Transcript Information Security Databases and (Inter)Networks

Information Security
Internet, Intranet, Extranet
Prof. dr. P.M.E. De Bra
Department of Computing Science
Eindhoven University of Technology
Parts / Topics / Issues
• Basics of Internet technology / Organization
• Application of encryption in networks
• Principles of Firewalls / Virtual Private
Networks.
• Financial transactions over Internet
• Basics of World Wide Web technology
• Server-side security issues
• Client-side security issues
• Accessing databases through the Web
What is Internet?
• A network of networks based on the TCP/IP
protocols.
• A community of people who use and
develop those networks.
• A collection of resources that can be
reached from those networks.
Internet standards are defined in RFCs.
Informal definition of Internet is rfc 1462:
http://www.normos.org/ietf/rfc/rfc1462.txt
Layered Internet protocols
• Hardware-level protocol (wire without
protocol, ethernet protocol, X.25, ATM, ...).
• IP (lowest level Internet Protocol).
• TCP, UDP, ICMP: TCP is used most,
provides reliable connections.
• SMTP, FTP, Telnet, ...: Application-level
protocols (mostly on top of TCP/IP).
We look at 1) TCP, 2) IP, 3) UDP and ICMP,
4) Application-level protocols, 5) Ethernet
Internet Basics: Addressing
• Every computer has a 32 bit (4 octet) address:
e.g. 131.155.70.196. Addresses reveal
something about the associated network:
– First octet 1..126: A networks, very large.
(Arpanet is one of these 126 networks.)
– First two octets 128.1 .. 191.254: B networks,
maximum of 64516 computers in each network.
– First three octets 192.1.1 .. 223.254.254: C
networks, maximum of 254 computers in each.
– Addresses above 224.1.1 are reserved for the
future, for still undefined D and E networks.
Internet Basics: Addressing
• Some addresses are never used.
They can be used behind firewalls on
company Intranets:
– 10.0.0.0 to 10.255.255.255 can be used for an
A class Intranet.
– 172.16.0.0 to 172.16.255.255 can be used for a
B class Intranet.
– 192.168.0.0 to 192.168.255.255 can be used for
C class Intranets.
– First octet 127 is not used on Internet or Intranets.
(127.0.0.1 is the “loopback” on every machine.)
Internet Basics: TCP protocol
• Provides connections of connectionless IP
protocol, through the use of ports.
– A connection is defined by a source and
destination IP address and a source and
destination port. (A TCP header contains ports,
the IP header the IP addresses.)
– “Standard” servers “listen” to predefined
(privileged) ports, with numbers below 1024.
– Clients use unprivileged ports.
– One computer can have many simultaneous
connections to many other computers. All
connections between a pair of computers must use
different source or destination port numbers.
Internet Basics: TCP protocol
• Data to be transmitted is divided in (a
sequence of) datagrams.
– TCP software on both ends says how large a
datagram may be. The smaller size is chosen.
Each datagram consists of a header and data.
– Each datagram gets a sequence number. Each
received datagram is acknowledged by returning
a datagram with an acknowledgement number.
– The acknowledgement contains a window size,
indicating how many datagrams may be sent
before the sender has to stop.
– Every datagram gets a checksum to verify that
the contents has arrived correctly.
Internet Basics: IP
• IP sends datagrams from a source IP address
to a destination IP address. (It may also split
the datagram when needed.)
– Each datagram contains an IP header, with a
checksum (of the header only).
– The header contains a protocol (code) to indicate
whether it is a TCP, UDP or ICMP datagram.
– Each datagram is routed separately.
– Some datagrams may arrive faster than others.
– Some datagrams may be lost. Each header has a
time to live to indicate how much longer (number
of hops) the datagram may live.
Internet Basics: Routing
• Routing is the task of finding how to get a
datagram to its destination.
– Each machine can send datagrams directly to
some other machines on a local network.
– Each machine knows a gateway machine it can
send datagrams to.
– A gateway has connections to a number of
networks and maintains a routing table of which
connection to use for which destination.
– A gateway can respond to a request with “I’m not
the best gateway for this destination”.
Internet Basics: Domain Names
• Most applications and users use domain
names instead of IP numbers. A redundant
hierarchy of name servers provides translation
of names to numbers.
–
–
–
–
–
Name to reach: pcnov290.win.tue.nl
Ask a root server for an nl server.
Ask a server for the nl domain for a tue server.
Ask a server for the tue domain for a win server.
