hw1

Homework 1 (secret key encryption)

This is encrypted with a monoalphabetic substitution cipher.

WAUXZOZOXGQNTBPOESXQNBOHBFOKKX TOACAUZCQZKBXKKQTNFONBQNMZWEBA TZXEPWCAZBPOCQZKBEXZBACBPQKXKK QTNFONBOFXQSBPQKESXQNBOHBCQSOX NGGOKMZQDOBPOKUDKBQBUBQANMQEPO ZUKOGCAZONMZWEBQANCAZBPOKOMANG EXZBQFESOFONBXGQCCOZONBKOMZOBY OWONMZWEBQANXNGGOMZWEBQANKMPOF OCAZBOHBCQSOKXNGKUDFQBWAUZKAUZ MOXSANTRQBPGAMUFONBXBQANXNGBOK BQNTCAZWAUZQFESOFONBXBQANUKQNT XEZATZXFFQNTSXNTUXTOACWAUZMPAQ MOCAZBPOBPQZGEXZBGOBOZFQNOBPOK BXBQKBQMXSEZACQSOKACONTSQKPXNG XNABPOZSXNTUXTODWRZQBQNTXEZATZ XFBAMAFEUBOBPOQZONBZAEQOKAIOZX SXZTOBOHBMAZEUKGAOKBPOKOMANGSX NTUXTOPXIOXPQTPOZONBZAEWBPXNON TSQKPBPQKXKKQTNFONBQKGUODWBPOF QGGSOACCODZUXZW

Part 1 (decrpytion)

I decrpyted this message mostly by hand partnered with sophiacarlone. We used some ngram frequencies to help with our analysis.

YOU ARE READING THE PLAIN TEXT MESSAGE OF OUR FIRST ASSIGNMENT IN CRYPTOGRAPHY FOR THE FIRST PART OF THIS ASSIGNMENT EMAIL THIS PLAIN TEXT FILE AND DESCRIBE THE SUBSTITUTION CIPHER USED FOR ENCRYPTION FOR THE SECOND PART IMPLEMENT A DIFFERENT SECRET KEY ENCRYPTION AND DECRYPTION SCHEME FOR TEXT FILES AND SUBMIT YOU SOURCE ALONG WITH DOCUMENTATION AND TESTING FOR YOUR IMPLEMENTATION USING A PROGRAMMING LANGUAGE OF YOUR CHOICE FOR THE THIRD PART DETERMINE THE STATISTICAL PROFILES OF ENGLISH AND ANOTHER LANGUAGE BY WRITING A PROGRAM TO COMPUTE THEIR ENTROPIES OVER A LARGE TEXT CORPUS DOES THE SECOND LANGUAGE HAVE A HIGHER ENTROPY THAN ENGLISH THIS ASSIGNMENT IS DUE BY THE MIDDLE OF FEBRUARY

Key:

A B C D E F G H I K M N O P Q R S T U W X Y Z
O T F B P M D X V S C N E H I W L G U Y A K R

Part 2 (different secret key encryption)

I used a linear shift feedback register as a psuedo random number generator to create a stream cipher. https://en.wikipedia.org/wiki/Linear-feedback_shift_register

If you don't have the go compiler you can find download instructions at https://go.dev/doc/install.

Running make is the easiest way to compile and test the program. It will create a new random key (a uint64), encrypt message.txt into cipher.txt and decrypt cipher.txt into plaintext.txt. Afterwards it runs diff to check if the decrypted message is the same as the original message.