Modified Viginere Encryption

Please Implement the encryption and decryption algorithm for this modified cipher

Consider the following enhancement of the Vigenre cipher. We again assume that the plaintext is a case- insensitive English text using only the 26 letters (without space or any other symbol). To encrypt a plaintext m of length n, one first uniformly at random generate a string over the alphabet (A..Z] of length 13. Then insert this string into the beginning of the plaintext. That is, we construct a string x = x122 ... In+13 such that XX13 is the string we have generated and 214 Pn+13 is the plaintext string. We then construct a string y as follows: Ci for 1