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 are two fundamental cryptography principles?

In this article we shall discuss about the two fundamental principles that govern a cryptographic system. 

1. Redundancy

- Some redundancy must be there in all the encrypted messages. 

- By redundancy here, we mean the information that is not required for understanding the message reducing the chances for a passive intruder to make attacks. 

- Passive intruder attacks involve putting the stolen information to misuse without understanding it. 

- This can be more easily understood by an example of a credit card. 

- The credit card number is not alone sent over the internet rather it is accompanied by other side info such as the DOB of the card holder, its validity date and so on. 

- Including such info with the card number cuts down on the changes for making up the number. 

- Adding a good amount of redundancy prevents the active intruders from sending garbage values and then getting it verified as some valid message. 

- The recipient must be capable of determining whether the message is valid or not by  doing some inspection and simple calculation. 

- Without redundancy the attackers would simply send junk message and the recipient will decode it as a valid message. 

- However, there is a little concern also with this. 

- N number of zeroes must not be put at the beginning or the end of the message for redundancy because such messages become easy to be predicted thus facilitating the crypt analysts work.

- Instead of zeroes, a CRC polynomial can be used because it proves to be more work. 

- Using cryptographic hash might be even better.

- Redundancy has also got a role to play in quantum cryptography. 

- Some redundancy is required in the messages for the bob to determine if the message has been tampered. 

- Repetition of the message twice is a crude form of redundancy.

- If the two copies are found to be identical, the bob states that somebody is interfering with the transmission or there is a lot of noise. 

- But such repetition process to be expensive. 

- Therefore, for error detection and correction the methods used are reed Solomon and hamming codes.

2. Update

- Measures must be compulsorily taken for the prevention of the attacks by active intruders who might play back the old messages. 

- The longer an encrypted message is held by an active intruder, the more is the possibility that he can break in to it. 

- One good example of this is the UNIX password file.

- For anybody who has an account on the host, the password is accessible. 

- A copy of this file can be obtained by the intruders and they can then easily de-crypt the password.

- Also, the addition of the redundancy allows the simplification of the messages’ decryption.

- It must be checked whether the message has been sent recently or is an old one. 

- One measure for doing so is including a time stamp of few seconds in the message. 

- This message then can be saved by the recipient for that many seconds and can be used for comparing with the incoming messages and filtering the duplicates.

- Messages which exceed this time period will be rejected as being too old.

Apart from the above two principles the following are some other principles of cryptography:

Ø Authentication: For ensuring that the message was generated by the sender itself and no one else so that no outsider can claim as being the owner of the message.

Ø Integrity: In cryptography, the integrity of the messages must be preserved while sending the message from one host to another. This involves ensuring that the message is not altered on the way. Using cryptographic hash is a way to achieve this.

Ø  Non-repudiation

What is WiMax technology?

Worldwide inter-operability for microwave access or wimax is standard developed for wireless communications that has been designed so as to deliver data rates of 30-40 mbps. The update in the technology in the year 2011 upgraded the technology to provide around 1 gbps for the stations that were fixed. 

- The Wimax forum is responsible for naming the technology as Wimax. 

- This forum was formed in the year of 2001 for the promotion of the inter-operability and conformity of this standard. 

- The Wimax has been defined by the forum as the technology based up on standards that enable the last mile wireless broadband delivery as alternative for the DSL and the cable thing. 

- The IEEE 802/ 16’s interoperability implementations are referred to as the WiMax. 

- The wimax forum has ratified this family of standards. 

- By virtue of the certification provided by this forum, the vendors are able to sell mobile and fixed products that are wimax certified. 

- This is done for ensuring that a level of inter-operability is maintained at par with the other products that have been also certified for the same profile. 

- The ‘fixed wimax’ is the name given to the original IEEE 802.16 standards.

- ‘Wifi on steroids’ is the term used to refer to WiMax sometimes. 

It has got a number of applications such as in:

Ø  Broadband connections

Ø  Cellular back-haul

Ø  Hot spots and so on.

- This technology shares some similarity with the Wifi technology however, this one is more capable of transmitting data at greater distances.

It is because of its range and bandwidth that the WiMax is suitable for the following applications:

Ø  Provides services such as the IPTV services and VoIP (telecommunications services).

Ø  Provides mobile broadband connectivity that is portable across the cities and countries and that can be accessed via different kinds of devices.

