REFERENCES.txt

This file lists the sources of important ideas/concepts/specs that
found their way into various source files:


ic.c:
=====

The method of using the Index of Coincidence to detect correct
wheel/ring positions is based on a paper by J. Gillogly [1].


hillclimb.c
===========

The general idea of using a hill climbing algorithm to recover
the correct stecker positions can be found in [1].

After experimenting with many steepest ascent algorithms on very
short messages (70 letters), I found that the order of testing
stecker presented by G. Sullivan and F. Weierud [2], which results
in a shallower ascent, is superior for longer messages (100-200
letters) while giving at least the same performance for short
messages.

Many of the shortcuts that avoid testing the full key space can
be found in [2].


SGT.c
=====

SGT.c was written by Professor Geoffrey Sampson of the University of Sussex
and is distributed with his kind permission. The file itself contains
detailed documentation. See also: [3]

SGT.c is located at http://www.grsampson.net/Resources.html


cipher.c
========

The internal wiring is based on a document titled "Wiring of Enigma Rotors
[I-VIII, gamma & beta]" by David H. Hamer.

The double stepping of the middle rotor is described by David H. Hamer in [4].
Wikipedia has good illustrations.



[1] Gillogly, J.J. 1995. Ciphertext-Only Cryptanalysis of Enigma.
    Cryptologia, 19(4): 321-413.

[2] Sullivan, G. and Weierud, F. 2005. Breaking German Army Ciphers.
    Cryptologia, 29(3): 193-232.

[3] Gale & Sampson, "Good-Turing Frequency Estimation Without Tears"
    (JOURNAL OF QUANTITATIVE LINGUISTICS, vol. 2, pp. 217-37 -- reprinted
    in Geoffrey Sampson, EMPIRICAL LINGUISTICS, Continuum, 2001).

[4] David H. Hamer. 1997. Enigma: Actions Involved in the "Double
    Stepping" of the middle rotor. Cryptologia. 21(1): 47-50