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Advantages & Disadvantages of Symmetric Key Encryption

by Steve Lander

Symmetric key encryption is a method of scrambling data by pressing the same key to both encrypt and decrypt it. This is different from asymmetric encryption, also known as public key encryption, where you use different keys to encrypt and decrypt. With symmetric key encryption, also known as secret key encryption, you have to keep the key secret, while asymmetric encryption lets you share the encryption key with anyone, since you keep your decryption key to yourself.

Advantage: Extremely Secure

When it uses a secure algorithm, symmetric key encryption can be extemely secure. One of the most widely-used symmetric key encryption systems is the U.S. Government-designated Advanced Encryption Standard. When you use it with its most secure 256-bit key length, it would take about a billion years for a 10 petaflop computer to guess the key through a brute-force attack. Since, as of November 2012, the fastest computer in the world runs at 17 petaflops, 256-bit AES is essentially unbreakable.

Advantage: Relatively Fast

One of the drawbacks to public key encryption systems is that they need relatively complicated mathematics to work, making them very computationally intensive. Encrypting and decrypting symmetric key data is relatively easy to do, giving you very good reading and writing performance. In fact, many solid state drives, which are typically extremely fast, use symmetric key encryption internally to store data and they are still faster than unencrypted traditional hard drives.

Disadvantage: Sharing the Key

The biggest problem with symmetric key encryption is that you need to have a way to get the key to the party with whom you are sharing data. Encryption keys aren't simple strings of text like passwords. They are essentially blocks of gibberish. As such, you'll need to have a safe way to get the key to the other party. Of course, if you have a safe way to share the key, you probably don't need to be using encryption in the first place. With this in mind, symmetric key encryption is particularly useful when encrypting your own information as opposed to when sharing encrypted information.

Disadvantage: More Damage if Compromised

When someone gets their hands on a symmetric key, they can decrypt everything encrypted with that key. When you're using symmetric encryption for two-way communications, this means that both sides of the conversation get compromised. With asymmetrical public-key encryption, someone that gets your private key can decrypt messages sent to you, but can't decrypt what you send to the other party, since that is encrypted with a different key pair.

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