-If Emacs crashed and dumps core, passphrase strings in memory are also
-dumped with the core file. `read-passwd' function clears passphrase
-strings by `(fillarray string 0)'. However, it is not perfect. Emacs
-does compaction of small strings in gc_sweep phase. If GC happens
-before `fillarray', passphrase strings may be copied elsewhere in
-memory. So, it is recommended that if you are done with passphrase
-you should clear it manually. However, PGG and gpg.el enables
-passphrase caching by default.