State v. Levie
The main purpose of encryption is to change any data to a humanly unreadable form. Nowadays, encryption is seen as one of the key solutions to prevent the unauthorized disclosure of information. 
Companies and governmental entities have been spending time and money implementing ways to fight cybercrime and increase awareness between internet users and general public with the purpose to reduce the occurrence of crimes such as Identity theft. 
Mainly, one can say that encryption is about privacy. The right to a "safety zone" and privacy exists in the First and Fourth Amendment rights in the USA where a remarkable and recent privacy-based law has been approved, the Gramm-Leach-Bliley Act. In Europe the Lisbon Treaty describes the protection of fundamental data as fundamental human right. 
While achieving privacy through the use of encryption seems to provide everyone with answers to decrease the disclosure of personal information, it benefits the possibility to conceal from authorities acts of terrorism, child pornography and others.
The use of encryption tools is becoming more and more disseminated; states are starting to make a crime "to use encryption". States like Illinois in USA are creating specific laws to handle this matter : "A person shall not knowingly use or attempt to use encryption, directly or indirectly, to:
Advanced Encryption Standard
The key size used for an AES cipher specifies the number of transformation rounds that convert the input, called the plaintext, into the final output, called the ciphertext. The number of rounds are as follows:Each round consists of several processing steps, including one that depends on the encryption key itself. A set of reverse rounds are applied to transform ciphertext back into the original plaintext using the same encryption key.In the SubBytes step, each byte formula_3 in the "state" array is replaced with a SubByte formula_4 using an 8-bit substitution box. This operation provides the non-linearity in the cipher. The S-box used is derived from the multiplicative inverse over , known to have good non-linearity properties. To avoid attacks based on simple algebraic properties, the S-box is constructed by combining the inverse function with an invertible affine transformation. The S-box is also chosen to avoid any fixed points (and so is a derangement), i.e., formula_5, and also any opposite fixed points, i.e., formula_6.
While performing the decryption, the InvSubBytes step (the inverse of SubBytes) is used, which requires first taking the inverse of the affine transformation and then finding the multiplicative inverse.