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9 September 2019

Asymmetric Encryption Algorithms



I remember a security administrator who told me he couldn’t enable encryption in a site to site VPN because the firewalls couldn’t encrypt high throughput traffic. He said the firewalls didn’t have enough CPU for VPN data encryption. Obviously, those firewalls weren’t well sized for his requirements. Encryption needs powerful CPU and/or powerful cryptographic cards but it also requires to choose the right cipher suites. Maybe, this security administrator didn’t have a good firewall to encrypt the site to site VPN but, maybe, he didn’t know either there are several encryption algorithms, and if they are configured properly, you will be able to get what you want.

I learnt at University how public-key cryptosystems work. It’s easy to understand. There are two keys. A public key and a private key. The public key is well-known for everyone. It’s like an open padlock. However, the private key is only known by the owner. It’s like the key to open the padlock. Therefore, when someone wants to send something encrypted into the padlock, only the owner can open the padlock and read the message. RivestShamirAdleman (RSA) is one of the first public-key cryptographic system and it’s the most used for data transmission.

Public Key Encryption

There is an alternative to the RSA. It’s the Digital Signature Algorithm (DSA). This algorithm was developed by the U.S government and it has the same security degree as RSA. However, it employs different mathematical algorithms for signing and encryption. DSA is also an asymmetric encryption scheme, like RSA, and it’s faster for signing but slower for verifying. Therefore, DSA is not a good choice if there is performance issues on the client side.

Diffie-Hellman is another algorithm I've learned, but this one, while I've been working with Virtual Private Networks (VPN). It’s an asymmetric algorithm useful to determine a secret key between peers. Firstly, peers agree to use a key, which could be listen by an attacker. Secondly, they use a private secret key, which is only known by each of them. Finally, these two keys are used to get a new one, which is the final key for the encryption process. This final key is, computationally speaking, difficult to get by an attacker.

Diffie-Hellman Key Exchange

These three algorithms are well-known by most security engineers. However, Elliptic Curve Cryptography (ECC) or Elliptic Curve Digital Signature Algorithm (ECDSA) is increasingly used because ECC cryptography provides much strong security than RSA or DSA with smaller keys. Therefore, ECC cryptography is the best option for mobile devices due to the fact that it requires less computational overhead.

Elliptic Curve Digital Signature Algorithm

On the whole, when you are going to configure encryption for whatever, it’s better to know what algorithm fits with your architecture because if you don’t choose the right one, the network performance could be degraded.

Regards my friends. Have a nice day!

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