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Introduction to Cryptography

What is Crypto?

Consider two people who wants to share an important secret had to split up. The only channel they have to communicate is an open, insecure channel. However, an eavesdropper named Eve also wants this information and has enough resources and ability to intercept the messages. Thus to protect the secrecy of messages,, a secret method is required. So, this is what Alice does: she locks her message in a box using a lock that only she and Bob knows the combination to. This is known as Encryption. She then sends the box to Bob, he opens it with the key they shared in advanced, this is called Decryption.

Cryptography is the use of ciphers insead of physical locks. Ciphers helps Alice and Bob to scramble their messages, so that it would look meaningless to Eve. It enables the intended users to maintain their privacy as well as enabling them to use the common channel for communication. The message in raw data is known as the plaintext whereas the encrypted (locked) messsage is known as ciphertext.


Cryptology is the study of techniques for the secure communication without disclosing the content to third parties.

Having said that, Cryptology is divided into two,

  • Cryptography
  • Cryptanalysis

Cryptography is the branch which deals with developing new cryptosystems, on the other hand, Cryptanalysis is the detailed study of cryptosystems, understanding as well as exploiting them for vulnerabilities.

Cryptography is generally classified into two,

  • Classical cryptography
  • Modern Cryptography

The main classical cipher types are transposition ciphers, which rearrange the order of letters in a message (e.g., 'hello world' becomes 'ehlol owrdl' in a trivially simple rearrangement scheme), and substitution ciphers, which systematically replace letters or groups of letters with other letters or groups of letters. More to it later. Under modern Cryptography, we have Block crypto and Public Key cryptosystems were complex structural and mathematical processes takes place to encrypt data. In addition to just securing messages, Cryptography offers more features like Digital Signatures, Hashing.