the author of this app says:
X509Tools is a proof of concept to provide S/MIME and X.509 certificate capabilities to Android.
The application is split into two parts:
* The "Certificate Store Management" allows you to show the system certificate root store and manage your own personal store. In your personal store you can import keys (*.p12) and certificate (*.cer, *.crt) of contacts you want to send encrypted mails to.
* The "Encryption/Decryption" part allows you to decrypt smime messages and send encrypted emails. Since this is not an email client use your preferred one and simply open the smime.p7m attachment to decrypt it with X509Tools (the application opens attachment with the mime-type "x-pkcs7-mime").
To provide this features we recompiled parts of bouncycastles crypto libraries and javamail for android, which lead to size of 1.3 MB.
Although the program is fully functional its still in development. So please help us to fix problems or add new features by sending request/bugreports to email@example.com. A log file is written to /sdcard/x509tools/ to help us reproduce you issues. If you got decryption error please send us an equivalent encrypted mail (Cert: http://rundquadrat.at/selbitschka.crt) that we can debug this issue.