Ask a server for the win domain for the address of
pcnov290.
Internet Basics: UDP and ICMP
• UDP: User Datagram Protocol
–
–
–
–
–
Provides port numbers like TCP.
Provides a checksum for header + data.
Does not split data into separate datagrams.
Does not put sequences of datagrams together.
Does not keep track of lost datagrams, for
retransmission.
• ICMP: Internet Control Message Protocol
– Used for messages (that fit into a single datagram).
– Interpreted by IP itself. There are no port numbers.
Application level Protocols
• Many TCP/IP protocols are text-based so
that humans can easily interpret them:
Example: Mail dialog between client and server
svis01:
220 svis01.win.tue.nl ESMTP Sendmail
8.8.7/1.45 ready at Fri, 5 Feb 1999 23:28:31
+0100 (MET)
pcnov290: HELO pcnov290.win.tue.nl
svis01:
250 svis01.win.tue.nl Hello pcnov290
[131.155.71.147], pleased to meet you
pcnov290: MAIL From: [email protected]
svis01:
250 [email protected]... Sender ok
...
Application level Protocols
• Telnet: allows to log in on any other
computer on the network (on which you have
an account). It requires an interactive login.
(Username and Password are transmitted
without encryption.)
• Rlogin: allows to remote log in as a specific
user. It is possible to log in without password,
based on domain name. (Insecure).
• Ssh: “secure shell”, allows remote log in,
using encrypted channel, with or without
password. (public/private keys used between
computers.)
Application level Protocols
• Ftp: File Transfer Protocol. Used in
anonymous mode to access public file
servers, and with passwords to copy to and
from machines. Ftp uses separate “channel”
for commands and for data transfer.
• Rcp: Remote copy, allowed based on domain
name / user name combination. Insecure.
• Scp: Secure copy, allowed based on domain
name / user name combination and
public/private key encryption. Uses encrypted
channel to avoid snooping.
Application level Protocols
• SMTP: Simple Mail Transfer Protocol
• NNTP: Network News Transfer Protocol
• RPC: There are different varieties of
protocols for remote execution. (Remote
shell, remote procedure call, etc.)
• NFS: Network File System. Introduced by
Sun Microsystems. Uses UDP, not TCP.
• Remote Printing
• ...
Ethernet
• Each ethernet board has a unique 48 bit
address. (16 bits are assigned to a vendor, 32
bits can be used by the vendor).
• Every ethernet packet contains a source
address and destination address.
• Every ethernet packet contains a checksum at
the end.
• Ethernet interfaces automatically listen to
packets with their address as destination.
It is possible to cheat (to listen to everything).
Ethernet
• An ARP request is used to find out which
ethernet address corresponds to an IP number.
• ARP is needed to talk to Internet hosts on the
local ethernet.
• (Local) ethernet routers can block packets that
originate from machines with an unknown
ethernet address. (It is easier to pretend to
have a different IP number than to pretend to
have a different ethernet number.)
Internet security: Issues
• How to achieve secure (secret and reliable)
communication over an insecure network.
(Which encryption techniques fit which
purpose.)
• How to prevent unauthorized access to
services while allowing authorized access to
other services.
• How to isolate a company network from
Internet, while allowing the use of Internet
by computers in the company.
Internet communication threats
• Snooping: Any computer on Internet can
intercept passing datagrams. One can
easily filter out the data belonging to a
single connection.
Internet communication threats
• Spoofing: A computer can pretend to be
another one (by using the other’s IP
number) and thus steal its traffic.
Internet communication threats
• Spoofing: Man in the middle variation
Spoofing machine talks to the “real” owner
of IP number, to pass on corrupted data.
Secure communication
• Four requirements:
– Confidentiality: others cannot eavesdrop on an
information exchange.
– Integrity: the messages cannot be tampered
with (without that being detected).
– Authenticity: the identity of the sender of a
message can be verified (through a digital
signature).
– Non-Repudiability: there must be a record of
the information exchange so that sender and
receiver cannot deny that the exchange took
place.
Encryption Techniques
• Secret key encryption: Two parties
exchanging information need to know the
same secret key. It is used for encryption
and decryption of a message.
• Public key encryption: Two keys work
together: a public and a private key. A
message encrypted with either key can be
decrypted with the other key. One key is
published, the other is kept secret.
Encryption Standards
• DES: Data Encryption Standard, developed
by IBM. (certified by NIST as FIPS 46-1,
and also known as ANSI standard X9.32)
– Uses 64-bit block size and 56-bit key (plus 8
parity bits).
