commit 1f862439170198372d09104ecd8b188dd2fd264c Author: Alexander Rosenberg Date: Mon Oct 7 01:29:11 2024 -0700 Initial commit diff --git a/LICENSE b/LICENSE new file mode 100644 index 0000000..f288702 --- /dev/null +++ b/LICENSE @@ -0,0 +1,674 @@ + GNU GENERAL PUBLIC LICENSE + Version 3, 29 June 2007 + + Copyright (C) 2007 Free Software Foundation, Inc. + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + Preamble + + The GNU General Public License is a free, copyleft license for +software and other kinds of works. + + The licenses for most software and other practical works are designed +to take away your freedom to share and change the works. By contrast, +the GNU General Public License is intended to guarantee your freedom to +share and change all versions of a program--to make sure it remains free +software for all its users. We, the Free Software Foundation, use the +GNU General Public License for most of our software; it applies also to +any other work released this way by its authors. You can apply it to +your programs, too. + + When we speak of free software, we are referring to freedom, not +price. Our General Public Licenses are designed to make sure that you +have the freedom to distribute copies of free software (and charge for +them if you wish), that you receive source code or can get it if you +want it, that you can change the software or use pieces of it in new +free programs, and that you know you can do these things. + + To protect your rights, we need to prevent others from denying you +these rights or asking you to surrender the rights. Therefore, you have +certain responsibilities if you distribute copies of the software, or if +you modify it: responsibilities to respect the freedom of others. + + For example, if you distribute copies of such a program, whether +gratis or for a fee, you must pass on to the recipients the same +freedoms that you received. You must make sure that they, too, receive +or can get the source code. And you must show them these terms so they +know their rights. + + Developers that use the GNU GPL protect your rights with two steps: +(1) assert copyright on the software, and (2) offer you this License +giving you legal permission to copy, distribute and/or modify it. + + For the developers' and authors' protection, the GPL clearly explains +that there is no warranty for this free software. For both users' and +authors' sake, the GPL requires that modified versions be marked as +changed, so that their problems will not be attributed erroneously to +authors of previous versions. + + Some devices are designed to deny users access to install or run +modified versions of the software inside them, although the manufacturer +can do so. This is fundamentally incompatible with the aim of +protecting users' freedom to change the software. The systematic +pattern of such abuse occurs in the area of products for individuals to +use, which is precisely where it is most unacceptable. Therefore, we +have designed this version of the GPL to prohibit the practice for those +products. If such problems arise substantially in other domains, we +stand ready to extend this provision to those domains in future versions +of the GPL, as needed to protect the freedom of users. + + Finally, every program is threatened constantly by software patents. +States should not allow patents to restrict development and use of +software on general-purpose computers, but in those that do, we wish to +avoid the special danger that patents applied to a free program could +make it effectively proprietary. To prevent this, the GPL assures that +patents cannot be used to render the program non-free. + + The precise terms and conditions for copying, distribution and +modification follow. + + TERMS AND CONDITIONS + + 0. Definitions. + + "This License" refers to version 3 of the GNU General Public License. + + "Copyright" also means copyright-like laws that apply to other kinds of +works, such as semiconductor masks. + + "The Program" refers to any copyrightable work licensed under this +License. Each licensee is addressed as "you". "Licensees" and +"recipients" may be individuals or organizations. + + To "modify" a work means to copy from or adapt all or part of the work +in a fashion requiring copyright permission, other than the making of an +exact copy. The resulting work is called a "modified version" of the +earlier work or a work "based on" the earlier work. + + A "covered work" means either the unmodified Program or a work based +on the Program. + + To "propagate" a work means to do anything with it that, without +permission, would make you directly or secondarily liable for +infringement under applicable copyright law, except executing it on a +computer or modifying a private copy. Propagation includes copying, +distribution (with or without modification), making available to the +public, and in some countries other activities as well. + + To "convey" a work means any kind of propagation that enables other +parties to make or receive copies. Mere interaction with a user through +a computer network, with no transfer of a copy, is not conveying. + + An interactive user interface displays "Appropriate Legal Notices" +to the extent that it includes a convenient and prominently visible +feature that (1) displays an appropriate copyright notice, and (2) +tells the user that there is no warranty for the work (except to the +extent that warranties are provided), that licensees may convey the +work under this License, and how to view a copy of this License. If +the interface presents a list of user commands or options, such as a +menu, a prominent item in the list meets this criterion. + + 1. Source Code. + + The "source code" for a work means the preferred form of the work +for making modifications to it. "Object code" means any non-source +form of a work. + + A "Standard Interface" means an interface that either is an official +standard defined by a recognized standards body, or, in the case of +interfaces specified for a particular programming language, one that +is widely used among developers working in that language. + + The "System Libraries" of an executable work include anything, other +than the work as a whole, that (a) is included in the normal form of +packaging a Major Component, but which is not part of that Major +Component, and (b) serves only to enable use of the work with that +Major Component, or to implement a Standard Interface for which an +implementation is available to the public in source code form. A +"Major Component", in this context, means a major essential component +(kernel, window system, and so on) of the specific operating system +(if any) on which the executable work runs, or a compiler used to +produce the work, or an object code interpreter used to run it. + + The "Corresponding Source" for a work in object code form means all +the source code needed to generate, install, and (for an executable +work) run the object code and to modify the work, including scripts to +control those activities. However, it does not include the work's +System Libraries, or general-purpose tools or generally available free +programs which are used