Encrypt the following plaintext using the given substitution key:

Plaintext: Lord Rama was a great king

Substitution Key:

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

Show your work: Write the substitution for each letter and provide the final ciphertext.

Key Space Analysis:

If we use a reduced alphabet = {a, b, c, d, e, f}, what is the total key space (number of possible substitution keys)?

Hint: Consider that each substitution key must be a permutation of the alphabet.

Decrypt the following ciphertext with the given key:

Ciphertext: libimi wio i rlkif dxmr

Substitution Key:

Plain:  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
          Cipher: i s y b k j r u x e d z q m c t p l o f n b w g a h
          

Cryptanalysis Challenge:

Decrypt the following mono-alphabetic substitution ciphertext using frequency analysis. No key is provided - you must discover it through cryptanalytic techniques.

Ciphertext:

LOJUM YLJME PDYVJ QXTDV SVJNL DMTJZ WMJGG YSNDL UYLEO SKDVC
          GEPJS MDIPD NEJSK DNJTJ LSKDL OSVDV DNGYN VSGLL OSCIO LGOYG
          ESNEP CGYSN GUJMJ DGYNK DPPYX PJDGG SVDNT WMSWS GYLYS NGSKJ
          CEPYQ GSGLD MLPYN IUSCP QOYGM JGCPL GDWWJ DMLSL OJCNY NYLYD
          LJQLO DLCNL YPLOJ TPJDM NJQLO JWMSE JGGJG XTUOY EOOJO DQDMM
          YBJQD LLOJV LOJTV YIOLU JPPES NGYQJ MOYVD GDNJE MSVDN EJM
          

Frequency Analysis:

• Calculate the frequency of each letter in the ciphertext from question 4
• Compare with standard English letter frequencies
• Identify the most likely plaintext letters for the most frequent ciphertext letters

Security Analysis:

• Explain why mono-alphabetic substitution ciphers are vulnerable to frequency analysis
• Describe at least two methods to break a substitution cipher
• Suggest improvements to make substitution ciphers more secure