Change the encryption algorithms for S/MIME or PGP protected messages
If a message has multiple recipients, your BlackBerry smartphone uses the first encryption algorithm that's selected in the
list and that all recipients are known to support.
On the home screen or in a folder, click the Options icon.
Click Security > S/MIME or PGP.
In the Allowed Content Ciphers section, select the checkbox beside one or more allowed content ciphers.
key > Save.