unmodified in performing those activities but +which are not part of the work. For example, Corresponding Source +includes interface definition files associated with source files for +the work, and the source code for shared libraries and dynamically +linked subprograms that the work is specifically designed to require, +such as by intimate data communication or control flow between those +subprograms and other parts of the work. + + The Corresponding Source need not include anything that users +can regenerate automatically from other parts of the Corresponding +Source. + + The Corresponding Source for a work in source code form is that +same work. + + 2. Basic Permissions. + + All rights granted under this License are granted for the term of +copyright on the Program, and are irrevocable provided the stated +conditions are met. This License explicitly affirms your unlimited +permission to run the unmodified Program. The output from running a +covered work is covered by this License only if the output, given its +content, constitutes a covered work. This License acknowledges your +rights of fair use or other equivalent, as provided by copyright law. + + You may make, run and propagate covered works that you do not +convey, without conditions so long as your license otherwise remains +in force. You may convey covered works to others for the sole purpose +of having them make modifications exclusively for you, or provide you +with facilities for running those works, provided that you comply with +the terms of this License in conveying all material for which you do +not control copyright. Those thus making or running the covered works +for you must do so exclusively on your behalf, under your direction +and control, on terms that prohibit them from making any copies of +your copyrighted material outside their relationship with you. + + Conveying under any other circumstances is permitted solely under +the conditions stated below. Sublicensing is not allowed; section 10 +makes it unnecessary. + + 3. Protecting Users' Legal Rights From Anti-Circumvention Law. + + No covered work shall be deemed part of an effective technological +measure under any applicable law fulfilling obligations under article +11 of the WIPO copyright treaty adopted on 20 December 1996, or +similar laws prohibiting or restricting circumvention of such +measures. + + When you convey a covered work, you waive any legal power to forbid +circumvention of technological measures to the extent such circumvention +is effected by exercising rights under this License with respect to +the covered work, and you disclaim any intention to limit operation or +modification of the work as a means of enforcing, against the work's +users, your or third parties' legal rights to forbid circumvention of +technological measures. + + 4. Conveying Verbatim Copies. + + You may convey verbatim copies of the Program's source code as you +receive it, in any medium, provided that you conspicuously and +appropriately publish on each copy an appropriate copyright notice; +keep intact all notices stating that this License and any +non-permissive terms added in accord with section 7 apply to the code; +keep intact all notices of the absence of any warranty; and give all +recipients a copy of this License along with the Program. + + You may charge any price or no price for each copy that you convey, +and you may offer support or warranty protection for a fee. + + 5. Conveying Modified Source Versions. + + You may convey a work based on the Program, or the modifications to +produce it from the Program, in the form of source code under the +terms of section 4, provided that you also meet all of these conditions: + + a) The work must carry prominent notices stating that you modified + it, and giving a relevant date. + + b) The work must carry prominent notices stating that it is + released under this License and any conditions added under section + 7. This requirement modifies the requirement in section 4 to + "keep intact all notices". + + c) You must license the entire work, as a whole, under this + License to anyone who comes into possession of a copy. This + License will therefore apply, along with any applicable section 7 + additional terms, to the whole of the work, and all its parts, + regardless of how they are packaged. This License gives no + permission to license the work in any other way, but it does not + invalidate such permission if you have separately received it. + + d) If the work has interactive user interfaces, each must display + Appropriate Legal Notices; however, if the Program has interactive + interfaces that do not display Appropriate Legal Notices, your + work need not make them do so. + + A compilation of a covered work with other separate and independent +works, which are not by their nature extensions of the covered work, +and which are not combined with it such as to form a larger program, +in or on a volume of a storage or distribution medium, is called an +"aggregate" if the compilation and its resulting copyright are not +used to limit the access or legal rights of the compilation's users +beyond what the individual works permit. Inclusion of a covered work +in an aggregate does not cause this License to apply to the other +parts of the aggregate. + + 6. Conveying Non-Source Forms. + + You may convey a covered work in object code form under the terms +of sections 4 and 5, provided that you also convey the +machine-readable Corresponding Source under the terms of this License, +in one of these ways: + + a) Convey the object code in, or embodied in, a physical product + (including a physical distribution medium), accompanied by the + Corresponding Source fixed on a durable physical medium + customarily used for software interchange. + + b) Convey the object code in, or embodied in, a physical product + (including a physical distribution medium), accompanied by a + written offer, valid for at least three years and valid for as + long as you offer spare parts or customer support for that product + model, to give anyone who possesses the object code either (1) a + copy of the Corresponding Source for all the software in the + product that is covered by this License, on a durable physical + medium customarily used for software interchange, for a price no + more than your reasonable cost of physically performing this + conveying of source, or (2) access to copy the + Corresponding Source from a network server at no charge. + + c) Convey individual copies of the object code with a copy of the + written offer to provide the Corresponding Source. This + alternative is allowed only occasionally and noncommercially, and + only if you received the object code with such an offer, in accord + with subsection 6b. + + d) Convey the object code by offering access from a designated + place (gratis or for a charge), and offer equivalent access to the + Corresponding Source in the same way through the same place at no + further charge. You need not require recipients to copy the + Corresponding Source along with the object code. If the place to + copy the object code is a network server, the Corresponding Source + may be