You can encrypt your password for NickServ authentication using blowfish and SASL.
To set “dh-blowfish” by default for all servers:
/set irc.server_default.sasl_mechanism dh-blowfish
(Note that this will only work if your WeeChat was built with libgcrypt support - otherwise, use the “plain” mechanism.)
Additionally, per-server username and password settings can be applied - for instance, with Freenode:
/set irc.server.freenode.sasl_username "_username_" /set irc.server.freenode.sasl_password "_password_"