To change a dynamic disk back to a basic disk using a command line

• The disk must not have any volumes nor contain any data before you can change it back to a basic disk.
  
• If you want to keep your data, back it up or move it to another volume before you convert the disk to a basic disk.
  
• Once you change a dynamic disk back to a basic disk, you can create only partitions and logical drives on that disk.

1. Back up all volumes on the disk you want to convert from dynamic to basic.

2. Open a command prompt and type diskpart.

3. At the DISKPART prompt, type list disk. Make note of the disk number you want to convert to basic.

4. At the DISKPART prompt, type select disk <disknumber>.

5. At the DISKPART prompt, type detail disk <disknumber>.

6. For each volume on the disk, at the DISKPART prompt, type select volume= <volumenumber> and then type delete volume.

7. At the DISKPART prompt, type select disk <disknumber>. Specify the disk number of the disk that you want to convert to a basic disk.

8. At the DISKPART prompt, type convert basic.

Disable USB ports on Windows PC via Registry

1. Click on Start.
2. Click on Run. If you cannot find RUN, type it in the search box.
3. Type "regedit" without quotes. This will launch the Registry Editor.
4. Navigate to  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\usbstor.
5. In the work area, double click on Start.
6. In the Value Data box, enter 4.
7. Click on OK.
8. Close Registry Editor and refresh your desktop.
9. To re-enable access to your USB ports, enter 3 in the Value Data box in Step 6.

Try it in your Risk.

Open Shortest Path First(Protocol)

Open Shortest Path First (OSPF) is a routhing Protocol.

protocol for Internet Protocol (IP) networks. It uses a link state routing algorithm and falls into the group of interior routing protocols, operating within a single autonomous system (AS).

Note:

• Link state Routing Protocol.
• No Limit of Hop Count.
• AD (Administrative Distance) value 110.
• OSPF support cost and bandwidth as Metric.
• OSPF was design only for IP Network.
• Develop by IETF(Internet Engineering Task Force ).
• Three Version of OSPF.

1.           Ver 1
2.           Ver 2
3.            Ver 3

• OSPF can Support Authentication  CIDR and VLSM.
• Support Multi casting.
• Work with Autonomous System and Area.
• Utilize the more hardware sunc as processor and ram.
• keep the entire Topology Information in Router memory.
• It always Computing the Network Information by sending Advertisement packet. 
  
  
   

Ciphertext

In cryptography, ciphertext or cyphertext is the result of encryption performed on plaintext using an algorithm, called a cipher. Ciphertext is also known as encrypted or encoded information because it contains a form of the original plaintext that is unreadable by a human or computer without the proper cipher to decrypt it. Decryption, the inverse of encryption, is the process of turning ciphertext into readable plaintext. Ciphertext is not to be confused with codetext because the latter is a result of a code, not a cipher.

                           
Types of ciphers(classical ciphers and Modern Ciphers)
The history of cryptography began thousands of years ago. Cryptography uses a variety of different types of encryption. Earlier algorithms were performed by hand and are substantially different from modern algorithms, which are generally executed by a machine.

Historical pen and paper ciphers used in the past are sometimes known as classical ciphers. They include:

•         Substitution cipher: the units of plaintext are replaced with ciphertext (Caesar cipher and One-time pad)

•         Transposition cipher: the ciphertext is a permutation of the plaintext (Rail fence cipher)

•         Polyalphabetic substitution cipher: a substitution cipher using multiple substitution alphabets (Vigenère cipher and Enigma machine)

•         Permutation cipher: a transposition cipher in which the key is a permutation

Historical ciphers are not generally used as a standalone encryption solution because they are quite easy to crack. Many of the classical ciphers can be cracked using brute force or by analyzing only ciphertext with the exception of the one-time pad.

Modern ciphers
Modern ciphers are more secure than classical ciphers and are designed to withstand a wide range of attacks. An attacker should not be able to find the key used in a modern cipher, even if he knows any amount of plaintext and corresponding ciphertext. Modern encryption methods can be divided into the following categories:
•         Private-key cryptography (symmetric key algorithm): the same key is used for encryption and decryption
•         Public-key cryptography (asymmetric key algorithm): two different keys are used for encryption and decryption
NOTE:-
 In a symmetric key algorithm (e.g., DES and AES), the sender and receiver must have a shared key set up in advance and kept secret from all other parties; the sender uses this key for encryption, and the receiver uses the same key for decryption. In an asymmetric key algorithm (e.g., RSA), there are two separate keys: a public key is published and enables any sender to perform encryption, while a private key is kept secret by the receiver and enables only him to perform correct decryption.
Symmetric key ciphers can be divided into block ciphers and stream ciphers. Block ciphers operate on fixed-length groups of bits, called blocks, with an unvarying transformation. Stream ciphers encrypt plaintext digits one at a time on a continuous stream of data and the transformation of successive digits varies during the encryption process.

Data Encryption and Decryption

• Encryption is the process of translating plain text data (plaintext) into something that appears to be random and meaningless (ciphertext). Decryption is the process of converting ciphertext back to plaintext.

• To encrypt more than a small amount of data, symmetric encryption is used. A symmetric key is used during both the encryption and decryption processes. To decrypt a particular piece of ciphertext, the key that was used to encrypt the data must be used.

• The goal of every encryption algorithm is to make it as difficult as possible to decrypt the generated ciphertext without using the key. If a really good encryption algorithm is used, there is no technique significantly better than methodically trying every possible key. For such an algorithm, the longer the key, the more difficult it is to decrypt a piece of ciphertext without possessing the key.
  
• It is difficult to determine the quality of an encryption algorithm. Algorithms that look promising sometimes turn out to be very easy to break, given the proper attack. When selecting an encryption algorithm, it is a good idea to choose one that has been in use for several years and has successfully resisted all attacks.