on a different server (operated by you or a third party) + that supports equivalent copying facilities, provided you maintain + clear directions next to the object code saying where to find the + Corresponding Source. Regardless of what server hosts the + Corresponding Source, you remain obligated to ensure that it is + available for as long as needed to satisfy these requirements. + + e) Convey the object code using peer-to-peer transmission, provided + you inform other peers where the object code and Corresponding + Source of the work are being offered to the general public at no + charge under subsection 6d. + + A separable portion of the object code, whose source code is excluded +from the Corresponding Source as a System Library, need not be +included in conveying the object code work. + + A "User Product" is either (1) a "consumer product", which means any +tangible personal property which is normally used for personal, family, +or household purposes, or (2) anything designed or sold for incorporation +into a dwelling. In determining whether a product is a consumer product, +doubtful cases shall be resolved in favor of coverage. For a particular +product received by a particular user, "normally used" refers to a +typical or common use of that class of product, regardless of the status +of the particular user or of the way in which the particular user +actually uses, or expects or is expected to use, the product. A product +is a consumer product regardless of whether the product has substantial +commercial, industrial or non-consumer uses, unless such uses represent +the only significant mode of use of the product. + + "Installation Information" for a User Product means any methods, +procedures, authorization keys, or other information required to install +and execute modified versions of a covered work in that User Product from +a modified version of its Corresponding Source. The information must +suffice to ensure that the continued functioning of the modified object +code is in no case prevented or interfered with solely because +modification has been made. + + If you convey an object code work under this section in, or with, or +specifically for use in, a User Product, and the conveying occurs as +part of a transaction in which the right of possession and use of the +User Product is transferred to the recipient in perpetuity or for a +fixed term (regardless of how the transaction is characterized), the +Corresponding Source conveyed under this section must be accompanied +by the Installation Information. But this requirement does not apply +if neither you nor any third party retains the ability to install +modified object code on the User Product (for example, the work has +been installed in ROM). + + The requirement to provide Installation Information does not include a +requirement to continue to provide support service, warranty, or updates +for a work that has been modified or installed by the recipient, or for +the User Product in which it has been modified or installed. Access to a +network may be denied when the modification itself materially and +adversely affects the operation of the network or violates the rules and +protocols for communication across the network. + + Corresponding Source conveyed, and Installation Information provided, +in accord with this section must be in a format that is publicly +documented (and with an implementation available to the public in +source code form), and must require no special password or key for +unpacking, reading or copying. + + 7. Additional Terms. + + "Additional permissions" are terms that supplement the terms of this +License by making exceptions from one or more of its conditions. +Additional permissions that are applicable to the entire Program shall +be treated as though they were included in this License, to the extent +that they are valid under applicable law. If additional permissions +apply only to part of the Program, that part may be used separately +under those permissions, but the entire Program remains governed by +this License without regard to the additional permissions. + + When you convey a copy of a covered work, you may at your option +remove any additional permissions from that copy, or from any part of +it. (Additional permissions may be written to require their own +removal in certain cases when you modify the work.) You may place +additional permissions on material, added by you to a covered work, +for which you have or can give appropriate copyright permission. + + Notwithstanding any other provision of this License, for material you +add to a covered work, you may (if authorized by the copyright holders of +that material) supplement the terms of this License with terms: + + a) Disclaiming warranty or limiting liability differently from the + terms of sections 15 and 16 of this License; or + + b) Requiring preservation of specified reasonable legal notices or + author attributions in that material or in the Appropriate Legal + Notices displayed by works containing it; or + + c) Prohibiting misrepresentation of the origin of that material, or + requiring that modified versions of such material be marked in + reasonable ways as different from the original version; or + + d) Limiting the use for publicity purposes of names of licensors or + authors of the material; or + + e) Declining to grant rights under trademark law for use of some + trade names, trademarks, or service marks; or + + f) Requiring indemnification of licensors and authors of that + material by anyone who conveys the material (or modified versions of + it) with contractual assumptions of liability to the recipient, for + any liability that these contractual assumptions directly impose on + those licensors and authors. + + All other non-permissive additional terms are considered "further +restrictions" within the meaning of section 10. If the Program as you +received it, or any part of it, contains a notice stating that it is +governed by this License along with a term that is a further +restriction, you may remove that term. If a license document contains +a further restriction but permits relicensing or conveying under this +License, you may add to a covered work material governed by the terms +of that license document, provided that the further restriction does +not survive such relicensing or conveying. + + If you add terms to a covered work in accord with this section, you +must place, in the relevant source files, a statement of the +additional terms that apply to those files, or a notice indicating +where to find the applicable terms. + + Additional terms, permissive or non-permissive, may be stated in the +form of a separately written license, or stated as exceptions; +the above requirements apply either way. + + 8. Termination. + + You may not propagate or modify a covered work except as expressly +provided under this License. Any attempt otherwise to propagate or +modify it is void, and will automatically terminate your rights under +this License (including any patent licenses granted under the third +paragraph of section 11). + + However, if you cease all violation of this License, then your +license from