Thursday, March 29, 2007

Overview of Layer 4 Switching

What is Layer 4 Switching ?

Layer 4, is the Transport layer in OSI model, which takes care of things like flow control and reliable and accurate delivery of the data to the next layer, uses protocols such as TCP and UDP. These protocols include the port number information in the header, which helps identify what application the packet is being used .A Layer 4 switch can identify this information, together with the IP address that is identified on Layer 3, it not only knows where the data needs to go, but also what application will use it. The combination of a Layer 4 TCP or UDP port number and the Layer 3 address is called a socket.


Layer 4 can be used to enhance the features of a Layer 3 switch, which essentially performs packet routing at high speeds by means of hardware, by allowing it to filter network traffic and perform switching based on the application the data is intended for. So, a Layer 4 switch has the ability to not only examine the IP address, but also to control the traffic based on the port numbers located at Layer 4 of the OSI model.


Thursday, March 22, 2007

UUCP

Introduction:

UUCP :Unix to Unix copy protocol was origianlly developed to connect Unix Hosts together ,UUCP has since been ported to many different architectures, including PCs, Macs, Amigas, Apple IIs, VMS hosts etc.UUCP and similar systems are batch-oriented systems: everything that they have to do is added to a queue, and then at some specified time, everything in the queue is processed .

Implementation Environment:

UUCP networks are commonly built using dial-up (modem) connections. This doesn't have to be the case though: UUCP can be used over any sort of connection between two computers, including an Internet connection. Building a UUCP network is a simple matter of configuring two hosts to recognize each other, and know how to get in touch with each other. Adding on to the network is simple; if hosts called A and B have a UUCP network between them, and C would like to join the network, then it must be configured to talk to A and/or B. Naturally, anything that C talks to must be made aware of C's existence before any connections will work. Now, to connect D to the network, a connection must be established with at least one of the hosts on the network.In a UUCP network, users are identified in the format host!userid. The ``!'' character (pronounced ``bang'' in networking circles) is used to separate hosts and users. A bangpath is a string of host(s) and a userid like A!Panda or C!B!A!Panda. If I am a user on host A and you are a user on host E, I might be known as A!Panda and you as E!you. Because there is no direct link between your host (E) and mine (A), in order for us to communicate, we need to do so through a host (or hosts!) that has connectivity to both E and A. In our sample network, C has the connectivity we need. So, to send me a file, or piece of email, you would address it to C!A!Panda. Or, if you feel like taking the long way around, you can address me as C!B!A!Panda.

Security:

UUCP, like any other application, has security tradeoffs. Some strong points for its security is that it is fairly limited in what it can do, and it's therefore more difficult to trick into doing something it shouldn't; it's been around a long time, and most its bugs have been discovered, analyzed, and fixed; and because UUCP networks are made up of occasional connections to other hosts, it isn't possible for someone on host E to directly make contact with host B, and take advantage of that connection to do something naughty.On the other hand, UUCP typically works by having a system-wide UUCP user account and password. Any system that has a UUCP connection with another must know the appropriate password for the uucp or nuucp account. Identifying a host beyond that point has traditionally been little more than a matter of trusting that the host is who it claims to be, and that a connection is allowed at that time. More recently, there has been an additional layer of authentication, whereby both hosts must have the same sequence number , that is a number that is incremented each time a connection is made.Hence, if I run host B, I know the uucp password on host A. If, though, I want to impersonate host C, I'll need to connect, identify myself as C, hope that I've done so at a time that A will allow it, and try to guess the correct sequence number for the session. While this might not be a trivial attack, it isn't considered very secure.

Wednesday, March 21, 2007

Are Digital Certificate, Digital Signature and Digital Envelope same?

Digital Envelop: As the name suggests, digital envelope is to seal the message in such a way that no one else other then the intended recipient can open the message. Practical implementation involves combination of symmetric key and public key methods, i.e. encrypting message using symmetric keys which in turn is protected using public key method. Digital envelops use symmetric keys to encrypt the message and assymetric keys to distribute the symmetric keys. Intention of Digital Envelope is to provide – Confidentiality & faster cryptographic operations.


Digital Signature: By digitally signing the message the recipient can make sure that message is from the intended sender and no one else has modified the message in transit. Digital signature uses both hashing algorithm and asymmetric encryption algorithm. First hash of the message is calculated and later the hash is encrypted using public key cryptography. Even a single bit change in original message results in entirely different hash. Few applications of digital signatures are digital certificates and binary sighning. Intention of Digital Certificate is to provide – authentication and integrity.



Digital Certificate: Digital envelope and digital signature do not ensure that public key being used is valid or belongs to intended recipient. Also they do not specify which hash and encryption algorithms are used. To eliminate this limitation, some third party (Certificate Authority) issues the certificate to user which binds the identity public key to its owner and also specifies additional parameter like algorithms used, validity period etc. Intention is to authenticate the public key and facilitate the use of public keys.