Ø  Provides an alternative for DSL and cable in the form of wireless last mile broadband access.

Ø  Acts as a source of internet connectivity.

Ø  Metering and smart grids.

- This technology can be used at home for providing internet access across the countries. 

- This has also caused a rise in the market competition. 

- The WiMax is even economically feasible. 

- Mobile wimax has been used as a replacement for the technologies like CDMA, GSM that are cellular phone technologies.  

- The technology has also been used as an overlay for increasing the capacity.  

- The fixed wimax is now used for 2g, 3g and 4g networks as a wireless back-haul technology in almost all the nations whether they are developed or developing.  

- In some states of North America, this technology is provided through a numbered of copper wire line connections. 

- On the other hand, the technology is back hauled via satellites in case of the remote cellular operations.  

- While in other cases even microwave Links are used. 

- The bandwidth requirements of the WiMAX demand more substantial back-haul when compared to other legacy cellular applications. 

- In some of the cases, the sites have been aggregated by the operators by use of Wireless Technology.  

- The traffic is then introduced to the fiber networks as per the convenience.  

- The technologies that provide triple play services are directed compatible with the WiMAX.  

- These services might include multi-casting and quality of service. 

- WiMax has been widely used for providing assistance in the communications. 

- The Intel Corporation has donated the hardware for WiMax technology for assisting the FCC (federal communications commission) and FEMA etc.

- The subscribers’ stations or SS are the devices which are used for connecting to a WiMAX Network. 

- These devices might be portable such as the following:

      > Handsets and smart phones

      > PC peripheral such as USB dongles, PC Cards and so on. 

      > Embedded devices in notebooks.

What are advantages and limitations of Wi-Fi?

The Wi-Fi has its own set of advantages and limitations. 

Advantages of WiFi

- WiFi makes the deployment of local Area Networks or LANs quite cheap.  

- There are some areas where the cables cannot be installed such as in historical buildings and outdoor areas. 

- But these spaces do not have any problem in hosting a wireless LAN.  

- Wireless Network adapters are being built into almost all the laptops by the manufacturers.

- A basic level of service is provided at which different brands concerning and client network interfaces access points that are competing with each other can inter-operate. 

- The products that have been certified by Wi-Fi alliance show back word compatibility. 

- A standard device for WiFi will work at any place in the whole world unlike our phones. 

- The WPA2 or the WiFi protected access encryption is secure provided a condition that the pass phrase used is quite strong.  

- The new protocols use for WMM i.e., Quality of service increase the suitability of the Wi-Fi regarding its use in latency - sensitive applications. 

- WMM is a power saving mechanism that is used for extending the life of the battery. 

Limitations of WiFi

- Inconsistency of the operation and spectrum assignments poses a problem worldwide.  

- The range all the WiFi networks is limited. 

- A wireless access point typically uses a stock antenna having a range of 100 m outdoors and 25m indoors.

- The frequency band is a major factor for producing variations in the range.  

- The range of Wi-Fi with a 2.4 ghz frequency block is better when compared with the 5.0 ghz frequency block Wi-Fi. 

- Some wireless routers come with detachable antennas. 

- These antennas can be removed for improving the range. 

- In their place upgraded antennas can be fitted. 

- The benefit of these antennas is that they have high directional gain at the remote devices. 

- The local regulations limit the maximum amount of power that can be transmitted by a Wi-Fi. 

- The power consumption of Wi-Fi is quite higher than the other standards.  

- This is so because of the reach requirements of the wireless LAN applications.

- There are technologies available that provide a propagation range that is much shorter. 

- One such technology is Bluetooth and has very low power consumption.  

- Other technologies such as zigbee have low power consumption, a long range but provides low data rate. 

- The most commonly used wireless encryption standard is WEP or wired equivalent privacy. 

- Even this standard has been proven to be breakable even if correct configuration is used. 

- This problem was addressed by WPA or Wi-Fi protected access standard to some extent. 

- By default the wireless access points use the encryption free mode. 

- The wireless security is disabled because of which the LAN can be openly accessed. 

What are uses of Wifi?

- Routers sometimes act as a Wi-Fi access point incorporating a cable modem or a DSL modem.

- These routers are installed in buildings and homes for providing Internet access and other inter networking services to the devices that in turn are connected to a either through a cable or wireless. 

