I believe there isn't any, the word encryption isn't even on the website.
We are using PBE for the messages in the secure chat ( you can choose whether to start a normal chat or a secure one ).
The encryption is done on the client side, so the message going through the network ,storing on the server are all encrypted. Only when you type the correct password then you can decrypt the message.
"We're using PBE" is obviously not quite the kind of answer that was expected here. For all we know, you could be OR-ing the characters of the password and doing a rotX with the result. Hardly secure.
Not sure why i cannot reply to the comment below, so i reply it here. The encryption use is PKCS #5 (5.3 PBE with MD5 and DES). The algorithms are outdated but in the subsequent release we can update it to SHA-2 and AES-256.