Asymmetric Encryption

asymmetric encryptionThe biggest disadvantage to using symmetric encryption algorithms relates to key management. In order to ensure confidentiality of communication between two parties, each communicating pair needs to have a unique secret key. As the number of communicating pair needs to have a unique secret key, As the number of communicating pairs increases, there is a need to manage a number of keys related to the square of the communicators, which quickly becomes a complex problem.

Introducing Asymmetric Encryption

Asymmetric encryption algorithms were developed to overcome this limitation. Also known as public-key cryptography, these algorithms use two different keys to encrypt and decrypt information. If cleartext is encrypted with an entity’s public key, it can only be decrypted by the public key. The basic principle is that the public key can be freely distributed, while the private key must be held in strict confidence. The owner of the private key can encrypt cleartext to create cyphertext that can only be decoded with its public key, thus assuring the identity of the source, or it can use the private key to decrypt cyphertext encoded with its public key, assuring the confidentiality of the data. Although these keys are generated together and are mathematically related, the private key cannot be derived from the public key.

Instead of relying on the techniques of substitution and transportation that symmetric key cryptography uses, asymmetric encryption algorithms rely on the use of large-integer mathematics problems. Many of these problems are simple to do in one direction but difficult to do in the opposite direction. For example, it is easy to multiply two numbers together, but it is more difficult to factor them back into the original numbers, especially if the integers used contain hundreds of digits. Thus, in general, the security of asymmetric encryption algorithms is dependent not upon the feasibility of brute-force attacks, but the feasibility of performing difficult mathematical inverse operations and advances in mathematical theory that may propose new “shortcut” techniques.

Asymmetric encryption  is much slower than symmetric encryption. There are several reasons for this. First, it relies on exponentiation of both a secret and public exponent, as well as generation of a modulus. Computationally, exponentiation is a processor-intensive operation. Second, the keys used by asymmetric encryption algorithms are generally larger than those used by symmetric algorithms, because the most common asymmetric attack, factoring, is more efficient than the most common symmetric attack: brute force.

Because of this, asymmetric encryption algorithms are typically used only for encrypting small amounts of information. In subsequent articles, we will example different asymmetric algorithms, such as Diffie-Hellman, RSA, and El Gamal.

External Links:

Public-key cryptography at Wikipedia

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