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From: Mike Brunner <>
Subject: ViaCrypt PGP Version 4.0
Date: 1996/03/19
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organization: ViaCrypt
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ViaCrypt PGP Version 4.0, which begins shipping this month, introduces
the capability to create and use 'single-function' keys.  Single-function
keys can be used for encryption/decryption or for digital signatures, 
but not both.  When a key pair is created, the type is specified:

  o Traditional dual-function key

  o Single-function, encryption/decryption only

  o Single-function, digital signature only

There are several reasons why the Business Edition and Personal Edition of 
ViaCrypt PGP Version 4.0 support single-function keys:

  o In the Corporate/Business environment, corporate security policy may
    dictate that the decryption capability be shared between the user and
    the corporation's security office.  Single-function keys meet this
    requirement without also providing the corporation with the capability
    to forge the user's digital signature.

  o Even though a user of ViaCrypt PGP Personal Edition may not be subject
    to the above requirement, he/she may still need to be interoperable
    with someone who is.

  o When the 'Freeware' PGP Version 3.0 is released later this year, it is
    expected to also support single-function keys in a compatible manner.  
    By including this feature in ViaCrypt PGP now, interoperability between 
    the two programs will be maintained.

  o Single-function keys are slightly cryptographically stronger.  Using 
    separate keys for encryption/decryption and digital signatures eliminates 
    the possibility of a chosen ciphertext attack.

Because single-function keys are formatted slightly differently than 
traditional dual-function keys, earlier versions of ViaCrypt PGP (and all 
current 'freeware' versions), will display a message similar to the
following when a single-function key is encountered:

"Unsupported packet format - you need a newer version of PGP for this file."

ViaCrypt urges users of ViaCrypt PGP Version 4.0 to keep in mind that until
the 'freeware' Version 3.0 is released, single-function keys posted in public
places (such as keyservers) will be usable only by other Version 4.0 users.

Similarly, ViaCrypt appologizes in advance for any confusion this will cause
current users of the 'freeware' PGP.  

For inquiries and additional information, please contact ViaCrypt directly
at or via telephone at (602) 944-0773.