Web Site Security Representation and Management of Data on the Web

We all know this page...

Would we want all to know this page?

Problem Want to restrict access to certain Web pages Must answer the following questions -Which pages should be restricted? -Who should access restricted pages? -How should users be authenticated? -Should Authentication data be Encrypted?

Authentication Methods Several security methods are used: Declarative Security -Use security mechanisms provided by the server -BASIC and FORM-based will be discussed Programmatic Security -Security is handled by the Web application programs

Declarative Security Advantage: Application programs (i.e. JSP and Servlets) do not have to do anything special Advantage: security holes due to bugs are less probable Disadvantage: Server specific process Disadvantage: All or nothing security -users can or cannot see the page -sometimes, what we really want is the page content to be dependent on the user

Programmatic Security Advantage: Not server specific Advantage: Very flexible Disadvantage: A lot of work to program + all Servlets and JSP have to cooperate for this to work Disadvantage: Programmer's bugs may lead to security holes

Declarative Security: BASIC Realm B Realm A /a/A.html /a/B.jsp /b/C.css /b/D.xml E.xsl GET E.xsl OK + Content F.xml

Declarative Security: BASIC Realm B Realm A /a/A.html /a/B.jsp /b/C.css /b/D.xml E.xsl GET /a/B.jsp Basic realm="A" F.xml

Declarative Security: BASIC Realm B Realm A /a/A.html /a/B.jsp /b/C.css /b/D.xml E.xsl GET /a/B.jsp + user:pass OK + Content F.xml

Declarative Security: BASIC Realm B Realm A /a/A.html /a/B.jsp /b/C.css /b/D.xml E.xsl GET /a/A.html + user:pass OK + Content F.xml

To restrict a set of pages for certain users, the server designates a realm name for these pages and defines the authorized users (usernames and passwords) When a page is requested without correct authentication information, the server returns a 401 (Unauthorized) response, with the "WWW-Authenticate" header like the following: WWW-Authenticate: Basic realm="realm-name" Declarative Security: BASIC

The browser then prompts the user for a username and a password, and sends them in the "Authorization" header: Authorization: Basic username:password The string username:password is trivially encoded (everyone can decode it...) Through the session, the browser automatically sends the latter authorization header when requesting files under the latter request's directory or when asked to authenticate in the same realm An Example

BASIC method in Tomcat 1.Set up usernames, passwords and roles 2.Tell the server that your application is using BASIC authentication, and designate a realm name to the application 3.Specify which URLs should be restricted to which roles

[more roles...] <user username="snoopy" password="snoopass" roles="special"/> [more users...] 1. Defining Usernames, Passwords, and Roles Define users, passwords and roles in the file $CATALINA_BASE/conf/tomcat-users.xml

2. Tell the Server to use BASIC Security + Define a Realm Name Add to the application's web.xml the login method (BASIC) and your chosen realm name BASIC Special Managers

3. Define the restrictions in web.xml restricted one /restricted1/* restricted two /restricted2/*

special... special

Custom Error Pages The default 401-designated error page is returned with the unauthorized response of the server A 401 page is not shown by the browser, unless -The user cancels the authentication -The page is returned without WWW-Authenticate In Tomcat, you can define an application-specific error page, however the WWW-Authenticate header must be added explicitly

A Custom Error Page Example Add to the application's web.xml the following: 401 /error401.jsp

A Custom Error Page Example (cont) <% response.setHeader ("WWW-Authenticate", "Basic realm=\"Special Managers\""); %> Unauthorized Go away! You are not authorized!! error401.jsp

Declarative Security: FORM In the BASIC method, it is the browser's responsibility to get the login and password from its user, and to send it throughout the session In the FORM method, this responsibility is the server's, while the browser is not aware of the fact that restricted pages are accessed

Declarative Security: FORM (cont) In the first request to a restricted page, the server forwards the request to a login page Using the form in the login page, the user submits its login and password to a special URL of the server, and the latter stores the information in the session object On subsequent requests, the server checks the session to see if it contains suitable authentication, in which case the required page is returned

Add to web.xml FORM /admin/login.jsp /admin/login-error.html

Create A Login Page Login Log In Sorry, you must log in before accessing this resource. " METHOD="POST"> User name: Password: myApp/admin/login.jsp

Create a Login-Error Page Unauthorized Go away! You are not authorized!! myApp/admin/login-error.html

