Security in Applications

What is Email?

• What is an e-mail?
  
  • An e-mail is a message made up of a string of ASCII characters in a format specified by RFC 822
• Contain Two parts, separated by blank line:
  
  • The header: sender, recipient, date, subject, delivery path,…
  • The body: containing the actual message content.

Security provided in E-mail

• Confidentiality
• Data origin authentication
• Message integrity
• Non-repudiation of origin
• Key management

MIME(Multipurpose Internet Mail Extensions)

• Extends the capabilities of RFC 822 to allow e-mail to carry non-textual content, non-ASCII character sets, long messages.
• Uses extra header fields in RFC 822 e-mails to specify form and content of extensions.
• Supports a variety of content types, but e-mail still ASCII-coded for compatibility.
• Specified in RFCs 2045-2049.

E-mail Security Threats

• Two main group:
  
  • Threats to the security of e-mail itself
  • Threats to an organisation that are enabled by the use of e-mail.
• Loss of confidentiality.
  
  • E-mails are sent in clear over open networks.
  • E-mails stored on potentially insecure clients and mail servers.
  • Ensuring confidentiality may be important for e-mails sent within an organisation.
• Loss of integrity.
  
  • No integrity protection on e-mails; body can be altered in transit or on mail server.
• Lack of data origin authentication.
  
  • Is this e-mail really from the person named in the From: field?
  • How many Kenny.Paterson’s are there?
  • Recall SMTP directly over telnet allows forgery of all e-mail fields!
  • E-mail could also be altered in transit.
  • Even if the From: field looks fine, who was logged in as Kenny.Paterson when the e-mail was composed?
  • Sharing of e-mail passwords common.

Threats Enabled by E-mail

• Disclosure of sensitive information.
  
  • It’s easier to distribute information by e-mail than it is by paper and snail mail.
  • Disclosure may be deliberate (and malicious) or unintentional.
  • Disclosure may be internal or external (e-mail crosses LANs as well as the Internet).
  • Disclosure may be of personal, inappropriate, commercially sensitive or proprietary information.
  Can lead to loss of reputation and ultimately dismissal of staff.
• Exposure of systems to denial of service attacks.
  
  • E-mail server attached to network, may be vulnerable to DoS attacks.
  • More relevant with increasing dependence on e-mail as a communications tool.
  • For example, a virulent worm using large percentage of network capacity to spread will prevent efficient use of e-mail as well as slowing down web browsing.
• Spamming.
  
  • Spam wastes bandwidth and decreases productivity.
  • Hotmail and other free e-mail systems are particularly victimised by spammers.
  • 50% and more of all e-mail is now spam.
  • Anti-spam legislation in development or on the statute books in many countries.

S/MIME

• Originated from RSA Data Security Inc. in 1995.
• Further development by IETF S/MIME working group at:
• www.ietf.org/html.charters/smime-charter.html.
• Version 3 specified in RFCs 2630-2634.
• Allows flexible client-client security through encryption and signatures.
• Widely supported, e.g. in Microsoft Outlook, Netscape Messenger, Lotus Notes.

PGP

• PGP=“Pretty Good Privacy”
  
  • First released in 1991, developed by Phil Zimmerman, provoked export control and patent infringement controversy.
  • Freeware: OpenPGP and variants:
  • www.openpgp.org, www.gnupg.org
  • Commercial: formerly Network Associates International, now PGP Corporation at www.pgp.com
  • OpenPGP specified in RFC 2440 and defined by IETF OpenPGP working group.
  • www.ietf.org/html.charters/openpgp-charter.html
  • Available as plug-in for popular e-mail clients, can also be used as stand-alone software.

Web Security

• Web security includes:
  
  • Security of server
  • Security of client
  • Network traffic security between a browser and a server

• SSL/TLS
• SSH
• SET

SSL/TLS

• SSL/TLS widely used in Web browsers and servers to support ‘secure e-commerce’ over HTTP.
  Built into Microsoft IE, Netscape, Mozilla, Apache, IIS
  The (in)famous browser lock.
• SSL architecture provides two layers:
  
  • SSL Record Protocol
  • Provides secure, reliable channel to upper layer.
• Upper layer carrying:
  SSL Handshake Protocol, Change Cipher Spec. Protocol, Alert Protocol, HTTP, any other application protocols.

