diff mbox series

[v6,9/9] ssh signing: add documentation

Message ID 275af516ebadebf0af6555f27508bdff98a35b94.1627501009.git.gitgitgadget@gmail.com (mailing list archive)
State New
Headers show
Series ssh signing: Add commit & tag signing/verification via SSH keys using ssh-keygen | expand

Commit Message

Fabian Stelzer July 28, 2021, 7:36 p.m. UTC
From: Fabian Stelzer <fs@gigacodes.de>

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
 Documentation/config/gpg.txt  | 39 +++++++++++++++++++++++++++++++++--
 Documentation/config/user.txt |  6 ++++++
 2 files changed, 43 insertions(+), 2 deletions(-)
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diff --git a/Documentation/config/gpg.txt b/Documentation/config/gpg.txt
index d94025cb368..dc790512e86 100644
--- a/Documentation/config/gpg.txt
+++ b/Documentation/config/gpg.txt
@@ -11,13 +11,13 @@  gpg.program::
 	Specifies which key format to use when signing with `--gpg-sign`.
-	Default is "openpgp" and another possible value is "x509".
+	Default is "openpgp". Other possible values are "x509", "ssh".
 	Use this to customize the program used for the signing format you
 	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
 	be used as a legacy synonym for `gpg.openpgp.program`. The default
-	value for `gpg.x509.program` is "gpgsm".
+	value for `gpg.x509.program` is "gpgsm" and `gpg.ssh.program` is "ssh-keygen".
 	Specifies a minimum trust level for signature verification.  If
@@ -33,3 +33,38 @@  gpg.minTrustLevel::
 * `marginal`
 * `fully`
 * `ultimate`
+	A file containing ssh public keys which you are willing to trust.
+	The file consists of one or more lines of principals followed by an ssh
+	public key.
+	e.g.: user1@example.com,user2@example.com ssh-rsa AAAAX1...
+	See ssh-keygen(1) "ALLOWED SIGNERS" for details.
+	The principal is only used to identify the key and is available when
+	verifying a signature.
+SSH has no concept of trust levels like gpg does. To be able to differentiate
+between valid signatures and trusted signatures the trust level of a signature
+verification is set to `fully` when the public key is present in the allowedSignersFile.
+Therefore to only mark fully trusted keys as verified set gpg.minTrustLevel to `fully`.
+Otherwise valid but untrusted signatures will still verify but show no principal
+name of the signer.
+This file can be set to a location outside of the repository and every developer
+maintains their own trust store. A central repository server could generate this
+file automatically from ssh keys with push access to verify the code against.
+In a corporate setting this file is probably generated at a global location
+from automation that already handles developer ssh keys.
+A repository that only allows signed commits can store the file
+in the repository itself using a path relative to the top-level of the working tree.
+This way only committers with an already valid key can add or change keys in the keyring.
+Using a SSH CA key with the cert-authority option
+(see ssh-keygen(1) "CERTIFICATES") is also valid.
+	Either a SSH KRL or a list of revoked public keys (without the principal prefix).
+	See ssh-keygen(1) for details.
+	If a public key is found in this file then it will always be treated
+	as having trust level "never" and signatures will show as invalid.
diff --git a/Documentation/config/user.txt b/Documentation/config/user.txt
index 59aec7c3aed..b3c2f2c541e 100644
--- a/Documentation/config/user.txt
+++ b/Documentation/config/user.txt
@@ -36,3 +36,9 @@  user.signingKey::
 	commit, you can override the default selection with this variable.
 	This option is passed unchanged to gpg's --local-user parameter,
 	so you may specify a key using any method that gpg supports.
+	If gpg.format is set to "ssh" this can contain the literal ssh public
+	key (e.g.: "ssh-rsa XXXXXX identifier") or a file which contains it and
+	corresponds to the private key used for signing. The private key
+	needs to be available via ssh-agent. Alternatively it can be set to
+	a file containing a private key directly. If not set git will call
+	"ssh-add -L" and try to use the first key available.