Encryption is the process of scrambling data so that it becomes very difficult to unscramble and interpret without the correct key.

Encrypted data is known as ciphertext, and the original interpretable data is known as plaintext. The process of encryption is carried out using a cryptographic algorithm and a key.

Symmetric (Private key) encryption
Symmetric encryption, also known as private key encryption, uses the same key to encrypt and decrypt data. This means that the key must also be transferred (known as key exchange) to the same destination as the ciphertext which causes obvious security problems. The key can be intercepted as easily as the ciphertext message to decrypt the data. For this reason asymmetric encryption can be used instead.

Asymmetric (Public key) encryption
Asymmetric encryption uses two separate, but related keys. One key, known as the public key, is made public so that others wishing to send you data can use this to encrypt the data. This public key cannot decrypt data. Another private key is known only by you and only this can be used to decrypt the data. It is virtually impossible to deduce the private key from the public key. It is possible that a message could be encrypted using your own public key and sent to you by a malicious third party impersonating a trusted individual. To prevent this, a message can be digitally ‘signed’ to authenticate the sender.

Caesar сipher online

XOR Encryption Algorithm


1. Explain what is "Encryption".

2. Describe defference between "privat key" and "public key".

3. Describe how to work "Ceasar cipher".


Ex. 1 (Prepared by Sultan, Aizhan, Aruzhan, grade 12, group 1, 2021)

Ex. 2

Test "Encryption"

Ex. 3

Test "Encryption-2"

Exam questions:

Question 1. It is possible to encrypt e-mails. Explain what is meant by encryption. (Marks: 2) Answer:
  • data is scrambled/enciphered (1), so that only those with the key can understand/descrypt it (1)


Question 2. In some countries, it is illegal to encrypt e-mails. Outline arguments for and against this restriction. (Marks: 2) Answer:
  • For restriction: can intercept criminal/terrorist communications, help reduce crime. (1)
  • Against restriction: personal freedom/privacy, the state controls enough of our lives as it is. (1)


Question 3. Explain difference between Symmetric and Asymmetric encryption(Marks: 2)
  • Answer.

Symmetric (Private key) Encryption

  • Uses the same key to encrypt and decrypt data (1)
  • The key must be transferred to the same destination as the ciphertext (1)

Asymmetric (Public key) Encryption

  • Uses two separate but related keys (1) 
  • A public key is made public. Others wishing to send you data use this to encrypt it (1)
  • Their private key only known by you and is used to decrypt it (1)


Question 4. Name one advantage of Asymmetric encryption (Marks: 1)
  • Answer. The two sides don't need to have already shared their secret key in order to communicte using encryption.


Категория: Protection data | Добавил: bzfar77 (01.11.2020)
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