PGP & PEM are programs that allow users to send encrypted messages to each other. What form of encryption do these programs use?

DES is a symmetric encryption algorithm that PGP/PEM might use for bulk data, but it's not the primary asymmetric algorithm for key exchange or signatures.

3DES is an improvement on DES, a symmetric encryption algorithm, and while used for data encryption, it's not the asymmetric algorithm that PGP/PEM primarily use for secure key exchange.

PGP (Pretty Good Privacy) and PEM (Privacy-Enhanced Mail) are email encryption standards that heavily rely on the RSA algorithm for asymmetric encryption, specifically for securely exchanging symmetric keys and creating digital signatures. While they use symmetric encryption algorithms (like DES, 3DES, or Blowfish) for encrypting the actual message content, RSA is fundamental to establishing the secure communication channel and verifying sender identity.

3RSA is not a recognized encryption algorithm.

Blowfish is a symmetric encryption algorithm that PGP can use for bulk data, but it's not the primary asymmetric algorithm for key exchange or signatures.

While PGP can use various symmetric algorithms, RSA is the fundamental asymmetric component for key exchange and digital signatures, making it the most accurate answer for the core 'form of encryption' that secures the keying material.