Routing Overview

1
Web Computing Security CS587x Lecture
13 Department of Computer Science Iowa State
University
2
What to Cover

• Internet security issues
• Introduction to cryptography
• Secured Socket Layer (SSL)

3
Internet Security Issues

• A TCP/IP packet could go through many
  intermediate computers and separate networks
• Possible ways for communication interference
• Eavesdropping
• Information remains intact, but its privacy is
  compromised. For example, someone could learn
  your credit card number, etc.
• Tampering
• Information in transit is changed or replaced and
  then sent on to the recipient. For example,
  someone could alter an order of goods
• Impersonation
• Information passes to a person who poses as the
  intended recipient. For example, a person can
  pretend to have the email address
  jdoe_at_mozilla.com or a computer can identify
  itself as www.mozilla.com while it is not

4
Public-Key Cryptography

• The goals of developing this standard
• Encryption and decryption
• Allow two communication parties to disguise
  information they send to each other.
• Tamper detection
• Allows the recipient of information to verify
  that it has not been modified in transit
• Authentication
• Allows the recipient of information to determine
  its origin, i.e., confirm the senders identity
• Nonrepudiation
• Prevents the sender of information from claiming
  at a later date that the information was never
  sent

5
Encryption and Decryption

• Encryption is a process of transforming
  information so it is intelligible to anyone but
  the intended recipient
• Decryption is a process of transforming encrypted
  information so it is intelligible again
• A cryptography algorithm (also called cipher) is
  a mathematical function used for encryption or
  decryption.
• In most cases, two related functions are
  employed, one for encryption and the other for
  decryption
• Cryptography algorithms are widely known
• The ability to keep encrypted information secret
  is based not on the cryptography, but on a number
  called key
• Key is used with the algorithm to produce an
  encrypted result or to decrypt previously
  encrypted information

6
Symmetric-Key Encryption

• With symmetric-key encryption, the encryption key
  can be calculated from the decryption key and
  vice versa
• With most symmetric-key encryption, the same key
  is used for both encryption and decryption

7
Symmetric-Key Encryption

• Advantages
• Highly efficient implementation
• fast encryption and decryption
• Provides some degree of authentication
• information encrypted with one symmetric key
  cannot be decrypted with any other symmetric key.
• Disadvantages
• Effective only if the key is kept secret by the
  two parties involved
• If anyone else discovers the key, it affects both
  confidentiality and authentication
• The person not only can decrypt messages sent
  with that key, but can encrypt new messages and
  send them as if they came from one of the two
  parties who were originally using the key

8
Public-Key Encryption

• Public-key encryption (also called asymmetric
  encryption) involves a pair of keys public key
  and private key
• Public key is published and could be well-known
• Private key is associated with an entity that
  needs to authenticate its identity electronically
  or to sign or encrypt data
• Data encrypted with a public key can be decrypted
  only with some corresponding private key
• To send data to someone, you encrypt the data
  with his public key, and the person receiving the
  encrypted data decrypts it with the corresponding
  private key
• Data encrypted with private key can be decrypted
  only with corresponding public key (more details
  later)

9
Public-Key Encryption

• Advantage
• Allow to freely distribute public key to the
  sender
• Private key can be kept in secret
• Disadvantage
• Compared with symmetric-key encryption,
  public-key encryption requires more computation
  and is therefore not always appropriate for large
  amounts of data
• The way to leverage the advantage and minimize
  the disadvantage
• Use public-key encryption to send a symmetric
  key, which can be then be used to encrypt
  additional data. This is the approach used by
  the SSL protocol

10
Temper Detection

• Encryption and decryption solves only the problem
  of eavesdropping
• The problem of tampering and impersonation
  remains
• Tamper detection is done by using public-key
  encryption for digital signature
• Impersonation can be addressed by certification
  and authentication

11
Digital Signature

• Tamer detection replies on a mathematical
  function called a one-way hash (also called a
  message digest)
• A one-way hash is a number of fixed length with
  the following characteristics
• Ideally, the value of the hash is unique for the
  hashed data. Any change in the data, even
  deleting or altering a single character, results
  in different value
• The content of the hashed data cannot, for all
  practical purposes, be deduced from the hash
  which is why it is called one-way

