@ -22,57 +22,108 @@ A new internal public key storage format that avoids forwards compatibility issu
## Motivation
GPG maintains backwards compatibility but not forwards compatibility. Users typically upgrade GPG but do not downgrade. This means that running a new GPG version will typially update the keyring storage files in a way that is not recognised by older versions of GPG. This is normally not a problem of typicaly GPG usage as users typically only upgrade and do not downgrade. It is a problem for git-secret as the keyring storage is committed to git and shared between users. Some uses can be using an older version of GPG that cannot open the upgraded keyring file.
GPG maintains backwards compatibility but not forwards compatibility. Running a new GPG version can and will upgrade the keyring storage files in a way that is not recognised by older versions of GPG. This is not normally a problem for typical GPG usage. Users only upgrade and rarely downgrade. It is a problem for git-secret as the keyring storage is committed to git and shared between users. Someone using an older version of GPG can no longer open the upgraded keyring file.
## Approach
git-secret will move away from using the keyring format as shared storage of public keys. Instead it will store public keys as seperate files. The export format is stable and forwards compatibile as it is normal for GPG uses to be running different versions and to exchange keys. Any future bugs that effect git-secret's ability to use the files will also effect typical GPG usage. Such bugs are likely to be fixed by the wider GPG community.
git-secret will move away from using the keyring format as shared storage of public keys. Instead it will store public keys as separate files. The export format is stable and forwards compatible. It is normal for GPG users to be running different versions and to exchange keys successfully. Any future bugs that effect git-secret's ability to use the files will affect typical GPG key exchange usage. Such bugs are likely to be fixed by the wider GPG community.
git-secret may need to store and process meta-data about keys to make it efficient to work with keys that are individually stored. It will use the matchine readable ["colon listings format"](https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gnupg.git;a=blob_plain;f=doc/DETAILS) for this purpose.
git-secret may need to store and process meta-data about keys to make it efficient to work with keys that are individually stored. It will use the machine-readable ["colon listings format"](https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gnupg.git;a=blob_plain;f=doc/DETAILS) for this purpose.
It is anticipated that `bash` and `gawk` will be suffient to be able to impliment and use the new shared key storage format.
It is anticipated that `bash` and `gawk` will be sufficient to be able to implement and use the new shared key storage format.
## Design
The storage format will be:
1. Keys will be stored in `~/.gitsecret/keys` in `gpg --armor --export` format. The use of ascii armour rather than binary format is to make debugging of key issues easier. The file name of the key will be the "64 bit keyid" (field 5 of the `colon listings` format) with extension `.pub.gpg`
1. Key meta data will be stored alongside the key file in the `gpg --keyid-format long --with-colons` format. The file name will be the "64 bit keyid" (field 5 of the `colon listings` format) with extension `.gpg.colon`
1. A "keyring cache" will be create at `~/.gitsecret/cache` and this folder will be added to `.gitignore`. At this location a public keyring will be maintained on a per user bases and it won't be shared by users.
1. A tombestone marker file with file name of the "64 bit keyid" with the extension `.killed` will be created by git-secret-killperson to mark a user as killed.
1. Keys will be stored in `~/.gitsecret/keys` in `gpg --armor --export` format. The use of ASCII armour rather than binary format is to make debugging of key issues easier. The filename of the key will be the "64-bit keyid" (field 5 of the `colon listings` format) `<keyid>.pub.gpg`
1. Key meta data will be stored alongside the key file in the `gpg --keyid-format long --with-colons` format. The file name will be `<keyid>.gpg.colon`
1. A "keyring cache" will be created at `~/.gitsecret/cache` and this folder will be added to `.gitignore`. At this location, a public keyring will be maintained on a per user bases and it won't be shared by users.
1. A tombstone marker file with <keyid>`.killed` will be created at `~/.gitsecret/keys` by git-secret-killperson to mark a user as killed.
The storage format will be used by git-secret-tell as follows:
git-secret-tell will:
1. Scan the set of `.gpg.colon` to find all currently told identities. If the told identity is in the current list do nothing.
