Each Problem Is Worth 10 Points. There Is a Maximum of 100 Points

CSC/MAT 483 – 001

Cryptology

Test Two

This is a test. You may not collaborate.

It is due no later than Monday 4 November. It may be submitted electronically or as a hard copy.

Each problem is worth 10 points. There is a maximum of 100 points.

Explain your approach to each problem that you do.

You may use software that is posted on the class website, use Mathematica, use a calculator, work by hand, or use software that you wrote.

1. Composed Vigenère key.

1a. A message is first enciphered with a Vigenère cipher with keyword “code” and then re-enciphered with a Vigenère cipher with keyword “norse.” What is the keyword for the composed cipher?

1b. A message is first enciphered with a Vigenère cipher with keyword “code” and then re-enciphered with a Vigenère cipher with keyword “cipher.” What is the keyword for the composed cipher?

1c. A message is first enciphered with a Vigenère cipher with an 18-letter keyword and then re-enciphered with a Vigenère cipher with a 42-letter keyword. What is the length of the keyword for the composed cipher?

1d. A message is first enciphered with a Vigenère cipher with keyword “cryptology” and then re-enciphered with a Caesar cipher with shift 7. What is the keyword for the composed cipher?

2. Cryptanalyze the following unknown ciphertext.

LLPFCVTJWZCIRDWVPAXYXBETRWJXZRLEXCXUXBEIJXJMLFAZEDFLQVITULLYLREDWORMJTFEZFSTBSXLCVFYWWZBVFYEEAUIDTLMJFEKLSMUGNFLWTOFYEBNIYFMKROLLEIJAWVLFIRKULLFEEWLIHPLVLTSAUQRMZITNXZVKEUQQLLAGZUIZLOVPGMEZSFVBOVGLMAYIUMZIZBYEWGJUHQSXJWHGSLKGJTNXYXEEAVGREEYZVGKAWSYLWYXHPHLWVGYPPFLTHFGLEXZGSTPNRFTFHANFCTOMAUXYXXSSXXIBGWPZTCXYMMGWRGVLHFVVVGVKRHKAJILNPSNEWPAEUWAXPBRUKZESYMJTFECVHJASTLASKXKMUTIITFHJBELMZSYBJKAWWORRRGVSHULRKESUL

3. Decipher autokey extended by plaintext.

The following message has been enciphered using an autokey cipher extended by plaintext. The key is “mamba.” Decipher the message.

FHQDIIOITBWHXPHBAKCPLEROJEKICVBZINVUXNZZKGVTYIT

4. Cryptanalyze autokey extended by ciphertext.

The following message has been enciphered using an autokey cipher extended by ciphertext. Cryptanalyze the message.

GZIYHALVTLXTPPTGRBVYFM

5. Generate a keystream.

Determine the first 20 bits of the keystream generated by a LFSR with taps C4 and seed 87. Do not include the first 8 bits, which are the seed.

6. Decipher a stream cipher.

A message in Baudot code is enciphered using the keystream:

11011 10011 01111 00000 11010 00110

The ciphertext stream is

10101 11001 11010 01101 11011 00101

Decipher the message.

7. Cryptanalyze the following running key message.

VHRDWLYNAGJZVNVOUWEWSYEOWKAIOINQRQRVY

8. Decipher the following running key message.

VHUHCKRVWERIGOYRQSSSDIYX

which was enciphered using the key:

Campus Recreation’s goal is to enrich your life, and all lives of the university community, by enhancing your academic experience through physical, mental and social development. We want you to have a healthy lifestyle, and our facilities and programs will add to your NKU experience.

9. Cryptanalyze the following unknown ciphertext.

omulnzplvxqzbaloklkyaqtlspphavalqlyayslzjzbqvxluzuoumuqaalaupaztlq

10. Cryptanalyze the following unknown ciphertext.

iepneorriqflandryadqdhnacjcgcqhimeumethaeearnawoiqtflpoanppe

11. The following is a message enciphered with a LFSR with an 8-bit register. The plaintext is in ASCII. It is known that the highlighted ciphertext corresponds to plaintext “rs” (lowercase r and lowercase s). Determine the taps for the register.

00010100 01000010 01100100 11111000 00100000