2. objectives
• Summarize Web security threats and web traffic security
approaches.
• Present an overview of Secure Sockets Layer (SSL).
• Understand the differences between Secure Sockets Layer
and Transport Layer Security.
• Present an overview of HTTPS (HTTP over SSL).
• Present an overview of Secure Electronic Transactions
(SET) and Dual Signature.
3. We cannot enter into alliance with neighboring
princes until we are acquainted with their
designs.
—The Art of War, Sun Tzu
4. Key points
• Secure socket layer (SSL) provides security services
between TCP and applications that use TCP.
• The Internet standard version is called Transport Layer
Security (TLS).
• SSL/TLS includes protocol mechanisms to enable two
TCP users to determine the security mechanisms and
services they will use.
5. Web Security
Considerations
• The World Wide Web is
fundamentally a client/server
application running over the Internet
and TCP/IP intranets
• The following characteristics of Web
usage suggest the need for tailored
security tools:
• Web servers are relatively easy to
configure and manage
• Web content is increasingly easy
to develop
• The underlying software is
extraordinarily complex
• May hide many potential
security flaws
• A Web server can be exploited as a
launching pad into the corporation’s
or agency’s entire computer complex
• Casual and untrained (in security
matters) users are common clients for
Web-based services
• Such users are not necessarily
aware of the security risks that
exist and do not have the tools or
knowledge to take effective
countermeasures
8. Tcp/ip protocol stack
The advantage of IPSec is
that it is transparent to end
users and applications and
provides a general-purpose
solution.
IPSec includes a filtering
capability so that only
selected traffic need incur
the overhead of IPSec
processing
9. Tcp/ip protocol stack
SSL or TLS also transparent to
applications or embedded in
specific packages e.g: MS IE
browsers come equipped
with SSL.
11. Secure Sockets Layer
(SSL)
• One of the most widely used security services
• A general purpose service implemented as a set of protocols
that rely on TCP
• Could be provided as part of the underlying protocol suite and
therefore be transparent to applications
• Can be embedded in specific packages
• e.g. most browsers come equipped with SSL
15. SSL Architecture
• SSL is designed to make use of TCP to provide a reliable
end-to-end secure service.
• It is a two layer protocol.
Used in the
management of
SSL exchanges
Provides basic
security to various
higher-layered
protocols
16. SSL Architecture
• Two important SSL concepts are:
SSL
connection
• A transport that provides a suitable type of
service
• For SSL such connections are peer-to-peer
relationships
• Connections are transient
• Every connection is associated with one session
SSL
session
• An association between a client and a server
• Created by the Handshake Protocol
• Define a set of cryptographic security parameters
which can be shared among multiple connections
• Are used to avoid the expensive negotiation of new
security parameters for each connection
17. A session state is defined by the
following parameters:
Session identifier
An arbitrary byte sequence chosen by the server to
identify an active or resumable session state
Peer certificate
An X509.v3 certificate of the peer; this element of
the state may be null
Compression method
The algorithm used to compress data prior to
encryption
Cipher spec
Specifies the bulk data encryption algorithm and a
hash algorithm used for MAC calculation; also
defines cryptographic attributes such as the
hash_size
Master secret
48-byte secret shared between the client and the
server
Is resumable
A flag indicating whether the session can be used
to initiate new connections
18. A connection state is defined by the
following parameters:
Server and
client
random
• Byte sequences that are chosen
by the server and client for each
connection
Server
write MAC
secret
• The secret key used in MAC
operations on data sent by the
server
Client
write MAC
secret
Initialization
vectors
• When a block cipher in CBC
mode is used, an initialization
vector (IV) is maintained for
each key
• This field is first initialized by
the SSL Handshake Protocol
• The final ciphertext block
from each record is preserved
for use as the IV with the
following record
Sequence
numbers
• Each party maintains separate
sequence numbers for
transmitted and received
messages for each connection
• When a party sends or
receives a change cipher spec
message, the appropriate
sequence number is set to zero
• Sequence numbers may not
exceed 264 - 1
• The secret key used in MAC
operations on data sent by the
client
Server
write key
• The secret encryption key for
data encrypted by the server and
decrypted by the client
Client
write key
• The symmetric encryption key
for data encrypted by the client
and decrypted by the server
19. SSL Record Protocol
The SSL Record
Protocol provides
two services for SSL
connections
Confidentiality
Message integrity
The Handshake
Protocol defines a
shared secret key that is
used for conventional
encryption of SSL
payloads
The Handshake
Protocol also defines a
shared secret key that is
used to form a message
authentication code
(MAC)
20. The Record Protocol takes an
application
message
to
be
transmitted, fragments the data into
manageable blocks, optionally
compresses the data, applies a
MAC, encrypts, adds a header, &
transmit the resulting unit in a TCP
segment. Received data are
decrypted, verified, decompressed,
& reassembled and then delivered
to higher-level users.
SEND
23. Change cipher spec
protocol
Figure 6.5 SSL Record Protocol Payload
• This protocol consists of a single message, which consists of a
single byte with the value of 1.
• The sole purpose of this message is to cause the pending state
to be copied into current state, which updated the cipher suite
to be used on this connection.
24. Alert protocol
Figure 6.5 SSL Record Protocol Payload
• Used to convey SSL-related alerts to peer entity.
• Alert messages are compressed and encrypted, as specified by
the current state.
25. Handshake
protocol
• The most complex part of
SSL.
• Allows the server and client
to authenticate each other.
• Negotiate an encryption,
MAC algorithm and
cryptographic keys.
• Used before any application
data is transmitted.
