RSA private key

An RSA private key is a cryptographic private key, notably used in combination with X.509 certificates.

It may be stored in a number of file formats, such as:
 * DER encoded RSA private key
 * PEM encoded RSA private key
 * PKCS12
 * PVK

Specifications

 * RFC 3447: PKCS #1 Version 2.1
 * RFC 2437: PKCS #1 Version 2.0 (obsolete)
 * RFC 2313: PKCS #1 Version 1.5 (obsolete)

Links

 * Wikipedia: RSA (algorithm)
 * Crypto Posters (graphics outlining RSA key formats)