Cryptography Exercises
Exercise 1
Decrypt each of the following Caesar encryptions...
(a) LWKLQNWKDWLVKDOOQHYHUVHHDELOOERDUGORYHOBDVDWUHH
(b) UXENRBWXCUXENFQRLQJUCNABFQNWRCJUCNAJCRXWORWMB
(c) BGUTBMBGZTFHNLXMKTIPBMAVAXXLXTEPTRLEXTOXKHHFYHKMAXFHNLX
Exercise 2
For this exercise, use the simple substitution table given in Table below.
a b c d e f g h i j k l m n o p q r s t u v w x y z
S C J A X U F B Q K T P R W E Z H V L I G Y D N M O
Table 1.11: Simple substitution encryption table
(a) Encrypt the plaintext message
The gold is hidden in the garden.
(b) Make a decryption table, that is, make a table in which the ciphertext alphabet is in order from A to Z and the plaintext alphabet is mixed up.
(c) Use your decryption table from (b) to decrypt the following message.
IBXLX JVXIZ SLLDE VAQLL DEVAU QLB
Exercise 3
Each of the following messages has been encrypted using a simple substitution cipher. Decrypt them.
A Piratical Treasure
JNRZR BNIGI BJRGZ IZLQR OTDNJ GRIHT USDKR ZZWLG OIBTM NRGJN
IJTZJ LZISJ NRSBL QVRSI ORIQT QDEKJ JNRQW GLOFN IJTZX QLFQL
WBIMJ ITQXT HHTBL KUHQL JZKMM LZRNT OBIMI EURLW BLQZJ GKBJT
QDIQS LWJNR OLGRI EZJGK ZRBGS MJLDG IMNZT OIHRK MOSOT QHIJL
QBRJN IJJNT ZFIZL WIZTO MURZM RBTRZ ZKBNN LFRVR GIZFL KUHIM
MRIGJ LJNRB GKHRT QJRUU RBJLW JNRZI TULGI EZLUK JRUST QZLUK
EURFT JNLKJ JNRXR S
The ciphertext contains 316 letters. Here is the frequency table: R J I L Z T N Q B G K U M O S H W F E D X V
Freq 33 30 27 25 24 20 19 16 15 15 13 12 12 10 9 8 7 6 5 5 3 2
The most frequent bigrams are: JN (11 times), NR (8 times), TQ (6 times), and LW, RB, RZ, and JL (5 times each).
Exercise 4
A transposition cipher is a cipher in which the letters of the plaintext remain the same, but their order is rearranged. ...
(a) Use this transposition cipher with key = 5 to encrypt the first 25 letters of the message
Four score and seven years ago our forefathers ...
(b) The following message was encrypted using this transposition
Decrypt each of the following Caesar encryptions...
(a) LWKLQNWKDWLVKDOOQHYHUVHHDELOOERDUGORYHOBDVDWUHH
(b) UXENRBWXCUXENFQRLQJUCNABFQNWRCJUCNAJCRXWORWMB
(c) BGUTBMBGZTFHNLXMKTIPBMAVAXXLXTEPTRLEXTOXKHHFYHKMAXFHNLX
Exercise 2
For this exercise, use the simple substitution table given in Table below.
a b c d e f g h i j k l m n o p q r s t u v w x y z
S C J A X U F B Q K T P R W E Z H V L I G Y D N M O
Table 1.11: Simple substitution encryption table
(a) Encrypt the plaintext message
The gold is hidden in the garden.
(b) Make a decryption table, that is, make a table in which the ciphertext alphabet is in order from A to Z and the plaintext alphabet is mixed up.
(c) Use your decryption table from (b) to decrypt the following message.
IBXLX JVXIZ SLLDE VAQLL DEVAU QLB
Exercise 3
Each of the following messages has been encrypted using a simple substitution cipher. Decrypt them.
A Piratical Treasure
JNRZR BNIGI BJRGZ IZLQR OTDNJ GRIHT USDKR ZZWLG OIBTM NRGJN
IJTZJ LZISJ NRSBL QVRSI ORIQT QDEKJ JNRQW GLOFN IJTZX QLFQL
WBIMJ ITQXT HHTBL KUHQL JZKMM LZRNT OBIMI EURLW BLQZJ GKBJT
QDIQS LWJNR OLGRI EZJGK ZRBGS MJLDG IMNZT OIHRK MOSOT QHIJL
QBRJN IJJNT ZFIZL WIZTO MURZM RBTRZ ZKBNN LFRVR GIZFL KUHIM
MRIGJ LJNRB GKHRT QJRUU RBJLW JNRZI TULGI EZLUK JRUST QZLUK
EURFT JNLKJ JNRXR S
The ciphertext contains 316 letters. Here is the frequency table: R J I L Z T N Q B G K U M O S H W F E D X V
Freq 33 30 27 25 24 20 19 16 15 15 13 12 12 10 9 8 7 6 5 5 3 2
The most frequent bigrams are: JN (11 times), NR (8 times), TQ (6 times), and LW, RB, RZ, and JL (5 times each).
Exercise 4
A transposition cipher is a cipher in which the letters of the plaintext remain the same, but their order is rearranged. ...
(a) Use this transposition cipher with key = 5 to encrypt the first 25 letters of the message
Four score and seven years ago our forefathers ...
(b) The following message was encrypted using this transposition