This feature decodes Base64 encrypted strings to their original byte form. Base64 is used in several Internet protocol standards like HTTP, MIME, IMAP .... to encode arbitrary data as plain ASCII text. The following picture shows the decoding of a Base64 password captured from an HTTP Basic authentication packet:
Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
Base64 Password Decoder dialog can be activated from the main menu under "Tools" or pressing the relative toolbar button. Simply cut and paste the Base64 encrypted string into the dialog, the decoder will do the rest.