In the Linux terminal (or Python)

I figured out 1 and 2: 1. Find a file in the treasure hunt directory tree that is exactly 54656 bytes in size. Type in the name of the file. (Do not include the pathname.) This file is used in to solve the next challenge in the treasure hunt.

Answer: csdpmi5a.

2. Once you have found the first file (see previous question), use dd to extract 128 bytes, starting at byte 27265 (counting the first byte of the file as byte #1, not #0). Those 128 bytes will contain the name of the next file in the treasure hunt.

Answer: os_osx2.h

But I am having issues with 3.

Decode os_osx2.h This next file has had the characters rotated in a substitution cypher. The set of letters a-zA-Z has been rotated by between 1 and 5 characters backwards (e.g., if rotating by 1 character, a becomes Z, b becomes a, c became b, etc.). You must rotate the characters in the file in the opposite direction the correct number of places (in the range of 1-5 places) to read the contents. Use 'tr' to rotate the letters back into place and get the name of the next file. What is the name of that file.