Merging branches with smudge filter

Hi, everybody. I'm new to git and I'd like to keep track of some codes
we have here in our company. They have some sensitive information I
would like to keep private. After some googling, I found some
solutions that encrypt/decrypt the files using filters as they're
committed/checked out. I've been using this approach and it suits my
needs. Now I need to merge two branches, but the process is failing
for two files in particular. First of all, here's my config file:

[filter "openssl"]
    clean = openssl enc -aes-256-cbc -a -nosalt -pass pass:password
    smudge = openssl enc -d -aes-256-cbc -a -nosalt -pass pass:password
    required

For these two files I mentioned, decryption fails. Then I did this:

    smudge = openssl enc -d -aes-256-cbc -a -nosalt -pass
pass:password || tee -a /out.txt

Based on the output, it seems like the input data is corrupted, but I
don't get it. These files are regular source code like any other file.
I can also check out both branches individually, so I'm assuming the
stored blob is fine. Every other file is perfectly merged. What should
I do?

Thank you.