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Explain the purpose, nature, function and operations of Symmetric Encryption Principles. What are the essential ingredients of a symmetric cipher? Differentiate between encryption and decryption.

Symmetric encryption is a class of algorithms for cryptography that use the same cryptographic keys for both encryption of plaintext and decryption of ciphertext. The keys may be identical or there may be a simple transformation to go between the two keys. The keys, in practice, represent a shared secret between two or more parties that can be used to maintain a private information link.

Encryption methods can be extremely efficient, requiring minimal processing, and Both sender and receiver must possess encryption key. If either copy of key is compromised, an intermediate can decrypt and read messages

A symmetric encryption has two components a block cipher and stream cipher. (i) A block cipher operates on groups of bits – typically groups of 64. If the final block of the plaintext message is shorter than 64 bits, it is padded with some regular pattern of 1s and 0s to make a complete block. Block ciphers encrypt each block independently, so the plaintext does not have to be processed in a sequential manner. (ii) A stream cipher generally operates on one bit of plaintext at a time, although some stream ciphers operate on bytes. A component called a keystream generator generates a sequence of bits, usually known as a keystream. In the simplest form of stream cipher, a modulo-2 adder (exclusive-OR or XOR gate) combines each bit in the plaintext with each bit in the keystream to produce the ciphertext. At the receiving end, another modulo-2 adder combines the ciphertext with the keystream to recover the plaintext.

A symmetric encryption has 5 ingredients, which are the following:

1.                 Plaintext: this is the original message or data that is fed into the algorithm as input.

2.                 Encryption algorithm: this algorithm performs various substitutions and transformations on the plaintext.

3.                 Secret Key: is also input to algorithm. The exact substitutions and transformations performed by the algorithm depend on the key.

4.                 Ciphertext: this is the scrambled message produced as output. It depends on the plaintext and secret key.

5.                 Decryption algorithm: this is essentially the encryption algorithm run in reverse. It takes the ciphertext and the same secret key and produces the original plaintext.

Provide several examples of IPSec. What services are provided by IPSec? What is the difference between Transport Mode and Tunnel Mode?

IPSec (Internet Protocol Security) is a capability that can be added to either current version of the internet protocol by means of additional headers. IPsec encompasses three functional areas authentication, confidentiality, and key management.

IPSec provides the capability to secure communications across a LAN, Private and public WANs, and across the internet. Examples of IPSec include the following:

Secure branch office connectivity over the internet: a company can build a secure virtual private network over the internet or over a public WAN. This enables a business to rely heavily on the internet and reduce its need for private networks, saving costs and network management overhead.

Another example of internet protocol security is secure remote access over the internet. On this case, an end user whose system is equipped with IP security protocols can make a local call to an internet service provider and gain secure access to a company network. This reduces the cost of toll charges for travelling employees and telecommuters.

Last but not least, enhancing electronic commerce security, even though some web and electronic commerce applications have built-in security protocols, the use of IPSec enhances that security.

The IPSec provides security services at the IP layer enabling a system to select required security protocols, determine the algorithms to use for services, and put in place any cryptographic keys required to provide the request services. The services provided by the IPSec are the following:

·         Access control

·         Connectionless integrity

·         Data origin authentication

·         Rejection of replayed packets (a form of partial sequence integrity)

·         Confidentiality (encryption)

·         Limited traffic flow confidentiality

The IPsec standards define two distinct modes of IPsec operation, transport mode and tunnel mode. The modes do not affect the encoding of packets. The packets are protected by AH, ESP, or both in each mode. The modes differ in policy application when the inner packet is an IP packet, as follows:

·                    In transport mode, the outer header determines the IPsec policy that protects the inner IP packet.

·                    In tunnel mode, the inner IP packet determines the IPsec policy that protects its contents.

In transport mode, the outer header, the next header, and any ports that the next header supports, can be used to determine IPsec policy. In effect, IPsec can enforce different transport mode policies between two IP addresses to the granularity of a single port. For example, if the next header is TCP, which supports ports, then IPsec policy can be set for a TCP port of the outer IP address. Similarly, if the next header is an IP header, the outer header and the inner IP header can be used to determine IPsec policy.

Tunnel mode works only for IP-in-IP datagrams. Tunneling in tunnel mode can be useful when computer workers at home are connecting to a central computer location. In tunnel mode, IPsec policy is enforced on the contents of the inner IP datagram. Different IPsec policies can be enforced for different inner IP addresses. That is, the inner IP header, its next header, and the ports that the next header supports, can enforce a policy. Unlike transport mode, in tunnel mode the outer IP header does not dictate the policy of its inner IP datagram.

Happy Birthday loved daughter

Happy Birthday Daughter! Thanks for bringing so much joy into our lives each and every single day. 
Feliz aniversario filha! Obrigado, por trazares tanta felicidades em nossas vidas.