12
Digital Signature

• Public-key encryption allows you to use your
  private key for encryption and your public key
  for decryption
• This feature can be used to digitally signing any
  data
• The signing software creates a one-way hash of
  the data, then uses your private key to encrypt
  the hash
• The encrypted hash, along with other information,
  such as the hashing algorithm, is known as a
  digital signature

13
Digital Signature

• The source sends data as follows
• One-way hash the original data is one-way hashed
• Encrypt it with your private key
• Send both the original data and digital signature
  to the recipient
• The recipient validates the data integrity as
  follows
• Decrypt the digital signature using the public
  key
• Use the same hash algorithm to one-way hash the
  received data
• The data has not been tempered if the two sets of
  data are the same

14
A Certificate Identifies an Entity

• What is certificate?
• A certificate is an electronic document used to
  identify an individual, a server, a company, or
  some other entity
• Just like a driver license identifies a person
• Who issues certificate?
• Certificate Authorities (CA)
• can be either independent third party or
  organizations running their certificate-issuing
  server software
• Before issuing a certificate, CA must go through
  certain verification procedures, depending on the
  CAs policies

15
Certificate Content

• Each certificate always
• binds a particular public key to the certified
  entity
• Only the public key certified by the certificate
  will work with the corresponding private key
  possessed by the owner of the certificate
• includes the digital signature of the issuing CA
• For tempering detection - you cannot change a
  certificate
• The signature allows the certificate to function
  as a letter of introduction for users who know
  and trust the CA but dont know the entity
  identified by the certificate
• Of course, a certificate also includes the name
  of the entity it identifies, an expiration date,
  the name the of CA that issued the certificate

16
Sample Certificate Content
Basic CA/Emailpersonal-basic_at_thawte.com
Subject Public Key Info Public Key
Algorithm rsaEncryption RSA Public Key
(1024 bit) Modulus (1024 bit)
00bcbc93536dc0504f8215e64894
a65abe6f42fa0f47ee777572dd8d49
9b9657a078d4ca3f51b3690b917617
2207976ac451934be08def3795a1
0c 4dda34901d178997e03538574
ac0f4 0870e93c447b507e619a90
e323d388 114627f50b070ebbddd1
7f200a88b9 560b2e1c80daf1e39
e29ef14bd0a44 fb1b5b18d1bf23
9321 Exponent 65537 (0x10001)
X509v3 extensions X509v3 Basic
Constraints critical CATRUE Signature
Algorithm md5WithRSAEncryption
2de2996bb03d7a89d759a294011f2bdd12
4b 53c2ad7faaa7005c914057254a38
aa8470b9 d9800fa57b5cfb73c6bdd7
8a615c03e32d27 a817e0848542dc5e
9bc6b7b26dbb74afe43f
cba7b7b0e05dbe78832594d2db810f7907
6d 4ff439155a52017bde32d64d38f6
125c0650 df055bbd144ba1df29ba3b
418df76356a1df 22b1
openssl x509 -noout -text -in thawte.
cer Certificate Data Version 3 (0x2)
Serial Number 0 (0x0) Signature Algorithm
md5WithRSAEncryption Issuer CZA, STWestern
Cape, LCape Town, OThawte Consulting,
OUCertification Services Division, CNThawte
Personal Basic CA/Emailpersonal-basic_at_thawte.com
Validity Not Before Jan 1 000000
1996 GMT Not After Dec 31 235959 2020
GMT Subject CZA, STWestern Cape, LCape
Town, OThawte Consulting, OUCertification
Services Division, CNThawte Personal
17
Authentication Confirms an Identity

• Password-based authentication
• A client submits user name and password
• Server checks database to see if name and
  password match
• Certificate-based authentication
• A client digitally signs some piece of data,
  which are randomly generated based on the input
  from server and client
• Both client and server must know exactly the data
  to be signed
• The client sends both the certificate and the
  signed data to the server
• The server uses the public key in the certificate
  to decode the signed data
• The signed data is an evidence used to verify
  if the client owns the private key corresponding
  to the public key stored in its certificate

18
Certificate-based authentication
19
Types of Certificates

• Client/server certificates
• Used to authenticate client/server via SSL
• S/MIMI certificates
• Used for signed and encrypted email
• Object certificates
• Used to identify signers of Java code or other
  signed files
• CA certificates
• Used to identify Certificate Authorities that can
  be trusted

