[RFC PATCH 0/6] ssh signing: verify key lifetime

@@ -769,8 +769,9 @@ static void prepare_push_cert_sha1(struct child_process *proc)
 		memset(&sigcheck, '\0', sizeof(sigcheck));
 
 		bogs = parse_signed_buffer(push_cert.buf, push_cert.len);
-		check_signature(push_cert.buf, bogs, push_cert.buf + bogs,
-				push_cert.len - bogs, &sigcheck);
+		check_signature(push_cert.buf, bogs, 0, NULL,
+				push_cert.buf + bogs, push_cert.len - bogs,
+				&sigcheck);
 
 		nonce_status = check_nonce(push_cert.buf, bogs);
 	}

@@ -1212,7 +1212,7 @@ int check_commit_signature(const struct commit *commit, struct signature_check *
 
 	if (parse_signed_commit(commit, &payload, &signature, the_hash_algo) <= 0)
 		goto out;
-	ret = check_signature(payload.buf, payload.len, signature.buf,
+	ret = check_signature(payload.buf, payload.len, 0, NULL, signature.buf,
 		signature.len, sigc);
 
  out:

@@ -533,8 +533,8 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 		else {
 			buf = payload.buf;
 			len = payload.len;
-			if (check_signature(payload.buf, payload.len, sig.buf,
-					    sig.len, &sigc) &&
+			if (check_signature(payload.buf, payload.len, 0, NULL,
+					    sig.buf, sig.len, &sigc) &&
 			    !sigc.output)
 				strbuf_addstr(&sig, "gpg verification failed.\n");
 			else

@@ -20,8 +20,9 @@ struct gpg_format {
 	const char **sigs;
 	int (*verify_signed_buffer)(struct signature_check *sigc,
 				    struct gpg_format *fmt, const char *payload,
-				    size_t payload_size, const char *signature,
-				    size_t signature_size);
+				    size_t payload_size, timestamp_t payload_timestamp,
+				    struct strbuf *payload_signer,
+				    const char *signature, size_t signature_size);
 	int (*sign_buffer)(struct strbuf *buffer, struct strbuf *signature,
 			   const char *signing_key);
 	const char *(*get_default_key)(void);

@@ -54,12 +55,14 @@ static const char *ssh_sigs[] = {
 
 static int verify_gpg_signed_buffer(struct signature_check *sigc,
 				    struct gpg_format *fmt, const char *payload,
-				    size_t payload_size, const char *signature,
-				    size_t signature_size);
+				    size_t payload_size, timestamp_t payload_timestamp,
+				    struct strbuf *payload_signer,
+				    const char *signature, size_t signature_size);
 static int verify_ssh_signed_buffer(struct signature_check *sigc,
 				    struct gpg_format *fmt, const char *payload,
-				    size_t payload_size, const char *signature,
-				    size_t signature_size);
+				    size_t payload_size, timestamp_t payload_timestamp,
+				    struct strbuf *payload_signer,
+				    const char *signature, size_t signature_size);
 static int sign_buffer_gpg(struct strbuf *buffer, struct strbuf *signature,
 			   const char *signing_key);
 static int sign_buffer_ssh(struct strbuf *buffer, struct strbuf *signature,

@@ -315,8 +318,9 @@ static void parse_gpg_output(struct signature_check *sigc)
 
 static int verify_gpg_signed_buffer(struct signature_check *sigc,
 				    struct gpg_format *fmt, const char *payload,
-				    size_t payload_size, const char *signature,
-				    size_t signature_size)
+				    size_t payload_size, timestamp_t payload_timestamp,
+				    struct strbuf *payload_signer,
+				    const char *signature, size_t signature_size)
 {
 	struct child_process gpg = CHILD_PROCESS_INIT;
 	struct tempfile *temp;

@@ -421,8 +425,9 @@ static void parse_ssh_output(struct signature_check *sigc)
 
 static int verify_ssh_signed_buffer(struct signature_check *sigc,
 				    struct gpg_format *fmt, const char *payload,
-				    size_t payload_size, const char *signature,
-				    size_t signature_size)
+				    size_t payload_size, timestamp_t payload_timestamp,
+				    struct strbuf *payload_signer,
+				    const char *signature, size_t signature_size)
 {
 	struct child_process ssh_keygen = CHILD_PROCESS_INIT;
 	struct tempfile *buffer_file;

