ssh signing: support non ssh-* keytypes

The user.signingKey config for ssh signing supports either a path to a
file containing the key or for the sake of convenience a literal string
with the ssh public key. To differentiate between those two cases we
check if the first few characters contain "ssh-" which is unlikely to be
the start of a path. ssh supports other key types which are not prefixed
with "ssh-" and will currently be treated as a file path and therefore
fail to load. To remedy this we move the prefix check into its own
function and introduce the prefix `key::` for literal ssh keys. This way
we don't need to add new key types when they become available. The
existing `ssh-` prefix is retained for compatibility with current user
configs but removed from the official documentation to discourage its

Signed-off-by: Fabian Stelzer <>
Signed-off-by: Junio C Hamano <>
Fabian Stelzer 1 year ago committed by Junio C Hamano
parent cd3e606211
commit 350a2518c8
  1. 17
  2. 36
  3. 3
  4. 24

@ -36,10 +36,13 @@ 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
gpg.ssh.defaultKeyCommand (e.g.: "ssh-add -L") and try to use the first
key available.
If gpg.format is set to `ssh` this can contain the path to either
your private ssh key or the public key when ssh-agent is used.
Alternatively it can contain a public key prefixed with `key::`
directly (e.g.: "key::ssh-rsa XXXXXX identifier"). The private key
needs to be available via ssh-agent. If not set git will call
gpg.ssh.defaultKeyCommand (e.g.: "ssh-add -L") and try to use the
first key available. For backward compatibility, a raw key which
begins with "ssh-", such as "ssh-rsa XXXXXX identifier", is treated
as "key::ssh-rsa XXXXXX identifier", but this form is deprecated;
use the `key::` form instead.

@ -707,6 +707,21 @@ int git_gpg_config(const char *var, const char *value, void *cb)
return 0;
* Returns 1 if `string` contains a literal ssh key, 0 otherwise
* `key` will be set to the start of the actual key if a prefix is present.
static int is_literal_ssh_key(const char *string, const char **key)
if (skip_prefix(string, "key::", key))
return 1;
if (starts_with(string, "ssh-")) {
*key = string;
return 1;
return 0;
static char *get_ssh_key_fingerprint(const char *signing_key)
struct child_process ssh_keygen = CHILD_PROCESS_INIT;
@ -714,15 +729,16 @@ static char *get_ssh_key_fingerprint(const char *signing_key)
struct strbuf fingerprint_stdout = STRBUF_INIT;
struct strbuf **fingerprint;
char *fingerprint_ret;
const char *literal_key = NULL;
* With SSH Signing this can contain a filename or a public key
* For textual representation we usually want a fingerprint
if (starts_with(signing_key, "ssh-")) {
if (is_literal_ssh_key(signing_key, &literal_key)) {
strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf", "-", NULL);
ret = pipe_command(&ssh_keygen, signing_key,
strlen(signing_key), &fingerprint_stdout, 0,
ret = pipe_command(&ssh_keygen, literal_key,
strlen(literal_key), &fingerprint_stdout, 0,
NULL, 0);
} else {
strvec_pushl(&ssh_keygen.args, "ssh-keygen", "-lf",
@ -757,6 +773,7 @@ static const char *get_default_ssh_signing_key(void)
const char **argv;
int n;
char *default_key = NULL;
const char *literal_key = NULL;
if (!ssh_default_key_command)
die(_("either user.signingkey or gpg.ssh.defaultKeyCommand needs to be configured"));
@ -774,7 +791,11 @@ static const char *get_default_ssh_signing_key(void)
if (!ret) {
keys = strbuf_split_max(&key_stdout, '\n', 2);
if (keys[0] && starts_with(keys[0]->buf, "ssh-")) {
if (keys[0] && is_literal_ssh_key(keys[0]->buf, &literal_key)) {
* We only use `is_literal_ssh_key` here to check validity
* The prefix will be stripped when the key is used.
default_key = strbuf_detach(keys[0], NULL);
} else {
warning(_("gpg.ssh.defaultKeyCommand succeeded but returned no keys: %s %s"),
@ -889,19 +910,20 @@ static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,
struct tempfile *key_file = NULL, *buffer_file = NULL;
char *ssh_signing_key_file = NULL;
struct strbuf ssh_signature_filename = STRBUF_INIT;
const char *literal_key = NULL;
if (!signing_key || signing_key[0] == '\0')
return error(
_("user.signingkey needs to be set for ssh signing"));
if (starts_with(signing_key, "ssh-")) {
if (is_literal_ssh_key(signing_key, &literal_key)) {
/* A literal ssh key */
key_file = mks_tempfile_t(".git_signing_key_tmpXXXXXX");
if (!key_file)
return error_errno(
_("could not create temporary file"));
keylen = strlen(signing_key);
if (write_in_full(key_file->fd, signing_key, keylen) < 0 ||
keylen = strlen(literal_key);
if (write_in_full(key_file->fd, literal_key, keylen) < 0 ||
close_tempfile_gently(key_file) < 0) {
error_errno(_("failed writing ssh signing key to '%s'"),