20
Establishing trust through CA Certificates

• Any client/server software that supports
  certificates maintains a collection of trusted CA
  certificates
• It is possible to delegate certificate-issuing
  responsibility to subordinate CAs, thus, creating
  CA hierarchies
• The root CAs certificate is a self-signed
  certificates, i.e., it is digitally signed by the
  same entity
• The CAs that are directly subordinate to the root
  CA have CA certificate signed by the root CA
• CAs under the subordinate CAs in the hierarchy
  have their CA signed the higher-level subordinate
  CAs

21
CA Hierarchies
Note each certificate is signed with the private
key of its issuer so that its authenticity can be
verified through its public key
22
Certificate Verification
23
Certificate Standards

• X.509 Standard
• Created to provide credentials for X.500
  directory objects
• V1 published as part of X.500 directory
  recommendations
• V3 (1996) added much flexibility
• added provisions for extension fields (V3
  extensions)
• V3 use pretty much universal for Internet
  applications
• supports mail, c/s, IPsec
• alternatives limited to special purposes, e.g PGP
  certificates

24
Design Goals of Secure Sockets Layer

• Negotiates and employs essential functions for
  secure transactions
• Mutual Authentication
• Establish trust with intended recipients
• Signed Digital Certificates
• Server Authenticates to Client
• Client Authenticates to Server (optional)
• Data Encryption
• Privacy and confidentiality
• Support different algorithms for different
  application needs
• Data Integrity
• Insure no one tampers with data transmissions
  intentionally or not
• Freshness of transactions to avoid replays
• As simple and transparent as possible, seamlessly
  integrated into existing protocols including
  TCP/IP

25
Secure Sockets Layer (SSL)

• Platform and Application Independent
• Operates between application and transport layers

26
TCP over IP
IP Header
IP Data
Src
Dst
TCP Header
TypeTCP
TCP Data
SrcPort
DstPort
SeqNum
Application Data
27
SSL over TCP over IP
IP Header
IP Data
Src
Dst
TypeTCP
TCP Header
TCP Data
TLS
TLS Payload
SrcPort
DstPort
SeqNum
EncryptedApplicationData
28
SSL 3.0 Layers

• Record Layer
• Fragmentation
• Compression
• Message Authentication (MAC)
• Encryption
• Alert Layer
• close errors
• message sequence errors
• bad MACs
• certificate errors
• Handshake Layer
• All messages are MACd
• Message order is absolute
• Negotiation messages are created here and handed
  to record layer

29
SSL Handshake

• SSL protocol uses a combination of public-key and
  symmetric key encryption
• Symmetric key encryption is much faster than
  public-key encryption
• Public-key encryption provides better
  authentication techniques
• Each SSL session always begin with an exchange of
  messages called SSL handshake
• Allows the server to authenticate itself to the
  client using public-key techniques
• Allows the client and the server to cooperate in
  the creation of symmetric keys used for rapid
  encryption, decryption, and tamper detection
  during the session that follows

30
Handshake Protocol

• The client sends the server
• the clients SSL version number, cipher settings,
  randomly generated data, etc.
• The server sends the client
• The servers SSL version number, cipher settings,
  randomly generated data, etc.
• The servers own certificate
• Request for the clients certificate if the
  client is requesting a server resource that
  requires client authentication
• The client and the server selects a common cipher
• Allows use of multiple ciphers because
• Some countries disallow the use of strong ciphers
• Strong ciphers may require too much computational
  overhead
• Some communications must be secured with a strong
  cipher
• SSL uses strongest commonly-allowed cipher suite

31
Handshake Protocol Summary

• The client uses some of the information sent by
  the server to authenticate the server
• If the authentication fails, terminate the
  connection
• The client creates the premaster secret for the
  session, using the data generated during the
  handshake so far
• The secret is sent to the server after encrypted
  with the servers public key (obtained from the
  servers certificate)
• Only the corresponding private key can correctly
  decrypts the secret, so the client has some
  assurance that it is talking to the authentic
  server
• If the server requests client authentication
  (optional), the client also signs another piece
  of data and sends it with the clients
  certificate
• The data must be unique to this handshake and
  known by both the client and the server (why?)
• Terminate the connection if authentication fails

