User and Security Management

User and Security User and Security ManagementManagement

Security Management in Web Security Management in Web ApplicationsApplications

HUJI-CSHUJI-CSDBI 2007DBI 2007

We all know this page...We all know this page...


Would we want all to know this page?Would we want all to know this page?


Problem FormulationProblem Formulation

• 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 MethodsAuthentication Methods

• Several authentication methods are used:

• Declarative Security– HTTP-level mechanisms

• Basic authentication scheme• Digest access authentication scheme

– Server-level mechanisms

• Programmatic Security


HTTP Basic MechanismHTTP Basic Mechanism

• In the basic authentication scheme of HTTP, the user's name and password need to be sent with each request for a protected resource

• When the server gets a request for a protected resource, it checks whether that request has the HTTP header

Authorization: Basic username:password

• If the name and password are accepted by the server (i.e., are those of a user that has the privilege to get the page), then the requested page is returned


HTTP Basic MechanismHTTP Basic Mechanism

• If the request does not have the authorization header or the name and password are not accepted, then the server replies with 401 (unauthorized)

• An 401 response can have the header

WWW-Authenticate: Basic realm="realm-name"

• That is, "in order to get this resource, you will have to authenticate using the basic method"

– Tell the user to supply authentication for pages in realm-name


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: BASICDeclarative Security: BASIC


Realm B

Realm A

/a/A.html/a/B.jsp

/b/C.css/b/D.xml

E.xsl

GET /a/B.jsp

401 + Basic realm="A"

F.xml




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



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


Browser CooperationBrowser Cooperation

• Throughout the session, the browser stores the user-name and password and automatically sends the authorization header in either one of the following cases:– The requested resource is under the directory

of the originally authenticated resource

– The browser received 401 from the Web server and the WWW-Authenticate header has the same realm as the previous protected resource


Digest Access SchemeDigest Access Scheme

• The most serious security flaw in the basic scheme is that the name and password are sent unencrypted, and hence everyone on the network path can read it

• If an attacker snoops a request with basic authentication, she can access to the whole protection space of the resource

• The digest access authentication scheme solves many of the flaws of the basic schemes, such as the one above


Digest OperationDigest Operation

• Like the basic, the digest scheme requires that authentication data is sent with each request for a protected resource

• However, passwords are not sent in clear text

• The idea is to use a one-way hash, such as MD5

• A one-way hash H is a mapping of strings that has the following properties:– It is "easy" to compute H(x), given the input x

– It is "hard" to compute x, given the mapping H(x)


Digest Operation (cont)Digest Operation (cont)

• In the digest scheme, instead of sending the password x in clear text, the client sends H(y)

• y is the concatenation of the user name, the password, an opaque generated by the server, the request URI, and more (why is the opaque needed?)

• A server that gets digested authentication data repeats the same encryption process and compares its output with the given H(y)

• More details can be found in RFC 2617


Server-Level AuthenticationServer-Level Authentication

• A Web server can use its own authentication mechanisms rather than those of HTTP

• Typically, server-level mechanisms act as follows

– The server requires authentication by redirecting the client to a special HTML form

– If authentication succeeds, then the server stores the username in the corresponding session object

• Note that the browser and the HTTP headers are oblivious to server-level authentication


Programmatic SecurityProgrammatic Security

• In declarative security, a page is either accessible to a user or is not

• But what if we wanted a page to include some data that will only be shown to privileged users?– E.g., the grades of the user

• In programmatic security, we enhance security checks in dynamic pages (e.g., JSP)

• Using this approach, an application can generate different contents for different users


Declarative-Security: Pros & ConsDeclarative-Security: Pros & Cons

• 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 for the page content to be dependent on the user

Authentication Management in Authentication Management in TomcatTomcat


Declarative Security in TomcatDeclarative Security in Tomcat

To apply declarative security in Tomcat:– Define roles and users

• A user has a username and a password

– Define the restricted pages and the roles that can access them

– Define the authentication method that is used in the Web application


Defining Users and RolesDefining Users and Roles

1. Create a database that stores users and roles• A table that stores usernames and passwords

• A table that stores usernames and roles

2. Tell Tomcat how to access your tables in the file TOMCAT_BASE/conf/server.xml

3. Users and roles can be dynamically added to the database


An ExampleAn Example

create table users (

username varchar(30) not null primary key,

pass varchar(30) not null

);

create table users_roles (

username varchar(30) not null,

role varchar(30) not null,

primary key (username,role),

foreign key (username) references users(username)

);


In server.xmlIn server.xml

<Realm

className="org.apache.catalina.realm.JDBCRealm"

driverName="org.postgresql.Driver"

connectionURL="jdbc:postgresql://dbserver/public?user=snoopy"

userTable="users"

userNameCol="username"

userCredCol="pass"

userRoleTable="users_roles"

roleNameCol="role"/>


<tomcat-users>

<role rolename="members"/>

[more roles...]

<user username="snoopy" password="snoopass"

roles="members"/>

[more users...]

