RFC 2015 (rfc2015) - Page 2 of 8

MIME Security with Pretty Good Privacy (PGP)

RFC 2015                 MIME Security with PGP             October 1996


2.  PGP data formats

   PGP can generate either ASCII armor (described in [3]) or 8-bit
   binary output when encrypting data, generating a digital signature,
   or extracting public key data.  The ASCII armor output is the
   REQUIRED method for data transfer.  This allows those users who do
   not have the means to interpret the formats described in this
   document to be able extract and use the PGP information in the
   message.

   When the amount of data to be transmitted requires that it be sent in
   many parts, the MIME message/partial mechanism should be used rather
   than the multipart ASCII armor PGP format.

3.  Content-Transfer-Encoding restrictions

   Multipart/signed and multipart/encrypted are to be treated by agents
   as opaque, meaning that the data is not to be altered in any way [1].
   However, many existing mail gateways will detect if the next hop does
   not support MIME or 8-bit data and perform conversion to either
   Quoted-Printable or Base64.  This presents serious problems for
   multipart/signed, in particular, where the signature is invalidated
   when such an operation occurs.  For this reason all data signed
   according to this protocol MUST be constrained to 7 bits (8- bit data
   should be encoded using either Quoted-Printable or Base64).  Note
   that this also includes the case where a signed object is also
   encrypted (see section 6).  This restriction will increase the
   likelihood that the signature will be valid upon receipt.

   Data that is ONLY to be encrypted is allowed to contain 8-bit
   characters and therefore need not be converted to a 7-bit format.

     Implementor's note: It cannot be stressed enough that applications
     using this standard should follow MIME's suggestion that you "be
     conservative in what you generate, and liberal in what you accept."
     In this particular case it means it would be wise for an
     implementation to accept messages with any content-transfer-
     encoding, but restrict generation to the 7-bit format required by
     this memo.  This will allow future compatibility in the event the
     Internet SMTP framework becomes 8-bit friendly.

4.  PGP encrypted data

   Before encryption with PGP, the data should be written in MIME
   canonical format (body and headers).

   PGP encrypted data is denoted by the "multipart/encrypted" content
   type, described in [1], and MUST have a "protocol" parameter value of



Elkins                      Standards Track