Questions about "custom" ciphers in php

Question

PHP

Task: decrypt this fragment (6245122585122554295262785262).
Explanation: the developer (who came up with the cipher) claims that:
a) the algorithm can only encrypt numbers, Latin letters, as well as several characters (- _ . @). The output is only numbers.
b) the algorithm allows you to decrypt them back.
c) there is a private key, not a word about the open one ...
Question 1: judging by the dog, there can be E-mail here, what is the probability of understanding the logic and how long will it take for an experienced programmer to solve this fragment?
Question 2: Are there any programs or web resources for data decryption?
Question 3: what is your personal opinion, what is it and can it still be solved?

Answer 1

Most likely, the algorithm simply shifts the ASCII code of characters, or some other mat. performs an operation on character codes. Then, probably, every two digits is a character code.
If there is no way to encode a known string in advance, then you have to kill a lot of time until a brilliant guess visits.

Answer 2

If you take two digits and consider them shifted ASCII codes , nothing will come of
it. , decrypted text: EVwb.wbMfOE5OE if xor + shift (2 keys), then the text is also obtained, not like the truth. more sophisticated variants assume that more than a very small piece of ciphertext is available.

Answer 3

maybe some kind of xor? There are options on how to decrypt a section of an encrypted message