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| author | Kai Stevenson <kai@kaistevenson.com> | 2022-10-08 18:40:34 -0700 |
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| committer | Kai Stevenson <kai@kaistevenson.com> | 2022-10-08 18:40:34 -0700 |
| commit | 7cdaa8b30fcd8ab333d11719dc4b280b28347a71 (patch) | |
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+ <h1>Principles of Crytography for Data Security | <a class="backbutton" href=".">[Back]</a></h1>
+ <p>As the amount of life spent online continues to increase, a great deal of private information is naturally
+ being transmitted: banking details, medical records, business correspondences. Where once these exchanges of
+ data would have occured between a small set of individuals in a shared space, they now happen between
+ continents, through hundreds of servers and over complex network infrastructures. It is a system that cannot
+ be fully accounted for by any individual, and so the means of transmission are insecure--much like having a
+ letter transmitted by a series of couriers, the data is liable to be intercepted or modified. And so both
+ parties in the exchange take on a risk that may prohibit especially critical data from being sent.
+ Cryptography is the study of data obfuscation--a means of making a message readable only by some. It is the
+ answer to the question "when the means of transmission cannot be trusted, how can information be conveyed
+ securely?</p>
+ <p>There are two classes of encryption: symmetric and asymmetric. Symmetric encryption allows a message to be
+ encoded and decoded with the same piece of information, or key. The ancient Caesar cipher is an example of
+ this; an arbitrary number acting as the key was agreed upon by both parties, and every letter in the message
+ was shifted through the alphabet by that amount. It could easily be decoded by anyone who knew the key by
+ simply shifting the letters backward through the alphabet. Simple algorithms such as the Caesar cipher are
+ vulnerable to various attacks due to the patterns that they create in the ciphertext. A given letter may
+ always be encoded in the same way, meaning that the key could be compromised if the attacker gained access
+ to the plaintext and ciphertext forms of the same message. And a message could be decrypted without the key
+ by recognizing repeated patterns in the ciphertext representing common words. More advanced symmetric
+ encryption methods--like the Advanced Encryption Standard (AES) algorithm, developed for the US National
+ Institute of Standards and Technologies--disrupt patterns in the message to prevent these types of attacks.
+ </p>
+ <p>Symmetric encryption is an imperfect solution in the internet age. Because it requires both parties to know
+ the same secret key, those parties must have a secure form of communication already established. In the days
+ of Caesar, this key exchange could be performed confidentially by two individuals in close proximity. When
+ encryption is used on the internet, it cannot be assumed that the communicating parties will have had any
+ physical interactions--and it would be impractical to expect every new customer of an online banking service
+ to perform a physical key exchange. Asymmetric encryption solves this problem by removing the key exchange.
+ Instead of encrypting and decrypting a message with the same key, an asymmetric encryption algorithm has a
+ keypair, comprising a public key, used for encrypting a message, and a private key, used for decrypting a
+ message. The keys are so named because the private key is never shared, while the public key can be
+ broadcast widely. </p>
+ <p>Typically, it demands more processing power to encrypt and decrypt messages with an asymmetric encryption
+ implementation than a comparable symmetric one. For this reason, it is desirable to use symmetric encryption
+ for most communications. An asymmetric implementation such as the Rivest--Shamir--Adleman (RSA) system is
+ used to perform the key exchange. One of the devices will broadcast its public RSA key to the other, which
+ will respond by generating an AES key, encrypting it with that RSA key, and returning it. This method of key
+ exchange is secure, even if every network packet is intercepted. Once the devices share an AES key, they can
+ communicate with the more efficient symmetric encryption method.</p>
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