a particular copyright holder is reinstated (a) +provisionally, unless and until the copyright holder explicitly and +finally terminates your license, and (b) permanently, if the copyright +holder fails to notify you of the violation by some reasonable means +prior to 60 days after the cessation. + + Moreover, your license from a particular copyright holder is +reinstated permanently if the copyright holder notifies you of the +violation by some reasonable means, this is the first time you have +received notice of violation of this License (for any work) from that +copyright holder, and you cure the violation prior to 30 days after +your receipt of the notice. + + Termination of your rights under this section does not terminate the +licenses of parties who have received copies or rights from you under +this License. If your rights have been terminated and not permanently +reinstated, you do not qualify to receive new licenses for the same +material under section 10. + + 9. Acceptance Not Required for Having Copies. + + You are not required to accept this License in order to receive or +run a copy of the Program. Ancillary propagation of a covered work +occurring solely as a consequence of using peer-to-peer transmission +to receive a copy likewise does not require acceptance. However, +nothing other than this License grants you permission to propagate or +modify any covered work. These actions infringe copyright if you do +not accept this License. Therefore, by modifying or propagating a +covered work, you indicate your acceptance of this License to do so. + + 10. Automatic Licensing of Downstream Recipients. + + Each time you convey a covered work, the recipient automatically +receives a license from the original licensors, to run, modify and +propagate that work, subject to this License. You are not responsible +for enforcing compliance by third parties with this License. + + An "entity transaction" is a transaction transferring control of an +organization, or substantially all assets of one, or subdividing an +organization, or merging organizations. If propagation of a covered +work results from an entity transaction, each party to that +transaction who receives a copy of the work also receives whatever +licenses to the work the party's predecessor in interest had or could +give under the previous paragraph, plus a right to possession of the +Corresponding Source of the work from the predecessor in interest, if +the predecessor has it or can get it with reasonable efforts. + + You may not impose any further restrictions on the exercise of the +rights granted or affirmed under this License. For example, you may +not impose a license fee, royalty, or other charge for exercise of +rights granted under this License, and you may not initiate litigation +(including a cross-claim or counterclaim in a lawsuit) alleging that +any patent claim is infringed by making, using, selling, offering for +sale, or importing the Program or any portion of it. + + 11. Patents. + + A "contributor" is a copyright holder who authorizes use under this +License of the Program or a work on which the Program is based. The +work thus licensed is called the contributor's "contributor version". + + A contributor's "essential patent claims" are all patent claims +owned or controlled by the contributor, whether already acquired or +hereafter acquired, that would be infringed by some manner, permitted +by this License, of making, using, or selling its contributor version, +but do not include claims that would be infringed only as a +consequence of further modification of the contributor version. For +purposes of this definition, "control" includes the right to grant +patent sublicenses in a manner consistent with the requirements of +this License. + + Each contributor grants you a non-exclusive, worldwide, royalty-free +patent license under the contributor's essential patent claims, to +make, use, sell, offer for sale, import and otherwise run, modify and +propagate the contents of its contributor version. + + In the following three paragraphs, a "patent license" is any express +agreement or commitment, however denominated, not to enforce a patent +(such as an express permission to practice a patent or covenant not to +sue for patent infringement). To "grant" such a patent license to a +party means to make such an agreement or commitment not to enforce a +patent against the party. + + If you convey a covered work, knowingly relying on a patent license, +and the Corresponding Source of the work is not available for anyone +to copy, free of charge and under the terms of this License, through a +publicly available network server or other readily accessible means, +then you must either (1) cause the Corresponding Source to be so +available, or (2) arrange to deprive yourself of the benefit of the +patent license for this particular work, or (3) arrange, in a manner +consistent with the requirements of this License, to extend the patent +license to downstream recipients. "Knowingly relying" means you have +actual knowledge that, but for the patent license, your conveying the +covered work in a country, or your recipient's use of the covered work +in a country, would infringe one or more identifiable patents in that +country that you have reason to believe are valid. + + If, pursuant to or in connection with a single transaction or +arrangement, you convey, or propagate by procuring conveyance of, a +covered work, and grant a patent license to some of the parties +receiving the covered work authorizing them to use, propagate, modify +or convey a specific copy of the covered work, then the patent license +you grant is automatically extended to all recipients of the covered +work and works based on it. + + A patent license is "discriminatory" if it does not include within +the scope of its coverage, prohibits the exercise of, or is +conditioned on the non-exercise of one or more of the rights that are +specifically granted under this License. You may not convey a covered +work if you are a party to an arrangement with a third party that is +in the business of distributing software, under which you make payment +to the third party based on the extent of your activity of conveying +the work, and under which the third party grants, to any of the +parties who would receive the covered work from you, a discriminatory +patent license (a) in connection with copies of the covered work +conveyed by you (or copies made from those copies), or (b) primarily +for and in connection with specific products or compilations that +contain the covered work, unless you entered into that arrangement, +or that patent license was granted, prior to 28 March 2007. + + Nothing in this License shall be construed as excluding or limiting +any implied license or other defenses to infringement that may +otherwise be available to you under applicable patent law. + + 12. No Surrender of Others' Freedom. + + If conditions are imposed on you (whether by court order, agreement or +otherwise) that contradict the conditions of this License, they do not +excuse you from the conditions of this License. If you cannot convey a +covered work