Please read the basics in https://www.researchgate.net/publication/220689414_Decrypted_secrets_-_methods_and_maxims_of_cryptology how to break monoalphabetic cipher with unknown keyword!

Book Decrypted Secrets – Methods and Maxims of Cryptology

Dear Gunter,

thank you for interesting proposition. I downloaded book from Springer. It looks encouragingly. Would you recommend other interesting books from Springer on cryptology?

By the way I wrote my own program in Java for encryption and decryption discussed problems.

Dear Radoslaw,

I suggest "Practical Cryptography" from Ferguson and Schneier as well as "Security Engineering" from Ross Anderson whose second edition is freely available at http://www.cl.cam.ac.uk/~rja14/book.html. Maybe you will not manufacture your own Java code if you knew https://www.cryptool.org.

Dear Radoslaw,

Günter already gave perfect answers. May I add some more information concerning his link to CrypTool. The program CrypTool 2 contains a sophisticated MAS analyzer, using a combination of a genetic attack and a dictionary attack. Currently it only uses an English dictionary, but as it is open source you could either add your language or ask the CT2 developers when they have further languages on their roadmap or give any other hints.

A screenshot running this template is attached (if you open the Startcenter tab in CT2, and then type "mono" in the filter for the "Templates" you see this templates as the fourth in a list).

May I ask: Which language do you need? What kind of course are you doing?

Best regards, Bernhard

Dear Bernhard,

I have just thought about the program CrypTool. I have to admit that I have heard about it but I had no time to experiment with it. If you have any interesting materials (tutorials) for this program I will be very grateful. 

You asked about language. I generally use English but sometimes I have examples for decryption in my mother tongue. I lead extra course for mathematicians on “Classical cryptanalysis”. By the way I am looking for interesting subjects for cryptanalysis to give students as topics for their own projects. If you have any proposition (with bibliography) I will be very satisfied.

Best wishes,

Radoslaw

Dear Gunter,

thank you for the interesting links and information about CrypTool. By the way I have written to Bernhard about interesting topics for students’ projects. If you have any  I will read that with pleasure.

Hello everyone,

If I may contribute, when trying to break an unknown keyword, one first needs to figure out what kind of cipher on it is. By the way, any monoalphabetic cipher can be broken with the aid of letter frequency analysis as suggested earlier. Moreover, secret code breaker monoalphabetic substitution solver can also use to break an unknown keyword.

Dear Radoslaw,

> I lead extra course for mathematicians on “Classical cryptanalysis”. By the way I

> am looking for interesting subjects for cryptanalysis to give students as topics for

> their own projects.

Here are some links which could be a good start for student's projects. What they can do depends on their skill and time:

a) https://github.com/jcryptool/core/wiki/Project-Ideas

This contains project ideas for the Java-based CrypTool version JCT.

E.g. we currently have in JCT no automatic solver for Hill, for mono-alphabetic substitution, for Caesar or for Vigenère (but some plugins which support the manual analysis).

There is also a link to a presentation showing some of the features what could be done already with JCT:

https://github.com/jcryptool/doc/raw/master/pdf/jcryptool_presentation_en.pdf

b) https://www.cryptool.org/en/ctp-documentation-en/ctp-functions-en

Here you can get an overview of the functionality of the different CrypTool programs (e.g. JCT currently has more visualizations; CT2 has more cryptanalysis plugins).

c) https://www.cryptool.org/trac/CrypTool2/wiki/WikiStart

    https://www.cryptool.org/trac/CrypTool2/wiki/StudentTasksProposals

This contains project ideas for the C#-based CrypTool version CT2.

d) If you'd like to discuss ideas for students' projects, please drop me an email with more details about these projects, and the CrypTool project could support you.

Dear Bernhard,

I have read your information with interest.

Generally they are connected with CrypTool software. Firstly I have to get to know the possibility of this program to discuss possible topics for students' projects. I appreciate your contribution as a leader of team for building such a professional tool for cryptanalysis.

I am very satisfied that I could meet you as the expert in the field of cryptology and get to know your CrypTool software.   

