PKA Key Algorithms

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:
```
ciphertext = cleartext^PU  (modulo M)
```
Similarly, this operation recovers cleartext from ciphertext:
```
cleartext = ciphertext^PR  (modulo M)
```
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.
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.