so as to satisfy simultaneously your obligations under this +License and any other pertinent obligations, then as a consequence you may +not convey it at all. For example, if you agree to terms that obligate you +to collect a royalty for further conveying from those to whom you convey +the Program, the only way you could satisfy both those terms and this +License would be to refrain entirely from conveying the Program. + + 13. Use with the GNU Affero General Public License. + + Notwithstanding any other provision of this License, you have +permission to link or combine any covered work with a work licensed +under version 3 of the GNU Affero General Public License into a single +combined work, and to convey the resulting work. The terms of this +License will continue to apply to the part which is the covered work, +but the special requirements of the GNU Affero General Public License, +section 13, concerning interaction through a network will apply to the +combination as such. + + 14. Revised Versions of this License. + + The Free Software Foundation may publish revised and/or new versions of +the GNU General Public License from time to time. Such new versions will +be similar in spirit to the present version, but may differ in detail to +address new problems or concerns. + + Each version is given a distinguishing version number. If the +Program specifies that a certain numbered version of the GNU General +Public License "or any later version" applies to it, you have the +option of following the terms and conditions either of that numbered +version or of any later version published by the Free Software +Foundation. If the Program does not specify a version number of the +GNU General Public License, you may choose any version ever published +by the Free Software Foundation. + + If the Program specifies that a proxy can decide which future +versions of the GNU General Public License can be used, that proxy's +public statement of acceptance of a version permanently authorizes you +to choose that version for the Program. + + Later license versions may give you additional or different +permissions. However, no additional obligations are imposed on any +author or copyright holder as a result of your choosing to follow a +later version. + + 15. Disclaimer of Warranty. + + THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY +APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT +HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY +OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, +THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR +PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM +IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF +ALL NECESSARY SERVICING, REPAIR OR CORRECTION. + + 16. Limitation of Liability. + + IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING +WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS +THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY +GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE +USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF +DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD +PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), +EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF +SUCH DAMAGES. + + 17. Interpretation of Sections 15 and 16. + + If the disclaimer of warranty and limitation of liability provided +above cannot be given local legal effect according to their terms, +reviewing courts shall apply local law that most closely approximates +an absolute waiver of all civil liability in connection with the +Program, unless a warranty or assumption of liability accompanies a +copy of the Program in return for a fee. + + END OF TERMS AND CONDITIONS + + How to Apply These Terms to Your New Programs + + If you develop a new program, and you want it to be of the greatest +possible use to the public, the best way to achieve this is to make it +free software which everyone can redistribute and change under these terms. + + To do so, attach the following notices to the program. It is safest +to attach them to the start of each source file to most effectively +state the exclusion of warranty; and each file should have at least +the "copyright" line and a pointer to where the full notice is found. + + + Copyright (C) + + This program is free software: you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation, either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see . + +Also add information on how to contact you by electronic and paper mail. + + If the program does terminal interaction, make it output a short +notice like this when it starts in an interactive mode: + + Copyright (C) + This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. + This is free software, and you are welcome to redistribute it + under certain conditions; type `show c' for details. + +The hypothetical commands `show w' and `show c' should show the appropriate +parts of the General Public License. Of course, your program's commands +might be different; for a GUI interface, you would use an "about box". + + You should also get your employer (if you work as a programmer) or school, +if any, to sign a "copyright disclaimer" for the program, if necessary. +For more information on this, and how to apply and follow the GNU GPL, see +. + + The GNU General Public License does not permit incorporating your program +into proprietary programs. If your program is a subroutine library, you +may consider it more useful to permit linking proprietary applications with +the library. If this is what you want to do, use the GNU Lesser General +Public License instead of this License. But first, please read +. diff --git a/hill.lisp b/hill.lisp new file mode 100644 index 0000000..347b21a --- /dev/null +++ b/hill.lisp @@ -0,0 +1,432 @@ +;; hill.lisp - A very bad implementation of a hill cipher along with some +;; unnessesary, insecure PRNG key stuff. +;; +;; This file is free software under the terms of the GPL3 license. You can find +;; a copy of the license at: https://www.gnu.org/licenses/gpl-3.0.en.html + +;; PRNG subroutines +(defparameter *system-rng-stream* + (open "/dev/random" :element-type '(unsigned-byte 8))) + +(defun number-bits (num) + "Return the number of bits in NUM." + (ceiling (log num 2))) + +(defun get-random (&key (size 8) (rng-stream *system-rng-stream*)) + "Read SIZE random bytes from the systems high-quality random source." + (let ((read-buf (make-array size))) + (read-sequence read-buf rng-stream) + (loop with out-val = 0 + for part across read-buf do + (setq out-val (+ (ash out-val 8) part)) + finally (return out-val)))) + +(defun xorshift*64 (seed) + "Generate the next number in the xorshift* sequence starting or continuing +from SEED. That is, SEED should either be an initial, non-zero seed or the last +number generated in the sequence." + (setq seed (logxor seed (ash seed -12)) + seed (logxor seed (ash seed 25)) + seed (logxor seed (ash seed -27))) + ;; #x2545F4914F6CDD1DULL + (logand (* seed 2685821657736338717) + #xFFFFFFFFFFFFFFFF)) + +(defun rand-clamp (num &key (bits 64) (min 0 has-min-p) + (max (1- (expt 2 bits)) has-max-p)) + "Clamp the randomly generated