@ -91,6 +91,7 @@ GPGSSH_KEY_PRIMARY="${GNUPGHOME}/ed25519_ssh_signing_key"
@ -119,6 +120,8 @@ test_lazy_prereq GPGSSH '
echo "\"principal with number 2\" $(cat "${GPGSSH_KEY_SECONDARY}.pub")" >> "${GPGSSH_ALLOWED_SIGNERS}" &&
ssh-keygen -t ed25519 -N "${GPGSSH_KEY_PASSPHRASE}" -C "git ed25519 encrypted key" -f "${GPGSSH_KEY_WITH_PASSPHRASE}" >/dev/null &&
echo "\"principal with number 3\" $(cat "${GPGSSH_KEY_WITH_PASSPHRASE}.pub")" >> "${GPGSSH_ALLOWED_SIGNERS}" &&
ssh-keygen -t ecdsa -N "" -f "${GPGSSH_KEY_ECDSA}" >/dev/null
echo "\"principal with number 4\" $(cat "${GPGSSH_KEY_ECDSA}.pub")" >> "${GPGSSH_ALLOWED_SIGNERS}" &&
ssh-keygen -t ed25519 -N "" -f "${GPGSSH_KEY_UNTRUSTED}" >/dev/null

@ -73,7 +73,29 @@ test_expect_success GPGSSH 'create signed commits' '
git tag eleventh-signed $(cat oid) &&
echo 12 | git commit-tree --gpg-sign="${GPGSSH_KEY_UNTRUSTED}" HEAD^{tree} >oid &&
test_line_count = 1 oid &&
git tag twelfth-signed-alt $(cat oid)
git tag twelfth-signed-alt $(cat oid) &&
echo 13>file && test_tick && git commit -a -m thirteenth -S"${GPGSSH_KEY_ECDSA}" &&
git tag thirteenth-signed-ecdsa
test_expect_success GPGSSH 'sign commits using literal public keys with ssh-agent' '
test_when_finished "test_unconfig commit.gpgsign" &&
test_config gpg.format ssh &&
eval $(ssh-agent) &&
test_when_finished "kill ${SSH_AGENT_PID}" &&
ssh-add "${GPGSSH_KEY_PRIMARY}" &&
echo 1 >file && git add file &&
git commit -a -m rsa-inline -S"$(cat "${GPGSSH_KEY_PRIMARY}.pub")" &&
echo 2 >file &&
test_config user.signingkey "$(cat "${GPGSSH_KEY_PRIMARY}.pub")" &&
git commit -a -m rsa-config -S &&
ssh-add "${GPGSSH_KEY_ECDSA}" &&
echo 3 >file &&
git commit -a -m ecdsa-inline -S"key::$(cat "${GPGSSH_KEY_ECDSA}.pub")" &&
echo 4 >file &&
test_config user.signingkey "key::$(cat "${GPGSSH_KEY_ECDSA}.pub")" &&
git commit -a -m ecdsa-config -S
test_expect_success GPGSSH 'verify and show signatures' '