# Introduction to Asymmetric Cryptography – Part 1/2

Before getting deep into the second part of the Cryptography (Asymmetric Cryptography), let’s do a quick recap of the previous part (Symmetric Cryptography).

There are two properties of the Symmetric (secret-key) crypto-systems:

1. The same secret key (k) is used for both encryption and decryption.
2. Encryption and Decryption are very similar or even identical functions.

For example, the safe box with a strong lock, where only Alice and Bob have a copy of the key.

• Alice encrypts (locks message in the safe with her key).
• While, Bob decrypts (uses his copy of the key to open the safe).

Fact: The Symmetric algorithms are very secure, fast & widespread such as, AES, 3DES and more. However, the problem consists of two things:

1. Key distribution problem, where the (secret key) must be transported securely.
2. Non-repudiation, where Alice or Bob can cheat each other, because they have identical keys. For example, Alice can claim that she never ordered an Apple TV online from Bob (he could have fabricated her order).
3. Number of keys in a network, where each pair of users requires an individual key. For example, (n) is the number of users in the network, while each user stores (n-1) number of keys. This means that we will be having a total of (6 users) and (15 keys). See the figure below for more details:

Therefore, Asymmetric Cryptography plays an important role to prevent this (non-repudiation) and to provide more security.