Chapter 7 Transport security SSH

Web now widely used by business, government, individuals but Internet & Web are vulnerable have a variety of threats o Integrity o Confidentiality o denial of service o authentication need added security mechanisms

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Lecturer: Nguyễn Thị Thanh Vân – FIT - HCMUTE

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capability so that only

selected traffic need

incur the overhead of

IPsec processing

could be provided as part of the underlying protocol suite, therefore be transparent to applications

can be embedded in specific packages

Ex, Netscape and IE

Application-specificsecurity servicesembedded within the particular application

the service can be tailored to the specific needs of a given application

 Web now widely used by business, government, individuals

 but Internet & Web are vulnerable

 have a variety of threats

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 Two types of web security threats:

o Passive attacks include eavesdropping on network traffic

between browser and server and gaining access to information

on a Web site that is supposed to be restricted

o Active attacks include impersonating another user, altering

messages in transit between client and server, and altering

information on a website

 Another way to classify Web security threats is in terms

of the location of the threat:

o Web server,

o Web browser, and

o network traffic between browser and server

 HTTPS (HTTP over SSL) refers to the combination of HTTP

and SSL to implement secure communication between a Web

browser and a Web server.

o HTTPS is simply HTTP inside of a TLS session

 Secure Socket Layer (SSL) provides security services

between TCP and applications that use TCP The Internet

standard version is called Transport Layer Service (TLS).

 SSL/TLS provides confidentiality using symmetric encryption

and message integrity using a message authentication code

(MAC).

 SSL/TLS includes protocol mechanisms to enable two TCP

users to determine the security mechanisms and services

they will use.

parties using both asymmetric cryptography as well as

symmetric cryptography to

o provide data privacy, integrity, and authentication

their messages

o Two parties are able to authenticate to ensure they really are

talking to whom they think

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the confidentiality of data transmitted electronically

name that contains information about the domain owner,

his address, etc.

Certificate Authorities (CAs):

o Domain Validated

o Organization Validated

o Extended Validation

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 Strong authentication, message privacy, and integrity

o secure transmitted data using encryption

o data integrity through an integrity check value

o help protect against masquerade attacks, man-in-the-middle,

rollback attacks, and replay attacks

 Interoperability: works with

o most Web browsers and on most OS and Web Server

o most of its operations are completely invisible to the client

o The client to have little or no knowledge of the security of

communications and still be protected from attackers

 Increased processor load

o Cryptography, specifically public key operations, is

CPU-intensive

o TLS uses the greatest resources while it is setting up

connections

o A TLS/SSL environment is complex and requires maintenance;

the system administrator must configure the system and manage

certificates

 SSL-secured transactions with an e-commerce Web site

o certificate of the Web site is valid,

o sends the client’s credit card information as cipher text

o must be enabled for the Web page: an order form

 Authenticated client access to an SSL-secured Web site

o Both the client and server need certificates from a mutually -trusted

certification authority (CA)

o provide authentication and data protection when users remotely log

in to Windows-based systems or networks

o client or server can be configured to require encryption of the data

that is transferred between them

 E-mail

o protect data in a server-to-server exchange allows companies to

use the Internet to securely transfer e-mail among divisions within

the same company

 Connection:

o A connection is a transportthat provides a suitable type of service

o Connections are peer-to-peer relationships

o The connections are transient

o Every connection is associated with one session

 Session:

o An association between a client and a server

o Sessions are created by the Handshake Protocol

o Sessions define a set of cryptographic security parameters which

can be shared among multiple connections

o Sessions are used to avoid the expensive negotiation of new

security parameters for each connection

 SSL is designed to make use of TCP to provide a reliable

end-to-end secure service

 SSL is not a single protocol but rather two layers of protocols

provides basic security services to various higher layer protocols

are used in the management

of SSL exchanges

provides the transfer service for Web client/server interaction

 The SSL Record Protocol provides two services for

SSL connections:

o Confidentiality:

The Handshake Protocol defines a shared secret key that is

used for conventional encryption of SSL payloads

o Message Integrity:

The Handshake Protocol also defines a shared secret key that is

used to form a message authentication code (MAC)

2 14 bytes (16384 bytes)

Comp Algo TLS: null

|| pad_1 || seq_num|| SSLCompressed.type

|| SLCompressed.length || SSLCompressed.fragment)) Encryption algorithms: Block Cipher (AES,

DES, 3DES, RC2,…) Stream Cipher (RC4 ) Header fields: Content Type (8 bits); Major Version (8 bits); Minor Version (8 bits);

Compressed Length (16 bits)

 Change Cipher Spec Protocol:

o is the simplest

o consists of a single message:

• consists of a single byte with the value 1

• to cause the pending state to be copied into the current state, which

updates the cipher suite to be used on this connection

o is used to convey SSL-related alerts to the peer entity

o alert messages are compressed and encrypted, as specified by

the current state

o Each message in this protocol consists of two bytes

• The first byte takes the value warning (1) or fatal (2) to convey the

severity of the message

• The second byte contains a code that indicates the specific alert

 Handshake Protocol

o The most complex part of SSL

o This protocol allows the server and client to authenticate each other

and to negotiate an encryption and MAC algorithm and cryptographic

keysto be used to protect data sent in an SSL record

o It is used before any application data is transmitted

o It consists of a series of messages exchanged by client and server

Each message has three fields:

• Type (1 byte): Indicates one of 10 messages Table 16.2 lists the defined

message types.

