While we are at it, I have an application, where using block ciphers is
prohibitively slow and thus I use ArcFour (RC4) in symmetrically encrypted
data packets in the following way:
The key (either from s2k specifiers or from asymmetrically encrypted
packets) is concatenated with an 8-byte salt at the beginning of the
encrypted packet, the result is hashed using RIPEMD-128 and the resulting
128 bits are used as the ArcFour key encrypting the data. The first 256
bytes are discarded from the key stream. The same format is used in both
MDC-protected data packets and in non-integrity-protected data packets, the
sole difference being the MDC packet at the end of the integrity-protected
kind.
Otherwise, the application is RFC2440-compliant. Right now, I use an
experimental/private number for this symmetric encryption algorithm, but
maybe it would make sense to include it in the standard as something
optional to allow interoperability with other OpenPGP applications.
I also have a patch for GnuPG.
--
Daniel
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