26. Transport Layer
Security (TLS)
• An IETF standardization
initiative whose goal is to
produce an Internet standard
version of SSL
• Is defined as a Proposed
Internet Standard in RFC 5246
• RFC 5246 is very similar to
SSLv3
Differences include:
• Version number
• Message Authentication
Code
• Pseudorandom function
• Alert keys
• Cipher suites
• Client certificate types
• Certificate_verify and
Finished Messages
• Cryptographic computations
• Padding
27. HTTPS
(HTTP over SSL)
• Refers to the combination of HTTP and SSL to implement secure communication
between a Web browser and a Web server
• The HTTPS capability is built into all modern Web browsers
• A user of a Web browser will see URL addresses that begin with https:// rather than
http://
• If HTTPS is specified, port 443 is used, which invokes SSL
• Documented in RFC 2818, HTTP Over TLS
•
There is no fundamental change in using HTTP over either SSL or TLS and both
implementations are referred to as HTTPS
• When HTTPS is used, the following elements of the communication are encrypted:
•
•
•
•
•
URL of the requested document
Contents of the document
Contents of browser forms
Cookies sent from browser to server and from server to browser
Contents of HTTP header
28. Connection
Initiation
For HTTPS, the agent acting as the
HTTP client also acts as the TLS
client
• The client initiates a connection to the server on
the appropriate port and then sends the TLS
ClientHello to begin the TLS handshake
• When the TLS handshake has finished, the
client may then initiate the first HTTP request
• All HTTP data is to be sent as TLS application
data
There are three levels of awareness
of a connection in HTTPS:
• At the HTTP level, an HTTP client requests a
connection to an HTTP server by sending a
connection request to the next lowest layer
• Typically the next lowest layer is TCP, but it
may also be TLS/SSL
• At the level of TLS, a session is established
between a TLS client and a TLS server
• This session can support one or more
connections at any time
• A TLS request to establish a connection begins
with the establishment of a TCP connection
between the TCP entity on the client side and
the TCP entity on the server side
29. Connection Closure
• An HTTP client or server can indicate the closing of a connection
by including the line Connection: close in an HTTP record
• The closure of an HTTPS connection requires that TLS close the
connection with the peer TLS entity on the remote side, which will
involve closing the underlying TCP connection
• TLS implementations must initiate an exchange of closure alerts
before closing a connection
• A TLS implementation may, after sending a closure alert, close the
connection without waiting for the peer to send its closure alert,
generating an “incomplete close”
• An unannounced TCP closure could be evidence of some sort of
attack so the HTTPS client should issue some sort of security
warning when this occurs
30. Secure electronic
transactions (set)
• An open encryption and security specification to protect
credit card transaction over the Internet.
• Companies involved:
• MasterCard, Visa, IBM, Microsoft, Netscape, RSA,
Terisa and Verisign.
• NOT a payment system.
• Rather, SET of security protocols and formats to enables
users to employ the existing credit card payment
infrastructure on an open network, such as the Internet.
31. Set services
• Provides a secure communication channel in a
transaction.
• Provides trust by the use of X.509v3 digital
certificates.
• Ensures privacy because the information is only
availble to parties in a transaction when and where
necessary.
33. Set participants
• A cardholder is an authorized holder of a
payment card (e.g., MasterCard, Visa) that
has been issued by an issuer.
• A merchant is a person or organization
that has goods or services to sell to the
cardholder.
• This is a financial institution, such as a
bank, that provides the cardholder with the
payment card.
34. Set participants
• This is a financial institution that establishes
an account with a merchant and processes
payment card authorizations and payments.
• The acquirer provides authorization to the
merchant that a given card account is active
and that the proposed purchase does not
exceed the credit limit.
• The acquirer also provides electronic transfer
of payments to the merchant's account.
35. Set participants
• This is a function operated by the acquirer or a
designated third party that processes merchant
payment messages.
• The payment gateway interfaces between SET and
the existing bankcard payment networks for
authorization and payment functions.
• This is an entity that is trusted to issue X.509v3
public-key certificates for cardholders, merchants,
and payment gateways.
• The success of SET will depend on the existence
of a CA infrastructure available for this purpose.
36. Key features of set
• Confidentiality of information:
• Cardholder account & payment information is secured
as it travels across the network.
• It prevents the merchant from learning the
cardholder’s credit card number; this is only provided
to the issuing bank.
• Conventional encryption by DES is used to provide
confidentiality.
37. Key features of set
• Integrity of data:
• Payment information sent from cardholders to
merchants includes order information, personal data,
and payment instructions.
• SET guarantees that these message contents are not
altered in transit.
• RSA digital signature (SHA-1 hash codes), provide
message integrity.
• Certain messages are also protected by HMAC using
SHA-1.
38. Key features of set
• Cardholder account authentication:
• SET uses X.509v3 digital certificates with RSA
signatures for enable merchant to verify that a
cardholder is a legitimate user of a valid card account
number.
39. Key features of set
• Merchant authentication:
• SET enables cardholders to verify that a merchant has
a relationship with a financial institution allowing it to
accept payment cards.
• SET uses X.509v3 digital certificates with RSA
signatures a range of applications.
Note : SET only provides only one choice for each cryptographic
algorithms as SET is a single application witha single set of
requirements, whereas IPSec and SSL/TLS are intended to
support a range of applications.
40. Sequence of events
for transactions
1.
The customer opens an account.
2.
The customer receives a certificate.
3.
Merchants have their own certificates.
4.
The customer places an order.
5.
The merchant is verified.
6.
The order and payment are sent.
7.
The merchant request payment authorization.
8.
The merchant confirm the order.
9.
The merchant provides the goods or service.
10. The merchant requests payments.
41. Dual signature
Purpose: is to link two messages that are
intended for two different recipients.
Example:
The customer wants to send the order
information (OI) to the merchant and the
payment information (PI) to the bank.
The merchant does not need to know the
customer’s credit card number, and the bank
does not need to know the details of the
customer’s order.