– Symmetric cryptosystem, built around a 16
round Feistel cipher.
– Originally designed for implementation in
hardware.
– Not approved for export outside the USA.
– DES can be broken, at considerable cost.
Encryption Standards
• Triple-DES: Variation of DES where each
message is encrypted three times. There are
three variations:
– DES-EEE3: three DES encryptions with three
different keys.
– DES-EDE3: encrypt, decrypt, encrypt with
three different keys.
– DES-EEE2 and DES-EDE2: same as before
but the first and third operations use the same
key.
Multiple encryption does not necessarily make
encryption harder to break.
Encryption Standards
• RC2: variable key-size block cipher (designed
by Ron Rivest, leading to the name “Ron’s Code” or
“Rivest Cipher”.)
– Symmetric cryptosystem.
– Can be made more secure or less secure by
using different key sizes.
– Uses a block size of 64 bits.
– Twice as fast as DES.
– Approved for US export with 40-bit key.
Encryption Standards
• RC4: variable key-size stream cipher with
byte-oriented operations.
– Symmetric cryptosystem.
– Can be made more secure or less secure by
using different key sizes.
– Can be implemented efficiently.
– Approved for US export with 40-bit keys.
• RC5: variable block-size, variable key-size,
variable number of rounds. (Patent by RSA)
– Symmetric cryptosystem.
– Can be implemented efficiently.
Encryption Standards
• IDEA: (International Data Encryption
Algorithm) is a 64 bit iterative block cipher
with a 128 bit key.
– Symmetric cryptosystem.
– Can be implemented efficiently in hardware
and software.
– Widely published about, and thus not subject to
export restrictions.
Encryption Standards
• RSA: public-key cryptosystem. Used for
encryption and for digital signatures:
– Asymmetric cryptosystem. Uses pairs of keys,
one public, one private.
– At least 100 times slower than DES, thus not
suitable for encrypting large messages or data
streams.
Encryption Standards
• Practical use of RSA (or other public-key
cryptosystems): supposes A wishes to send a
secret, signed message to B.
1.A applies a hash function to the message to create
a message digest, a digital fingerprint of the
message.
2.A encrypts the digest with her private key.
3.A encrypts the message and digest with B’s public
key and sends that to B.
4.B decrypts the message and digest with B’s
private key.
5.B decrypts the digest with A’s public key.
6.B performs the hash function on the message and
compares it to the digest.
Secure Hash Functions
• SHA: Secure Hash Algorithm (NIST FIPS
PUB 180) produces a 160-bit message
digest.
• MD2: Hash algorithm for 8 bit machines.
• MD4, MD5: Hash algorithms for 32 bit
machines. They produce a 64-bit message
digest.
Secure Sockets Layer
• Introduced by Netscape Communication to
enable secure communication between a
Web browser and servers.
• Extra layer between application and TCP/IP.
• Is application independent. Applications see
an (unencrypted) data channel.
• Performs
– Encryption of communication.
– Server validation.
– Optional client validation.
Secure Sockets Layer
• Supported encryption techniques:
–
–
–
–
–
RC2:
RC4:
IDEA:
DES:
Triple-DES:
• Supported message digest technique:
– MD5
Secure Sockets Layer
1. Client opens a channel to the server.
2. Server sends its certificate and cipher preferences.
3. Client generates a master key, encrypts it with the
server’s public key, and sends it to the server.
4. Server decrypts the master key, and authenticates
itself by returning a message to the client, encrypted
using the master key.
5. The server may send a challenge to the client.
6. The client authenticates itself by returning the
client’s digital signature on the challenge and its
public key certificate.
Encryption at the IP level
• S/WAN (Secure Wide Area Network)
promotes the deployment of Internet-based
Virtual Private Networks (VPNs).
– Standard specification for implementing IPsec.
– Possibly lower level security than SSL.
– S/WAN uses RC5 encryption with keys ranging
from 40 to 128 bits.
– Protocol formats for Authentication Header
and Encapsulating Security Payload are
independent of cryptographic algorithm.
– Host-to-host, subnet-to-subnet and host-tosubnet secure communication.
Secure Shell
• Protocol for secure remote access from one
computer to another.
– Can be used for secure login on a server, or for
setting up a virtual private network.
– Ssh can be configured to forward X11
connections over the encrypted “tunnel”.
– Other TCP/IP connections can also be tunneled
through ssh to the server to give secure access
to mail, web, file systems, ftp, etc.
