In brute force attack, on average half of all possible keys must be tried to achieve success.

Classical Encryption Techniques include: Transportation and substitution techniques, number theory and symmetric cipher models. Classical cryptography can be divided into two major branches: Secret or symmetric key cryptography Public key cryptography: Also known as asymmetric cryptography  Classical encryption techniques include: Caesar cipher: A substitution cipher that replaces each letter in the plaintext with a letter a fixed number of places down the alphabet. The key is a number that represents how many letters of the alphabet to shift. Symmetric encryption: A cryptosystem that... Show more

Classical Encryption Techniques include: Transportation and substitution techniques, number theory and symmetric cipher models.

Classical cryptography can be divided into two major branches:
Secret or symmetric key cryptography
Public key cryptography: Also known as asymmetric cryptography 

Classical encryption techniques include:
Caesar cipher: A substitution cipher that replaces each letter in the plaintext with a letter a fixed number of places down the alphabet. The key is a number that represents how many letters of the alphabet to shift.
Symmetric encryption: A cryptosystem that uses the same key for encryption and decryption.
Substitution cipher: A classical method of cryptography that replaces each plaintext letter with a corresponding ciphertext letter.
Transposition cipher: A classical cryptographic algorithm that rearranges the order of characters to a fixed permutation.
Playfair cipher: A symmetric substitution encryption cipher invented in 1854 by British scientist Charles Wheatstone Playfair. 

Classical cryptanalysis is the art of obtaining the key by exploiting the nature of the locking or encryption algorithm.

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