What are secret-key and public-key signatures?

- Asymmetric cryptography is often referred to as the public-key cryptography. 

- It is a cryptographic algorithm which makes use of two individual keys namely the secret key and the public key. 

- The secret is kept private and the public key is open. 

- Even though these two keys are different, there is some mathematical link between the two. 

- The key which is used for the encryption of the plain text and verification of the digital signature is the public key. 

- So, the private key is one that is used for the decryption of the cipher text in to plain text or for creation of a digital signature. 

- Both these keys are contrast of each other unlike in the symmetric cryptography where the same key serves both the purposes. 

- The public keys are created based up on some mathematical problems for which presently there is no efficient solution such as the following:

Ø  Elliptic curve relationships

Ø  Discrete logarithms

Ø  Integer factorization

- Generating the public and the private key pair is computationally easy for the users. 

- The strength of the public keys lies in the fact that determining the private key from its public key is computationally in feasible or almost impossible. 

- Thus, without fearing any compromise with the security, the public key can be published whereas the private key is kept hidden from everyone so as not to reveal it to anyone who does not has authorization for performing the digital signatures or reading the messages. 

- Unlike for the symmetric key algorithms, a secure initial exchange of the secret keys is not required for the public key algorithms. 

- In the process of message authentication, a private key is used for processing a message for producing the digital signature. 

- After doing so, the signature can be verified by anyone by processing the value of the signature using the corresponding public key of the signer. 

- The result is then compared with the message. 

- The unmodified nature of the message is confirmed a success signal. 

- Also, it is presumed that the private key of the signer has been kept hidden from the others. 

- However, in practical applications, the message’s digest or hash is encrypted and used as the signature. 

- The fundamental security components of the cryptosystems, protocols and applications are the public key algorithms.

These systems underpin the following internet standards:

Ø  PGP

Ø  GPG

Ø  TLS or transport layer security

- Secrecy as well as Key distribution is provided by some of the public key algorithms such as the Diffie-Hellman key exchange algorithm while some algorithms like Digital signature algorithm provide the digital signature and some others offer both the things.

- An example of such algorithm is RSA. 

- All these algorithms have been widely accepted. 

- A pair of cryptographic keys (i.e., a public key for encryption and a private key for decryption) is provided to each of the users. 

- Similarly, for digital signatures the pair of keys consists of a private key for signing and a public key for verification. 

- The concept of the private key has been introduced so as to ensure the confidentiality. 

- The digital signatures can be verified by anyone possessing the corresponding public key. 

- With such a confirmation it is confirmed the private key is possessed by the sender. 

- This is also a way to confirm that no tampering has been done to the message. 

- If the message has been tampered, it will introduce changes in the encoded message digest. 

- Mail box having a mail slot and a personal wax seal can be taken as an analogy to public – key encryption and digital signatures respectively. 

What is link encryption method?

- Link encryption method is one of the classic methods used in the digital communications for the application of the crypto.

- Link encryption method has been designed for hiding the secrets and preventing the forgery of data. 

- It is quite a simple concept that has been discussed here and it fits for all the types of existing applications and software used in the communication.  

- Even though this method does not works well enough for most of the applications, it is the simplest of all. 

- Link encryption method is a security measure that should be used only if your security objectives match with those of the link encryption method. 

- It is commonly used in the applications where a boundary has to be maintained between the internal users and the external users. 

- With the link encryption it gets easy for the internal users to share data whereas it is just the opposite for the external users. 

- It provides transparent protection except for the separation that is maintained between the two classes of the users. 

Below we mention some security objectives that can be met with the link encryption:

Ø  Maintaining confidentiality: Our systems of course store very sensitive data. While exchanging the data with other systems, it is required that the risk of leakage involved should be as minimum as possible.

Ø  Communication with the outsiders: Obviously, we do not want to share our data with the unwanted outsiders and unauthorized sites and so we want these to be blocked. Such exchanges should be prevented from happening even by carelessness or accident.

Ø  Hiding data traffic: As much as possible we want our data and its details to be shielded from the outsiders. This data might contain information about the destination host and other info necessary for communication control. However, here it is assumed that the information will not be leaked by the insiders.

Ø  Familiarity and safety: We rank these two factors above the cost.

Ø  Protection of the data transfers: We need protection for our data against any sort of tampering or forgery by the outsiders during the transition. An assurance is important.  This objective is unconditionally met by this link encryption method.

- From security standpoint, a design is yielded by the link encryption that is highly reliable. 

- If in your organization some security parameter has been established that is strong enough, link encryption is the best technique for its maintenance. 

- A strict control is kept over the flow of physical documents through this security parameter. 

- The link encryption provides a complementary protection for the flow of the electronic documents. 

- We can have an environment with every data link that traverses the boundary having encryptors. 

