Provided are a computer program product, method and system for dynamically providing algorithm-based password/challenge authentication. A page is provided to authenticate a presenter of a username including a string and a field for entry of a password. An entered password entered into the page is received. An algorithm associated with the username is applied to the string included in the page to generate a generated password. A determination is made as to whether the entered password matches the generated password. The username is successfully authenticated in response to determining that the entered password matches the generated password.