Adding Some Programmatic Security So far, all or nothing: -can see page or -can't see page Sometimes we want to allow page content to be dependant on the authorization of the user Use the following request methods to control content restriction: - boolean isUserInRole(String role) - String getRemoteUser()

Example salary /salary.jsp executive employees

Example (cont) Average Salary Employee average salary: 3895NIS Executive average salary: 42764NIS salary.jsp

Important: Disable the Servlet Invoker You protect certain URLs in the application The format of the Servlet invoker will probably not match the patterns of the protected URLs Thus, the security restrictions are bypassed if the invoker is enabled For this reasons (and others), the invoker should not be used in published applications

SSL Connections

Security on the Internet The Internet is used to transmit sensitive data from clients to servers and vice versa -User passwords -Credit card numbers -Private client data on remote servers (e.g. Banks) However, data packets are read by several computers on the way from the client to the server and vice versa -Routers, proxies, etc.

Security on the Internet (cont) The following should be provided: -Only the server can read the client requests -Only the client can read the server's responses -Only the client can send requests on behalf of itself -Only the server can send responses on behalf of itself In short, no one should be able to interfere in the interaction, either be reading the transferred data or by impersonating to one of the sides

Symmetric and Asymmetric Keys Data can be encrypted and decrypted using keys, which are simply large numbers Symmetric keys: the same key is used for both encoding and decoding of the message Asymmetric keys: one key is used to encode the message, and another is used to decode it It is considered practically impossible to decode a message without knowing the decoding key

The RSA Cryptography System RSA was developed in 1977 by Ron Rivest, Adi Shamir and Leonard Adleman It is the based on the asymmetric key mechanism: -Each participant has a private key and a public key -The public key is known to all and the private key is kept in secret within its owner -Asymmetric keys: the public key is the encoding key and the private key is the decoding key

Secure Connection: A Naive Approach Consider the following protocol: -Server and Client send their public keys to each other -Data is encrypted using the public key of the receiver What is wrong with this protocol? -Decryption methods (public keys) are known to everyone - everyone can impersonate the participants -A participant cannot tell whether its received key was indeed sent by the other participant

SSL Connections The SSL (Secure Socket Layer) protocol is used to manage security of message transmission on the Internet Data encryption and decryption is based on symmetric and asymmetric keys The HTTPS (HTTP over Ssl) protocol is actually the HTTP protocol above SSL transportation

TCP/IP SSL SSL in the Network Layers HTTP Protocols

The SSL Handshake Server hello + SSL settings Client SSL Settings + Certificate Is this a good certificate? 1. Client gets the Server's certificate

The SSL Handshake Server Client 2. Client creates a master secret and shares it with the server

The SSL Handshake Server Client 3. Client and server create symmetric session keys from the master secret

The SSL Handshake Server Client Data is transferred using the session keys (Http Response) (Http Request)

SSL Certificates To assure that the replier of the first request is the server, the server sends a certificate The certificate contains both the server's name and its public key The certificate is issued by a Certificate Authority (CA), which is known to the client in advance -For example: VeriSign, Thawte, RSA Secure Server, etc. CA signs the certificate using a digital signature, which the client can verify using a method similar to the private-public key method

Issuer's Name Public Key Serial Number Validity Period Server's Name The Server's Certificate Issuer's Digital Signature

An Example: The Certificate of bankleumi.co.il

Authentication via SSL If the server needs to assure the client's identity, the first interaction after the SSL handshake will typically be a clients authentication Client authentication is done using the regular HTTP authentication methods What is the difference, though?

SSL in Tomcat 5.0 To use SSL connections in Tomcat 5.0, we need to do the following: -Acquire a certificate -Enable the https service, that listens to a designated port -Declare the pages that require SSL connections

Generating a Certificate Acquiring a certificate from a known CA costs money Instead, we will generate our own certificate Naturally, the browser will not recognize the CA as a known one and will alert the user

Generating a Certificate (cont) From the Unix shell, type the following: keytool -genkey -alias tomcat -keyalg RSA -keystore keyfile

Enable HTTPS Service Add the following to $CATALINA_BASE/conf/server.xml under the Service "catalina": Declare the redirection port for the HTTP Connector:

Declare Secured Pages In the application's web.xml, add the following element under the security constraint for which you want SSL to be used CONFIDENTIAL