So I only heard about this app recently from news that its users had been crackdown upon by EU governments including UK.

Did anyone else know about this app? and how it was encrypted

Encro-chat?

Was that the encrypted app of choice for criminals working internationally? IIRC, it's encryption was broken by French police, who informed other police forces at the highest level. They did nothing initially - just listened. Then when everybody had enough evidence to secure convictions, there were simultaneous Europe-wide raids in large numbers and a great time was had by all - police forces, of course.

Here in Ireland, many big criminals were arrested, mules and routes for contraband in were uncovered, international arrests were made. There was some guys in international haulage who also were big in international drug smuggling … not any more.

i think that was it.
here at Finland they busted one darknet drugs site, probably connected to encro-chat.

As for how Encro-Chat was encrypted, I imagine stupidly. It certainly wasn't PGP, because once they got into one, they got into everybody's Encro-chat.

By contrast, I read about ZRTP. Basically, client & server have a 'let's talk about what keys we will use' conversation and cobble up highest level keys of the weaker party. Then they exchange data.

Related video that I saw on utube. Some things that encrypted chat are used for.

https://m.youtube.com/watch?v=S80biBdpOiE

Anytime I send emails with business associates, these emails are automatically and transparently-to-me encrypted using PGP certificates. Or, at the very least, they are signed. I do not have to be conscious of this: it simply happens. I receive an email from these people and I instantly know that it is authentic and not tampered-with, whether or not it was sent in secret.

"Very strong encryption" can be just as transparent, and just as verifiable, and just as easy, as the "also, very strong encryption" that puts the padlock on the address-bar of this website. Convenient, compatible tools or add-ons are available for the email client programs of every operating system, and every type of phone.

I would feel – and, in fact, would be – "utterly naked" if I didn't do this. Strong security is easy. "Don't leave home without it."

Protonmail.com is also good. Your password IS your encryption key. You are encouraged to use a long 0one, and it is used to decrypt your mailbox. Protonmail <--> Protonmail conversations are consequently extremely difficult to crack. It does send text to unencrypted boxes.

The problem with encrypting email is that it only works if both parties do it. Then you can exchange public keys. None of the people I write emails to would know what a public key was if it jumped up and bit them on the nose.

Same thing with protonmail. You get end-to-end encryption only if the other party is on protonmail too or if they have a public key that you can store there.