Because my course is for beginners it is rather difficult to propose more advanced subjects to do. I think that your interesting ideas can help me to find problems which can be suitable for my students. In the future I would like to extend my course and your ideas will be very useful.

Dear Radoslaw,

> my course is for beginners

No problem. The CrypTool projects wants to offer easier ciphers as well as contemporary ciphers, and their cryptanalysis.  Some of the old ciphers in JCT have been implemented even by pupils.

Maybe you attract your students by asking them to solve crypto challenges from MysteryTwister C3, which offers the riddles in 4 levels:

www.mysterytwisterc3.org

Dear Bernhard,

Thanks for information about crypto challenges. I saw Cesar problem. I think it is very good idea which can attract my students and not only. Students and pupils like new challenges and quizzes.

• To decode monoalphabetic cipher we should use frequency analysis. In mono alphabetic cipher every character is replaced with a unique other character in the set. For example in English, if E is replaced with K then every occurance of E is replaced with K. So frequency of plain text character E is same as frequency of cipher text character K. Hence for decoding K is replaced with E.
• For implementation, first take large data set of characters in your language. For example, for English take more paragraphs from news etc. and find frequency of Each character i.e. a,b,c,d,e...z in source language. Sort it from low to high.
• Take cipher text to be decoded. Find frequency of each character and sort it from low to high.
• Compare both sorted lists and pair the characters in plain and cipher texts.
• Perform replacement. Almost u will get most probable plain text.
• The disadvantage in this method is if two characters have almost same frequency then mapping may be swapped. 

Dear Bhadri,

Thank you for your interesting comprehensive comment to discussion. If you have any interesting website links or could you recommend books related to this issue I will be very grateful.

Hi Radoslaw,

All those who have answered so far have given you variable suggestions. Apart from that I would like to suggest the following

You can use the following practical tips

You can develop or use available statistics of the language you are working in and use them, as explained in the file I have attached.

You can follow strikeing patterns (like success, assassination, etc.) and unique features (like in English the letter sanwithched between two least frequent letters is always vowel, letter 'y' can be considered as vowel for cryptanalysis purpose) to guess words.

Keep two lists of alphabets arranged in order - one for plain text (say, a-z) and other for cipher text (say A-Z). As you guess each letter mark them against the corresponding plain and cipher texts letters. For eg. you are guessing the plain text corresponding to the cipher text 'Z' as 'a'. Then write 'a' against the 'Z' of cipher text alphabet list and 'Z' against the 'a' of plain text list. You may strike at a pattern or key word.

Wish you all success in your work.

1. Cryptanalysis by Helen F Gaines-Deals with practical approach for cryptanalysis of classical ciphers

2. Cryptography and Network Security by William Stallings Gives good account of modern cryptology.

3. Handbook of Applied Cryptography by A.J. Menezes, et al. 

Good wishes.

Hannah

Dear Hannah,

thank you for your valuable suggestions and tips. The attachment is very interesting and can be used for my students. The recommended books are also interesting. I have already one of them (written by Menezes). If you could recommend other materials I would be very grateful.

Best wishes

Radoslaw

Yes, I shall keep updating you

Good wihshes

Radoslaw

I am attaching links for the useful e-books.  

Understanding Cryptography is by Dr. Christof Paar, Professor in Ruhr University, Bochum.  His lecture videos are available online.  They would be useful for you.

Good wihses.

Hannah.

https://books.google.co.in/books?id=Zb2RBQAAQBAJ&pg=PR1&dq=cryptanalysis+by+helen+fouche+gaines&hl=en&sa=X&ved=0CBwQ6AEwAGoVChMI3cuopYuMxwIVzRiOCh3oaQ0A#v=onepage&q=cryptanalysis%20by%20helen%20fouche%20gaines&f=false

https://books.google.co.in/books?id=f24wFELSzkoC&printsec=frontcover&dq=understanding+cryptography+by+christof+paar&hl=en&sa=X&ved=0CBwQ6AEwAGoVChMI3ca-54uMxwIVCHKOCh311AJa#v=onepage&q=understanding%20cryptography%20by%20christof%20paar&f=false

Dear Hannah,

thanks for the next very interesting e-books. The second book I can download from Springer house.

Best wishes

Radoslaw