Is it possible in NiFi to check an input file for correct checksum with its md5 file before loading and processing it to workflow?

[#1]

You can achieve this by using the HashContent processor or the ExecuteStreamCommand processor to calculate the MD5 hash of the content and compare it to the contents of the prepared *.md5 digest file, which you can read with GetFile and then ExtractText/RouteOnContent/RouteText to compare the MD5 value in a flowfile attribute with the contents of the file.

[#2]

Here's a working example using separate signature files in the filesystem (e.g. 'filename.tgz' is the file and 'filename.sig' is a file containing the hash), and storing these in a distributed map cache.

verify-sha256-hash.xml

[#3]

Thank you!