GPG: Sign Multiple Files Faster

TL;DR

Yes, you can sign multiple files in parallel with GnuPG (gpg) using a loop and background processes. This significantly speeds up signing large numbers of files compared to signing them one by one.

How to Sign Multiple Files in Parallel

1. Understand the Problem: Signing each file sequentially takes time, especially with many files. We want to use multiple CPU cores to speed this up.
2. Create a List of Files: You need a list of the files you want to sign. This can be created using shell commands like find or ls.

   ls *.txt > filelist.txt

   This creates a file named filelist.txt containing a newline-separated list of all .txt files in the current directory.

3. Loop Through Files and Sign in Background: Use a shell loop to iterate through each file in your list and start a signing process for each one in the background.

   #!/bin/bash
   while read -r file;
   do
     gpg --sign "$file" & 
   done < filelist.txt
   wait

   This script reads each filename from filelist.txt, signs it using gpg --sign and sends the process to the background (&). The wait command ensures that the script waits for all background processes to finish before exiting.

4. Explanation of the Script:
   • #!/bin/bash: Shebang line, specifies the interpreter.
   • while read -r file; do ... done < filelist.txt: Reads each line (filename) from filelist.txt into the variable $file. The -r option prevents backslash escapes from being interpreted.
   • gpg --sign "$file" &: Signs the file using GPG and runs it in the background. The quotes around $file are important for filenames containing spaces.
   • wait: Waits for all background processes to complete before continuing. Without this, your script might exit before all files are signed.
5. Adjusting Parallelism (Optional): If you have a very large number of files and want to limit the number of concurrent signing processes, use xargs -P.

   find . -name "*.txt" | xargs -P 4 gpg --sign

   This command finds all .txt files in the current directory and pipes them to xargs. The -P 4 option tells xargs to run a maximum of 4 signing processes at a time. Adjust '4' to match your CPU core count or desired level of parallelism.

6. Verify Signatures: After signing, verify the signatures.

   gpg --verify *.sig

   This command verifies all .sig files in the current directory against their corresponding original files.

7. Important Considerations:
   • Disk I/O: Parallel signing can put a heavy load on your disk, especially if you're using a slow hard drive. Consider using an SSD for better performance.
   • CPU Usage: Monitor your CPU usage to ensure that you aren't overloading the system. Adjust the number of parallel processes accordingly.
   • Key Server Load: If you are automatically retrieving keys, be mindful of key server load and consider caching keys locally.