- Similarly, there are routers that are powered by battery and they consist of a Wi-Fi access point and a mobile Internet radio modem. 

- Today smartphones come with this as a built-in capability.  

- However, this feature is disabled by the carriers. 

- The carriers might charge extra money for this. 

- The standalone facilities are provided by Internet packs. 

- The places where there is no network access, wifi is used. 

- Using Wi-Fi, a direct communication link between two computers can be established.  

- There is no intermediate point.  

- This type of transmission is termed as ad hoc wifi transmission. 

- This network mode is now very popular with the multi-player game consoles. Examples are:

       > Nintendo DS

       > PlayStation portable

       > Digital cameras

       > Other consumer electronic devices.

- A citywide Wi-Fi plan has been implemented by a number of the cities around the world.  

- In India, the first city to do so was Mysore.  

- The first city in the world was Jerusalem.

- The first city in United States was Sunnyvale in California to offer city-wide wifi. 

- Another type of wifi implementation is campus-wide wifi.  

- A number of colleges in United States have set up this kind of wifi network.  

- The first university to have it was Carnegie Mellon University. 

- Using wifi, the local area Network can be deployed in very less cost.  

- There are places where it is not possible for the physical transmission medium such as cables to reach. 

- In such places wifi network is of crucial importance.  

- Also, wifi can be easily deployed in historical buildings and outdoor areas.  

- Now, because of the increasing popularity of the Wi-Fi, the manufacturers are developing Wireless Network adapters for most of the notebooks and laptops.  

- This eventually led to a fall in the price of the Wi-Fi chip set. 

- Today, the Wi-Fi chip set is economically feasible and is included in most of the devices.  

- There are many brands of client network interfaces and access-points that are competing with each other.  

- These interfaces are able to inter-operate at a basic level. 

- The Wi-Fi certification for the products is issued by wifi alliance. 

- This makes them backwards compatible with each other. 

- A standard Wi-Fi Device is supposed to work anywhere in the world. 

- The encryption standard that is considered secure is the WPA2 or wifi protected access.  

- But, this would work only if the pass phrase that is being used is strong enough. 

- The Wi-Fi has been made more suitable with the use of new protocols such as quality of service.  

- This has made wifi compatible with latency sensitive applications.  

- Nowadays, for extending battery life power saving mechanisms such as WMM are being used.  

- These are the major uses of wifi technology.

- The usage wifi has been limited because of its limited range. 

- Therefore, in order to cover up a large area several intermediate Wi-Fi access-points have to be set up. 

- The variations in the range can be produced by varying the frequency band.  

- Wifi with a small frequency block works better than wifi with a larger frequency block.

- Wifi with the larger frequency blocks are optionally used. 

- The power of wifi network can be harnessed by using high gain direction antennas instead of using detachable antennas.  

- Another factor limiting the performance of wifi transmission is the local regulations. 

- Wifi also requires high power to operate upon. 

- This is a cause of concern for the devices' batteries.

What is Wifi technology? How does it work?

- Wifi has emerged as a very popular technology. 

- This technology has enabled the electronic devices to exchange information between them and to share the internet connection without using any cables or wires. 

- It is a wireless technology. 

- This technology works with the help of the radio waves. 

- The Wifi is defined as a WLAN (wireless local area network) product by the wifi alliance that is based on the standards defined by IEEE (802.11 standards). 

- Most of the WLANs are based upon these standards only and so this technology has been named as wifi which is the synonymous with the term WLAN. 

- The wifi-certified trademark might be used by only those wifi products which have the complete certification for the wifi alliance inter-operability. 

- A number of devices now use wifi such as the PCs, smart phones, video game consoles, digital cameras, digital audio players, tablet computers and so on. 

- All these devices can connect to the network and access internet by means of a wireless network access point. 

- Such an access point is more commonly known as a ‘hotspot’. 

- The range of an access point is up to 20 m. 

- But it has a much greater range outside.  

- An access point can be installed in a single room or in an area of many square miles. 

- This can be achieved by using a number of overlapping access points. 

- However, the security of the wifi is less compared to the wired connections for example Internet.

- This is so because a physical connection is not required by an intruder. 

- The web pages using SSL have security but the intruders can easily access the non-encrypted files on the internet. 

- It is because of this, that the various encryption technologies have been adopted by the wifi. 

