Vwrite actual code in an actual programming

Question

Challenge: Write actual code in an actual programming language that . . .

(a) . . . encrypts a message using a shift cipher of 12 letters.

(b) . . . decrypts a message encrypted using a shift cipher of 6 letters.

(c) . . . encrypts a message using atbash.

(d) . . . decrypts a message encrypted using atbash.

(e) . . . encrypts a message using the original Vigen`ere cipher.

(f) . . . decrypts a message using the standard Vigen`ere cipher.