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Symmetric Cipher Essentials

The essential ingredients of a symmetric cipher are: 1) Plaintext, which is the original intelligible message or data that is fed into the algorithm. 2) An encryption algorithm that performs substitutions and transformations on the plaintext. 3) A secret key that is also input to the encryption algorithm and determines the substitutions and transformations. 4) Ciphertext, which is the scrambled output that depends on both the plaintext and secret key. 5) A decryption algorithm that is the encryption algorithm run in reverse to decrypt the ciphertext back to plaintext.

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512 views1 page

Symmetric Cipher Essentials

The essential ingredients of a symmetric cipher are: 1) Plaintext, which is the original intelligible message or data that is fed into the algorithm. 2) An encryption algorithm that performs substitutions and transformations on the plaintext. 3) A secret key that is also input to the encryption algorithm and determines the substitutions and transformations. 4) Ciphertext, which is the scrambled output that depends on both the plaintext and secret key. 5) A decryption algorithm that is the encryption algorithm run in reverse to decrypt the ciphertext back to plaintext.

Uploaded by

sameer khan
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Question No.

What are the essential ingredients of a symmetric cipher?

A symmetric encryption scheme has five ingredients (as shown in the following figure):

 Plaintext: This is the original intelligible message or data that is fed into the algorithm as input.

 Encryption algorithm: The encryption algorithm performs various substitutions and transformations on
the plaintext.

 Secret key: The secret key is also input to the encryption algorithm. The key is a value independent of
the plaintext and of the algorithm. The algorithm will produce a different output depending on the
specific key being used at the time. The exact substitutions and transformations performed by the
algorithm depend on the key.

 Ciphertext: This is the scrambled (unintelligible) message produced as output.

It depends on the plaintext and the secret key. For a given message, two different keys will produce two
different ciphertexts.

 Decryption algorithm: This is essentially the encryption algorithm run in reverse. It takes the ciphertext
and the secret key and produces the original plaintext.

Question No.2

What are the two basic functions used in encryption algorithms?

1. substitution - alphanumeric texts are replaced by other letters or special characters or by numbers. It
involves replacing clear text bit patterns with cipher (encoded) text bit patterns

2. Transposition - the order of the characters are interchanged and jumbled.

In both of these, the aim is to increase the entropy to some level that retracing and recovering the
original text would get hared.

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