1. Scan the set of `.gpg.colon` to find all currently told identities. If the told identity is in the list do nothing.
1. If the told identity isn't listed run `gpg --armor --export` against the users `$HOME` keyring. Run `--keyid-format long --with-colons` of the exported key. The result being two new files `<key-id>.pub.gpg` and `<key-id>.gpg.colon` in `~/.gitsecret/keys`
Note that the steps to ensure that older versions of git-secret know about the newly told user will be outlined below.
Note that the additional steps to ensure that older versions of git-secret know about the newly told user will be outlined below.
The storage format will be used by git-secret-hide as follows:
git-secret-hide will:
1. The list of "64bit keyid"s who are told will be computed from the `.gpg.colon` files. This will be checked against the list of "64bit keyid"s in the "keyring cache" at `~/.gitsecret/cache`. Any missing keys are imported into the "keyring cache". It is anticipated that `grep` and `gawk` will be suffient to be perform this calculation. The code then runs as normal using the keyring cache.
1. The list of "64-bit keyid"s who are told will be computed from the `.gpg.colon` files. This will be checked against the list of "64-bit keyid"s in the "keyring cache" at `~/.gitsecret/cache`. Any missing keys are imported into the "keyring cache". It is anticipated that `grep` and `gawk` will be sufficient to perform this calculation. The code then runs as before using the "keyring cache".
The storage format will be used by git-secret-killperson as follows:
git-secret-whoknows will:
TBD
1. The list of identities will be loaded by parsing the `.gpg.colon` files. Note that multiple identities can be listed against each key.
The storage format will be used by git-secret-xxx as follows:
git-secret-usage will:
TBD
1. Document the git-secret-migrate command discussed in the next section.
Forwards compatibility with older versions of git-secret will be mantained as follows:
git-secret-reveal will:
TBD
* Be unchanged.
git-secret-remove will:
* Be unchanged.
git-secret-list will:
* Be unchanged.
git-secret-killperson will:
1. Remove the key from the keyring cache then delete the `<key-id>.pub.gpg` and `<key-id>.gpg.colon` in `~/.gitsecret/keys`.
git-secret-init will:
1. Add `~/.gitsecret/cache` into `.gitignore` and do any initialisation work of the public keyring at that location.
git-secret-clean will:
* Be unchanged.
git-secret-changes will:
1. Show differences the files `<key-id>.pub.gpg` and `<key-id>.gpg.colon` in `~/.gitsecret/keys`
git-secret-add will:
* Be unchanged.
A new command git-secret-migrate will:
1. Create the folder `~/.gitsecret/cache` and add it to the `.gitignore` file.
1. Extract any keys from the old keyring generating `<key-id>.pub.gpg` and `<key-id>.gpg.colon` files in `~/.gitsecret/keys`
## Version compatibility
Backwards compatibility will the old keyring storage approach will be maintained as follows:
1. For each changed command a guard will be added that checks for the existence of the .gitsecret/cache
1. If the folder exists it proceeds as normal.
1. If it does not exist it will report that the repo was initialised by an older version of git-secret and tell the user to run git-secret-migrate
Forwards compatibility with older versions of git-secret will be maintained as follows.
git-secret-hide will:
1. Have a guard that will check for the existence of the old keyring. If it exists it will check it for any new public keys and extract them into the new format prior to running.
git-secret-tell will:
1. Will check for the existence of the old keyring. If it exists it will load the new public key into it.
## Drawbacks
To maintain forward compatibility the approach requires the eixsting logic to kept working for a perod of time... TBD
To maintain forward compatibility the approach requires the existing logic to kept working for a period of time. We can give a deprecated warning if the forwards compatibility logic is running. The warning can be suppressed using a command-line flag.
## Alternatives
What other designs have been considered? Unknown.
What is the impact of not doing this? Team members are locked out of their secrets broken when one user upgrades. This can go undetected until the victim needs the secrets in a hurry for production support. Bad things then happen.
What is the impact of not doing this? Team members are locked out of secrets when only one other team member upgrades GPG. This can go undetected until the victim needs the secrets in a hurry for production support. Bad things then happen.
Simon Massey
6 years ago