- The documents will be kept within the parameter limits. 

- The data leaving the parameter will be protector by means of the encryptors. 

- Link encryption method is being used since years in banking organizations and military communications for providing secure links. 

- The link encryption uses the in-line encryptors as its building blocks.

- This hardware devices takes plain text and converts it into cipher text.

The encryptors have their own vulnerabilities as mentioned below:

Ø  Rewrite attacks: It is also known as the plain-text attack, it is used for forging the messages. Few crypto algorithms are vulnerable to these attacks.

Ø  Replay attacks: Most of us think that the encrypted data is self-validating and so by matching the encryptor with its keys a sensibly de-crypting message can be generated. Since the encrypted data is accessible to the outsiders, they can also access the message that decrypts sensibly.

Ø  Covert signaling attacks: This attack is based on the idea that there is always a way to leak info if there exists an internal process that tries to do so. 

What is meant by multiplexing?

- Multiplexing or muxing is a very important process in computer networks and the telecommunications. 

Using this process, a number of digital data streams or analog message signals are combined as one signal and then transported over the common medium. 

- Multiplexing is used wherever it is required to share a resource that is very expensive. 

- The most common example of multiplexing is of using one wire for several telephone calls. 

- The origin of the multiplexing dates back to 1870s when telegraphy was started.

- Now it is used to a great extent in the field of communications. 

- The telephone carrier multiplexing was developed by George Owen Squire in the field of telephony. 

- The communication channel over which the multiplexed signal might be transmitted might be a physical transmission medium. 

- The high level communication channel’s capacity is divided by multiplexing process in to a number of low level logical channels where for each message or data stream one channel is used. 

- Demultiplexing is the reverse process of multiplexing. 

- This is used for the extraction of the original signals on the reception side.

- A multiplexer or MUX is a device that is used for carrying out the multiplexing process and the demultiplexer or DEMUX is the device that performs demultiplexing. 

- IMUX or inverse multiplexing is another process whose aim is just the opposite of the multiplexing.

- It breaks down a single data stream in to various streams while transferring them at the same time over various communication channels.

- Later, the original stream is recreated.

Types of Multiplexing

Many different types of multiplexing technologies are available today. Each has its own significance:

Ø SDM or space-division multiplexing: 

This technique implies on using different point – to – point wires for individual communication channels. For example, an audio cable of analogue stereo, multi – pair telephone cable, switched star network, mesh network. However typically the wired SDM is not usually considered as multiplexing. In SDM a phased array antenna is formed by multiple antennas. For example MIMO (multiple – input and multiple – output), SIMO (simple – input and multiple – output), MISO (multiple – input and single – output) etc.

Ø  FDM or frequency-division multiplexing: 

This is considered to be an analog process, here the signals are sent in to different frequency ranges over a shared medium. For example, TV and radio broadcasting from satellite stations through the earth’s atmosphere. One cable is given in each house but over this cable many signals can be sent to other subscribers also. For accessing the desired signal, the users require to tune to that particular frequency. WDM or wavelength division multiplexing is a variant of FDM.

Ø TDM or time-division multiplexing: 

Unlike FDM, TDM is a digital technology but very rarely it might be used as an analog technology also. The process involves putting bytes in a sequence for each input stream one by one. this sequencing is done in such a way that the receiver can appropriately  receive them. If this is done quickly, the fact that another logical communication path was served in that circuit time won’t be detected by the receiver.

Ø  CDM or code-division multiplexing: 

In this multiplexing technique, the same frequency spectrum is shared by the several channels at the same time. Also the bandwidth of the spectrum is quite high when compared to the symbol rate or the bit rate. It is implemented in either of the two forms namely direct sequence spread spectrum and frequency hopping.

Some other types of multiplexing techniques which are less prominent are:

Polarization-division multiplexing: Used in optical and radio communications.

Orbital angular momentum multiplexing

What is Throughput, Turnaround time, waiting time and Response time?

In this article we discuss about four important terms that we often come across while dealing with processes. These 4 factors are:

1.  Throughput

2.  Turnaround Time

3. Waiting Time

4.  Response time

What is Throughput?

- In communications networks like packet radio, Ethernet etc., throughput refers to the rate of the successful delivery of data over the channel. 

- The data might be delivered via either logical link or physical link depending on the type of communication that is being used. 

- This throughput is measured in the terms of bps or bits per second or data packets per slot. 

- Another term common in networks performance is the aggregate throughput or the system throughput. 

- This equals to the sum of all the data rates at which the data is delivered to each and every terminal in a network. 

- In computer systems, throughput means the rate of successful completion of the tasks by the CPU in a specific period of time. 

- Queuing theory is used for the mathematical analyzation of the throughout. 

- There is always a synonymy between the digital bandwidth consumption and the throughput. 

