Git Alias Resign: Sign Old Commits and Keep commit date same as author date using rebase

git.resign.sh

echo "Don't execute this script directly. Edit it and copy the command you need.";
exit;
# Make sure you backup your .git folder (better the entire repository) before running this! 
# USE AT YOUR OWN RISK!

# Tested with git version 2.33.1
# If on ubuntu, make sure to add the official repo from git to get the latest version.

# This will add a git alias 
# Usage: git resign HASH
# In the interactive editor, make sure the correct commits are beign rebased.
# This command will resign all the commits until the HASH commit (not including)

git config --global alias.resign "rebase --exec 'GIT_COMMITTER_DATE=\"\$(git log -n 1 --format=%aD)\" git commit --amend --no-edit -n -S' -i"

# remove the -i if you like to live dangerously.

# Once done, before pushing, check the CommitDate value using
# git log --pretty="fuller"

# This will also run git log automatically
# git config --global alias.resign '!'"git rebase --exec 'GIT_COMMITTER_DATE=\"\$(git log -n 1 --format=%aD)\" git commit --amend --no-edit -n -S' -i \$1 && git log --pretty=\"fuller\" \$1..HEAD"

For Git Bash on Windows, use double quotes if you execute the command manually:

git rebase --exec "GIT_COMMITTER_DATE=\"\$(git log -n 1 --format=%aD)\" git commit --amend --no-edit -n -S" -i YOUR_HASH