encrypter and the decrypter share the
  same key.
• Key space The set of possible keys that work
  with a cipher determined by the number of bits
  used in the cipher.
• The larger the key space is, the more secure the
  encryption will be.
• Each additional bit added to the key length
  doubles its security.

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Encryption

• Symmetric Encryptions
• Two types of symmetric ciphers block ciphers and
  stream ciphers.
• Examples of symmetric encryptions
• DES (Data Encryption Standard) TripleDES block
  ciphers
• Blowfish a faster and more secure replacement of
  DES
• RC4 (Rivests Code 4) a stream cipher
• AES (Advanced Encryption Standard) a block cipher

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Encryption

• Limitations of Symmetric Encryptions
• Key distribution can be a vulnerability.
• If the key is exposed, the encrypted message and
  all future communication using the same key will
  suffer the eavesdropping attack.
• Key management problems distribution, update,
  revoking

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Encryption

• Asymmetric Encryptions
• Also known as public key encryption
• Messages encrypted with the public key can only
  be decrypted by the corresponding private key.
• The public key can be made known to the public,
  but the private key is kept as secret and only
  known to the owner of the key.
• Examples of asymmetric encryption algorithms
• Merkel Hellman Knapsacks
• RSA Rivest, Shamir, Adleman
• El Gamal

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Encryption

• Limitations of asymmetric Encryptions
• Asymmetric encryption requires much larger keys
  than symmetric encryption.
• A 1024-bit asymmetric key a 128-bit symmetric
  key
• Why?
• Asymmetric encryption is much slower ( 1000
  times slower) than symmetric encryption.
• It is subject to man-in-the-middle attack.
• Solution? Digital certificates (Ch. 6)

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Encryption

• Session-key Encryption
• A session-key is a symmetric key that is used to
  encrypt the plaintext message. The session key
  itself is encrypted using a public key.
• Sender
• C Spub ( S ) Sencrypt (message) ? Recipient
• Recipient
• Spriv ( Spub (S) )? S
• Sdecrypt (Sencrypt (message)) ? message
• Alternatively, the session key may be assigned an
  expiration time and be used over several sessions.

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Encryption

• Examples of Session-key Encryption
• PGP (Pretty Good Privacy)
• Originally (1991) used to encrypt e-mail using
  session-key encryption
• Supports RSA, TripleDES, etc.
• http//www.pgp.com/
• S/MIME (Secure/MIME)
• Invented by RSA to secure e-mail
• Backed by Microsoft, RSA, and AOL
• SSL/TLS (Secure Socket Layer/Transport Layer
  Security) Ch. 9
• Originally an attempt to secure TCP/IP traffic
  using encryptions

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Encryption

• Key Agreement Algorithm
• A key agreement algorithm takes the private and
  the public keys of two distinct parties (Apriv
  Bpub or Apub Bpriv) and generates a common
  shared secret key, which is then used to generate
  a session key. See the diagram on p.41.
• Diffie-Hellman Key Agreement Algorithm The first
  ever public key encryption
• Allows two parties to independently generate the
  shared key The session key is never transmitted.
• References
• See http//www.apocalypse.org/pub/u/seven/diffie.h
  tml
• IETF RFC2631 http//www.ietf.org/rfc/rfc2631.txt

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Encryption

• Strength of Encryption Algorithms
• Two factors
• The algorithm used
• The size of the key space
• See the tables comparing symmetric ciphers (p.42)
  and asymmetric ciphers (p.43)

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Alternative Data-hiding Methods

• Steganography hiding messages inside another
  message or in a picture.
• See Steganography Hidden Data. By Deborah
  Radcliff. ComputerWorld. June 10, 2002.
• Elliptic Curve Cryptography (ECC) based on the
  elliptic curve logarithm problem a more
  efficient public key encryption (faster, smaller
  key size)
• An intro http//world.std.com/dpj/elliptic.html
  
• Codes, one-time pads, etc.

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Authentication

• The process of determining the authenticity of a
  message or user.
• Methods
• Message Digest
• a check value generated from a document, usually
  generated by a hash function
• to prove that the data in the document has not
  been tampered with.
• Commonly used for password authentication (i.e.,
  one-way authentication)
• Examples MD4, MD5, SHA (secure hash algorithm)
• Any problem? Man-in-the-middle attack Why?

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Authentication Methods

• MAC (Message Authentication Codes)
• A message digest created with a key
• Typically used for data verification in a context
  where a secure connection is already available.
• Example SSL uses MACs to verify the data
  received, using a secret key that is exchanged at
  the beginning of the session.
• Example MACs
• HmacMD5 (Hashing MAC using MD5)
• HmacSHA1 (Hashing MAC using SHA-1)

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Authentication Methods

• Digital Signatures
• Based on public key encryption
• Computed with a persons private key and verified
  with the persons public key
• An example of creating a digital signature p.48
• The sender applies a message digest algorithm to
  get a message digest (md) out of the message to
  be sent.
• The message digest is then encrypted by the
  persons private key. The ciphertext is the
  digital signature (ds).
• To check the digital signature
• The recipient applies the digest algorithm to get
  a message digest (md-2).
• The recipient decrypts the ds using the senders
  public key.
• The output from step 2 is verified against md-2.

