Are there any formal tests to estimate encryption strength? So I'm trying to design/make my own encryption algorithm and I believe it to be ok. I'm not saying it's extra secure but I know it's not useless so, what I was wondering is if there are any specific tests I can carry out in order to try and get a better representation of how secure my algorithm is.
Here is some data from tests that I have carried out:

Repeated blocks of data are different from each other
1-bit change in password will completely change the result
1-bit change in input text completely changes the output
even if you encrypt the same file with the same password you will get a different output each time because each encryption gets a different random salt
when tested over a large number of files matching bytes in both encrypted and unencrypted file that matched in the same place was 0.3% random is about 0.34% other encryptions get about 0.28-0.29%

here I have tried to layout the mode of operation for my algorithm. I believe it to be closest related to a PCBC mode of operation but there are some differences in the way I have laid mine out
TLDR: There are no tests that prove that some algorithm have particular strength.
Statistical metrics can only prove that an algorithm is weak. If the metrics give &quot;good&quot; results, it does not mean anything.
Example: If your algorithm produces encrypted messages that are indistinguishable from a random stream of bytes, you can get &quot;good&quot; metric values. But if this algorithm uses effectively only the first 40 bits of the 128-bit password, it can be relatively easy brute-forced.
Brute-forcing as iterative trying of all possible values is not used in serious cases, because it may require the computational power of the whole planet and even 1 000 000 000 years may be insufficient to try all possible password candidates.
Instead, first the analysis of the encryption algorithm should be done to reduce the amount of work needed for decrypt. For instance, if some algorithm uses 128-bit passwords, a straight forward brute-forcing may need 2^128 &quot;units of work&quot;, which means that it is practically impossible to find a password. But if somebody finds a way (an algorithm, an &quot;attack&quot;) to exclude many passwords or in some other way to reduce the number of &quot;units of work&quot; from 2^128 to only 2^40, then this will require little resources and it can be successfully brute-forced.
Finding ways to reduce the amount for work needed for brute-forcing is a very complex activity. It cannot be formalized fully. This is the reason why we need cryptographers.
What can you do? Such question was already answered many times on Crypto SE: Pay a professional cryptographer who will analyze your algorithm. If there are some trivial weaknesses, they will be found. But even if not found, it does not mean there are no any weaknesses.