The Advanced Encryption Standard (AES) was introduced in 2000 after a long search by NIST for an encryption standard that would be hard to break, inexpensive to use, easy to implement and would work on both hardware and software.
One of the two important factors that make an encryption standard hard to break is the encryption process (encryption algorithm). Theories can’t accurately predict how easy it will be to break a particular algorithm, so NIST published a few contenders and experts all over the world tried to break them.
The second factor in making an encryption standard hard to break, especially a standard based on symmetric key cryptography, or a shared secret, is the key length. In general, the longer the key, the harder it is to figure it out by just trying random strings of characters. The AES can use a key length of 128, 192 or 256 bits.
The algorithm to be chosen also had to be made available to the public without royalty fees. After years of testing and multiple comment cycles, the Rijndael algorithm, written by two Belgium cryptographers, was adopted as the AES and was published as FIPS 192.
There is an inherent weakness in a symmetric key process because the key has to be transferred from the sender to the receiver as well as the encrypted text. Frequently, AES is used as part of a set of encryption tools where an asymmetric encryption method is used to transfer the key.