Caesar cipher

Description:

• The Caesar Cipher is a private-key encryption scheme
• used by Julius Caesar (100 BC-44 BC) to communicate with his generals
• encryption is achieved by “shifting” each alphabet by some fixed amount (the key).
• Let message space $M={A,B,...,Z}^{\ast }$ and key space $K=0,1,...,25$

Gen:

• a uniformly random key $k$ from $K=0,1,...,25$

Enc:

• Encryption shifts the alphabet of each letter in the plain-text by $k$: ${\text{Enc}}_k(m_1{m}_2...m_n)=c_1{c}_2...c_n,\text{ where }{c}_i=m_i+k\mathrm{mod}26$

Dec:

• Decryption shifts each letter back: ${\text{Dec}}_k(c_1{c}_2...c_n)=m_1{m}_2...m_n,\text{ where }{m}_i=c_i-k\mathrm{mod}26$