bcrypt isn't reversible (with respect to the password). The point is that Blowfish(key1, "message") is not at all similar to Blowfish(key2, "message"). This is

bcrypt isn't reversible (with respect to the password). The point is that Blowfish(key1, "message") is not at all similar to Blowfish(key2, "message"). This is called resistance to related-key attacks (look this up for a formal definition), and is an explicit design goal of every real-world block cipher. bcrypt is just Blowfish(key-derived-from-salt-and-password, "OrpheanBeholderScryDoubt"), so it inherits this property.