number NUM to between [MIN, MAX]. The random +numbers is assumed to be between 0 and 2^BITS - 1." + (if (or has-min-p has-max-p) + (+ (* (- max min) (/ num (1- (expt 2 bits)))) min) + num)) + +(defclass xorshift*64-stream () + ((state :initarg :seed + :initform 1 + :documentation "The last generated number. If no number has yet been +generated, this is the seed.")) + (:documentation "A stream of random numbers generated and xorshift*64 +algorithm.")) + +(defun make-xorshift* (&key (seed (get-random)) (bits 64)) + (case bits + (64 (make-instance 'xorshift*64-stream :seed seed)) + (t (error "Invalid prandom number size: ~d" bits)))) + +(defmethod next-int ((stream xorshift*64-stream) &key (max #xFFFFFFFFFFFFFFFF) + (min 0)) + "Get the next random integer between MIN and MAX from STREAM." + (with-slots (state) stream + (setf state (xorshift*64 state)) + (floor (rand-clamp state :bits 64 :max max :min min)))) + +(defparameter *default-rng* (make-xorshift*) + "The default RNG source to use when generating matrices.") + +;; Matrix subroutines +(defun mat-minor (transpose-mat i j) + "Find the minor of MAT for I and J." + (destructuring-bind (height width) + (array-dimensions transpose-mat) + (let ((minor (make-array (list (1- height) + (1- width))))) + (dotimes (row height minor) + (dotimes (col width) + (unless (or (= row i) + (= col j)) + (let ((out-row (if (> row i) + (1- row) + row)) + (out-col (if (> col j) + (1- col) + col))) + (setf (aref minor out-row out-col) (aref transpose-mat row col))))))))) + +(defun cofactor-sgn (i j) + "Return the sign of the cofactor at I and J." + (expt -1 (+ i j))) + +(defun cofactor (mat i j) + "Find the cofactor for I and J in MAT." + (* (cofactor-sgn i j) (det (mat-minor mat i j)))) + +(defun first-column-cofactors (mat) + "Find the cofactors for the first column of MAT." + (let* ((height (array-dimension mat 0)) + (out-arr (make-array height))) + (dotimes (i height out-arr) + (setf (aref out-arr i) (cofactor mat i 0))))) + +(defun det2x2 (mat) + "Find the determinate of a 2x2 matrix MAT." + (let ((a (aref mat 0 0)) + (b (aref mat 0 1)) + (c (aref mat 1 0)) + (d (aref mat 1 1))) + (- (* a d) (* b c)))) + +(defun det (mat &key first-column-cofactors) + "Find the determinant of MAT. If the cofactors for the first column have +already been calculated, they can be supplied in FIRST-COLUMN-COFACTORS." + (destructuring-bind (height width) + (array-dimensions mat) + (if (and (= height 2) + (= width 2)) + (det2x2 mat) + (loop for i below height + when first-column-cofactors + summing (* (aref mat i 0) (aref first-column-cofactors i)) + else + summing (* (aref mat i 0) (cofactor mat i 0)))))) + +(defun map-mat (function mat) + "Return a new matrix of the same dimensions as MAT, with each element being +the result of applying FUNCTION to each index of MAT. FUNCTION is passed two +values, (i j), where i and j are the row and column of the element." + (destructuring-bind (height width) + (array-dimensions mat) + (let ((out-mat (make-array (list height width)))) + (dotimes (row height out-mat) + (dotimes (col width) + (setf (aref out-mat row col) + (funcall function row col))))))) + +(defun extended-gcd (n1 n2) + "Return the greatest common denominator of N1 and N2. As a second value, +return a cons of (x . y) such char x * N1 + y * N2 = GCD." + (if (zerop n1) + (values n2 (cons 0 1)) + (multiple-value-bind (div rem) (floor n2 n1) + (destructuring-bind (gcd (x . y)) + (multiple-value-list (extended-gcd rem n1)) + (values gcd (cons (- y (* div x)) x)))))) + +(defun modular-multiplicative-inverse (n m) + "Find the modular multiplicative inverse of N with respect to M. That is, some +integer i such that (N * i) mod M = 1." + (destructuring-bind (gcd (x . y)) + (multiple-value-list (extended-gcd n m)) + (declare (ignorable y)) + (unless (= 1 gcd) + (error "N and M must be coprime. N: ~d, M: ~d" n m)) + (+ x m))) + +(defun modular-inverse-det (mat modulo &key first-column-cofactors) + "Calculate the inverse determinant of MAT under MODULO. If MODULO is nil, this +is just 1/det." + (let ((det (det mat :first-column-cofactors first-column-cofactors))) + (if modulo + (modular-multiplicative-inverse det modulo) + (/ det)))) + +(defun invert-2x2-mat (mat &key modulo) + "Invert the 2x2 matrix MAT." + (let ((a (aref mat 0 0)) + (b (aref mat 0 1)) + (c (aref mat 1 0)) + (d (aref mat 1 1)) + (ood (modular-inverse-det mat modulo))) + (make-array '(2 2) + :initial-contents (list (list (* ood d) (* ood (- b))) + (list (* ood (- c)) (* ood a)))))) + +(defun invert-mat (mat &key modulo) + "Invert MAT. This naively assumes that MAT is not singular." + (destructuring-bind (height width) + (array-dimensions mat) + (if (and (= width 2) + (= height 2)) + (invert-2x2-mat mat :modulo modulo) + (let* ((first-column-cofactors (first-column-cofactors mat)) + (one-over-det (modular-inverse-det mat modulo + :first-column-cofactors + first-column-cofactors))) + (map-mat (lambda (i j) + ;; this calculates 1/det * adjugate[i][j] + (* one-over-det + (if (and first-column-cofactors (zerop i)) + (aref first-column-cofactors j) + (cofactor mat j i)))) + mat))))) + +(defun transpose-mat (mat) + "Transpose MAT." + (map-mat (lambda (i j) + (aref mat j i)) + mat)) + +(defun dot-row-col (mat1 mat2 row col) + "Take the dot (scalar) product of ROW of MAT1 and COL of MAT2." + (let ((sum 0)) + (dotimes (n (array-dimension mat2 0) sum) + (setq sum (+ sum (* (aref mat1 row n) + (aref mat2 n col))))))) + +(defun *mm (mat1 mat2 &key modulo) + "Multiply MAT1 by MAT2. This naively assumes that these matrices can be +multiplied without issue. The result will be taken under MODULO, if it is +non-nil." + (let* ((width (array-dimension mat1 0)) + (height (array-dimension mat2 1)) + (out-mat (make-array (list height width)))) + (dotimes (i height out-mat) + (dotimes (j width) + (let ((dot (dot-row-col mat1 mat2 i j))) + (setf (aref out-mat i j) + (if modulo + (mod dot modulo) + dot))))))) + +(defun *mv (mat vec &key modulo) + "Multiply MAT by VEC. This naively assumes that these can be multiplied +without issue. The result will be taken under MODULO, if it is non-nil." + (let* ((width (array-dimension mat 1)) + (height (array-dimension mat 0)) + (out-vec (make-array height))) + (dotimes (row height out-vec) + (setf (aref out-vec row) + (loop for col below width + summing (* (aref vec col) (aref mat row col)) into sum + finally (return (if modulo + (mod sum modulo) + sum))))))) + +(defun generate-matrix (width height &key (rng *default-rng*) max) + "Generate a random matrix of size WIDTH x HEIGHT. Use RNG to get the random +data for this matrix." + (map-mat (lambda (i j) + (declare (ignorable i j)) + (if max + (next-int rng :max max) + (next-int rng))) + (make-array (list height width)))) + +(defun generate-invertible-matrix (width height &key (rng *default-rng*) max) + "Generate a random invertible matrix of size WIDTH x HEIGHT. Use RNG to get +the random data for this matrix. This generates a strictly diagonally dominant +matrix." + (let ((rand-mat (generate-matrix width height :rng rng :max max))) + (dotimes (row height rand-mat) + (let ((sum 0)) + (dotimes (col width) + (setq sum (+ sum (abs (aref