In various embodiments of the present invention, a first software entity, such as a program, routine, library, or module, authenticates a second software entity by extracting an authentication block from memory, validating the extracted authentication block, and comparing a value stored in the authentication block with a computable or pre-computed authentication value in order to authenticate the second software entity. In certain alternative embodiments, a program can authenticate itself at run-time. Additional embodiments of the present invention include methods for constructing and inserting authentication blocks into software entities to facilitate authentication by the authentication methods that represent embodiments of the present invention.