This article is from the PGP FAQ, by Jeff Licquia jalicqui@prairienet.org with numerous contributions by others.
PGP does this because of the "-----BEGIN PGP MESSAGE-----" (and
related) headers it uses to mark the beginning of PGP messages. To
keep it from getting confused, it tacks a "- " to the beginning of
every line in the regular text which has a dash at the start. It
strips the extra dash and space when you check the message's
signature, and writes the original text to the output.
 
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