Put differently, the legal problem for law enforcement is not the Fourth Amendment. Investigators and prosecutors can and do obtain warrants to authorize searches, seizures and surveillance of encrypted digital evidence. The problem is that there is no law that clearly empowers governmental actors to obtain court orders to compel third parties (such as equipment manufacturers and service providers) to configure their systems to allow the government to obtain the plain text (i.e., decrypted) contents of, for example, an Android or iPhone or messages sent via iMessage or WhatsApp. In other words, under current law, the most the government can do with respect to encrypted systems where the manufacturer or service provider does not hold the encryption keys is to demand that companies provide it with an encrypted blob for which they have no mechanism to decrypt.
One suggested workaround is better use of metadata to support crime enforcement:
If, in fact, governments more aggressively support encryption, they will have to focus even more on collecting and analyzing noncontent metadata, increasingly aided by advanced data analytics driven by machine learning and other artificial intelligence tools. I know full well that obtaining noncontent metadata, while useful, is not the same as collecting the full content of communications and documents. It is hard to use metadata, for example, to prove criminal intent or to understand exactly what a spy or a terrorist is plotting. But we are in a world where content is increasingly unavailable and there is a wealth of metadata. So, the government should focus on collecting the right data and developing or buying top-notch analytical tools. In doing so, of course, it needs to make sure that such metadata collection and analysis is consistent with the Fourth Amendment. Admittedly, that will be more complicated in light of the U.S. Supreme Court’s decision in Carpenter v. United States. And it will be harder to do all this in the face of efforts by some companies to further anonymize public internet metadata. Nevertheless, this is where law enforcement finds itself since it has not persuaded Congress to act.
However, what this all highlights is that every country has a different set of rules, therefore this is a debate that needs to be had in a number of places.