Keyword Cipher

Challenge Difficulty: Hard | Estimated completion time: ~45 minutes

A Keyword Cipher replaces each letter of a message with a letter from a shifted alphabet built using a keyword.

1. Start with the keyword.
2. Add the remaining letters of the alphabet (A–Z) in order, skipping any that already appeared in the keyword.
   • Example keyword: "KEYWORD"
   • Cipher alphabet: KEYWORDABCFGHIJLMNPQSTUVXZ
3. Encrypt by replacing each letter in the message with the letter at the same position in the cipher alphabet.
   • Plain alphabet: ABCDEFGHIJKLMNOPQRSTUVWXYZ
   • Cipher alphabet: KEYWORDABCFGHIJLMNPQSTUVXZ

Write a function that takes a key and a message, and returns the encrypted message.

Examples

keyword_cipher("keyword", "abchij")
Output = "keyabc"
 
keyword_cipher("purplepineapple", "abc")
output = "pur"
 
keyword_cipher("mubashir", "edabit")
output = "samucq"
 
keyword_cipher("etaoinshrdlucmfwypvbgkjqxz", "abc")
Output = "eta"
 
keyword_cipher("etaoinshrdlucmfwypvbgkjqxz", "xyz")
Output = "qxz"
 
keyword_cipher("etaoinshrdlucmfwypvbgkjqxz", "aeiou")
Output = "eirfg"