- Another related term is the maximum throughput.This bears synonymy with the digital bandwidth capacity.

What is Turnaround Time?

- In computer systems, the total time taken by the CPU from submission of a task or thread for execution to its completion is referred to as the turnaround time. 

- The turnaround time varies depending on the programming language used and the developer of the software.

- It deals with the whole amount of time taken for delivering the desired output to the end user following the start of the task completion process. 

- This is counted among the metrics that are used for the evaluation of the scheduling algorithms used by the operating systems. 

- When it comes to the batch systems, the turnaround time is more because of the time taken in the formation of the batches, executing and returning the output.

What is Waiting Time?

 

- This is the time duration between the requesting of an action and when it occurs. 

- Waiting time depends up on the speed and make of the CPU and the architecture that it uses. 

- If the processor supports pipeline architecture, then the process is said to be waiting in the pipe. 

- When the current task in processor is completed, the waiting task is passed on to the CPU for execution. 

- When the CPU starts executing this task, the waiting period is said to be over. 

- The status of the task that is waiting is set to ‘waiting’. From waiting status, it changes to active and then halts.

What is Response Time?

 

- The time taken by the computer system or the functional unit for reacting or responding to the input supplied is called the response time. 

- In data processing, there are various situations for which the user would perceive the response time:

Ø  Time between operator entering a request at a terminal  and

Ø  The instant at which appears the first character of the response.

- Coming to the data systems, the response time can be defined as the time taken from the receipt of EOT (end of transmission) of a message inquiry and start of the transmission in response to that inquiry. 

- Response is an important concept in the real time systems and it is the time that elapses between the dispatch of the request until its completion. 

- However, one should not confuse response time with the WCET.

- It is the maximum time taken by the execution of the task without any interference. 

- Response time also differs from the deadline. 

- Deadline is the time for which the output is valid. 

What is meant by Conditional Access System?

- Conditional access system or CAS is a system that has been developed as a means for providing the protection to content by setting certain criteria that should be met before the access to it is granted. 

- The concept of conditional access is however related closely to the digital television systems such as the satellite television. 

- The standards for the conditional access system have been defined under the following specification documents of the digital video broadcasting standard (DVB):

1. DVB – CA (conditional access)
2. DVB – CSA (common scrambling algorithm)
3. DVB – CI (common interface)

- All of these standards together define a method for obfuscating a digital television stream, thus providing access to only those possess the ‘valid description smart cards’. 

- All of these specifications are available on the standards page of the DVB web site.

- Conditional access is the result of combination of encryption and scrambling technologies. 

- Firstly, the data stream is subjected to scrambling with a secret key of 48 – bits usually called the control word. 

- The control word is generated in such a pattern in which the successive word cannot be predicted. 

- It is recommended by the DVB that a physical process should be used for that. 

- For a person to unscramble the data stream it is required that he/ she should know about the current control word. 

- In order to provide the protection to control word during the course of transmission, encryption methodology is used. 

- The control word will be de-crypted by the conditional access system only when there is authorization. 

- This authorization is given in the form of EMM or entitlement management message. 

- They are specific for each subscriber. 

- Different ECMs can also transmit the control word at one allowing the usage of many conditional access systems at once and simultaneously. 

- The simulscrypt of the DVB allows all the multiplex operators to cooperate while at the same time saves bandwidth. 

- Channels such as the hot bird satellites and the CNN international make use of several CASs in parallel. 

- The data from the decryption is read from the cards and updated if required through either of the following:

1. CAM or conditional access module
2. PC card – format card reader
3. Built – in ISO/ IEC 7816 card reader

- Conditional access systems include two major types namely analog systems and the digital systems both categorized at shown below:

1. Analog systems:

Ø  Nagravision

Ø  Videocrypt

Ø  Videocipher

Ø  Eurocrypt

2. Digital systems:

Ø  Abel Quintic

Ø  ABV (alliance broadcast vision)

Ø  Accessgate

- These systems are the key component for all the digital TV operations.

- Their purpose is to secure the investments of the operators through the encryption of the signals. 

- The payment from the customers in order to watch TV is also ensured by the conditional access systems. 

- But the TV operators usually have limited knowledge about the conditional access systems. 

- Encryption is involved with the whole conditional access system. 

- Operators have the analyzers for finding the cause of the common signal problems. 

- But they do lack tools that can debug the CASs. 

- Most of the conditional access system monitoring tools follow the ETSI TR 101 290 standard (a DVB promoted standard) even though the CAS is not fully covered by this specification. 

- Analyzing tools as such let the operators to know about the problems of conditional access system before the customers notice it. 

- But practically also, it is not possible to take care of all the problems that may affect the subscriber. 

What is meant by email spoofing in detail?

What is meant by Email or Electronic Mail?

