Chosen prefix means somebody doing this attack gets to pick the start of both the colliding documents. For example maybe I want two children's stories, one which starts "Donald was an innocent young boy," and the other begins "Steve was a corrupt old gangster,"
The attack will calculate suffixes for these two documents such that both documents have the same hash result.
This means the attacker can then show some people a document about Donald, and others the one about Steve and if they rely on the same hash to validate that they're the same document they'd be fooled.
Digital certificates are the most prominent way computers deliberately depend on this assumption which a collision attack makes untrustworthy.
The attack will calculate suffixes for these two documents such that both documents have the same hash result.
This means the attacker can then show some people a document about Donald, and others the one about Steve and if they rely on the same hash to validate that they're the same document they'd be fooled.
Digital certificates are the most prominent way computers deliberately depend on this assumption which a collision attack makes untrustworthy.