rand-mat row col))))) + (setf (aref rand-mat row row) sum))))) + +;; Base64 subroutines +(defparameter +base64-alphabet+ + "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" + "Lookup table for base64 encode.") + +(defparameter +inverse-base64-alphabet+ + (loop with alph = (make-array 123 :initial-element 0) + for i below (length +base64-alphabet+) + for char = (aref +base64-alphabet+ i) + do (setf (aref alph (char-code char)) i) + finally (return alph)) + "Inverse lookup table for base64 decode.") + +(defun base64-encode-block (b1 &optional b2 b3) + "Base64 encode B1, B2, and B3, each of which should be a single byte. The +result of this function is a list of the 4 encoded characters." + ;; allow B2 and B3 to be nil, so we can't just check if they where passed, we + ;; need to know if they where nil when the function was called + (let ((has-b2-p b2) + (has-b3-p b3)) + (unless b2 + (setq b2 0)) + (unless b3 + (setq b3 0)) + (let ((e1 (ash (logand b1 #b11111100) -2)) + (e2 (logior (ash (logand b1 #b11) 4) + (ash (logand b2 #b11110000) -4))) + (e3 (logior (ash (logand b2 #b1111) 2) + (ash (logand b3 #b11000000) -6))) + (e4 (logand b3 #b111111))) + (cond + ((and has-b2-p has-b3-p) + (list (aref +base64-alphabet+ e1) + (aref +base64-alphabet+ e2) + (aref +base64-alphabet+ e3) + (aref +base64-alphabet+ e4))) + (has-b2-p + (list (aref +base64-alphabet+ e1) + (aref +base64-alphabet+ e2) + (aref +base64-alphabet+ e3) + #\=)) + (t + (list (aref +base64-alphabet+ e1) + (aref +base64-alphabet+ e2) + #\= #\=)))))) + +(defun base64-encode (data) + "Encode DATA, a vector of numbers, as base64." + (loop with output = () + for i upfrom 0 by 3 below (- (length data) 2) + do (setf output (nconc (nreverse (base64-encode-block + (aref data i) + (aref data (+ i 1)) + (aref data (+ i 2)))) + output)) + finally + (return + (coerce (if (< i (length data)) + (let ((b1 (aref data i)) + (b2 (when (< (1+ i) (length data)) + (aref data (1+ i))))) + (nreverse (nconc (nreverse + (base64-encode-block b1 b2)) + output))) + (nreverse output)) + 'string)))) + +(defun base64-decode-block (e1 e2 e3 e4) + "Base64 decode E1, E2, E3, and E4, each of which is a single character. The +result of this function is a list of 3 bytes." + (let ((i1 (aref +inverse-base64-alphabet+ (char-code e1))) + (i2 (aref +inverse-base64-alphabet+ (char-code e2))) + (i3 (aref +inverse-base64-alphabet+ (char-code e3))) + (i4 (aref +inverse-base64-alphabet+ (char-code e4)))) + (list (logior (ash i1 2) + (ash (logand i2 #b110000) -4)) + (unless (eq e3 #\=) + (logior (ash (logand i2 #b1111) 4) + (ash (logand i3 #b111100) -2))) + (unless (eq e4 #\=) + (logior (ash (logand i3 #b11) 6) + i4))))) + +(defun base64-decode (data) + "Decode DATA, a string, as base64." + (coerce (loop for i upfrom 0 by 4 below (length data) + append (delete-if 'null + (base64-decode-block (aref data i) + (aref data (+ i 1)) + (aref data (+ i 2)) + (aref data (+ i 3))))) + 'vector)) + +;; Hill subroutines +(defun nth-hill-block (plain n &key (size 4)) + "Get the Nth hill block in PLAIN. If there are not enough characters in PLAIN, +pad the block with zeros. Each block is SIZE characters." + (let* ((start (* size n)) + (end (+ start size))) + (when (< (length plain) end) + (setq end (+ start (- (length plain) start)))) + (cond + ((> start (length plain)) + (make-array size :initial-element 0)) + ((>= end (length plain)) + (loop with out-vec = (make-array size :initial-element 0 :fill-pointer 0) + for elem across (subseq plain start (length plain)) do + (vector-push elem out-vec) + finally + (setf (fill-pointer out-vec) size) + (return out-vec))) + (t + (subseq plain start end))))) + +(defun hill-block-count (plain &key (size 4)) + "Return the number of hill blocks in PLAIN." + (ceiling (length plain) size)) + +(defmacro do-hill-blocks ((var plain &optional retval) (&key (size 4)) + &body body) + "Evaluate BODY once for each hill cipher block in PLAIN, with VAR bound to +that block." + (let ((i-var (gensym)) + (plain-var (gensym))) + `(let ((,plain-var ,plain)) + (dotimes (,i-var (hill-block-count ,plain-var :size ,size) ,retval) + (let ((,var (nth-hill-block ,plain-var ,i-var :size ,size))) + ,@body))))) + +(defun make-hill-matrix (key &key (size 4)) + "Get the hill cipher matrix for KEY and block size SIZE." + (let ((rng (make-xorshift* :seed key))) + (generate-invertible-matrix size size :rng rng :max 128))) + +(defun hill-process (data mat size dict-size) + "Perform hill encryption or decryption on DATA. Each block is SIZE bytes. MAT +is taken to be the key matrix (or its inverse). DICT-SIZE is the modulus." + (let ((processed (make-array 0))) + (do-hill-blocks (bl data (map 'vector (lambda (elem) + (mod elem dict-size)) + processed)) + (:size size) + (setq processed (concatenate 'vector processed + (*mv mat bl)))))) + +(defun hill-encrypt (plain key &key (size 4) (dict-size 251)) + "Encrypt PLAIN using a hill cipher, using KEY as the secret and SIZE as the +block size. DICT-SIZE is the largest character code in PLAIN." + (hill-process (map 'vector 'char-code plain) + (make-hill-matrix key :size size) + size dict-size)) + +(defun make-inverse-hill-matrix (key &key (size 4) (dict-size 251)) + "Create an inverse hill matrix for KEY. SIZE and DICT-SIZE are as they are to +`hill-decrypt'." + (invert-mat (make-hill-matrix key :size size) :modulo dict-size)) + +(defun hill-remove-padding (plain-vec) + "Remove trailing null bytes from PLAIN-VEC." + (loop for i downfrom (1- (length plain-vec)) + while (and (>= i 0) (eq (aref plain-vec i) #\Nul)) + finally (return (subseq plain-vec 0 (1+ i))))) + +(defun hill-decrypt (cipher key &key (size 4) (dict-size 251)) + "Perform the inverse operation of `hill-encrypt', restoring the plaintext +of CIPHER that was encrypted using KEY with a block size of SIZE. DICT-SIZE must +be the same value originally used to encrypt the text." + (coerce (hill-remove-padding + (map 'vector 'code-char + (hill-process cipher + (make-inverse-hill-matrix key :size size + :dict-size dict-size) + size dict-size))) + 'string)) + +;; Local Variables: +;; jinx-local-words: "adjugate cofactor cofactors det plaintext prandom unnessesary xorshift" +;; End: diff --git a/shift-affine.lisp b/shift-affine.lisp new file mode 100644 index 0000000..13549e8 --- /dev/null +++ b/shift-affine.lisp @@ -0,0 +1,142 @@ +;; shift-affine.lisp - Some simple subroutines for working with affine and shift +;; ciphers. +;; +;; This file is free software under the terms of the GPL3 license. You can find +;; a copy of the license at: https://www.gnu.org/licenses/gpl-3.0.en.html + +(defpackage shift-affine + (:use :cl) + (:export + :char-letter :letter-char :affine-encrypt :extended-gcd + :modular-multiplicative-inverse :affine-encrypt :affine-decrypt + :shift-encrypt :shift-decrypt :*english-letter-frequencies* + :relative-frequencies :chi-squared :count-letters :shift-guess-key + :shift-try-break)) + +(in-package shift-affine) + +(defun char-letter (char) + "Return the index of CHAR in the alphabet. The returned number is 0 for A, 1 +for B, 2 for C, etc. Note that this will return the save value for upper and +lower case letters." + (- (char-code char) + (if (upper-case-p