@@ -556,8 +561,9 @@ static int verify_ssh_signed_buffer(struct signature_check *sigc,
 	return ret;
 }
 
-int check_signature(const char *payload, size_t plen, const char *signature,
-	size_t slen, struct signature_check *sigc)
+int check_signature(const char *payload, size_t plen, timestamp_t payload_timestamp,
+		    struct strbuf *payload_signer, const char *signature,
+		    size_t slen, struct signature_check *sigc)
 {
 	struct gpg_format *fmt;
 	int status;

@@ -569,8 +575,9 @@ int check_signature(const char *payload, size_t plen, const char *signature,
 	if (!fmt)
 		die(_("bad/incompatible signature '%s'"), signature);
 
-	status = fmt->verify_signed_buffer(sigc, fmt, payload, plen, signature,
-					   slen);
+	status = fmt->verify_signed_buffer(sigc, fmt, payload, plen,
+					   payload_timestamp, payload_signer,
+					   signature, slen);
 
 	if (status && !sigc->output)
 		return !!status;

@@ -71,6 +71,7 @@ const char *get_signing_key(void);
  */
 const char *get_signing_key_id(void);
 int check_signature(const char *payload, size_t plen,
+		    timestamp_t payload_timestamp, struct strbuf *payload_signer,
 		    const char *signature, size_t slen,
 		    struct signature_check *sigc);
 void print_signature_buffer(const struct signature_check *sigc,

@@ -513,7 +513,7 @@ static void show_signature(struct rev_info *opt, struct commit *commit)
 	if (parse_signed_commit(commit, &payload, &signature, the_hash_algo) <= 0)
 		goto out;
 
-	status = check_signature(payload.buf, payload.len, signature.buf,
+	status = check_signature(payload.buf, payload.len, 0, NULL, signature.buf,
 				 signature.len, &sigc);
 	if (status && !sigc.output)
 		show_sig_lines(opt, status, "No signature\n");

@@ -583,7 +583,7 @@ static int show_one_mergetag(struct commit *commit,
 	status = -1;
 	if (parse_signature(extra->value, extra->len, &payload, &signature)) {
 		/* could have a good signature */
-		status = check_signature(payload.buf, payload.len,
+		status = check_signature(payload.buf, payload.len, 0, NULL,
 					 signature.buf, signature.len, &sigc);
 		if (sigc.output)
 			strbuf_addstr(&verify_message, sigc.output);

@@ -25,7 +25,7 @@ static int run_gpg_verify(const char *buf, unsigned long size, unsigned flags)
 		return error("no signature found");
 	}
 
-	ret = check_signature(payload.buf, payload.len, signature.buf,
+	ret = check_signature(payload.buf, payload.len, 0, NULL, signature.buf,
 				signature.len, &sigc);
 
 	if (!(flags & GPG_VERIFY_OMIT_STATUS))

@@ -90,6 +90,10 @@ test_lazy_prereq RFC1991 '
 GPGSSH_KEY_PRIMARY="${GNUPGHOME}/ed25519_ssh_signing_key"
 GPGSSH_KEY_SECONDARY="${GNUPGHOME}/rsa_2048_ssh_signing_key"
 GPGSSH_KEY_UNTRUSTED="${GNUPGHOME}/untrusted_ssh_signing_key"
+GPGSSH_KEY_EXPIRED="${GNUPGHOME}/expired_ssh_signing_key"
+GPGSSH_KEY_NOTYETVALID="${GNUPGHOME}/notyetvalid_ssh_signing_key"
+GPGSSH_KEY_TIMEBOXEDVALID="${GNUPGHOME}/timeboxed_valid_ssh_signing_key"
+GPGSSH_KEY_TIMEBOXEDINVALID="${GNUPGHOME}/timeboxed_invalid_ssh_signing_key"
 GPGSSH_KEY_WITH_PASSPHRASE="${GNUPGHOME}/protected_ssh_signing_key"
 GPGSSH_KEY_PASSPHRASE="super_secret"
 GPGSSH_ALLOWED_SIGNERS="${GNUPGHOME}/ssh.all_valid.allowedSignersFile"

