I'm very uneducated when it comes to cryptography. I have tried to find an answer to my question, but what I've read doesn't quite cover what I'm asking.
I have thought up my own encryption algorithm (which I'm sure is nothing new) and I would like to know why this sort of algorithm is not used in terms of security, efficiency and any other reasons.
It stems from the Caesar Cipher. But, instead of shifting each letter by 13, you shift each character (using computer character values) by a certain value each time.
So, let's say I had the sentence:
My dog's name is Rover.
And I have an array of numbers:
1, 4, 3, 2
I would shift
M up by 1 character,
y by 4,
[space] by 3,
d by 2 and then continue with the rest of the sentence, looping through the number array.
So, the sentence would be converted into
Let's call the array your "key". Only someone with the key could decipher the message, unless someone figures it out. The more items in your array (key), the safer you are from someone deciphering your message.
Apologies if my explanation is poor. To summarize my question:
Why is this bad (or, not used)
Is it inefficient/insecure compared to other encryption methods
Is there anything else about this that should be considered