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Add `del-gpg-user` to delete (and re-encrypt) repository #47

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reedloden opened this Issue Mar 25, 2015 · 25 comments

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@reedloden

reedloden commented Mar 25, 2015

Need to be able to remove a GPG key for a user and then re-encrypt the repository. Obviously, the user would be able to decrypt old revisions but any new revisions would not be encrypted with the user's key.

@dupuy

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dupuy commented Apr 7, 2015

This is definitely an issue that should also be addressed in the documentation - for security to be meaningful it is important for end-users to fully understand the security implications of the use of a tool - and even if there is a del-gpg-user subcommand that re-encrypts the repository, end users need to understand that they need to revoke and regenerate any credentials that were (ever) stored in the repository - and that is something that git-crypt cannot implement itself as revocation/regeneration is entirely outside the Git ecosystem.

Something that del-gpg-user could do to "help" or "encourage" such revocation/regeneration would be to replace all encrypted files with empty ones, but the implications of that need to be examined as it might just make things more confusing for less experienced users.

Perhaps rather than (or as a simpler step before) adding del-gpg-user a better approach might be to add a re-init command that just does the regeneration of encryption key (with optional removal of encrypted files and/or their contents).

Anyhow, I've no experience with Go, but can probably contribute to the documentation a section on the implications of putting credentials or other types of secrets in a git-crypt-enabled repository, and what revocation of access may mean - I'll look at what I could do and try to submit a PR with an outline sometime next week.

@AGWA

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AGWA commented Apr 8, 2015

This issue has been on my radar for a while. It's surprisingly complicated, because you have to rotate git-crypt's internal symmetric key and re-encrypt all files with the new symmetric key, in order to preserve confidentiality of future commits. To avoid breaking history, you have to keep around the old versions of the key and use them when dealing with old commits. Fortunately, git-crypt already has the framework for this - it just needs to be wired up, and tested extensively. I suspect that there will be big problems with merging if the key has been rotated on one branch of the merge. So, a lot of the work will be testing how key rotation interacts with various other Git operations. Fortunately, that's something anyone can help with, without having to do any coding.

@dupey you are correct about credentials protected by git-crypt needing to be rotated too, but that's definitely outside the domain of git-crypt, and I don't like the idea of git-crypt automatically truncating files. A discussion in the documentation would definitely be warranted though. Thanks for offering to help with this.

@erikthorselius

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erikthorselius commented May 11, 2015

👍

1 similar comment
@alexkli

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alexkli commented May 16, 2015

👍

@redterror

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redterror commented May 19, 2015

Just curious - what are the use cases people have in mind for this feature? I had convinced myself I needed it if I wanted to revoke access from a former employee, but after thinking some more, I don't actually need it. In my situation github's access controls + secret rotation are sufficient.

@reedloden

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reedloden commented May 20, 2015

@redterror git-crypt supports two forms of encryption -- symmetric key and GPG. In the former case (which it sounds like you use), rotation of the key is all you can do. In the latter, you need to be able to remove a user's GPG public key and re-encrypt the entire repository. The user would be able to access old copies of the repository that were encrypted with his/her public key, but any new changes would not be encrypted with his/her GPG public key, so they would be inaccessible.

@dupuy

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dupuy commented May 20, 2015

@reedloden Technically, a symmetric key is used for encryption of files in every case - it is just that in the second case the symmetric key itself is encrypted with one or more GPG keys and those copies of the encrypted key are committed to the repository, allowing a user whose GPG key was "added" to decrypt the encrypted contents in the repository using nothing more than their private key and the repository itself.

@redterror

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redterror commented May 20, 2015

@dupuy - I'm with you on all that, what I was suggesting was that the use-case of a privileged user that becomes unprivileged but still retains repo access at all may be uncommon. In my case removing access at the github level solves the problem entirely.

I get that this is useful out of completeness, it just seems like a scenario that folks may think they need but actually don't. I don't know really know, I'm just suggesting that this may not be all that important in real deployments.

pfalcon added a commit to pfalcon/git-crypt that referenced this issue Dec 1, 2015

README.md: Disclose the fact that revoking access is not supported.
Perpetual grant of access is certainly a security issue, so goes to
the corresponding section. Based on the discussion in
AGWA#47
@pfalcon

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pfalcon commented Dec 1, 2015

With the thoughts in #23 (comment) , I'd like to make a step forward with further progressing git-crypt, by making it be fair about its deficiencies: #72

@geowa4

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geowa4 commented Dec 17, 2015

This would be a nice feature. I had to jump through some interesting hoops to re-initialize the repo after a coworker left. For my use case, I don't really care about history; the value of the old database password isn't exactly useful.

