There are a number of reasons Peerio uses computer generated passphrases. The short answer is that Peerio needs users to have strong passwords to generate strong cryptographic keys, and to ensure users are protected from password cracking attacks.
Unfortunately, most people aren't great at choosing their own passwords. This makes some security guarantees hard to make. We could be using alien-gifted quantum cryptography from the future, but if your password is "p@ssword1", even alien blessings wouldn't help much.
After extensive research and consultations from various experts in cryptography and usability, we found that computer generated passphrases were able to provide significantly stronger security for most users while also being much easier to remember!
By giving computer generated passwords to all users, you can rest assured that not only is your account protected with a strong passphrase, but so are the accounts of everyone you share messages and files with.
For a comprehensive explanation of how we decided on five-word computer generated passphrases, read our blog post, "How to build a billion dollar password"