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Public-key algorithms

Public-key algorithms base their security on the solving of complex mathematical problems that are reliant on large keys for numbers. The nature of the mathematical problems distinguish the different algorithms.

Two of the more common algorithms include:

RSA — Named for its inventors, Ron Rivest, Adi Shamir, and Len Adleman, this algorithm works on very large numbers that can be factored into large primes.
Digital Signature Algorithm (DSA) — A U.S. Government standard, this algorithm works on large numbers that can be used to determine discrete logarithms.

The minimum practical key size for both RSA and DSA keys is typically 1024 bits. As the size of the keys implies, public-key algorithms are highly compute-intensive and are much slower than symmetric-key algorithms, but they are also far more secure. This far greater security and the ease of public key distribution is what makes them ideal as the basis for a data security infrastructure. However, their relatively slow speed makes them less than ideal to provide the sole cryptographic mechanism for all services of a PKI.