Interoperability of S/Mime and PGP encrypted email products

This chart is current as of November 10, 1998 and as such is woefully outdated. It contains information on the various features and interoperability of different secure email products. There are two different and incompatible security mechanisms: Secure MIME (S/Mime) and Pretty Good Privacy (PGP). Each product has a range of different features, as show in the table below.

There are two different categories of products: the first set contains stand-alone email client software products. Many of these products, such as Outlook and Notes, require both client and server components to perform encryption functions. The second set contains plug-ins for existing email products, and we indicate the products supported by each vendor. Note that interoperability isn't guaranteed across a single vendor's product line necessarily.

Some products are only available for 32-bit Windows (NT, 95 and 98). Others have versions for Macintosh and older 3.1 Windows.
Some products may have the ability to trust certificates issued by individuals and by certificate authorities (CA), some do not offer this ability.
Messages can be encrypted either with a signature inside the digital "envelope" (opaque) or outside (clear). Some products cannot send signatures, some cannot receive signatures: we note the limitations. (Ideally, for 100% complete interoperability, all S/Mime products should be able to send and receive both kinds, and all PGP products should be able to send and receive both kinds, which would be indicated on the table as S/R C/O.)
Finally, each product uses a different series of encryption algorithms to encode its encryption keys: RC2 and RC4 (created by RSA) and Diffie-Hellman, among others. We indicate the appropriate bit-length for the keys for each algorithm in the table.

S/MIME and PGP Products

	S/Mime or PGP	Clients Supported			Trust individual certs	Trust CA root certs	Send/receive clear/opaque msg.	Key encrption schema
	S/Mime or PGP	Win 3.1	Win 32	Mac	Trust individual certs	Trust CA root certs	Send/receive clear/opaque msg.	Key encrption schema
Microsoft Outlook Express	S/Mime	No	Yes	No	Yes (1)	Yes	S/R C; S only O	RC2 (40, 64, 128)
Microsoft Outlook 98 (7)	S/Mime	No	Yes	Yes	Yes (1)	Yes	S/R C/O	RC2 (40, 64, 128)
Netscape Messenger 4.5	S/Mime	Yes	Yes	Yes	Yes	Yes	S/R C; R only O	RC2 (40, 64, 128)
OpenSoft ExpressMail 2.5	S/Mime	Yes	Yes	No	No	No	S/R C/O (5)	RC2 (40, 64, 128, 255)
Lotus Notes	S/Mime	Coming in R5			Yes (1)
Cyrusoft Mulberry	PGP	No	Yes	Yes	Yes	N/A	S/R C only	DH

S/MIME and PGP Plug-ins

	S/Mime or PGP	Clients Supported			Trust individual certs	Trust CA root certs	Send/receive clear/opaque msg.	Key encrption schema	Products supported
	S/Mime or PGP	Win 3.1	Win 32	Mac	Trust individual certs	Trust CA root certs	Send/receive clear/opaque msg.	Key encrption schema	Products supported
WorldTalk WorldSecure Client 2.2	S/Mime	Yes	Yes	No	Yes	No	S/R C/O (5) (6)	RC2 (40, 64, 128, 255)	Eudora, Outlook
Labcal Technologies' IsoShield/Mail	S/Mime	Yes	Yes	No	Yes (1)	No	S/R C/O	RC2 (40, 64)	Notes
LJL Enterprises' ArmorMail	S/Mime	Yes	Yes	No	Yes	Yes	S/R C; R only O (5)	RC4 (40, 128) (3)	MS Mail, cc:Mail, Outlook, Notes, Eudora
Baltimore Mail Secure	S/Mime	Yes	Yes	No	Yes	Yes	Limited (2) (5)	RC2 (40, 64, 128)	Eudora, Outlook
Novell Groupwise w/Entrust	S/Mime	No	Yes	No	Yes	Yes	S/R C/O	RC2 (40, 64, 128)	Groupwise
PGP for Business Privacy (4)	PGP	No	Yes	Yes	Yes	N/A	S/R C only	DH	Eudora, Exchange, Outlook, Claris Emailer
Novell Groupwise w/ PGP	PGP	No	Yes	No	Yes	N/A	S/R C only	DH	Groupwise
Entrust Lite	S/Mime	Yes	Yes	Yes	Yes	Yes	S/R C/O	RC2 (40, 64, 128), DH	MS Mail, Outlook, cc:Mail, QuickMail

Notes:

(1) Certificates are stored in user's own address book.

(2) Can exchange opaque signed messages only with Outlook.

(3) LJL plans on offering DH support in future products.

(4) There are several PGP versions available from Network Associates and others, including business and personal products, those available with and without support for earlier RSA encryption.

(5) Sends signed messages in p7m format.

(6) Eudora plug-in can't process HTML-encoded messages, Outlook plug-in can't receive signed messages.

(7) Outlook 97 has no S/Mime support, this was added for Outlook 98. Outlook for Windows 3.1 does not have S/Mime support. For Outlook for Macintosh, you will need to apply Exchange Server 5.5 Service Pack 1.