@@ -112,7 +116,20 @@ 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")" >> "${GPGSSH_ALLOWED_SIGNERS}" &&
-	ssh-keygen -t ed25519 -N "" -f "${GPGSSH_KEY_UNTRUSTED}" >/dev/null
+	ssh-keygen -t ed25519 -N "" -C "git ed25519 key" -f "${GPGSSH_KEY_UNTRUSTED}" >/dev/null
+'
+
+test_lazy_prereq GPGSSH_VERIFYTIME '
+	# Check if ssh-keygen has a verify-time option by passing an invalid date to it
+	ssh-keygen -Overify-time=INVALID -Y check-novalidate -s doesnotmatter 2>&1 | grep -q -F "Invalid \"verify-time\"" &&
+	ssh-keygen -t ed25519 -N "" -C "timeboxed valid key" -f "${GPGSSH_KEY_TIMEBOXEDVALID}" >/dev/null &&
+	echo "\"timeboxed valid key\" valid-after=\"20050407000000\",valid-before=\"200504100000\" $(cat "${GPGSSH_KEY_TIMEBOXEDVALID}.pub")" >> "${GPGSSH_ALLOWED_SIGNERS}" &&
+	ssh-keygen -t ed25519 -N "" -C "timeboxed invalid key" -f "${GPGSSH_KEY_TIMEBOXEDINVALID}" >/dev/null &&
+	echo "\"timeboxed invalid key\" valid-after=\"20050401000000\",valid-before=\"20050402000000\" $(cat "${GPGSSH_KEY_TIMEBOXEDINVALID}.pub")" >> "${GPGSSH_ALLOWED_SIGNERS}" &&
+	ssh-keygen -t ed25519 -N "" -C "expired key" -f "${GPGSSH_KEY_EXPIRED}" >/dev/null &&
+	echo "\"principal with expired key\" valid-before=\"20000101000000\" $(cat "${GPGSSH_KEY_EXPIRED}.pub")" >> "${GPGSSH_ALLOWED_SIGNERS}" &&
+	ssh-keygen -t ed25519 -N "" -C "not yet valid key" -f "${GPGSSH_KEY_NOTYETVALID}" >/dev/null &&
+	echo "\"principal with not yet valid key\" valid-after=\"29990101000000\" $(cat "${GPGSSH_KEY_NOTYETVALID}.pub")" >> "${GPGSSH_ALLOWED_SIGNERS}"
 '
 
 sanitize_pgp() {

@@ -509,12 +509,18 @@ static void show_signature(struct rev_info *opt, struct commit *commit)
 	struct strbuf signature = STRBUF_INIT;
 	struct signature_check sigc = { 0 };
 	int status;
+	struct strbuf payload_signer = STRBUF_INIT;
+	timestamp_t payload_timestamp = 0;
 
 	if (parse_signed_commit(commit, &payload, &signature, the_hash_algo) <= 0)
 		goto out;
 
-	status = check_signature(payload.buf, payload.len, 0, NULL, signature.buf,
-				 signature.len, &sigc);
+	if (parse_signed_buffer_metadata(payload.buf, "committer", &payload_timestamp, &payload_signer))
+		goto out;
+
+	status = check_signature(payload.buf, payload.len, payload_timestamp,
+				 &payload_signer, signature.buf, signature.len,
+				 &sigc);
 	if (status && !sigc.output)
 		show_sig_lines(opt, status, "No signature\n");
 	else

@@ -524,6 +530,7 @@ static void show_signature(struct rev_info *opt, struct commit *commit)
  out:
 	strbuf_release(&payload);
 	strbuf_release(&signature);
+	strbuf_release(&payload_signer);
 }
 
 static int which_parent(const struct object_id *oid, const struct commit *commit)

@@ -558,6 +565,8 @@ static int show_one_mergetag(struct commit *commit,
 	int status, nth;
 	struct strbuf payload = STRBUF_INIT;
 	struct strbuf signature = STRBUF_INIT;
+	struct strbuf payload_signer = STRBUF_INIT;
+	timestamp_t payload_timestamp = 0;
 
 	hash_object_file(the_hash_algo, extra->value, extra->len,
 			 type_name(OBJ_TAG), &oid);

