#+date:        [2018-11-28 Wed 00:00:00]
#+title:       AES Encryption
#+description: Let's learn about AES encryption, its method, and how it can be used.
#+slug:        aes-encryption
#+filetags:    :security:

* Basic AES

If you're not familiar with encryption techniques, the Advanced Encryption
Standard ([[https://en.wikipedia.org/wiki/Advanced_Encryption_Standard][AES]]) is a specification for encryption of electronic data. The
National Institute of Standards and Technology established this specification,
sub-selected from the Rijndael family of ciphers (128, 192, and 256 bits)
in 2001. Furthering its popularity and status, the US government chose AES as
their default encryption method for top-secret data, removing the previous
standard which had been in place since 1977.

AES has proven to be a safe encryption method, with 7-round and 8-round attacks
making no material improvements since the release of this encryption standard
almost two decades ago.

#+begin_quote
Though many papers have been published on the cryptanalysis of AES, the fastest
single-key attacks on round-reduced AES variants [20, 33] so far are only
slightly more powerful than those proposed 10 years ago [23,24].

- [[http://research.microsoft.com/en-us/projects/cryptanalysis/aesbc.pdf][Bogdanov, et al.]]
#+end_quote

* How Secure is AES?

In theory, AES-256 (AES using a 256-bit key) is non-crackable due to the massive
number of combinations that can the encryption process can produce. However,
AES-128 is no longer recommended as a viable implementation to protect important
data due the 128-bit key's short length.

A semi-short [[http://www.moserware.com/2009/09/stick-figure-guide-to-advanced.html][comic strip]] from Moserware quickly explains AES for the public to
understand. Basically, AES encrypts the data by obscuring the relationship
between the data and the encrypted data. Additionally, this method spreads the
message out. Lastly, the key produced by AES is the secret to decrypting it.
Someone may know the method of AES, but without the key, they are powerless.

To obscure and spread the data out, AES creates a substitution-permutation
network. Wikipedia has a wonderful [[https://upload.wikimedia.org/wikipedia/commons/thumb/c/cd/SubstitutionPermutationNetwork2.png/468px-SubstitutionPermutationNetwork2.png][example of an SP network]] available. This
network sends the data through a set of S boxes (using the unique key) to
substitute the bits with another block of bits. Then, a P box will permute, or
rearrange, the bits. This is performed numerous times, with the last round
deriving the key. For AES, the key size specifies the number of transformation
rounds: 10, 12, and 14 rounds for 128-bit, 192-bit, and 256-bit keys,
respectively.

* The Process

1. *KeyExpansion*: Using [[https://en.m.wikipedia.org/wiki/Advanced_Encryption_Standard][Rijndael's key schedule]], the keys are dynamically
   generated.
2. *AddRoundKey*: The process combines each byte of the data with the generated
   key(s) using bitwise xor.
3. *SubBytes*: Next, the process substitutes each byte of data.
4. *ShiftRows*: Then, the process shifts the final three rows a specific number
   of steps, dictated by the cipher.
5. *MixColumns*: Finally, the process mixes and combines the columns into the
   final data for this round of processing.

This process does not necessarily stop after one full round. Steps 2 through 5
will repeat for the number of rounds specified by the key. However, the final
round excludes the MixColumns step. As you can see, this is a fairly complex
process. One must have a solid understanding of general mathematical principles to
fully understand how the sequence works (and to even attempt to find a
weakness).

According to research done by Bogdanov et al., it would take billions of years
to brute force a 126-bit key with current hardware. Additionally, this brute
force attack would require storing 2^{88} bits of data! However, people have
shown different attacks displaying vulnerabilities with the use of this
technology. Side-channel attacks use inadvertent leaks of data from the hardware
or software, which can allow attackers to obtain the key or run programs on a
user's hardware.

Please note that this is not something you should run out and try to implement
in your =Hello, World!= application after only hours of research. While AES
(basically all encryption methods) is efficient in what it does, it takes a lot
of time and patience to understand. If you're looking for something which
currently implements AES, check out the [[https://www.bouncycastle.org/documentation.html][Legion of the Bouncy Castle]] for Java
implementations of cryptographic algorithms.

* Why Does Encryption Matter?

There are limitless reasons to enable encryption at-rest or in-transit for
aspects of your digital life. You can research specific examples, such as
[[https://arstechnica.com/tech-policy/2018/12/australia-passes-new-law-to-thwart-strong-encryption/][Australia passes new law to thwart strong encryption]]. However, I will simply
list basic reasons to always enable encryption, where feasible:

1. Privacy is a human right and some countries recognize it as a national right
   (e.g., [[https://www.law.cornell.edu/wex/fourth_amendment][US Fourth Amendment]]).
2. "Why not?" Encryption rarely affects performance or speed, so there's usually
   not a reason to avoid it in the first place.
3. Your digital identity and activity (texts, emails, phone calls, online
   accounts, etc.) are valuable and can result in consequences, such as identity
   theft, if leaked to other parties. Encrypting this data prevents such leaks
   from ruining lives.
4. Wiping or factory-resetting does not actually wipe all data from the storage
   device. There are methods to read data from the physical disks/boards inside
   devices.
5. Corporations, governments, and other groups or individuals are actively
   looking for ways to collect personal information about anyone they can. If
   someone's data is not encrypted, that person may become a target due to the
   ease of data collection.

* Read More

- [[http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.197.pdf][Federal Information Processing Standards Publication 197]]