32
SSL Handshake Protocol

• Both the server and client follow the same steps
  to generate the master secret from the same
  premaster secret
• If the server does not have the right private
  key, it cannot generate the right master secret
• Both the client and the server use the master
  secret to generate the session keys, which are
  symmetric keys used to
• encrypt and decrypt information exchanged during
  the SSL session
• verify data integrity, i.e., detect any changes
  in the data between the time it was sent and the
  time it was received
• Finishing handshake
• The client and the server send each other a
  message informing that future messages from will
  be encrypted with the session key

33
Session Key Generation
Premaster Secret
Master Secret
Session Key

• Both server and client need to generate the
  session key
• The session key is not sent via network

34
A Simplified Way?
send its public key to the client
client
server
Use the public key to encrypt the session key

• Server sends its public key to the client
• Client generates the session key, encrypts it
  with the public key and then sends the
  encrypted session key to the server
• The server decrypts the message and gets the key
• Server and client now use the same session key to
  encrypt and decrypt their communication

35
Man-In-The-Middle Attack
key
key
M
C
S
session key encrypted with key
session key encrypted with key

• A simple scenario
• When M receives the public key from S, M replaces
  the public key with its own public key
• M sends its own public key to C
• C generates the session key, encrypts it with the
  public key and then sends the encrypted session
  key to M
• M decrypts the message with its own private key
  and gets the session key
• M encrypts the session key with the public key
  from S and forwards the result to S
• M can now eavesdrop all communication between S
  and C
• How about verifying the digital signature of C?

36
Checking Server Certificate
37
Checking Client Certificate
38
Java SSL

• Java 1.4 includes Java Secure Socket Extention
  (JSSE)
• JSSE can be downloaded and installed into
  previous versions of Java
• Obtain SSLSocket or SSLServerSocket objects via
  javax.net.ssl's SSLServerSocketFactory and
  SSLSocketFactory classes

39
JSSE API Client Socket Factory Methods

• javax.net.ssl.SSLSocketFactory methods
• static SocketFactory getDefault()
• Socket createSocket(String host, int port)
• Socket createSocket(String host, int port,
  InetAddress localHost, int localPort)
• Socket createSocket(InetAddress host, int port)
• Socket createSocket(InetAddress host, int port,
  InetAddress localHost, int localPort)
• Socket createSocket(Socket socket, String host,
  int port, boolean autoClose)
• String getDefaultCipherSuite()
• String getSupportedCipherSuites()

40
JSSE API Client Socket Methods

• javax.net.ssl.SSLSocket methods (extends Socket)
• Supported SSL cipher suites
• String getEnabledCipherSuites()
• String getSupportedCipherSuites()
• void setEnabledCipherSuites(String suites)
• SSL session creation enabled?
• boolean getEnableSessionCreation()
• void setEnableSessionCreation(boolean flag)
• SSL client authentication required?
• boolean getNeedClientAuth()
• void setNeedClientAuth(boolean need)

41
JSSE API Client Socket Methods (2)

• Change from SSL client to SSL server mode
• boolean getUseClientMode()
• void setUseClientMode(boolean mode)
• Initiate the SSL handshake protocol
• void startHandshake()
• Add/remove SSL handshake listener (notified when
  SSL handshake operations complete on the socket)
• void addHandshakeCompletedListener
  (HandshareCompletedListener listener)
• void removeHandshakeCompletedListener
  (HandshareCompletedListener listener)

42
JSSE API Server Socket Factory Methods

• javax.net.ssl.SSLServerSocketFactory methods
• static ServerSocketFactory getDefault()
• ServerSocket createServerSocket(int port)
• ServerSocket createServerSocket(int port, int
  LQsize)
• ServerSocket createServerSocket(int port, int
  LQsize, InetAddress localAddress)
• String getDefaultCipherSuites()
• String getSupportedCipherSuites()