SSL/TLS Applications

• Secure e-commerce using SSL/TLS.
• Client authentication not needed until client decides to buy something.
• SSL provides secure channel for sending credit card information, personal details, etc.
• Client authenticated using credit card information, merchant bears (most of) risk.
• Very successful (amazon.com, on-line supermarkets, airlines,…)
• Secure e-commerce: some issues.
  
  • No guarantees about what happens to client data (including credit card details) after session: may be stored on insecure server.
  • Does client understand meaning of certificate expiry and other security warnings?
  • Does client software actually check complete certificate chain?
  • Does the name in certificate match the URL of e-commerce site? Does the user check this?
  • Is the site the one the client thinks it is?
  • Is the client software proposing appropriate ciphersuites?
• Secure electronic banking.
  
  • Client authentication may be enabled using client certificates.
  • Issues of registration, secure storage of private keys, revocation and re-issue.
  • Otherwise, SSL provides secure channel for sending username, password, mother’s maiden name,…
  • What else does client use same password for?
  • Does client understand meaning of certificate expiry and other security warnings?
  • Is client software proposing appropriate ciphersuites?
  • Enforce from server.

SSH

• SSH = Secure Shell.
  
  • Initially designed to replace insecure rsh, telnet utilities.
  • Secure remote administration (mostly of Unix systems).
  • Extended to support secure file transfer and e-mail.
  • Latterly, provide a general secure channel for network applications.
  • SSH-1 flawed, SSH-2 better security (and different architecture).
• SSH provides security at Application layer.
  
  • Only covers traffic explicitly protected.
  • Applications need modification, but port-forwarding eases some of this (see later).
  • Built on top of TCP, reliable transport layer protocol.

SSH Applications

• Anonymous ftp for software updates, patches...
  
  • No client authentication needed, but clients want to be sure of origin and integrity of software.
• Secure ftp.
  
  • E.g.upload of webpages to webserver using sftp.
  • Server now needs to authenticate clients.
  • Username and password may be sufficient, transmitted over secure SSH transport layer protocol.
• Secure remote administration.
  
  • SysAdmin (client) sets up terminal on remote machine.
  • SysAdmin password protected by SSH transport layer protocol.
  • SysAdmin commands protected by SSH connection protocol.
• Guerilla Virtual Private Network.
  
  • E.g. use SSH + port forwarding to secure e-mail communications.

SET Flow
SET Security Issues

• Two pairs of PKs per entity
  
  • One pair for signing
  • One pair for exchanging keys
• Assumes full PKI is available
  
  • Including revocation
• Merchant does not see payment instrument used

Web Vulnerabilities

• Revealing private information on server
• Intercept of client information
• Execute unauthorized programs
• Denial of service

How to Secure the Web

• Access control via addresses
  
  • Basic (username, password)
    Can be used along with cookie
  • Digest
• Access control via addresses
• Multi-layered:
  
  • S-http (secure http), just for http
  • Proposed by CommerceNet, pretty much dead
• SSL (TLS), generic for TCP
  
  • https: http over SSL
• IPSec
  

HTTP Authentication

• Client doesn’t know which method
• Client attempts access (GET, PUT, …)
• Server returns
  
  • “401 unauthorized”
  • Realm: protection space
• Client tries again with (user:password)
  
  • Passwords in the clear
  • Repeated for each access

HTTP Access Control - Digest
Server sends www-authenticate parameters:

• Realm
• Domain
• Nonce, new for each 401 response
  
  • E.G. H(client-IP:timestamp:server-secret)
• Algorithm
  
  • E.G., MD5

Client sends authorization response:

• Same nonce
• H(A1), where a1=user:realm:password, and other information
• Steal H(A1)
  
  • Only good for realm

HTTPS

• HTTPS = Secure Hypertext Transfer Protocol
• HTTPS is a communications protocol designed to transfer encrypted information between computers over the World Wide Web (WWW)
• Essentially an implementation of HTTP
• Commonly used Internet protocol using an SSL
• Used to enable online purchasing or the exchange of private information and resources over insecure networks