@@ -582,9 +591,14 @@ static int show_one_mergetag(struct commit *commit,
 
 	status = -1;
 	if (parse_signature(extra->value, extra->len, &payload, &signature)) {
+
+		if (parse_signed_buffer_metadata(payload.buf, "tagger", &payload_timestamp, &payload_signer))
+			strbuf_addstr(&verify_message, _("failed to parse timestamp and signer info from payload"));
+
 		/* could have a good signature */
-		status = check_signature(payload.buf, payload.len, 0, NULL,
-					 signature.buf, signature.len, &sigc);
+		status = check_signature(payload.buf, payload.len, payload_timestamp,
+					 &payload_signer, signature.buf,
+					 signature.len, &sigc);
 		if (sigc.output)
 			strbuf_addstr(&verify_message, sigc.output);
 		else

@@ -597,6 +611,7 @@ static int show_one_mergetag(struct commit *commit,
 	strbuf_release(&verify_message);
 	strbuf_release(&payload);
 	strbuf_release(&signature);
+	strbuf_release(&payload_signer);
 	return 0;
 }
 

@@ -1626,6 +1626,24 @@ test_expect_success GPGSSH 'setup sshkey signed branch' '
 	git commit -S -m signed_commit
 '
 
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'create signed commits with keys having defined lifetimes' '
+	test_config gpg.format ssh &&
+	touch file &&
+	git add file &&
+
+	echo expired >file && test_tick && git commit -a -m expired -S"${GPGSSH_KEY_EXPIRED}" &&
+	git tag expired-signed &&
+
+	echo notyetvalid >file && test_tick && git commit -a -m notyetvalid -S"${GPGSSH_KEY_NOTYETVALID}" &&
+	git tag notyetvalid-signed &&
+
+	echo timeboxedvalid >file && test_tick && git commit -a -m timeboxedvalid -S"${GPGSSH_KEY_TIMEBOXEDVALID}" &&
+	git tag timeboxedvalid-signed &&
+
+	echo timeboxedinvalid >file && test_tick && git commit -a -m timeboxedinvalid -S"${GPGSSH_KEY_TIMEBOXEDINVALID}" &&
+	git tag timeboxedinvalid-signed
+'
+
 test_expect_success GPGSM 'log x509 fingerprint' '
 	echo "F8BF62E0693D0694816377099909C779FA23FD65 | " >expect &&
 	git log -n1 --format="%GF | %GP" signed-x509 >actual &&

@@ -1663,6 +1681,31 @@ test_expect_success GPGSSH 'log --graph --show-signature ssh' '
 	grep "${GOOD_SIGNATURE_TRUSTED}" actual
 '
 
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'log shows failure on expired signature key' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	git log --graph --show-signature -n1 expired-signed >actual &&
+	! grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'log shows failure on not yet valid signature key' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	git log --graph --show-signature -n1 notyetvalid-signed >actual &&
+	! grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'log show success with commit date and key validity matching' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	git log --graph --show-signature -n1 timeboxedvalid-signed >actual &&
+	grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${GPGSSH_BAD_SIGNATURE}" actual
+'
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'log shows failure with commit date outside of key validity' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	git log --graph --show-signature -n1 timeboxedinvalid-signed >actual &&
+	! grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
+'
+
 test_expect_success GPG 'log --graph --show-signature for merged tag' '
 	test_when_finished "git reset --hard && git checkout main" &&
 	git checkout -b plain main &&

@@ -64,6 +64,11 @@ 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.
 +
+Since OpensSSH 8.8 this file allows specifying a key lifetime using valid-after &
+valid-before options. Git will mark signatures as valid if the signing key was
+valid at the time of the signatures creation. This allows users to change a
+signing key without invalidating all previously made signatures.
++
 Using a SSH CA key with the cert-authority option
 (see ssh-keygen(1) "CERTIFICATES") is also valid.
 