• Length (3 bytes): The length of the message in bytes.

• Content ( bytes): The parameters associated w ith this message

certificate chain of X.509v3 certificates

server_key_exchange parameters, signature

certificate_request type, authorities

server_done null

certificate_verify signature

client_key_exchange parameters, signature

finished hash value

Establish security capabilities, including protocol version,

session ID, cipher suite, compression method, and initial

random numbers.

 Phase 2

Server may send certificate, key exchange, and request

certificate Server signals end of hello message phase.

 Phase 3

Client sends certificate if requested Client sends key

exchange Client may send certificate verification.

 Phase 4

Change cipher suite and finish handshake protocol

Two further items are of interest:

o the creation of a shared master secret by means of the key

exchange and

• a one-time 48-byte value

• generated using secure key exchange (RSA / DiffieHellman) and then

hashing info

• tw o stages

• First, a pre_master_secret is exchanged ( RSA / DiffieHellman)

• Second, the master_secret is calculated by both parties

o the generation of cryptographic parameters from the master secret

• Client and Server w rite:

• MAC secret,

• key,

• Initialization Value

• generated by hashing master secret into a sequence of secure bytes of

sufficient length for all needed parameters

produce an Internet standard version of SSL.

5246

o in record format version number

o uses HMAC for MAC

o a pseudo-random function expands secrets

- based on HMAC using SHA-1 or MD5

o has additional alert codes

o some changes in supported ciphers

o changes in certificate types & negotiations

o changes in crypto computations & padding

 need to ensure that their private keys are not used anywhere with server software that allows SSLv2 connections:

o w eb servers, SMTP servers, IMAP and POP servers

o is documented in RFC 2818, HTTP Over TLS or SSL

o refers to the combination of HTTP and SSL to implement secure

communication between a Web browser and a Web server

o is built into all modern Web browsers

o Its use depends on the Web server supporting HTTPS

communication

• For example, search engines do not support HTTPS

• If HTTPS is specified, port 443 is used, which invokes SSL

 When HTTPS is used, the following elements of the

communication are encrypted:

o URL of the requested document

o Contents of the document

o Contents of browser forms (filled in by browser user)

o Cookies sent from browser to server and from server to browser

o Contents of HTTP header

either SSL or TLS, and both implementations are

referred to as HTTPS.

 1 Session establishment (authentication, key exchange)

 2 Exchange of data over SSL, often a 1KB file over HTTP

 3 Session closure

 Connection Initiation:

o The client initiates a connection to the server on the appropriate port

o begin the TLS handshake: client sends the TLS ClientHello

o Then, the client initiate the first HTTP request

o All HTTP data is to be sent as TLS application data

o requires that TLS close the connection with the peer TLS entity on

the remote side (closing the underlying TCP connection)

o TLS level exchange close_notify alerts

o must handle TCP close before alert exchange sent or completed

 SSH:

o is a protocol for secure netw ork communications designed to be relatively

and inexpensive to implement

 SSHv1:

o w as focused on providing a secure remote logon facility,

o can be used for such netw ork functions as file transfer and e-mail

o fixes a number of security flaw s in the original scheme.

o is documented as a proposed standard in IETF RFCs 4250 through 4256

 SSH client and server applications are widely available for most

operating systems

 It has become the method of choice for remote login and X tunneling

and is rapidly becoming one of the most pervasive applications for

encryption technology outside of embedded systems

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- These strings are used in the

DiffieHellman key exchange

The cryptographic algorithm

include: key exchange, encryption,

MAC algorithm, and compression

algorithm

Diffie-Hellman key exchange are

specified

At this point, both sides may start

using the keys generated from K

- Request: User Authentication or the

Connection Protocol

- Then, all data is exchanged as the payload

of an SSH Transport Layer packet, protected

by encryption and MAC

 Defines which the client is authenticated to the server

 three message types:

o SSH_MSG_USERAUTH_REQUEST

o SSH_MSG_USERAUTH_FAILURE

SSH_MSG_USERAUTH_SUCCESS

 Authentication methods:

Client sends: (Pub,M(Sign_Pri))

Serrver: checks key is acceptable for authentication; checks

signature is correct or not

• Client send a signature created w ith the private key of the client host

• The SSH server verifies the identity of the client host—and

• then believes the host w hen it says the user has already authenticated

on the client side

 The SSH Connection Protocol used a tunnel to multiplex a number

of logical channels

 Channel Mechanism:

o Support all types of communication using SSH

o Each side associates a unique channel

o Channels are flow controlled using a w indow mechanism

o No data may be sent to a channel until a message is received to indicate

that w indow space is available.

 Channel Types

o Session: may be a shell, an application such as file transfer or e-mail, a

system command, or some built-in subsystem

o x11: allow s applications to run on a netw ork server but to be displayed

on a desktop machine.

o forw arded-tcpip: This is remote port forw arding

o direct-tcpip: This is local port forw arding

 The life of a channel progresses

through three stages:

o SSH Transport Layer Protocol establishes a TCP

connection between SSH client & server

o client traffic redirected to local SSH, travels via tunnel,

then remote SSH delivers to server

supports two types of port forwarding

o local forwarding – hijacks selected traffic

o remote forwarding – client acts for server

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 Experience

o HTTPS:

• Check if a web broswer can establish a secure connection

(TLS/SSL) with the site

and Practice, William Stallings, Prentice Hall,

Sixth Edition, 2013

o Chapter 16

o Others