Dates

Only such encryption systems can be considered secure that have open and publicized algorithms. Even though the algorithm may be publicized, encrypted messages can only be decrypted with justifiable effort if the key is also known. Keys consist of character strings used for encryption and decryption which must be fully or partly known to all involved parties. The algorithms meeting these requirements can be divided into two categories: symmetric and asymmetric encryption methods.

Symmetric Methods

Symmetric encryption - also known as the Private Key Method - uses the same key for encryption and decryption. The inherent weakness of this method is mostly the requirement of a key exchange between communications partners. Direct transport of keys via a public network is impossible, since access to unauthorized third parties cannot be prevented which in turn could discriminate all encrypted communications.

Keys may be transferred by means of conventional mail - e.g. using sealed envelopes and personal pick up (a typical method used for online banking). However, a better method may be to encrypt the symmetric key using an asymmetric encryption method.

Examples for symmetric encryption methods are IDEA, DES, Twofish and others.

Asymmetric Methods

Asymmetric encryption - also known as the Public Key Method - uses two different keys: the so called public key, which may be distributed freely and the private key which is known only to the owner of a key. The two keys have a (mathematical) relationship. However, for obvious reasons, calculation of a private key on the basis of the public key must be impossible or at least not feasible.

Both keys have different functions depending on the application at hand. In the case of data encryption, data is encoded using the public key. The private key is required in order to decrypt the message. The private key can also be used to generate digital signatures which can later be verified using the public key.

The most well known key of this type of algorithm is RSA. This algorithm is based on the observation, that two (very large) numbers can be multiplied easily while the determination of the two factors is a complex problem.

The disadvantage of this method compared to symmetric encryption is the greater amount of processing time required for the calculation. This is why usually the so called hybrid technology - a mix of both asymmetric and symmetric encryption - is used when dealing with a greater amount of data. In this case, symmetric encryption is used to encode the data but the symmetric key is communicated on a previously determined frequency using asymmetric encryption.