Question

One symbol could be substituted with a key using substitution cipher?

Answer 1

A substitution cipher is a complex code that has been in use from the times of Roman kings. It involves the use of a pre-set key which unlocks the cipher and makes it readable. The only way to break the cipher is through a brute force attack which is time consuming or through possession of the key.

 

Any symbol could substitute a letter of the alphabet in this code and each was then shuffled. Without the key, the cipher was undecipherable since the symbols had no meaning to outsiders. Those in possession of the key knew exactly what each symbol represented and in what order it should be read.

 

The brute force approach was very lengthy although it was useful when trying to break a code without the key. To use this method, all possible combinations of the symbols were tried in a series, matching them against all the letters of the alphabet until a legible sentence was formed. With this match, the code could be broken. However, it could be a very lengthy and tedious process, depending on the correct combination.

Answer 2

'One symbol' could be 'substituted with a key' using 'substitution cipher' is False statement.

Explanation:

• A substitution cipher is a method of cryptography which converts standard language or plaintext into coded language or ciphertext, by replacing units of plaintext in accordance with a fixed set of rules. These plaintext units may be individual letters or characters, letter pairs, triplets, or other combinations.
• Substitution ciphers may replace only the letters of the standard alphabet with ciphertext, or apply substitutions to spaces and punctuation marks as well.

To know more

Distinguish between a substitution cipher and a transposition cipher.

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The substitution cipher uses a key domain of 20 keys and the alphabet of 20 characters. Assume the redundancy is 0.5. What is the unicity distance?

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