- The earlier WEP encryption was weak and so was easy to break.

- Later, came the higher quality protocols such as the WPA2 and WPA. 

- The WPS or the wifi protected set up was an optional feature that was added in the year of 2007. 

- This option a very serious flaw which is that it allowed the recovery of the password of the router by an attacker.

- The certification and the test plan has been updated by the wifi alliance for ensuring that there is resistance against attacks in all the devices that have been newly certified.

- For connecting to a wifi LAN, a wireless network interface controller has to be incorporated in to the computer system.

- This combination of the interface controller and the computer is often called as the station. 

- The same radio frequency communication channel is shared by all the stations.

- Also, all the stations receive any transmission on this channel. 

- Also, the user is not informed of the fact that the data was delivered to the recipient and so is termed as the ‘best–effort delivery mechanism’. 

- For transmitting the data packets, a carrier wave is used. 

- These data packets are commonly known as the ‘Ethernet frames’. 

- Each station regularly tunes in to the radio frequency channel for picking up the transmissions that are available. 

- A device that is wifi enabled can connect to the network if it lies in the range of the wireless network. 

- One condition is that the network should have been configured for permitting such a connection. 

- For providing coverage in a large area multiple hotspots are required. 

- For example, wireless mesh networks in London. 

- Through wifi, services can be provided in independent businesses, private homes, public spaces, high street chains and so on. 

- These hotspots have been set up either commercially or free of charge. 

- Free hotspots are provided at hotels, restaurants and airports. 

What is a transposition cipher method?

- The transposition cipher method is one of the cryptography methods used for securing the communication from eavesdroppers. 

- This method of encryption shifts the positions of the units or letters of the plain text based up on some regular system so that a permutation of the plain text is generated. 

- This permuted plain text is termed as the cipher text. 

- Thus, the cipher text is generated by changing the order of the units. 

- Mathematically the following functions are used:

Ø  Bijective function: For encryption of the character’s position and

Ø  Inverse function: For decrypting the message

Now we shall see about some of the implementations of the transposition cipher:

1. Rail fence cipher: 

- This form of the transposition cipher has been named so because of the way that it follows for encoding.

- Here, the characters of the plain text are written on the successive rails in a downwards manner of some imagined fence.

- Then, we move upwards once getting to the bottom. 

- For reading the message, it is taken in rows.

2. Route cipher: 

- In this form of transposition cipher, a grid of given dimensions is taken on which the characters of the plain text are written out. 

- Then, the message is read based up on the pattern mentioned in the key. 

- For example, the pattern might be inwards spiral in clockwise direction starting from topmost right.

- The route ciphers may use many keys unlike the rail fence cipher. 

- In fact, the number of keys used for enumerating the messages of reasonable length by modern machinery might be too great. 

- Also, it is not necessary that all the keys might be good in equal terms. 

- Excessive chunks of the plain text might be left if bad routes are chosen. 

- Also, the plain text might be simply reversed, thus giving a clue to the crypt analysts about the routes. 

- The union route cipher is a variation of the traditional route cipher. 

- The difference between the two is that this one transposed the whole words unlike route cipher which transposed individual letters.

- But since transposing the whole words could expose them, they were first hidden by a code.

- The entire null words might be added for adding humor to the cipher text.

3. Columnar transposition: 

- In this form of transposition cipher, a fixed length is determined for the rows in which the message is written. 

- But for reading the message a column by column approach is followed where some scrambled order if followed for choosing the columns. 

- A keyword is chosen which is used for defining the permutation of the columns as well as the width of the rows. 

- The spare spaces might be filled with the null characters in case of the regular columnar transposition. 

- On the other hand, in these spaces are left as such in the irregular columnar transposition cipher. 

- The keyword specifies some order following which the message is read column - wise. 

- The column lengths have to be worked out by the recipient for deciphering the message. 

- This is done based up on division of the length of the message specified by the key length.

4. Double transposition: 

- A single columnar transposition is vulnerable to attacks since the possible lengths of the column and anagrams can be guessed. 

- Therefore, a stronger version of it i.e., the double transposition is followed. 

- This is a two-time application of the columnar transposition. 

- For both the transpositions, either the same key might be used or different keys.

- This was the most complicated cipher before the coming of the VIC cipher. 

- It offered reliable operation under difficult conditions.