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Authentication Methods

• Digital Certificates
• Purpose To authenticate a persons public key
• Vouching one party certifies that another
  partys identity is authentic. e.g., passport,
  id cards
• A digital certificate for A is As public key
  plus some identifying information, signed by the
  private key of a certification authority (CA)
  verifying As identity.
• Other example usage of certificates
• To authenticate a host/server (e.g., SSL
  certificates)
• To sign and encrypt e-mail

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Authentication Methods

• Digital Certificates (Cont.)
• Certificates are often chained. That is, a CA
  may be authenticated by a root CA.
• The top CA of a certificate chain must be
  self-signed.
• Verisign has been accepted as the top CA.
• Example of certificate chaining Both Internet
  Explorer and Netscape Communicator include
  certificates from Verisign in their install. So
  when the browser makes an SSL connection to a
  server, if the server presents a certificate that
  is signed by Verisign, the servers certificate
  will be automatically accepted.

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Cryptanalysis

• The practice of analyzing and breaking
  cryptography
• Mehtods
• Brute force attack versus the key space
• Common cryptanalytic tools Frequency
  distribution, Digram/trigram study, IC, Repeated
  patterns, Probable letters
• 4 cryptanalytic cases
• Ciphertext only ? Ciphertext-only attack
• Full or partial plaintext
• Known plaintext attack
• Probable plaintext analysis
• Ciphertext of any plaintext ? Chosen plaintext
  attack
• Algorithm Ciphertext ? Chosen ciphertext attack

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Key Management (storage)

• A dilemma Keys must be securely stored while
  allowing users easy access when necessary.
• A typical solution is to encrypt the stored keys
  with passwords and then protect the storage with
  the OS access control.
• A key storage is an attractive target for attack.
• The smart card solution A smart card stores a
  private key and a certificate, which can be used
  to encrypt and/or decrypt information.
• An example of smart card solution See Protection
  of Keys (RSA vs nCipher)

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Cryptographical Protocols

• Cryptographical protocols determine the exact
  order and way in which each algorithm must be
  used in order to maximize security.
• Examples of protocols
• Distribution of keys,
• Certificates, Digital signatures,
• Key escrow,
• Mental poker,
• Electronic voting,
• oblivious transfer, contract signing,
• certified mail

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JCA/JCE

• Java Cryptography Architecture (JCA) is part of
  the Java 2 run-time environment. ?
  java.security.
• JCE (Java Cryptography Extension), on the other
  hand, is an extension to the JCA. JCE adds
  encryption and decryption APIs to the JCA. ?
  java.crypto.
• Major classes defined in JCA
• MessageDigest, Signature, KeyPairGenerator,
  KeyFactory, CertificateFactory, KeyStore,
  AlgorithmParameters, AlgorithmParameterGenerator,
  SecureRandom,

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JCA/JCE

• A cryptographic service provider implements
  various cryptographic algorithms.
• See page 54 for a list of algorithms implemented
  in the SUN provider (sun.security.provider.Sun),
  Java 2 (v1.2).
• A second provider, the RSAJCA provider
  (com.sun.rsajca.Provider) is shipped with JDK
  v1.3, to provide RSA-specific cryptos.

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JCA

• An example of using MessageDigest in the JCA
• Get an instance of a message digest.
• MessageDigest myMessageDigest
• MessageDigest.getInstance (MD5)
• Or MessageDigest myMessageDigest
• MessageDigest.getInstance (MD5,Sun)
• Add data to be digested.
• myMessageDigest.update (myData)
• Get the digest.
• byte signatureBytes
• myMessageDigest.digest ( )

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JCE

• Major JCE classes
• Cipher, KeyAgreement, KeyGenerator, MAC,
  SecretKey, SecretKeyFactory
• JCE needs to be separately downloaded and
  installed if you have JDK older than v1.4.  For
  JDK1.4 or higher, JCE is an integrated component.
   
• See http//java.sun.com/products/jce/index-14.html
  for more details.

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JCE

• Installation of JCE security provider
• Sample programs http//nas.cl.uh.edu/yang/teachin
  g/csci5931webSecurity/JCE20provider.htm
• Visit http//sce.cl.uh.edu/yang/teaching/proJavaSe
  curityCode.html and download all the sample
  programs from the book.

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Next

• Symmetric Encryption (GS 4)
• Asymmetric Encryption (GS 5)