</tomcat-users>

Static Users and RolesStatic Users and Roles

You can alternatively define a static set of users and roles in

$CATALINA_BASE/conf/tomcat-users.xml


Tomcat ManagerTomcat Manager

• The default resource of users is the file tomcat-users

• If you use database users, then you need to add a manager for Tomcat to your tables– Otherwise, you (and Eclipse) will not be able to log into

the manager application

• A manager is a user that belongs to the role "manager"


<security-constraint>

<web-resource-collection>

<web-resource-name>restricted one</web-resource-name>

<url-pattern>/restricted1/*</url-pattern>

</web-resource-collection>

<web-resource-collection>

<web-resource-name>restricted two</web-resource-name>

<url-pattern>/restricted2/*</url-pattern>

</web-resource-collection>

Defining Restrictions in web.xmlDefining Restrictions in web.xml


<auth-constraint>

<role-name>members</role-name>

</auth-constraint>

</security-constraint>

<login-config>...</login-config>

<security-role>

<role-name>members</role-name>

</security-role>

Defining Restrictions in web.xmlDefining Restrictions in web.xml


BASIC Authentication in TomcatBASIC Authentication in Tomcat

Add to the application's web.xml the login method (BASIC) and your chosen realm name

<login-config>

<auth-method>BASIC</auth-method>

<realm-name>Members</realm-name>

</login-config>


FORM-Based Authentication in TomcatFORM-Based Authentication in Tomcat

• Tomcat provides a built-in form-based authentication

• 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 which is automatically handled by Tomcat.

• If authentication is successful, the special URL stores the information in the session object and forwards the requerst the the restricted page originally requested (how does Tomcat know which page this is?)

• On subsequent requests for restricted pages, the server checks the session to see if it contains suitable authentication, and if so the requested page is returned (instead of forwarding to the login page)


Add to web.xmlAdd to web.xml

<login-config>

<auth-method>FORM</auth-method>

<form-login-config>

<form-login-page>/admin/login.html

</form-login-page>

<form-error-page>/admin/login-error.html

</form-error-page>

</form-login-config>

</login-config>


<html>

<head><title>Log In</title></head>

<body style="background-color:yellow">

<h2>Log in for accessing this resource.</h2>

<form action="j_security_check" method="post">

<p>Login: <input type="text" name="j_username"/></p>

<p>Password: <input type="password"

name="j_password"/></p>

<p><input type="submit" value="Log In"/></p>

</form>

</body>

</html> myApp/admin/login.html

Create A Login PageCreate A Login Page


<html>

<head>

<title>Login Failure</title>

</head>

<body style="background-color:yellow">

<h1>Wrong username and password!</h1>

</body>

</html>

Create an Error PageCreate an Error Page

myApp/admin/login-error.html

SSL ConnectionsSSL Connections


Security on the InternetSecurity 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)Security on the Internet (cont)

• For secure communication, 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 by reading the transferred data or by impersonating one of the sides


Symmetric and Asymmetric KeysSymmetric 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 SystemThe 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 ApproachSecure 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?

– Encryption 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 ConnectionsSSL 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/IPTCP/IP

SSLSSL

SSL in the Network LayersSSL in the Network Layers

HTTPHTTP Email ProtocolsEmail Protocols


The SSL HandshakeThe SSL Handshake

Server

hello + SSL settings

ClientSSL Settings + Certificate

Is this a good

certificate?

1. Client gets the Server's certificate



Server

Client

2. Client creates a master secret and shares it with the

server

( )



Server

Client

3. Client and server create symmetric session keys from

the master secret



Server

Client

Data is transferred using the session keys

(Http Response)

(Http Request)


SSL CertificatesSSL 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 CertificateThe Server's Certificate

Issuer's Digital Signature


An Example: The Certificate of bankleumi.co.ilAn Example: The Certificate of bankleumi.co.il


Authentication via SSLAuthentication via SSL

• If the server needs to assure the client's identity, the first interaction after the SSL handshake will typically be a client authentication

• Client authentication is done using the regular (e.g., HTTP) authentication mechanisms

• What is the difference, though?


SSL in Tomcat 6.0SSL in Tomcat 6.0

• To use SSL connections in Tomcat 6.0, 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 CertificateGenerating 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 therefore alert the user


Generating a Certificate (cont)Generating a Certificate (cont)

From the command line, type the following:

keytool -genkey -alias tomcat -keyalg RSA -keystore keyfile



Enable the HTTPS ServiceEnable the HTTPS Service

• Add the following to $CATALINA_BASE/conf/server.xml under the Service "catalina":

• Declare the redirection port for the HTTP Connector:

<Connector port="8090" redirectPort="8443"/>

<Connector port="8443" scheme="https" secure="true"

sslProtocol="TLS" keystoreFile="keyfile"

keystorePass="keypass"/>server.xml


Declare Secured PagesDeclare Secured Pages

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

<user-data-constraint>

<transport-guarantee>

CONFIDENTIAL

</transport-guarantee>

</user-data-constraint>

web.xml

Date post:	01-Jan-2016
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User and Security Management

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