– info: http://www.ssh.fi/
Kerberos
• Authentication service, part of Project
Athena at MIT.
– Uses secret key encryption (originally DES).
– Designed to authenticate requests for network
resources, not authorship of documents.
– A server performs centralized key management.
It contains the secret keys for all users.
This creates a single point of failure.
– Considered adequate for local networks or
networks within one administrative domain.
PGP: Pretty Good Privacy
• Software package that provides
cryptographic routines for e-mail and file
storage.
– Provides message encryption, digital signatures,
data compression and e-mail compatibility.
– RSA and Diffie Hellman for key transport.
– CAST and Triple-DES for message encryption.
– RSA or DSA for signing. (export restrictions!)
– MD5, RIPEMD-160 or SHA-1 for computing
message digests.
– Compression through the ZIP program.
S/MIME
• Secure/Multipurpose Internet Mail Extensions.
– Adds digital signatures and encryption to MIME.
– (MIME standards, see rfc1521 and rfc822)
– Endorsed by many messaging vendors, including
Microsoft, Lotus, Wollongong, Banyan, NCD,
VeriSign, Netscape and Novell.
– Uses hierarchies of trusted third parties to verify
the authenticity of the keys provided by users (or
servers).
– Secret key algorithms DES, Triple-DES, RC2.
– Private key algorithm: RSA.
Host (or Subnet) Security
• Any technical solution for security must be
used as a means of implementing a chosen
security policy:
–
–
–
–
–
What are we protecting?
How important is it?
How likely is it that it will be attacked?
What should happen if an attack is successful?
What is permitted, by whom and for what
purpose?
– What Internet connectivity is needed from the
host or subnet?
Firewalls: background
• A firewall provides security for an Intranet
by controlling what and how can be
communicated with Internet.
Firewalls cannot protect against:
– Attacks that do not go through the firewall
(hand carried tapes/disks, modem connections).
– Data-driven attacks: something (malicious) is
uploaded or copied through a legitimate
channel, and then executed.
– Denial of service attacks that overload the data
connection between Intranet and Internet.
Firewall architectures
• Approaches:
– packet filtering: allow only datagrams with
certain properties to pass.
– proxy services: application-level gateways that
forward datagrams and hide the Intranet.
• Architectures:
– dual-homed host: one host with two network
interfaces, one for Intranet, one for Internet.
– screened host: packet filter combined with
bastion host providing gateway/proxy services.
– screened subnet: trusted/untrusted subnets.
Packet filtering (screening router)
Packet filtering (screening router)
• Selectively blocks or lets through packets
between the Intranet and Internet, based on:
–
–
–
–
–
Source IP address
Destination IP address
Protocol (TCP, UDP)
Source port
Destination port
• For each combination one can configure the
filter to allow or deny all values, certain
ranges, or single values.
Proxy Services
Proxy Services
• Specialized services (application-level
gateways) take a request from an Intranet
computer and forward it to Internet.
– Proxies are most useful when Intranet computers
can only reach Internet through the proxy.
– Many applications can be configured to use
proxies. SOCKS is a proxy construction toolkit
used to modify clients for proxy operation.
– To the Internet hosts all Intranet requests appear to
come from the proxy server. A proxy is
sometimes used to hide where a request came
from.
Dual-Homed Hosts
Dual-Homed (Bastion) Hosts
• Requires a host with two network interfaces.
– High level of control, but possibly also a high
workload on the bastion host.
– All traffic must pass through the bastion host.
– The bastion host offers proxy services.
– The IP addresses of the Intranet computers are
invisible on Internet. Special ranges are reserved
for this: 10.x, 172.16 and 192.168.
– The bastion host should off as few services as
possible. It should not have user accounts.
Screened Host
Screened Host
• Requires a screening router and a bastion
host.
– The router blocks all traffic to and from the
Intranet except to and from the bastion host.
– The bastion host offers proxy services just like
the dual-homed host, but needs no second
network interface.
– Combination of router and bastion host may offer
better protection than dual-homed host.
– Internal network is vulnerable for denial of
service attacks.
Screened Subnet
Screened Subnet
• Extra layer of security by adding a perimeter
network.
– Vulnerable bastion host is isolated from the
internal network.
– Prevents possibility of snooping on the Intranet
after breaking in to the bastion host.
– Services from bastion host to Internet may differ
from services from bastion host to Intranet.