@@ -1207,17 +1207,25 @@ int check_commit_signature(const struct commit *commit, struct signature_check *
 	struct strbuf payload = STRBUF_INIT;
 	struct strbuf signature = STRBUF_INIT;
 	int ret = 1;
+	struct strbuf payload_signer = STRBUF_INIT;
+	timestamp_t payload_timestamp = 0;
 
 	sigc->result = 'N';
 
 	if (parse_signed_commit(commit, &payload, &signature, the_hash_algo) <= 0)
 		goto out;
-	ret = check_signature(payload.buf, payload.len, 0, NULL, signature.buf,
-		signature.len, sigc);
+	if (parse_signed_buffer_metadata(payload.buf, "committer",
+					 &payload_timestamp, &payload_signer))
+		goto out;
+
+	ret = check_signature(payload.buf, payload.len, payload_timestamp,
+			      &payload_signer, signature.buf,
+			      signature.len, sigc);
 
  out:
 	strbuf_release(&payload);
 	strbuf_release(&signature);
+	strbuf_release(&payload_signer);
 
 	return ret;
 }

@@ -439,6 +439,13 @@ static int verify_ssh_signed_buffer(struct signature_check *sigc,
 	struct strbuf ssh_principals_err = STRBUF_INIT;
 	struct strbuf ssh_keygen_out = STRBUF_INIT;
 	struct strbuf ssh_keygen_err = STRBUF_INIT;
+	struct strbuf verify_time = STRBUF_INIT;
+	const struct date_mode verify_date_mode = {
+		.type = DATE_STRFTIME,
+		.strftime_fmt = "%Y%m%d%H%M%S",
+		/* SSH signing key validity has no timezone information - Use the local timezone */
+		.local = 1,
+	};
 
 	if (!ssh_allowed_signers) {
 		error(_("gpg.ssh.allowedSignersFile needs to be configured and exist for ssh signature verification"));

@@ -456,18 +463,27 @@ static int verify_ssh_signed_buffer(struct signature_check *sigc,
 		return -1;
 	}
 
+	if (payload_timestamp != 0) {
+		strbuf_addf(&verify_time, "-Overify-time=%s",
+			    show_date(payload_timestamp, 0, &verify_date_mode));
+	}
+
 	/* Find the principal from the signers */
 	strvec_pushl(&ssh_keygen.args, fmt->program,
 		     "-Y", "find-principals",
 		     "-f", ssh_allowed_signers,
 		     "-s", buffer_file->filename.buf,
+		     verify_time.buf,
 		     NULL);
+
 	ret = pipe_command(&ssh_keygen, NULL, 0, &ssh_principals_out, 0,
 			   &ssh_principals_err, 0);
+
 	if (ret && strstr(ssh_principals_err.buf, "usage:")) {
 		error(_("ssh-keygen -Y find-principals/verify is needed for ssh signature verification (available in openssh version 8.2p1+)"));
 		goto out;
 	}
+
 	if (ret || !ssh_principals_out.len) {
 		/*
 		 * We did not find a matching principal in the allowedSigners

@@ -478,7 +494,9 @@ static int verify_ssh_signed_buffer(struct signature_check *sigc,
 			     "-Y", "check-novalidate",
 			     "-n", "git",
 			     "-s", buffer_file->filename.buf,
+			     verify_time.buf,
 			     NULL);
+
 		pipe_command(&ssh_keygen, payload, payload_size,
 				   &ssh_keygen_out, 0, &ssh_keygen_err, 0);
 

@@ -512,6 +530,7 @@ static int verify_ssh_signed_buffer(struct signature_check *sigc,
 				     "-f", ssh_allowed_signers,
 				     "-I", principal,
 				     "-s", buffer_file->filename.buf,
+				     verify_time.buf,
 				     NULL);
 
 			if (ssh_revocation_file) {

@@ -557,10 +576,36 @@ static int verify_ssh_signed_buffer(struct signature_check *sigc,
 	strbuf_release(&ssh_principals_err);
 	strbuf_release(&ssh_keygen_out);
 	strbuf_release(&ssh_keygen_err);
+	strbuf_release(&verify_time);
 