@phunehehe

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phunehehe commented Apr 21, 2016

So here's what I did to re-encrypt files to remove a user:

  • Make a backup (with decrypted files): cp -r . /path/to/backup
  • Save a list of files that are encrypted: git crypt status | grep -v 'not encrypted' > ../encrypted-files.txt
  • Make git-crypt forget about itself: rm .git-crypt
  • Delete the encrypted files: awk '{print $2}' ../encrypted-files.txt | xargs rm
  • Commit (at this point you get a repo without git-crypt stuff)
  • Add git-crypt from scratch (init and add-gpg-user)
  • Copy the decrypted files from the backup: awk '{print $2}' ../encrypted-files.txt | while read l; do cp /path/to/backup/$l $l; done
  • Commit (at this point you are done, but be sure to verify things are properly encrypted before publishing)

Hope that help until we get there 😅

@TiagoTT

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TiagoTT commented Apr 21, 2016

I have a suggestion for the implementation that may work.

  • Each encrypted file would include the encryption key name in its header metadata.
  • git-crypt unlock would be able to load multiple git-crypt secret keys into .git/git-crypt/keys.
  • git-crypt would use the right key to decrypt each file automatically based on the header metadata.
  • .gitattributes would be checked only for encryption rules, but not for decryption anymore.

It might be possible to use the existing support for multiple keys to achieve the desired user access revocation (for the future commits only of course).

Consider the following steps:

  • Create new key: git-crypt init -k A.
  • Add all users except the one to remove to the new key: git-crypt add-gpg-user -k A user.
  • Swap the new key A with the default key.

All new or updated files would be encrypted with the new default key.
All old files would be decrypted with the old key.

Would this work?

@glogiotatidis

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glogiotatidis commented May 24, 2016

Based on phunehehe's comment I hacked together a script to get the job done. You can find it here https://gist.github.com/glogiotatidis/e0ab45ed5575a9d7973390dace0552b0

@tgjamin

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tgjamin commented Mar 23, 2017

Any updates on this?

@voltechs

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voltechs commented Apr 14, 2017

Any thoughts on using the oft-misunderstood-and-avoided-but-very-powerful-and-actually-not-scary-at-all feature git rebase for when a user is removed?

@VanAxe

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VanAxe commented May 15, 2017

I'd like to poke the proverbial bear.

Bump. 😈

@avanier

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avanier commented Aug 1, 2017

For some odd reason, I now need this feature. 😛

Halp!

@inhumantsar

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inhumantsar commented Oct 26, 2017

Bump

@inhumantsar

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inhumantsar commented Oct 28, 2017

I wrote a bash script that will rekey the repo on-demand using a remote list of users (currently, JSON in S3).

Use git-crypt-team -e to edit the user file and upload it to S3. It should be formatted like [{"key": "KEYID123", ...}, ...]. You can include any additional attributes with each key, but only key is required. Then run git-crypt-team -r to re-encrypt everything using the current team list in S3.

The script will take care of getting GPG keys from public sources, signing them, backing up and restoring encrypted files, plus all of the cleanup, init, and git work required. It even does it all in a branch, if things go wrong just run git reset --hard HEAD && git checkout master.

https://github.com/inhumantsar/bash-git-crypt-team/

@Constantin07

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Constantin07 commented Mar 9, 2018

I also need this feature - be able to revoke access to encrypted files.
Another thing which is not quite clear to me is how to get the list already added users ? so that we know which GPG key to delete ...

@aasm-moura

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aasm-moura commented Mar 11, 2018

So, what is the best approach ? Use symmetric key and rotate?

@shazChaudhry

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shazChaudhry commented Mar 17, 2018

I am also interested in what the recommended approach is.

@vonglasow

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vonglasow commented Mar 23, 2018

I have seen this gist from @glogiotatidis do we have another approach to remove GPG key added ?

@glogiotatidis

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glogiotatidis commented Mar 23, 2018

I have seen this gist from @glogiotatidis do we have another approach to remove GPG key added ?

slightly off-topic but since i'm mentioned: For new repos we have experimenting with keybase's encrypted git and teams and so far works OK.

@vonglasow

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vonglasow commented Mar 26, 2018

@glogiotatidis thanks for the feedback

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