- Email or electronic mail is the most popular and convenient means for exchange of digital messages and information in the modern world.

- E- Mail facility is harnessed through a computer network probably over an internet connection.

- Earlier the email can be used for sending messages only when both the sender and the recipient were online and such messages were called instant messages.

- But, today the email system is somewhat changed and is entirely based up on a store and forward model.

- When an email is sent, it is stored by the server and later is delivered accordingly.

- The sender and recipient do not require being online though they need to connect to the particular email server in order to send and receive the emails.

- The whole email system is today governed by the simple mail transfer protocol or SMTP rather than FTP or file transfer protocol that was used earlier.

Problems faced by Email Systems
These email system like any other system has too got many problems like:

1. Attachment size limitation
2. Overloading of information
3. Spamming
4. Computer viruses
5. Email spoofing
6. Email bombing
7. Tracking of sent and received emails
8. Privacy concerns

This article is dedicated to the worst problem being faced by the email today i.e., “email spoofing”.

Introduction to Email Spoofing

Most of us are aware about the content spoofing; the email spoofing is also somewhat same only with the only difference being that it affects emails rather than web sites or web applications.

"An email is said to have been spoofed when its sender’s address as well as its header part have been altered to make it seem as though it has been originated from a source different from the actual source."

What makes these emails so vulnerable to email spoofing?

- More and more emails fall victims to email spoofing since the simple mail transfer protocol (SMTP) does not provide any techniques or methodologies for the authentication of these emails.

- It becomes comparatively easy for the attackers to forging and impersonating the emails.

- In some cases there might be legitimate causes for forging an email but in other cases the cause can be quite mischievous like phishing and spamming in order to hide the origination of the email.

- The attacker can easily change the email properties like its return path, reply to and from fields etc and make it appear as though somebody else had sent the email hiding the identity of the actual email sender.

- The recipient comes in to believing that the email has been received from the address as altered and stated in the “from” field when it is actually form a different source.

- Such emails are said to be spammed and bear the address of the spam email in the “reply to” field.

- Most of the spam emails are malicious in nature and may be infected with a Trojan, virus or worm and so on.

- Some might be just for the sake of advertisement of some cause.

- Earlier before the advent of the spam, the legitimately spoofed emails were used as a viable business model.

- Consequently the spam emails came to be recognized as an annoying problem. This problem called for the need of anti spam methodologies.

- Spoofing the IP address is somewhat difficult as compared to spoofing of the email content.

- This is so because of the great bit size of the IP address.

- To overcome such spoofing problems techniques such as following are used:
1. PGP cryptographic signatures technique
2. Using SSL or TLS in mail transfer software
3. Other encryption techniques.

Proper authentication is the only solution for preventing spoofing and bombing of emails.

Quick Tech Tip: CDMA - Code Division Multiple Access

CDMA (Code-Division Multiple Access) refers to any of several protocols used in so-called second-generation (2G) and third-generation (3G) wireless communications. As the term implies, CDMA is a form of multiplexing, which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth. CDMA, a proprietary standard designed by Qualcomm in the United States, has been the dominant network standard for North America and parts of Asia.
Coverage: The most important factor is getting service in the areas you will be using your phone. Upon viewing competitors' coverage maps you may discover that CDMA carriers offer cellular service in your area. If so, there is no decision to be made, but most people will find that they do have a choice.
For radio systems there are two resources, frequency and time. Division by frequency, so that each pair of communicators is allocated part of the spectrum for all of the time, results in Frequency Division Multiple Access (FDMA). Division by time, so that each pair of communicators is allocated all (or at least a large part) of the spectrum for part of the time results in Time Division Multiple Access (TDMA). In Code Division Multiple Access (CDMA), every communicator will be allocated the entire spectrum all of the time. CDMA uses codes to identify connections.


CDMA is a form of spread-spectrum, a family of digital communication techniques that
have been used in military applications for many years. The core principle of spread
spectrum is the use of noise-like carrier waves, and, as the name implies, bandwidths
much wider than that required for simple point-to-point communication at the same data rate. CDMA is a Direct Sequence Spread Spectrum system. The CDMA system works directly on 64 kbit/sec digital signals. These signals can be digitized voice, ISDN channels, modem data, etc.
CDMA is altering the face of cellular and PCS communication by:
· Dramatically improving the telephone traffic capacity.
· Dramatically improving the voice quality and eliminating the audible effects of
multipath fading.
· Reducing the incidence of dropped calls due to handoff failures.
· Providing reliable transport mechanism for data communications, such as
facsimile and internet traffic.
· Reducing the number of sites needed to support any given amount of traffic.
· Simplifying site selection.
· Reducing deployment and operating costs because fewer cell sites are needed.
· Reducing average transmitted power.
· Reducing interference to other electronic devices.
· Reducing potential health risks.