-*** There is no way to clear strings safely.
-To prevent passphrases from been stealing from cores, `read-passwd'
-function clears passphrase strings by `(fillarray string 0)'.
-However, it is not enough. Emacs does compaction of small strings in
-GC sweep phase. If GC happens before `fillarray', passphrase strings
-may be copied elsewhere in the memory. PGG and gpg.el enables
-passphrase caching by default.
+Fortunately, there is gpg-agent to cache passphrases in more secure
+way, so the EasyPG Library dares *not* to cache passphrase by itself.
+Elisp programs can set `epg-context-passphrase-callback' to cache
+user's passphrases.