Internationally Available Strong Crypto Products

Part II: Secure Email and VPNs

By Seán Boran

Go to Part I: Introduction, Secure Telnet and File Encryption

September 13, 1999. This is the second part in a series of three articles devoted to Persons needing strong crypto Internationally. Part two focuses on Secure Email and Virtual Private Networks.

If we missed out on one of your favourite international products below, or you like to submit corrections/feedback contact us.

Secure Email

For secure email applications, there are currently two standards, PGP and S/MIME. Whereas PGP is probably the dominant method of exchanging secure Email today, S/MIME is expected to become the standard over the next year or two, because it is backed by most of major players (RSA, Microsoft, Netscape, Lotus). PGP5 is very interesting, in both free & commercial forms. It should be considered for any short to medium term solution. A pity that it is not S/MIME compatible!

PGP

PGP (Pretty Good Privacy) is an encryption system developed by Philip Zimmerman for ensuring data confidentiality and (partially) proof of origin. It is primarily used together with Internet email products for signing and/or encryption of information. Local files may also be signed/encrypted. It has been around for a long time.
PGP was originally developed in the U.S., but was exported internationally by distributing the source code in book (paper) form. This has caused friction with certain U.S. Government agencies.  PGP  works on almost every platform from mainframes to PCs.
PGP is being standardised by the IETF under the OpenPGP banner. See www.ietf.org/html.charters/openpgp-charter.html

There are two principal international versions:

  1. The old "standard" version was stopped at 2.6.3 (released Feb.96). IDEA was the symmetric algorithm, RSA the public key algorithm supported.
  2. Version 5 was released in late 1997. This improved version provides an easy-to-use GUI for PCs and Macintosh and directory services publishing/lookup out of the box.

    3. It supports IDEA, CAST and 3DES algorithms for symmetric encryption.
    Version 6 was released in early 1999. Seems to be backward compatible with V5, but offers quite a few new interesting features. Very professional looking. V6 is not available for UNIX (only MAC & Win32).
    PGP can work as an Email plugin for Eudora, Exchange / Outlook, Outlook Express or as an external program (for other Email clients).
Products:

S/MIME

Secure MIME (Multi Purpose Mail Extensions)  is a proposed Internet standard for secure message exchange, developed by RSA, adopted by several vendors and now undergoing the IETF standards process.  S/MIME is based on existing standards - MIME bodies and PKCS objects. There are two versions, V2 was finalised in March 1998, V3 is not yet finalised.
S/MIME is based on RFC 2311 and RFC 2313, which specify how PKCS#7 is used for message encryption/signing, PKCS#1 for RSA encryption, X509 for certificate formats (v1 &v3) and PKCS#10 for certificate requests.

Algorithms: Symmetric key DES, 3DES and RC2 40-128bit, public key 512-2048 bit RSA and SHA-1 / MD5 hashing algorithms are used in S/MIME 2.

Products:

SSL

Secure Sockets Layer (SSL - see below) can be used to protect Email during transport, but does not offer user authentication, nor digital signatures/non-repudiation. The use of SSL for protecting POP, IMAP, SMTP is discussed in the Secured Web Services section.

Non standard products

Ascom offer a secure email product for Exchange which is based on their patented IDEA algorithm. See http://www.ascom.ch/systec/mail/exchange/technica.htm .

Sapher Server Ltd., from England produce Secrets for Exchange for encrypting emails.

Ironware (Czech republic) produce the Ironware Mail tool . IDEA or Blowfish algorithms are used to encrypt "marked" folders on shutdown and decrypt them on startup (like F-Secure Desktop above). Several users with different passwords can use the same PC.

ABI-Software Development of Toronto, Canada offer free email encryption software.

VPN

VPNs (Virtual Private Network) are use to protect the privacy and integrity of information
exchanged between two parties over an untrusted network. VPNs provide a means of securing network traffic and authenticating entities by providing a gateway at each point of access into a business. Based on the IPsec standards (increasingly), VPNs provide the necessary data privacy, access control, data integrity and authentication services at a low level in the network and are independent of the
applications using the network.

The term "client" (or VPN client) refers to the initiating part presumably on an insecure
network and the "server"  is on the other side, waiting for
connections. A "gateway" is a special server that connects clients to "clear text" servers, providing secured traffic to the client, but clear text traffic to the destination server. Examples of VPN usage:

Protocols

IPsec IPv6 is the up-and-coming replacement for the current V4 Internet Protocol. V6 is needed especially for it's much greater address range, but it also provides security features
for improved integrity, authentication and confidentiality not found in the current version.
IPsec is the V6 security protocols (covered in RPCs 1825 to 1829), but which can be
used with IPv4. Hopefully IPsec is the standard that will bring us VPNs that interoperate. See also www.ietf.org/html.charters/ipsec-charter.html ,
Architecture: http://search.ietf.org/internet-drafts/draft-ietf-ipsec-arch-sec-06.txt
ISAKMP: http://search.ietf.org/internet-drafts/draft-ietf-ipsec-isakmp-09.txt

IPsec is located on the network layer and can encrypt all data above this layer (including for example the transport headers). The are two basic encryption modes:

In their initial connection, each pair of entities negotiates the security policy that is to be used in their subsequent communications. This key exchange protocol is known as IKE (formerly ISAKMP/Oakley) and is based on DH.
Algorithms supported: MD5 and SHA-1 hashing, DSS and RSA signatures, DES / 3DES / Blowfish symmetric encryption, RSA PK encryption along with support for X509 v3 certificates.

PKI certs provide reliable authentication and secure key negotiation by allowing each party to protect their key by either signing it and verifying with digital signatures, or encrypting and decrypting it with their public-private key pairs. Lookup of revoked certificates is provided by directories, which are used to publish revoked certificates within the PKI.

ICSA run an IPsec certification process to ensure interoperability between products. See
www.icsa.net  and www.anxo.com/whatis.htm#csp

SKIP  www.skip.org  offers link level encryption, the encryption taking place below the transport layer. It also includes a scheme for authentication, key management and certification authority. Many different encryption algorithms may be used (3DES, DES, RC4, the public key exchange is based on Diffie-Hellman). SKIP could be used for encrypted VPNs (end-to-end, firewall-firewall or end-to-firewall) or encrypted client to server communication. SKIP was developed by Sun Microsystems, who put the source code into the public domain.
SKIP was proposed as an Internet Standard at the December 1995 IETF meeting by Sun. The IETF allowed SKIP to proceed as a proposed and elective/optional standard. Version 0.5 was released in November 1995. The current version is V2.
SKIP was not adopted by IPsec, probably because of political reasons, technically it was years ahead of IPsec, which came on stream in 1999.

L2TP(layer 2 tunnelling protocol) is based on PPTP and Cisco's L2F and addresses many of the problems found in both. It will use IPsec for authentication & encryption, with a fallback to CHAP/PAP. It is quicker that PPTP, using UDP rather than TCP.
The IETF is considering L2TP, see http://search.ietf.org/internet-drafts/draft-ietf-pppext-12tp-11.txt and  http://search.ietf.org/internet-drafts/draft-ietf-pppext-12tp-security-02.txt
No strong international L2TP (or PPTP) products are known.

Products

Sean Boran is an IT security consultant based in Switzerland and the author of the online IT Security Cookbook.