-If Emacs crashed and dumps core, passphrase strings in memory are also
-dumped within the core file. `read-passwd' function clears passphrase
-strings by `(fillarray string 0)'. However, Emacs performs compaction
-in gc_sweep phase. If GC happens before `fillarray', passphrase
-strings may be moved elsewhere in memory. It is recommended that as
-soon as you are done with passphrase you should clear it manually.
-However, PGG and gpg.el can keep passphrase strings in cache for a
-while and this behavior is their default!