Modern cryptographic systems include symmetric-key algorithms (such as DES and AES) and public-key algorithms (such as RSA). Symmetric-key algorithms use a single shared key; keeping data secret requires keeping this key secret. Public-key algorithms use a public key and a private key. The public key is made available to anyone (often by means of a digital certificate). A sender will encrypt data with the public key; only the holder of the private key can decrypt this data.
- One party receives the other's public key, and encrypts a small piece of data (either a symmetric key or some data that will be used to generate it).
- The remainder of the conversation (the remaining party) uses a (typically faster) symmetric-key algorithm for encryption.
The simplest method to read encrypted data is a brute force attack–simply attempting every number, up to the maximum length of the key. Therefore, it is important to use a sufficiently long key length; longer keys take exponentially longer time to attack, making a brute force attack invisible and impractical.
Currently, commonly used key lengths are:
Key generation algorithmsEdit
In computer cryptography keys are integers. In some cases keys are randomly generated using a random number generator (RNG) or pseudorandom number generator (PRNG), the latter being a computer algorithm that produces data which appears random under analysis. Some types the PRNGs algorithms utilize system entropy to generate a seed data, such seeds produce better results, since this makes the initial conditions of the PRNG much more difficult for an attacker to guess.
- Distributed key generation: For some protocols no party should be in the sole possession of the secret key. Rather, during distributed key generation every party obtains a share of the key. A threshold of the participating parties need to work together in order to achieve a cryptographic task, such as decrypting a message.