43
JSSE API Server Socket Methods

• javax.net.ssl.SSLServerSocket methods
• Supported SSL cipher suites
• String getEnabledCipherSuites()
• String getSupportedCipherSuites()
• void setEnabledCipherSuites(String suites)
• SSL session creation enabled?
• boolean getEnableSessionCreation()
• void setEnableSessionCreation(boolean flag)
• SSL client authentication required on accepted
  sockets?
• boolean getNeedClientAuth()
• void setNeedClientAuth(boolean need)
• Switch accepted sockets from SSL client mode to
  SSL server mode
• boolean getUseClientMode()
• void setUseClientMode(boolean mode)

44
Example Server

• import java.io.
• import javax.net.ssl.
• public class EchoServer
• public static void main(String arstring)
• try
• SSLServerSocketFactory sslserversocketfactor
  y
• (SSLServerSocketFactory)SSLServerSocketFac
  tory.getDefault()
• SSLServerSocket sslserversocket
• (SSLServerSocket)sslserversocketfactory.cr
  eateServerSocket(9999)
• SSLSocket sslsocket (SSLSocket)sslserverso
  cket.accept()
• InputStream inputstream
  sslsocket.getInputStream()
• InputStreamReader inputstreamreader new
  InputStreamReader(inputstream)
• BufferedReader bufferedreader new
  BufferedReader(inputstreamreader)
• String string null
• while ((string bufferedreader.readLine())
  ! null)
• System.out.println(string)
• System.out.flush()

45
Example Client

• import java.io.
• import javax.net.ssl.
• public class EchoClient
• public static void main(String arstring)
• try
• SSLSocketFactory sslsocketfactory
  (SSLSocketFactory)SSLSocketFactory.getDefault()
• SSLSocket sslsocket (SSLSocket)sslsocketfa
  ctory.createSocket("localhost", 9999)
• InputStream inputstream System.in
• InputStreamReader inputstreamreader new
  InputStreamReader(inputstream)
• BufferedReader bufferedreader new
  BufferedReader(inputstreamreader)
• OutputStream outputstream
  sslsocket.getOutputStream()
• OutputStreamWriter outputstreamwriter new
  OutputStreamWriter(outputstream)
• BufferedWriter bufferedwriter new
  BufferedWriter(outputstreamwriter)
• String string null
• while ((string bufferedreader.readLine())
  ! null)
• bufferedwriter.write(string '\n')

46
Running the Samples

• java -Djavax.net.ssl.keyStorekeystore
  -Djavax.net.ssl.keyStorePasswordkeystorePassword
  EchoServer
• java -Djavax.net.ssl.trustStoretruststore
  -Djavax.net.ssl.trustStorePasswordtruststorePassw
  ord EchoClient

47
Java Certificate Classes

• java.security.cert
• Certificate (abstract class)
• CRL (abstract class)
• CertificateFactory
• To obtain instances of Certificates and CRLs
• X509Certificate extends Certificate
• X509CRL extends CRL

48
CertificateFactory Class

• public static CertificateFactory
  getInstance(String stringType)
• Type is, e.g., X.509
• public static CertificateFactory
  getInstance(String stringType, String
  stringProvider)
• public final Certificate generateCertificate(Input
  Stream inputstream)
• public final Collection generateCertificates(Input
  Stream inputstream)
• public final CRL generateCRL(InputStream
  inputstream)
• public final Collection generateCRLs(InputStream
  inputstream)

49
Certificate Interface

• public abstract PublicKey getPublicKey()
• public abstract byte getEncoded()
• public abstract void verify(PublicKey publickey)
• public abstract void verify(PublicKey publickey,
  String stringProvider)

50
X.509 Certificate Interface

• public abstract byte getEncoded()
• Returns certificate encoded in DER format
• public abstract int getVersion()
• public abstract Principal getSubjectDN()
• public abstract Principal getIssuerDN()
• public abstract Date getNotBefore()
• public abstract Date getNotAfter()
• public abstract BigInteger getSerialNumber()
• public abstract String getSigAlgName()
• public abstract String getSigAlgOID()
• public abstract int getBasicConstraints()
• public abstract boolean getKeyUsage()
• public Set getCriticalExtensionOIDs()
• public Set getNonCriticalExtensionOIDs()

51
Summary

• Introduction to cryptography
• Symmetric key and public key encryption/decryption
  
• Digital signature
• Certificate
• Secure Sockets Layer
• SSL handshake
• Java Secure Sockets Extensions
• Socket factories
• SSLSockets and SSLServerSockets
• Sample client and server