Public key cryptography uses a key pair consisting of a public key and a private key. The PKA public key uses one of the following algorithms:

• Rivest-Shamir-Adleman (RSA)

  The RSA algorithm is the most widely used and accepted of the public key algorithms. It uses three quantities to encrypt and decrypt text: a public exponent (PU), a private exponent (PR), and a modulus (M). Given these three and some cleartext data, the algorithm generates ciphertext as follows:

  Similarly, this operation recovers cleartext from ciphertext:

  An RSA key consists of an exponent and a modulus. The private exponent must be secret, but the public exponent and modulus need not be secret.

• Digital Signature Standard (DSS)

  The U.S. National Institute of Standards and Technology (NIST) defines DSS in Federal Information Processing Standard (FIPS) Publication 186.

• Elliptic Curve Digital Signature Algorithm (ECDSA)

  The ECDSA algorithm uses elliptic curve cryptography (an encryption system based on the properties of elliptic curves) to provide a variant of the Digital Signature Algorithm.