privacy enhanced mail (Internet) (PEM)
Privacy Enhanced Mail (PEM) is one of the oldest standards for the encryption of e-mails on the Internet. Both the RSA method and the symmetric Data Encryption Standard( DES) or Triple DES( 3DES) are provided as encryption methods.
With Privacy Enhanced Mail (PEM), if a file is to be sent encrypted, it is first encoded using DES encryption with the aid of a randomly generated DES key. The DES key is then encoded with the recipient's public key using the RSA algorithm and transmitted together with the file encrypted using the DES method. The advantage of this combined method is that decryption of the DES-encrypted file is not very computationally intensive and the RSA-encoded key provides a high level of security.
Documents secured with PEM are suitable for data transport over networks and for signature verification. In addition, the PEM protocol accepts digital certificates according to X.509. Privacy Enhanced Mail is described in RFCs 1421 to 1424.