 	return ret;
 }
 
+int parse_signed_buffer_metadata(const char *payload, const char *signer_header,
+				 timestamp_t *payload_timestamp,
+				 struct strbuf *payload_signer)
+{
+	const char *ident_line = NULL;
+	size_t ident_len;
+	struct ident_split ident;
+
+	ident_line = find_commit_header(payload, signer_header, &ident_len);
+	if (ident_line && ident_len) {
+		if (!split_ident_line(&ident, ident_line, ident_len)) {
+			if (payload_timestamp && ident.date_begin && ident.date_end)
+				*payload_timestamp = parse_timestamp(
+					ident.date_begin, NULL, 10);
+			if (payload_signer)
+				strbuf_add(payload_signer, ident.mail_begin,
+					(ident.mail_end - ident.mail_begin));
+
+			return 0;
+		}
+	}
+
+	return 1;
+}
+
 int check_signature(const char *payload, size_t plen, timestamp_t payload_timestamp,
 		    struct strbuf *payload_signer, const char *signature,
 		    size_t slen, struct signature_check *sigc)

@@ -65,6 +65,14 @@ int git_gpg_config(const char *, const char *, void *);
 void set_signing_key(const char *);
 const char *get_signing_key(void);
 
+/*
+ * Tries to find "signer_header" (usually committer or tagger) in the payload,
+ * and sets the corresponding timestamp and signer parameters if found.
+ */
+int parse_signed_buffer_metadata(const char *payload, const char *signer_header,
+				 timestamp_t *payload_timestamp,
+				 struct strbuf *payload_signer);
+
 /*
  * Returns a textual unique representation of the signing key in use
  * Either a GPG KeyID or a SSH Key Fingerprint

@@ -76,6 +76,23 @@ test_expect_success GPGSSH 'create signed commits' '
 	git tag twelfth-signed-alt $(cat oid)
 '
 
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'create signed commits with keys having defined lifetimes' '
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+
+	echo expired >file && test_tick && git commit -a -m expired -S"${GPGSSH_KEY_EXPIRED}" &&
+	git tag expired-signed &&
+
+	echo notyetvalid >file && test_tick && git commit -a -m notyetvalid -S"${GPGSSH_KEY_NOTYETVALID}" &&
+	git tag notyetvalid-signed &&
+
+	echo timeboxedvalid >file && test_tick && git commit -a -m timeboxedvalid -S"${GPGSSH_KEY_TIMEBOXEDVALID}" &&
+	git tag timeboxedvalid-signed &&
+
+	echo timeboxedinvalid >file && test_tick && git commit -a -m timeboxedinvalid -S"${GPGSSH_KEY_TIMEBOXEDINVALID}" &&
+	git tag timeboxedinvalid-signed
+'
+
 test_expect_success GPGSSH 'verify and show signatures' '
 	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
 	test_config gpg.mintrustlevel UNDEFINED &&

@@ -122,6 +139,31 @@ test_expect_success GPGSSH 'verify-commit exits failure on untrusted signature'
 	grep "${GPGSSH_KEY_NOT_TRUSTED}" actual
 '
 
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'verify-commit exits failure on expired signature key' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	test_must_fail git verify-commit expired-signed 2>actual &&
+	! grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'verify-commit exits failure on not yet valid signature key' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	test_must_fail git verify-commit notyetvalid-signed 2>actual &&
+	! grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'verify-commit succeeds with commit date and key validity matching' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	git verify-commit timeboxedvalid-signed 2>actual &&
+	grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${GPGSSH_BAD_SIGNATURE}" actual
+'
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'verify-commit exits failure with commit date outside of key validity' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	test_must_fail git verify-commit timeboxedinvalid-signed 2>actual &&
+	! grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
+'
+
 test_expect_success GPGSSH 'verify-commit exits success with matching minTrustLevel' '
 	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
 	test_config gpg.minTrustLevel fully &&

@@ -524,6 +524,8 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 		unsigned long len = size;
 		struct signature_check sigc = { NULL };
 		struct strbuf payload = STRBUF_INIT, sig = STRBUF_INIT;
+		struct strbuf payload_signer = STRBUF_INIT;
+		timestamp_t payload_timestamp = 0;
 
 		if (!buf || type != OBJ_TAG)
 			goto next;

