Specified padding mode is not valid for this algorithm - c# - System.Security.Cryptography

Question

pretty new to c# and currently having a problem decrypting long passwords with an error of

Specified key is not a valid size for this algorithm

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Answer 1

Two changes are required in the function public string DecryptString(string cipherText)

 var cipher = new byte[fullCipher.Length - IV.Length];

and

 Buffer.BlockCopy(fullCipher, IV.Length, cipher, 0, fullCipher.Length - IV.Length);