Wednesday, December 29, 2010 3 comments
If you are familiar with hacking, you know the name of MD5 or Digital signature. These are parts of cryptography. I am writing this post because today i have my semester exam of cryptography, and i think as a hacker you must know about cryptography. Cryptography is a science and art of securing data by changing it in a coded form by some encoding method.
When Julius Caesar sent messages to his generals, he didn’t trust his messengers. So he replaced every A in his messages with a D, every B with an E, and so on through the alphabet. Only someone who knew the “shift by 3” rule could decode his messages.
this was an practical example of cryptography. This is also use in securing data on the network. Cryptography is the science of information security.
Cryptography is the science of using mathematics to encrypt and decrypt data. Cryptography enables you to store sensitive information or transmit it across insecure networks (like the Internet) so that it cannot be read by anyone except the intended recipient.
Plain text: Message in it's original form
Cipher Text: Encoded message
Key: a sequence of bit used in encryption and decryption
Encryption: Algorithm of encoding Plain text to cipher text using key.
Decryption: Algorithm of decoding Cipher text to Plain text using key.
A cryptographic algorithm works in combination with a keyr to encrypt the plaintext. The same plaintext encrypts to different ciphertext with different keys. The security of encrypted data is entirely dependent on two things: the strength of the cryptographic algorithm and the secrecy of the key.
Types of Cryptography:
Symmetric key cryptography or Secret key Cryptography: In a symmetric cipher, both parties must use the same key for encryption and decryption. This means that the encryption key must be shared between the two parties before any messages can be decrypted. Symmetric systems are also known as shared secret systems or private key systems.
Asymmetric key cryptography or public key Cryptography: In an asymmetric cipher, the encryption key and the decryption keys are separate. In an asymmetric system, each person has two keys. One key, the public key, is shared publicly. The second key, the private key, should never be shared with anyone. When you send a message using asymmetric cryptography, you encrypt the message using the recipients public key. The recipient then decrypts the message using his private key. That is why the system is called asymmetric.
This was the simple introduction of cryptography. I will write more on various cryptographic algorithms and hash functions used in cryptography.
Hash algorithms: Hash algorithms are based upon one way hash function.
y=f(x) is said to be one way if for every x it is easy to find y but for a given y it is computationally infeasible to get x.
Cryptographic hash function is a mathematical transformation that takes a message m of any length and produce a corresponding message digest (a number of fixed length) of fixed length.
for any two messages m1 and m2:
h(m1) != h(m2) NOT EQUAL
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