@@ -533,9 +535,16 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 		else {
 			buf = payload.buf;
 			len = payload.len;
-			if (check_signature(payload.buf, payload.len, 0, NULL,
+
+			if (parse_signed_buffer_metadata(payload.buf, "tagger",
+							 &payload_timestamp,
+							 &payload_signer))
+				strbuf_addstr(&sig, _("failed to parse timestamp and signer info from payload"));
+
+			if (check_signature(payload.buf, payload.len,
+					    payload_timestamp, &payload_signer,
 					    sig.buf, sig.len, &sigc) &&
-			    !sigc.output)
+			!sigc.output)
 				strbuf_addstr(&sig, "gpg verification failed.\n");
 			else
 				strbuf_addstr(&sig, sigc.output);

@@ -564,6 +573,7 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 		}
 		strbuf_release(&payload);
 		strbuf_release(&sig);
+		strbuf_release(&payload_signer);
 	next:
 		free(origbuf);
 	}

@@ -91,6 +91,26 @@ test_expect_success GPGSSH 'created ssh signed commit and tag' '
 	git tag -s -u"${GPGSSH_KEY_UNTRUSTED}" -m signed-ssh-tag-msg-untrusted signed-untrusted-ssh-tag left
 '
 
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'create signed tags with keys having defined lifetimes' '
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+	git checkout -b signed-expiry-ssh &&
+	touch file &&
+	git add file &&
+
+	echo expired >file && test_tick && git commit -a -m expired -S"${GPGSSH_KEY_EXPIRED}" &&
+	git tag -s -u "${GPGSSH_KEY_EXPIRED}" -m expired-signed expired-signed &&
+
+	echo notyetvalid >file && test_tick && git commit -a -m notyetvalid -S"${GPGSSH_KEY_NOTYETVALID}" &&
+	git tag -s -u "${GPGSSH_KEY_NOTYETVALID}" -m notyetvalid-signed notyetvalid-signed &&
+
+	echo timeboxedvalid >file && test_tick && git commit -a -m timeboxedvalid -S"${GPGSSH_KEY_TIMEBOXEDVALID}" &&
+	git tag -s -u "${GPGSSH_KEY_TIMEBOXEDVALID}" -m timeboxedvalid-signed timeboxedvalid-signed &&
+
+	echo timeboxedinvalid >file && test_tick && git commit -a -m timeboxedinvalid -S"${GPGSSH_KEY_TIMEBOXEDINVALID}" &&
+	git tag -s -u "${GPGSSH_KEY_TIMEBOXEDINVALID}" -m timeboxedinvalid-signed timeboxedinvalid-signed
+'
+
 test_expect_success 'message for merging local branch' '
 	echo "Merge branch ${apos}left${apos}" >expected &&
 

@@ -137,6 +157,40 @@ test_expect_success GPGSSH 'message for merging local tag signed by unknown ssh
 	! grep "${GPGSSH_BAD_SIGNATURE}" actual &&
 	grep "${GPGSSH_KEY_NOT_TRUSTED}" actual
 '
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'message for merging local tag signed by expired ssh key' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	git checkout main &&
+	git fetch . expired-signed &&
+	git fmt-merge-msg <.git/FETCH_HEAD >actual 2>&1 &&
+	! grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'message for merging local tag signed by not yet valid ssh key' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	git checkout main &&
+	git fetch . notyetvalid-signed &&
+	git fmt-merge-msg <.git/FETCH_HEAD >actual 2>&1 &&
+	! grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'message for merging local tag signed by valid timeboxed ssh key' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	git checkout main &&
+	git fetch . timeboxedvalid-signed &&
+	git fmt-merge-msg <.git/FETCH_HEAD >actual 2>&1 &&
+	grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${GPGSSH_BAD_SIGNATURE}" actual
+'
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'message for merging local tag signed by invalid timeboxed ssh key' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	git checkout main &&
+	git fetch . timeboxedinvalid-signed &&
+	git fmt-merge-msg <.git/FETCH_HEAD >actual 2>&1 &&
+	! grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
+'
+
 test_expect_success 'message for merging external branch' '
 	echo "Merge branch ${apos}left${apos} of $(pwd)" >expected &&
 

@@ -48,6 +48,23 @@ test_expect_success GPGSSH 'create signed tags ssh' '
 	git tag -u"${GPGSSH_KEY_UNTRUSTED}" -m eighth eighth-signed-alt
 '
 
