The AES algorithm (also known as the Rijndael algorithm) is a symmetrical block cipher algorithm that takes plain text in blocks of 128 bits and converts them to ciphertext using keys of 128, 192, and 256 bits. Since the AES algorithm is considered secure, it is in the worldwide standard.
The AES algorithm uses a substitution-permutation,
or SP network, with multiple rounds to produce ciphertext.
The number of rounds depends on the key size being
used.
A 128-bit key size dictates ten rounds, a 192-bit
key size dictates 12 rounds, and a 256-bit key size has 14 rounds.
Each of these rounds requires a round key, but since
only one key is inputted into the algorithm, this key needs to be expanded to
get keys for each round, including round 0.
Steps in each round
Each round in the algorithm consists of four steps.
1. Substitution of the bytes
In the first step, the bytes of the block text are substituted based on rules
dictated by predefined S-boxes (short for substitution boxes).
2. Shifting the rows
Next comes the permutation step. In this step, all rows except the first are
shifted by one.
3. Mixing the columns
In the third step, the Hill cipher is used to jumble up the message
more by mixing the block’s columns.
4. Adding the round key
In the final step, the message is XORed with the respective round key.
When done repeatedly, these steps ensure that the
final ciphertext is secure.
Applications
of AES:
Wireless networks are secured using the Advanced
Encryption Standard to authenticate routers and clients.
AES plays a huge role in securing website server
authentication from both client and server end. With both symmetric and asymmetric
encryption being used, this algorithm helps in SSL/TLS encryption
protocols to always browse with the utmost security and privacy.
AES is also used to transfer files between
associates in an encrypted format. The encrypted information can extend to chat
messages, family pictures, legal documents, etc.
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