Cryptology - Unofficial St. Mary's College of California Web Site

158 CHAPTER 8. POLYALPHABETIC CIPHERS
To do this, use the first keyword to mix the alphabet. Then under the
usual alphabet copy the cipheralphabet a number of times so that the
first letters of the rows spells the second keyword. Then use the alphabets
cyclically.
(a) Use a Keyword Mixed cipher with keyword ONCE to mix the cipheralphabet,
and then a Vigenére cipher with keyword TWICE to encipher
three times a lady.
(b) Use a Keyword Transposed cipher with keyword AGAIN to mix the
cipheralphabet, and then a Vigenére cipher with keyword REPEAT to
encipher Over and out.
(c) The ciphertext UIKQEYM BU TN JRBA was enciphered with a Vigenére
cipher with keyword SIMPLE, using a cipheralphabet mixed via a Keyword
Mixed cipher with keyword TWIST. What was the plaintext
(d) The plaintext microwave oven was enciphered with a Vigenére cipher
with keyword QUICK, using a cipheralphabet mixed via a simple
Keyword cipher to produce the ciphertext CCYNYMUZU YFYR. What
was the Keyword Cipher’s keyword
11. A Vigenère Cipher with two keywords has the mathematical formulation
C = P + K 1 + K 2 , where K 1 and K 2 are the first and second keywords.
What if we instead used C = P ∗ K 1 + K 2 , perhaps calling this the
Linear Vigenère Cipher The Linear Cipher (from Chapter 4), while not
very secure, is certainly harder to break than the Caesar Cipher. Is the
Linear Vigenère Cipher more secure than the Vigenère with two keywords
Explain.
12. Encipher or decipher the following definitions using an Auto Key cipher
with the given priming key.
(a) Encipher Autobiography is a story with priming key T.
(b) Encipher autoclave is an oven with priming key F.
(c) Decipher OUNHQ TRCAG ASGUJ ZVEZQ RG with priming key O.
(d) Decipher CUNHU OZFWA SHLPT KQDIX V with priming key C.
(e) Encipher autograph is a signature with priming key RI.
(f) Decipher CLTIF CNWMM TWIUA T with priming key CR.
(g) Decipher PYTIF OFIVO GGVSY AMBNL VGGOV LWEWA with priming key
PE.
(h) Decipher FLXOH HALWE GVVMC HRSIA FI with priming key FRE.
(i) Decipher SNTSS OZUWM ZOSFB ABBBZ LDGVQ XF with priming key STAE.
(j) Decipher ZSTIF BUFIE IEXWA PTYO with priming key ZY.