President Obama spoke at length today about privacy and encryption. He cautioned against an “absolutist view of encryption”, claiming that search warrants can apply to the virtual world just as well as the physical provided we build our technology wisely.

Alas, Obama is fundamentally wrong. Digital encryption has no analogue in the physical world. Doors locked by lost keys can be busted down. Digital doors locked by lost encryption keys can never be re-opened.

What Obama misunderstands is that “encryption absolutism” is not an ideological position. It’s a technical one.