Web Security

CS-431

HTTP Authentication

• Protect web content from those who don’t have a “need to know”• Require users to authenticate using a userid/password before they

are allowed access to certain URLs• HTTP/1.1 requires that when a user makes a request for a protected

resource the server responds with a authentication request header– WWW-Authenticate

• contains enough pertinent information to carry out a “challenge-response” session between the user and the server

Web ServerClient

Client requests a protected resource

Server responds with a 401 (not authorized and a challenge requestfor the client to authenticate

Client Response• Well established clients like Firefox, Internet Explorer …. will respond to

the challenge request (WWW-Authenticate) by presenting the user with a small pop-up window with data entry fields for– userid– password – a Submit button and a Cancel button

• entering a valid userid and password will post the data to the server, the server will attempt authentication and if authenticated will serve the originally requested resource.

WWW-Authenticate

• The authentication request received by the browser will look something like:– WWW-Authenticate = Basic realm=“defaultRealm”

• Basic indicates the HTTP Basic authentication is requested• realm indicates the context of the login

– realms hold all of the parts of security puzzle» Users» Groups» ACLs (Access Control Lists)

• Basic Authentication– userid and password are sent base 64 encoded (might as well be plain

text)– hacker doesn’t even need to unencode all he has to do is “replay” the

blob of information he stole over and over ( this is called a “replay attack”)

WWW-Authenticate

• Digest Authentication– attempts to overcome the shortcomings of Basic Authentication– WWW-Authenticate = Digest realm=“defaultRealm” nonce=“Server SpecificString”– see RFC 2069 for description of nonce, each nonce is different– the nonce is used in the browser in a 1-way function (MD5, SHA-1….) to encode the

userid and password for the server, this function essentially makes the password good for only one time

• Common browsers don’t use Digest Authentication but an applet could as an applet has access to all of the Java Encryption classes needed to create the creation of a Digest.

WWW-Authenticate• Secure Sockets Layer (SSL)

– Invented by Netscape and made public domain for everyone’s use– An additional layer to the TCP/IP stack that sits between the Application

and Transport layers• ensures that all application data is encrypted but TCP/IP headers are not• usually run on port 443 (default HTTPS port)

• Public Key Cryptography– owner of a private key sends a public key to all who want to

communicate with him (keys are both prime factors of a large (1024 bit) number). Owner keeps the private key secret and uses it to decrypt information sent to him that has been encrypted with the public-key

– RSA algorithm is most notable public-key cipher algorithm

• Digital Certificates– issued by a disinterested third party (ex. Verisign)– the Certificate contains the public-key for the specific Web Server and a

digital signature of the certifying authority

back to SSL• Once a secure session is established the source requests the destinations

certificate ( sent in the http header (uncncrypted))• once the source accepts the authenticity of the certificate it uses the

public-key from the certificate to encrypt the generated session key for protecting the conversation between the source and destination.

• Session is encrypted using a symmetric cipher (slow)• conversation is encrypted using an asymmetric cipher (fast)• its done this way to speed up overall communications, strong encryption

(slow) is used as little as possible while weaker encryption is used for most exchanges

• actual cipher algorithms are negotiated on a per-session basis

Java Cryptographic Packages

• Separate packages that are now included as part of JDK

– JCE - Java Cryptography classes– JSSE - Java Secure Sockets Extension– JAAS - Java Authentication and Authorization Services– Java GSS API - Java Generic Security Services API– Java Certification Path API

JCE

• JCE covers– encryption and decryption

• symmetric bulk encryption, such as DES, RC2, and IDEA • Symmetric stream encryption, such as RC4• Asymmetric encryption, such as RSA• Password-based encryption (PBE)

– key agreement– Message Authentication Code (MAC)

• Strong Cryptography is the default– unlimited is available (depending on export restrictions)

JSSE• Provides support for communications using SSL (Secure Sockets

Layer) and TLS (Transport Layer Security)– commonly thought of as HTTPS

• part of javax.net• SSL (and thus HTTPS) permits encrypted traffic to be exchanged

between the client and server. – After an SSL client initiates a conversation with an SSL server, the server sends an

X.509 certificate back to the client for authentication. The client then checks the validity of the certificate. Assuming the server is verified, the client generates a premaster secret key, encrypts it with the server's public key from the certificate, and sends the encrypted key back to the server. From this premaster key, the client and server generate a master key for the session. After some basic handshaking, the encrypted exchange can commence.

• The JSSE library hides these inner workings of the SSL protocol from you.

JAAS• JAAS provides for the authentication of users and the authorization of

tasks based upon that authentication• Previously, anyone authenticated had access to the same security

restrictions. Now, you can control what tasks are available for a specific authenticated user

• requires modification of security policies

Java GSS-API

• adds Kerberos V5 support to the Java platform.• Kerberos originated at the Massachusetts Institute of Technology

(MIT) as project Athena back in 1987. • Essentially, a network authentication protocol.

– Defined in RFC 1510 from 1993– biggest draw is not having to send passwords over the net. – offers single sign-on within one domain -- if everything within the domain

has been Kerberos-enabled. – support is also provided for single sign-on across different security realms

over a network. – Used in conjunction with JAAS, once a user's identity is established,

future authentication requests are no longer necessary.

Java Certification Path API• Certification Path API provides classes for building and validating

certificate chains, an important requirement of a Public Key Infrastructure (PKI).

• These certificates provide for the storage of security keys for users. By trusting the issuer of a certificate that holds the keys, and trusting the issuer of the certificate that trusts the original certificate, you establish chains of trust

• Building and validating certification paths is an important part of many standard security protocols, such as SSL/TLS, Secure/MIME (S/MIME), and IP Security (IPsec).