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'create signed tags with keys having defined lifetimes' '
+	test_when_finished "test_unconfig commit.gpgsign" &&
+	test_config gpg.format ssh &&
+
+	echo expired >file && test_tick && git commit -a -m expired -S"${GPGSSH_KEY_EXPIRED}" &&
+	git tag -s -u "${GPGSSH_KEY_EXPIRED}" -m expired-signed expired-signed &&
+
+	echo notyetvalid >file && test_tick && git commit -a -m notyetvalid -S"${GPGSSH_KEY_NOTYETVALID}" &&
+	git tag -s -u "${GPGSSH_KEY_NOTYETVALID}" -m notyetvalid-signed notyetvalid-signed &&
+
+	echo timeboxedvalid >file && test_tick && git commit -a -m timeboxedvalid -S"${GPGSSH_KEY_TIMEBOXEDVALID}" &&
+	git tag -s -u "${GPGSSH_KEY_TIMEBOXEDVALID}" -m timeboxedvalid-signed timeboxedvalid-signed &&
+
+	echo timeboxedinvalid >file && test_tick && git commit -a -m timeboxedinvalid -S"${GPGSSH_KEY_TIMEBOXEDINVALID}" &&
+	git tag -s -u "${GPGSSH_KEY_TIMEBOXEDINVALID}" -m timeboxedinvalid-signed timeboxedinvalid-signed
+'
+
 test_expect_success GPGSSH 'verify and show ssh signatures' '
 	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
 	(

@@ -80,6 +97,31 @@ test_expect_success GPGSSH 'verify and show ssh signatures' '
 	)
 '
 
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'verify-tag exits failure on expired signature key' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	test_must_fail git verify-tag expired-signed 2>actual &&
+	! grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'verify-tag exits failure on not yet valid signature key' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	test_must_fail git verify-tag notyetvalid-signed 2>actual &&
+	! grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
+'
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'verify-tag succeeds with tag date and key validity matching' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	git verify-tag timeboxedvalid-signed 2>actual &&
+	grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual &&
+	! grep "${GPGSSH_BAD_SIGNATURE}" actual
+'
+
+test_expect_success GPGSSH,GPGSSH_VERIFYTIME 'verify-tag failes with tag date outside of key validity' '
+	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
+	test_must_fail git verify-tag timeboxedinvalid-signed 2>actual &&
+	! grep "${GPGSSH_GOOD_SIGNATURE_TRUSTED}" actual
+'
+
 test_expect_success GPGSSH 'detect fudged ssh signature' '
 	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
 	git cat-file tag seventh-signed >raw &&

@@ -16,6 +16,8 @@ static int run_gpg_verify(const char *buf, unsigned long size, unsigned flags)
 	struct strbuf payload = STRBUF_INIT;
 	struct strbuf signature = STRBUF_INIT;
 	int ret;
+	struct strbuf payload_signer = STRBUF_INIT;
+	timestamp_t payload_timestamp = 0;
 
 	memset(&sigc, 0, sizeof(sigc));
 

@@ -25,8 +27,13 @@ static int run_gpg_verify(const char *buf, unsigned long size, unsigned flags)
 		return error("no signature found");
 	}
 
-	ret = check_signature(payload.buf, payload.len, 0, NULL, signature.buf,
-				signature.len, &sigc);
+	if (parse_signed_buffer_metadata(payload.buf, "tagger", &payload_timestamp,
+					 &payload_signer))
+		return error(_("failed to parse timestamp and signer info from payload"));
+
+	ret = check_signature(payload.buf, payload.len, payload_timestamp,
+			      &payload_signer, signature.buf, signature.len,
+			      &sigc);
 
 	if (!(flags & GPG_VERIFY_OMIT_STATUS))
 		print_signature_buffer(&sigc, flags);

@@ -34,6 +41,7 @@ static int run_gpg_verify(const char *buf, unsigned long size, unsigned flags)
 	signature_check_clear(&sigc);
 	strbuf_release(&payload);
 	strbuf_release(&signature);
+	strbuf_release(&payload_signer);
 	return ret;
 }