What is the "key" to a caesar cipher that someone needs to know (or discover) to decrypt the message? a) a secret word only known to caesar. b) the number of characters to shift each letter in the alphabet. c) the letter that occurs most often in the encrypted message. d) the day of the month that the encrypted message was sent.

The number of characters to shift each letter in the alphabet.

Explanation:

Caeser Cipher is the technique of encryption of data, to make it secure by adding characters between alphabets. These are the special characters that make the message secure while transmitting.

According to the standards, For Decryption, we remove these special characters between alphabets to make message understandable.

So, we can say that,to de-crypt the message, the number of characters to shift each letter in the alphabet.