Software security

Kerckhoff’s Principle
•A cryptosystem should be secure even if everything about the system, except the key, is public knowledge. (Opposite of security through obscurity)
•A famous counter-example: Enigma in WWII, how British forces break the encryption of the war messages of Nazi Germany( if you have watched the movie The Imitation Game (2014) you know what i’m taking about….😁😁)
1. Encryptions

Figure 1: The process of Encryption and Decryption
Encryption and Decryption Algorithms (E, D) are widely known and used in co-operation with keys to convert plain text to cipher and cipher to pain text respectively. Keys (KE, KD) may be Symmetric or Asymmetric in nature. The Ciphertext is the only information that’s available to the public world. The Plaintext is known only by the people with the keys (in an ideal world…😁 ). The Plaintext is the message before encryption. The Ciphertext is the message after encryption. Key is the information needed to convert from Plaintext to Ciphertext (and vice-versa). Apart from that Confusion and Diffusion are two key factors of the Encryption system.

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  Confusion: Hides the relation between Key and Ciphertext.
  
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  Diffusion: Hides the relation between Ciphertext and Plaintext.
  

In the above paragraph, I have mentioned two types of keys used in the encryption process; Symmetric Key Encryption and Asymmetric Key Encryption.
1). Symmetric Key Encryption: This is a type of encryption where only one key (a secret key) is used for both encryption and decryption of plaintext and ciphertext. The entities communicating via symmetric encryption must exchange the key. So that it can be used in the decryption process. There are several types of Symmetric Key encryptions;

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  Data Encryption Standard (DES)
  
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  Electronic Code Book (ECB)
  
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  Cipher block Chain(CBC)
  
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  Advanced Encryption Standard (AES)
  

The main advantage of symmetric key encryption is it is Fater since using one Key. But the drawbacks are Key management and distribution issues and guarantees only confidentiality.

Figure 2: Symmetric Key Encryption Process