– There may be several hosts on the perimeter
network: for e-mail, ftp server, WWW server,
DNS server, etc.
Screened Subnet
• Interior router:
– Allows selected services outbound to Internet,
and only through the bastion host (proxies).
– Limits services between bastion host and
Intranet (in case bastion is broken into).
• Exterior router:
– Protects perimeter and Intranet.
– Allows most outbound services.
– Allows only incoming and outgoing services
needed by bastion host.
– Blocks packets with forged Intranet addresses.
Variation: sub-Intranets
Variation: sub-Intranets
• Firewalls can be used to protect parts of
internal networks from each other.
– Test or demonstration networks with less
security.
– Highly confidential networks with more security.
• Different configurations are possible, with
more connections to Internet and between
internal networks.
Internet Tunneling: Extranets
Internet Tunneling: Extranets
Internet Tunneling: Extranets
• Encapsulating data in wrapper packets.
Not only TCP/IP traffic can be tunneled,
also Novell IPX or other protocols.
– Source and destination do not notice the
tunneling. No modifications to applications.
– Encryption can be done for the whole group-togroup connection or on a point-to-point basis.
– PPTP Point-to-Point Tunneling Protocol is
embedded in operating systems such as
Windows 95 and Windows-NT.
– There are many proprietary tunneling protocols.
Point to Point Tunneling Protocol
• PPTP was developed by Microsoft. It is
aimed at dial-in connections using PPP.
– User access is first controlled through PAP
(Password Authentication Protocol) or CHAP
(Challenge Handshake Authentication Protocol).
– Each PPP packet is encoded with 40-bit RC4.
The encryption prevents the network from
reading the destination information.
– The PPP packet is encapsulated within a GRE
(Generic Routing Encapsulation) packet which
includes destination information.
IPsec
• IPsec might be a successor/replacement for
PPTP, and has much wider applications than
just tunneling. It addresses authentication,
integrity, access control and confidentiality.
– Supports a variety of encryption algorithms
(including a standard set to be used in the global
Internet).
– Uses two headers: AH (Authentication Header)
and ESP (Encapsulating Security Payload).
– AH verifies that the data hasn’t been altered.
– ESP encrypts the data so it remains confidential.
IPsec (cont.)
•
IPsec can be used to protect
communication:
–
–
–
•
between a pair of hosts; (i.e. these hosts do the
encryption and decryption and must be trusted)
between a pair of security gateways; (e.g.
group-to-group tunneling between remote parts
of an extranet)
between a security gateway and a host; (e.g.
personal-to-group tunneling in an extranet)
Each packet is afforded IPsec security,
allowed to bypass IPsec, or discarded.
IPsec (cont.)
•
The IP Authentication Header (AH):
–
–
–
•
The Encapsulating Security Payload (ESP):
–
–
–
•
provides connectionless integrity;
provides data origin authentication;
provides (optional) anti-replay service (i.e. a
form of sequence integrity).
provides confidentiality (encryption);
provides traffic flow confidentiality;
may also provide connectionless integrity, data
origin authentication and an anti-replay service.
AH and ESP can provide access control.
IPsec (cont.)
•
The user can control granularity:
–
–
A single encrypted tunnel can be used to carry
all the traffic between two security gateways;
A separate encrypted tunnel can be created for
each TCP connection between each pair of hosts
communicating through the gateways.
Note that the granularity of SSL is finer than
the single tunnel and coarser than the separate
tunnel for each TCP connection.
Home Networks
• To connect several computers at home (consisting
of PCs):
– Local lan consists of ethernet.
– Connection to ISP through modem or “fixed”
network (cable modem, isdn router, etc.).
– This effectively creates a dual-homed host.
– The internal network can use 192.168 range.
– On the bastion host you must enable IP
forwarding.
– In the network “security” options you need to
select TCP and UDP ports to enable/disable.
– You need to setup proxy services on bastion.
– You need to configure the other PCs to use the
proxies. (e.g. through a package like Sygate.)
Interesting URLs
• Tutorial on TCP/IP:
http://tecnet0.jcte.jcs.mil:9000/htdocs/utl/iis/tcp.txt.html
• Encryption-related info from RSA labs:
ftp://ftp.rsa.com/pub/labsfaq/labsfaq4.pdf
• Virtual Private Networks (student paper):
http://amir.fullerton.edu/msis410/Projects/Group12/vpnpap
er.htm
• Working group on IPsec:
http://www.ietf.org/html.charters/ipsec-charter.html