S/MIME v3 and OpenPGP

Differences and Commonalities Between S/MIME v3 and OpenPGP

S/MIME v3 and OpenPGP are both protocols for adding authentication and privacy to messages. However, they differ in many ways, and are not designed to be interoperable. Some cryptography algorithms are the same between the two protocols, but others differ. The following chart is a comparison of many relevant features of the two protocols, showing where they differ and where they are the same.

Mandatory features	S/MIME v3	OpenPGP
Message format	Binary, based on CMS	Binary, based on previous PGP
Certificate format	Binary, based on X.509v3	Binary, based on previous PGP
Symmetric encryption algorithm	TripleDES (DES EDE3 CBC)	TripleDES (DES EDE3 Eccentric CFB)
Signature algorithm	Diffie-Hellman (X9.42) with DSS or RSA	ElGamal with DSS
Hash algorithm	SHA-1	SHA-1
MIME encapsulation of signed data	Choice of multipart/signed or CMS format	multipart/signed with ASCII armor
MIME encapsulation of encrypted data	application/pkcs7-mime	multipart/encrypted