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 are different methods of broadcasting a packet?

Without broadcasting, our information theory and telecommunications does not mean anything. 

- It is broadcasting that actually makes the transfer of data possible from one point to another. 

- Broadcasting can be defined as the method of transfer of a message to a number of recipients, all at the same time. 

- Broadcasting is often considered to be a sort of high – level operation in some programs while low level operation in some other programs. 

- For example, in message passing interface, broadcasting is a high level operation whereas in broadcasting on Ethernet, it is considered to be a low level operation in networking. 

We have many kinds of routing schemes suiting for various kinds of broadcasting requirements:

1. Anycast
2. Broadcast
3. Multicast
4. Unicast
5. Geocast

- Broadcasting is transmission of a packet to each and every device that is attached to the network. 

- However, the broadcasting is limited to transmission in the broadcast domain in practical applications. 

- Broadcasting can be contrasted with uni cast routing scheme in the sense that in uni cast, the datagrams are transmitted by one host and are received by another single host only. 

- This receiving host is identified with an IP address on the network that is unique to it. 

- All the technologies used in networking are not capable of supporting broadcasting. 

For example, the following do not have this capability:

Ø  X.25 relay

Ø  Frame relay

- The broadcast method cannot be implement with IPv6 i.e., the successor of the IPv4 (internet protocol version 4).

- This is for the avoidance of the disturbance to the nodes. 

- Also, there does not exist anything such as the internet wide broadcast. 

- Therefore, this limits the scope of the broadcasting to the LAN technologies such as token ring and Ethernet since here the impact of the broadcasting performance is small.

Categories of Broadcasting Methods

The broadcasting methods can be classified in to 4 major categories as per the IEEE 802.11 standard:

1. Simple flooding method: 

- In this method the packets are rebroadcast-ed by each of the nodes.

- A message is disseminated to all the neighboring nodes by a source node in the MANET. 

- If the neighboring nodes would have received this message already, then this time the message will be dropped.

- If not, they will re-disseminate the message to their neighbors simultaneously. 

- This process continues until all the nodes have received this message. 

- Only for a MANET this method proves to be reliable that too only if the nodes have low density as well as high mobility. 

- This method has a good potential for harming the network and make it unproductive. 

- This happens so because it will cause congestion in the network thereby exhausting the power of the battery.

2. Area based broadcasting method: 

- Here, we assume a transmission distance.

- Only if sufficient coverage area is detected, the node can rebroadcast otherwise not. 

- This method can be of two types namely location based scheme and the distance based scheme.

3. Probability tested: 

- Rebroadcasting is done by the nodes depending up on the network’s topology and probabilities assigned to them. 

- This somewhat resembles the flooding algorithm with the only exception that a predetermined probability is used for rebroadcasting by the nodes.

- The transmission coverage might be shared by the multiple nodes where the network is too dense.

4. Neighborhood based broadcasting method: 

- Neighborhood method is used for maintaining a state in the neighborhood and rebroadcasting is done with the help of the info obtained from the nodes in this neighboring area. 

- There are two types of this method namely self-pruning approach and ad hoc broadcasting approach.      

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.