"Finite Field Arithmetic." Chapter 20D: "Litmus" Errata: Support for Nested Clearsigned Texts.
This article is part of a series of hands-on tutorials introducing FFA, or the Finite Field Arithmetic library. FFA differs from the typical "Open Sores" abomination, in that -- rather than trusting the author blindly with their lives -- prospective users are expected to read and fully understand every single line. In exactly the same manner that you would understand and pack your own parachute. The reader will assemble and test a working FFA with his own hands, and at the same time grasp the purpose of each moving part therein.
- Chapter 1: Genesis.
- Chapter 2: Logical and Bitwise Operations.
- Chapter 3: Shifts.
- Chapter 4: Interlude: FFACalc.
- Chapter 5: "Egyptological" Multiplication and Division.
- Chapter 6: "Geological" RSA.
- Chapter 7: "Turbo Egyptians."
- Chapter 8: Interlude: Randomism.
- Chapter 9: "Exodus from Egypt" with Comba's Algorithm.
- Chapter 10: Introducing Karatsuba's Multiplication.
- Chapter 11: Tuning and Unified API.
- Chapter 12A: Karatsuba Redux. (Part 1 of 2)
- Chapter 12B: Karatsuba Redux. (Part 2 of 2)
- Chapter 13: "Width-Measure" and "Quiet Shifts."
- Chapter 14A: Barrett's Modular Reduction. (Part 1 of 2)
- Chapter 14A-Bis: Barrett's Modular Reduction. (Physical Bounds Proof.)
- Chapter 14B: Barrett's Modular Reduction. (Part 2 of 2.)
- Chapter 15: Greatest Common Divisor.
- Chapter 16A: The Miller-Rabin Test.
- Chapter 17: Introduction to Peh.
- Chapter 18A: Subroutines in Peh.
- Chapter 18B: "Cutouts" in Peh.
- Chapter 18C: Peh School: Generation of Cryptographic Primes.
- Chapter 19: Peh Tuning and Demo Tapes.
- Chapter 20: "Litmus", a Peh-Powered Verifier for GPG Signatures.
- Chapter 20B: Support for Selected Ancient Hash Algos in "Litmus."
- Chapter 20C: Support for 'Clearsigned' GPG texts in "Litmus."
- Chapter 20D: "Litmus" Errata: Support for Nested Clearsigned Texts.
You will need:
- A Keccak-based VTron (for this and all subsequent chapters.)
- All of the materials from Chapters 1 - 20C.
- ffa_ch20d_litmus_nested_fix.kv.vpatch
- ffa_ch20d_litmus_nested_fix.kv.vpatch.asciilifeform.sig
Add the above vpatches and seals to your V-set, and press to ffa_ch20d_litmus_nested_fix.kv.vpatch.
As of Chapter 20D, the versions of Peh and FFA are 250 and 253, respectively. FFA and Peh themselves have not changed from Chapter 19.
Compile Peh:
cd ffacalc gprbuild
... and install it to a path visible in your shell (e.g. /usr/bin.)
Litmus as given in the previous chapter would choke (failing safe, i.e. rejecting the signature) when fed "nested" clearsigned texts. This bug has been fixed:
# 'ASCII-Armoured' PGP signatures have mandatory start and end markers: START_MARKER="^\-\-\-\-\-BEGIN PGP SIGNATURE\-\-\-\-\-" END_MARKER="^\-\-\-\-\-END PGP SIGNATURE\-\-\-\-\-" ....... CLEAR_MARKER="^\-\-\-\-\-BEGIN PGP SIGNED MESSAGE\-\-\-\-\-" .......
To test, invoke Litmus with two arguments: the public key, followed by the input file:
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 This is a test-fire GPG 'clearsigned' document written for FFA Chapter 20C. - -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQEcBAEBCgAGBQJeGimSAAoJELmCKKABq//HfgsH/1bg0zpL1PoApHE5BMNXmJ7U 7vWKQJ3ZCsGvkUSIgIZESTp6EpGDclBQqvBsdBZ9KVnBpGiIbmKbNjDNlZU5YcWt WQ7FO+r4LiUZOJRiPADWMM7tpI3azXelPyuge7hFe6o3UG0aErSceKXcoFGKFDO2 MCZXkR6Lfd3rYKHcySOEvkoCMQ4ytbEQM4IBE57AqQIpmnI7Mo1033TnDgL2KdXd PHLtedNyaKwzVJw08BtKjzole130GvElSMmxilrHZ0w+2J4uHRuBELyZbJ55vu+x Bx+Q5OpMwz0ZG4vjz8ncZE/nCvK/sZv/RXsdNow95fETH5DKC9HfIP279kKlBRg= =3ozu - -----END PGP SIGNATURE----- -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQEcBAEBCgAGBQJeHgg9AAoJELmCKKABq//HHywH/3cfUfV8SH2yuxHNBPmk3Yha Nw/40YK52/DJ/H+RUY6Zei2X3tJPYe3vDN2P3iRqKBycpUPtNnCDaF3BAvg7cyRQ PghpykoSeERxIQZaIQWTUyMQRBwoMF90wiQpcgCEXRH3xZo/p0M3M6zPrqKElXf4 essZmM3jsvfU9T8JGho0RPyK1J42fTBCiRb0Y++ZQGWVEwJugtVnQOL76fYmSUpW vDBKgNJfvGOMNTCTLemqD2nn6DZzLN9TOrRlmLvfr0lbzu9rSGAMtRKqozhZeCXf LiTWWVZkCUGr/SEk5olhbHQnfoYMH1V071qJnpv1/5QqIiZ1z2KbP65Ba/i3i0A= =o/9T -----END PGP SIGNATURE-----
./litmus.sh asciilifeform.peh asciilifeform-clearsigned-twice.txt... which will yield the output:
VALID GPG RSA signature from asciilifeform <stas@loper-os.org>
Naturally, no verification is performed on the embedded clearsigned text (just as in traditional GPG. If you want to operate on the embedded text, you must extract it.)
~To be continued!~