char) + (char-code #\A) + (char-code #\a)))) + +(defun letter-char (letter) + "Return the Lisp character object for LETTER. Letter should be the index of a +letter in the alphabet. For example, 0 for A, 1 for B, 2 for C, etc." + (code-char (+ letter (char-code #\A)))) + +(defun affine-encrypt (plain coef offset) + "Encrypt PLAIN using an affine encryption algorithm. COEF cannot be coprime +with 26. That is, it cannot be a multiple of 2 or 13. The algorithm used is: + f(p) = (COEF * p + OFFSET) mod 26 +where this function is used to transform every letter of PLAIN." + (when (or (zerop (mod coef 2)) + (zerop (mod coef 13))) + (error + "COEF must be coprime with 26 (not divisible by 2 or 13), but it was ~d" + coef)) + (map 'string (lambda (char) + (if (alpha-char-p char) + (let ((letter (char-letter char))) + (letter-char + (mod (+ (* coef letter) offset) 26))) + char)) + plain)) + +(defun extended-gcd (n1 n2) + "Return the greatest common denominator of N1 and N2. As a second value, +return a cons of (x . y) such char x * N1 + y * N2 = GCD." + (if (zerop n1) + (values n2 (cons 0 1)) + (multiple-value-bind (div rem) (floor n2 n1) + (destructuring-bind (gcd (x . y)) + (multiple-value-list (extended-gcd rem n1)) + (values gcd (cons (- y (* div x)) x)))))) + +(defun modular-multiplicative-inverse (n m) + "Find the modular multiplicative inverse of N with respect to M. That is, some +integer i such that (N * i) mod M = 1." + (destructuring-bind (gcd (x . y)) + (multiple-value-list (extended-gcd n m)) + (declare (ignorable y)) + (unless (= 1 gcd) + (error "N and M must be coprime. N: ~d, M: ~d" n m)) + (+ x m))) + +(defun affine-decrypt (cipher coef offset) + "Decrypt CIPHER, which should be a string encrypted by `affine-encrypt'. COEF +and OFFSET should be the same as the values passed when encrypting CIPHER." + (let ((ic (modular-multiplicative-inverse coef 26))) + (affine-encrypt cipher ic (- (* offset ic))))) + +(defun shift-encrypt (plain offset) + "Encrypt PLAIN by shifting each letter by OFFSET." + (affine-encrypt plain 1 offset)) + +(defun shift-decrypt (cipher offset) + "Decrypt CIPHER by shifting each letter by -1 * OFFSET." + (affine-encrypt cipher 1 (- offset))) + +(defparameter *english-letter-frequencies* + #(8.2 1.5 2.8 4.3 12.7 2.2 2.0 6.1 7.0 0.15 0.77 4.0 2.4 6.7 7.5 1.9 0.095 6.0 + 6.3 9.1 2.8 0.98 2.4 0.15 2.0 0.074) + "Percent frequency of each letter of the English alphabet in standard writing. +Source: https://en.wikipedia.org/wiki/Letter_frequency") + +(defun relative-frequencies (seq) + "Find the relative percent frequency of the sample data in SEQ." + (let ((sample-count (reduce '+ seq))) + (map 'vector (lambda (elem) + (/ elem sample-count)) + seq))) + +(defun chi-squared (data ref-data &key (offset 0)) + "Return the sum of the square of the error between each index of DATA and +REF-DATA. Before performing the calculation, shift each element in DATA by +OFFSET indexes, wrapping. That is, with OFFSET 1, index 0 becomes index 1, and +the last index becomes index 0." + (loop for ref across ref-data + for i upfrom offset + for sample = (aref data (mod i (length data))) + summing (/ (expt (- sample ref) 2) ref))) + +(defun count-letters (str) + "Count the number of times each letter appears in STR. Return a vector with +each index being the number of times that letter appeared." + (loop with freq-data = (make-array '(26) :initial-element 0) + for char across str + for letter = (char-letter char) + when (alpha-char-p char) + do (incf (aref freq-data letter)) + finally (return freq-data))) + +(defun shift-guess-key (cipher &key (reference *english-letter-frequencies*)) + "Try to guess the shift offset for CIPHER. This is done by analyzing the +frequencies of letters in CIPHER and finding the shift offset that most closely +matches those listed in REFERENCE, which defaults to `*english-letter-frequencies*'." + ;; We also try CIPHER as is, just in case + (let ((best-chi-squared most-positive-fixnum) + (best-offset 0) + (freq-data (relative-frequencies (count-letters cipher)))) + (dotimes (i (length reference) best-offset) + (let ((chi-squared (chi-squared freq-data reference + :offset i))) + (when (< chi-squared best-chi-squared) + (setq best-chi-squared chi-squared + best-offset i)))))) + +(defun shift-try-break (cipher &key (reference *english-letter-frequencies*)) + "Attempt to decrypt CIPHER by guessing the shift offset. This uses +`shift-guess-key' (which see) internally. REFERENCE is passed verbatim to +`shift-guess-key'. As a second value, return the key used for decryption." + (let ((key (shift-guess-key cipher :reference reference))) + (values (shift-decrypt cipher key) + key))) + +;; Local Variables: +;; jinx-local-words: "coprime" +;; End: diff --git a/vigenere.lisp b/vigenere.lisp new file mode 100644 index 0000000..3d049ea --- /dev/null +++ b/vigenere.lisp @@ -0,0 +1,63 @@ +;; vigenere.lisp - Simple implementation of a Vigenere cipher. +;; +;; This file is free software under the terms of the GPL3 license. You can find +;; a copy of the license at: https://www.gnu.org/licenses/gpl-3.0.en.html + +(defpackage vigenere + (:use :cl) + (:export + :+vigenere-alphabet+ :+vigenere-inverse-alphabet+ :vigenere-letter-char + :vigenere-char-letter :vigenere-add :vigenere-encrypt :vigenere-invert-char + :vigenere-decrypt)) + +(in-package vigenere) + +(defparameter +vigenere-alphabet+ + " abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789." + "Alphabet for use in `vigenere-encrypt'.") + +(defparameter +vigenere-inverse-alphabet+ + (loop with alph = (make-array 123 :initial-element 0) + for i below (length +vigenere-alphabet+) + for char = (aref +vigenere-alphabet+ i) + do (setf (aref alph (char-code char)) i) + finally (return alph)) + "Inverse lookup table for `vigenere-encrypt'.") + +(defun vigenere-letter-char (letter) + "Convert LETTER to a Lisp char object." + (aref +vigenere-alphabet+ letter)) + +(defun vigenere-char-letter (char) + "Convert a Lisp char object CHAR to a letter." + (aref +vigenere-inverse-alphabet+ (char-code char))) + +(defun vigenere-add (elem by) + "Add ELEM and BY under the modulo (length `+vigenere-alphabet+')" + (mod (+ elem by) (length +vigenere-alphabet+))) + +(defun vigenere-encrypt (plain key) + "Encrypt PLAIN using a vigenere cipher. This works by shifting each element of +PLAIN by each consecutive elements of KEY, wrapping around if there are no more +elements left in KEY." + (let ((done (make-array (length plain)))) + (dotimes (i (length plain) (map 'string 'vigenere-letter-char + done)) + (setf (aref done i) + (vigenere-add (vigenere-char-letter (aref plain i)) + (vigenere-char-letter + (aref key (mod i (length key))))))))) + +(defun vigenere-invert-char (char) + "Invert CHAR. That is, return the character that will invert the effect that +CHAR had during encryption." + (let ((letter (vigenere-char-letter char))) + (vigenere-letter-char (- (length +vigenere-alphabet+) letter)))) + +(defun vigenere-decrypt (cipher key) + "Decrypt CIPHER using a vigenere cipher, with the key KEY." + (vigenere-encrypt cipher (map 'string 'vigenere-invert-char key))) + +;; Local Variables: +;; jinx-local-words: "vigenere" +;; End: