diff --git a/Makefile b/Makefile
index 3c4d0c2aa8..bfbad086a2 100644
--- a/Makefile
+++ b/Makefile
@@ -529,6 +529,7 @@ LIB_H += fmt-merge-msg.h
 LIB_H += fsck.h
 LIB_H += gettext.h
 LIB_H += git-compat-util.h
+LIB_H += gpg-interface.h
 LIB_H += graph.h
 LIB_H += grep.h
 LIB_H += hash.h
@@ -622,6 +623,7 @@ LIB_OBJS += entry.o
 LIB_OBJS += environment.o
 LIB_OBJS += exec_cmd.o
 LIB_OBJS += fsck.o
+LIB_OBJS += gpg-interface.o
 LIB_OBJS += graph.o
 LIB_OBJS += grep.o
 LIB_OBJS += hash.o
diff --git a/builtin/commit-tree.c b/builtin/commit-tree.c
index d083795e26..a17811f958 100644
--- a/builtin/commit-tree.c
+++ b/builtin/commit-tree.c
@@ -8,8 +8,9 @@
 #include "tree.h"
 #include "builtin.h"
 #include "utf8.h"
+#include "gpg-interface.h"
 
-static const char commit_tree_usage[] = "git commit-tree <sha1> [(-p <sha1>)...] < changelog";
+static const char commit_tree_usage[] = "git commit-tree [-S<signer>] <sha1> [(-p <sha1>)...] < changelog";
 
 static void new_parent(struct commit *parent, struct commit_list **parents_p)
 {
@@ -25,6 +26,14 @@ static void new_parent(struct commit *parent, struct commit_list **parents_p)
 	commit_list_insert(parent, parents_p);
 }
 
+static int commit_tree_config(const char *var, const char *value, void *cb)
+{
+	int status = git_gpg_config(var, value, NULL);
+	if (status)
+		return status;
+	return git_default_config(var, value, cb);
+}
+
 int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 {
 	int i;
@@ -32,11 +41,19 @@ int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 	unsigned char tree_sha1[20];
 	unsigned char commit_sha1[20];
 	struct strbuf buffer = STRBUF_INIT;
+	const char *sign_commit = NULL;
 
-	git_config(git_default_config, NULL);
+	git_config(commit_tree_config, NULL);
 
 	if (argc < 2 || !strcmp(argv[1], "-h"))
 		usage(commit_tree_usage);
+
+	if (!memcmp(argv[1], "-S", 2)) {
+		sign_commit = argv[1] + 2;
+		argv++;
+		argc--;
+	}
+
 	if (get_sha1(argv[1], tree_sha1))
 		die("Not a valid object name %s", argv[1]);
 
@@ -56,7 +73,8 @@ int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 	if (strbuf_read(&buffer, 0, 0) < 0)
 		die_errno("git commit-tree: failed to read");
 
-	if (commit_tree(buffer.buf, tree_sha1, parents, commit_sha1, NULL)) {
+	if (commit_tree(buffer.buf, tree_sha1, parents, commit_sha1,
+			NULL, sign_commit)) {
 		strbuf_release(&buffer);
 		return 1;
 	}
diff --git a/builtin/commit.c b/builtin/commit.c
index c46f2d18e1..be196cc322 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -26,6 +26,7 @@
 #include "unpack-trees.h"
 #include "quote.h"
 #include "submodule.h"
+#include "gpg-interface.h"
 
 static const char * const builtin_commit_usage[] = {
 	"git commit [options] [--] <filepattern>...",
@@ -85,6 +86,8 @@ static int all, edit_flag, also, interactive, patch_interactive, only, amend, si
 static int quiet, verbose, no_verify, allow_empty, dry_run, renew_authorship;
 static int no_post_rewrite, allow_empty_message;
 static char *untracked_files_arg, *force_date, *ignore_submodule_arg;
+static char *sign_commit;
+
 /*
  * The default commit message cleanup mode will remove the lines
  * beginning with # (shell comments) and leading and trailing
@@ -144,6 +147,8 @@ static struct option builtin_commit_options[] = {
 	OPT_BOOLEAN('e', "edit", &edit_flag, "force edit of commit"),
 	OPT_STRING(0, "cleanup", &cleanup_arg, "default", "how to strip spaces and #comments from message"),
 	OPT_BOOLEAN(0, "status", &include_status, "include status in commit message template"),
+	{ OPTION_STRING, 'S', "gpg-sign", &sign_commit, "key id",
+	  "GPG sign commit", PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
 	/* end commit message options */
 
 	OPT_GROUP("Commit contents options"),
@@ -1324,6 +1329,7 @@ static void print_summary(const char *prefix, const unsigned char *sha1,
 static int git_commit_config(const char *k, const char *v, void *cb)
 {
 	struct wt_status *s = cb;
+	int status;
 
 	if (!strcmp(k, "commit.template"))
 		return git_config_pathname(&template_file, k, v);
@@ -1331,7 +1337,9 @@ static int git_commit_config(const char *k, const char *v, void *cb)
 		include_status = git_config_bool(k, v);
 		return 0;
 	}
-
+	status = git_gpg_config(k, v, NULL);
+	if (status)
+		return status;
 	return git_status_config(k, v, s);
 }
 
@@ -1484,7 +1492,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	}
 
 	if (commit_tree(sb.buf, active_cache_tree->sha1, parents, sha1,
-			author_ident.buf)) {
+			author_ident.buf, sign_commit)) {
 		rollback_index_files();
 		die(_("failed to write commit object"));
 	}
diff --git a/builtin/merge.c b/builtin/merge.c
index 98cf65f57b..bec09c3124 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -27,6 +27,7 @@
 #include "resolve-undo.h"
 #include "remote.h"
 #include "fmt-merge-msg.h"
+#include "gpg-interface.h"
 
 #define DEFAULT_TWOHEAD (1<<0)
 #define DEFAULT_OCTOPUS (1<<1)
@@ -63,6 +64,7 @@ static int allow_rerere_auto;
 static int abort_current_merge;
 static int show_progress = -1;
 static int default_to_upstream;
+static const char *sign_commit;
 
 static struct strategy all_strategy[] = {
 	{ "recursive",  DEFAULT_TWOHEAD | NO_TRIVIAL },
@@ -208,6 +210,8 @@ static struct option builtin_merge_options[] = {
 	OPT_BOOLEAN(0, "abort", &abort_current_merge,
 		"abort the current in-progress merge"),
 	OPT_SET_INT(0, "progress", &show_progress, "force progress reporting", 1),
+	{ OPTION_STRING, 'S', "gpg-sign", &sign_commit, "key id",
+	  "GPG sign commit", PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
 	OPT_END()
 };
 
@@ -570,7 +574,11 @@ static int git_merge_config(const char *k, const char *v, void *cb)
 		default_to_upstream = git_config_bool(k, v);
 		return 0;
 	}
+
 	status = fmt_merge_msg_config(k, v, cb);
+	if (status)
+		return status;
+	status = git_gpg_config(k, v, NULL);
 	if (status)
 		return status;
 	return git_diff_ui_config(k, v, cb);
@@ -905,7 +913,8 @@ static int merge_trivial(struct commit *head)
 	parent->next->item = remoteheads->item;
 	parent->next->next = NULL;
 	prepare_to_commit();
-	commit_tree(merge_msg.buf, result_tree, parent, result_commit, NULL);
+	commit_tree(merge_msg.buf, result_tree, parent, result_commit, NULL,
+		    sign_commit);
 	finish(head, result_commit, "In-index merge");
 	drop_save();
 	return 0;
@@ -936,7 +945,8 @@ static int finish_automerge(struct commit *head,
 	strbuf_addch(&merge_msg, '\n');
 	prepare_to_commit();
 	free_commit_list(remoteheads);
-	commit_tree(merge_msg.buf, result_tree, parents, result_commit, NULL);
+	commit_tree(merge_msg.buf, result_tree, parents, result_commit,
+		    NULL, sign_commit);
 	strbuf_addf(&buf, "Merge made by the '%s' strategy.", wt_strategy);
 	finish(head, result_commit, buf.buf);
 	strbuf_release(&buf);
diff --git a/builtin/tag.c b/builtin/tag.c
index 9b6fd95494..cca120552a 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -14,6 +14,7 @@
 #include "parse-options.h"
 #include "diff.h"
 #include "revision.h"
+#include "gpg-interface.h"
 
 static const char * const git_tag_usage[] = {
 	"git tag [-a|-s|-u <key-id>] [-f] [-m <msg>|-F <file>] <tagname> [<head>]",
@@ -23,8 +24,6 @@ static const char * const git_tag_usage[] = {
 	NULL
 };
 
-static char signingkey[1000];
-
 struct tag_filter {
 	const char **patterns;
 	int lines;
@@ -208,60 +207,7 @@ static int verify_tag(const char *name, const char *ref,
 
 static int do_sign(struct strbuf *buffer)
 {
-	struct child_process gpg;
-	const char *args[4];
-	char *bracket;
-	int len;
-	int i, j;
-
-	if (!*signingkey) {
-		if (strlcpy(signingkey, git_committer_info(IDENT_ERROR_ON_NO_NAME),
-				sizeof(signingkey)) > sizeof(signingkey) - 1)
-			return error(_("committer info too long."));
-		bracket = strchr(signingkey, '>');
-		if (bracket)
-			bracket[1] = '\0';
-	}
-
-	/* When the username signingkey is bad, program could be terminated
-	 * because gpg exits without reading and then write gets SIGPIPE. */
-	signal(SIGPIPE, SIG_IGN);
-
-	memset(&gpg, 0, sizeof(gpg));
-	gpg.argv = args;
-	gpg.in = -1;
-	gpg.out = -1;
-	args[0] = "gpg";
-	args[1] = "-bsau";
-	args[2] = signingkey;
-	args[3] = NULL;
-
-	if (start_command(&gpg))
-		return error(_("could not run gpg."));
-
-	if (write_in_full(gpg.in, buffer->buf, buffer->len) != buffer->len) {
-		close(gpg.in);
-		close(gpg.out);
-		finish_command(&gpg);
-		return error(_("gpg did not accept the tag data"));
-	}
-	close(gpg.in);
-	len = strbuf_read(buffer, gpg.out, 1024);
-	close(gpg.out);
-
-	if (finish_command(&gpg) || !len || len < 0)
-		return error(_("gpg failed to sign the tag"));
-
-	/* Strip CR from the line endings, in case we are on Windows. */
-	for (i = j = 0; i < buffer->len; i++)
-		if (buffer->buf[i] != '\r') {
-			if (i != j)
-				buffer->buf[j] = buffer->buf[i];
-			j++;
-		}
-	strbuf_setlen(buffer, j);
-
-	return 0;
+	return sign_buffer(buffer, buffer, get_signing_key());
 }
 
 static const char tag_template[] =
@@ -270,21 +216,11 @@ static const char tag_template[] =
 	"# Write a tag message\n"
 	"#\n");
 
-static void set_signingkey(const char *value)
-{
-	if (strlcpy(signingkey, value, sizeof(signingkey)) >= sizeof(signingkey))
-		die(_("signing key value too long (%.10s...)"), value);
-}
-
 static int git_tag_config(const char *var, const char *value, void *cb)
 {
-	if (!strcmp(var, "user.signingkey")) {
-		if (!value)
-			return config_error_nonbool(var);
-		set_signingkey(value);
-		return 0;
-	}
-
+	int status = git_gpg_config(var, value, cb);
+	if (status)
+		return status;
 	return git_default_config(var, value, cb);
 }
 
@@ -463,7 +399,7 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 
 	if (keyid) {
 		sign = 1;
-		set_signingkey(keyid);
+		set_signing_key(keyid);
 	}
 	if (sign)
 		annotate = 1;
diff --git a/builtin/verify-tag.c b/builtin/verify-tag.c
index 3134766049..28c2174338 100644
--- a/builtin/verify-tag.c
+++ b/builtin/verify-tag.c
@@ -11,6 +11,7 @@
 #include "run-command.h"
 #include <signal.h>
 #include "parse-options.h"
+#include "gpg-interface.h"
 
 static const char * const verify_tag_usage[] = {
 		"git verify-tag [-v|--verbose] <tag>...",
@@ -19,42 +20,16 @@ static const char * const verify_tag_usage[] = {
 
 static int run_gpg_verify(const char *buf, unsigned long size, int verbose)
 {
-	struct child_process gpg;
-	const char *args_gpg[] = {"gpg", "--verify", "FILE", "-", NULL};
-	char path[PATH_MAX];
-	size_t len;
-	int fd, ret;
+	int len;
 
-	fd = git_mkstemp(path, PATH_MAX, ".git_vtag_tmpXXXXXX");
-	if (fd < 0)
-		return error("could not create temporary file '%s': %s",
-						path, strerror(errno));
-	if (write_in_full(fd, buf, size) < 0)
-		return error("failed writing temporary file '%s': %s",
-						path, strerror(errno));
-	close(fd);
-
-	/* find the length without signature */
 	len = parse_signature(buf, size);
 	if (verbose)
 		write_in_full(1, buf, len);
 
-	memset(&gpg, 0, sizeof(gpg));
-	gpg.argv = args_gpg;
-	gpg.in = -1;
-	args_gpg[2] = path;
-	if (start_command(&gpg)) {
-		unlink(path);
-		return error("could not run gpg.");
-	}
+	if (size == len)
+		return error("no signature found");
 
-	write_in_full(gpg.in, buf, len);
-	close(gpg.in);
-	ret = finish_command(&gpg);
-
-	unlink_or_warn(path);
-
-	return ret;
+	return verify_signed_buffer(buf, len, buf + len, size - len, NULL);
 }
 
 static int verify_tag(const char *name, int verbose)
diff --git a/commit.c b/commit.c
index 73b7e00292..2792c47adc 100644
--- a/commit.c
+++ b/commit.c
@@ -6,6 +6,7 @@
 #include "diff.h"
 #include "revision.h"
 #include "notes.h"
+#include "gpg-interface.h"
 
 int save_commit_buffer = 1;
 
@@ -840,6 +841,77 @@ struct commit_list *reduce_heads(struct commit_list *heads)
 	return result;
 }
 
+static const char gpg_sig_header[] = "gpgsig ";
+static const int gpg_sig_header_len = sizeof(gpg_sig_header) - 1;
+
+static int do_sign_commit(struct strbuf *buf, const char *keyid)
+{
+	struct strbuf sig = STRBUF_INIT;
+	int inspos, copypos;
+
+	/* find the end of the header */
+	inspos = strstr(buf->buf, "\n\n") - buf->buf + 1;
+
+	if (!keyid || !*keyid)
+		keyid = get_signing_key();
+	if (sign_buffer(buf, &sig, keyid)) {
+		strbuf_release(&sig);
+		return -1;
+	}
+
+	for (copypos = 0; sig.buf[copypos]; ) {
+		const char *bol = sig.buf + copypos;
+		const char *eol = strchrnul(bol, '\n');
+		int len = (eol - bol) + !!*eol;
+
+		strbuf_insert(buf, inspos, gpg_sig_header, gpg_sig_header_len);
+		inspos += gpg_sig_header_len;
+		strbuf_insert(buf, inspos, bol, len);
+		inspos += len;
+		copypos += len;
+	}
+	strbuf_release(&sig);
+	return 0;
+}
+
+int parse_signed_commit(const unsigned char *sha1,
+			struct strbuf *payload, struct strbuf *signature)
+{
+	unsigned long size;
+	enum object_type type;
+	char *buffer = read_sha1_file(sha1, &type, &size);
+	int saw_signature = -1;
+	char *line, *tail;
+
+	if (!buffer || type != OBJ_COMMIT)
+		goto cleanup;
+
+	line = buffer;
+	tail = buffer + size;
+	saw_signature = 0;
+	while (line < tail) {
+		char *next = memchr(line, '\n', tail - line);
+		if (!next)
+			next = tail;
+		else
+			next++;
+		if (!prefixcmp(line, gpg_sig_header)) {
+			const char *sig = line + gpg_sig_header_len;
+			strbuf_add(signature, sig, next - sig);
+			saw_signature = 1;
+		} else {
+			if (*line == '\n')
+				/* dump the whole remainder of the buffer */
+				next = tail;
+			strbuf_add(payload, line, next - line);
+		}
+		line = next;
+	}
+ cleanup:
+	free(buffer);
+	return saw_signature;
+}
+
 static const char commit_utf8_warn[] =
 "Warning: commit message does not conform to UTF-8.\n"
 "You may want to amend it after fixing the message, or set the config\n"
@@ -847,7 +919,7 @@ static const char commit_utf8_warn[] =
 
 int commit_tree(const char *msg, unsigned char *tree,
 		struct commit_list *parents, unsigned char *ret,
-		const char *author)
+		const char *author, const char *sign_commit)
 {
 	int result;
 	int encoding_is_utf8;
@@ -890,6 +962,9 @@ int commit_tree(const char *msg, unsigned char *tree,
 	if (encoding_is_utf8 && !is_utf8(buffer.buf))
 		fprintf(stderr, commit_utf8_warn);
 
+	if (sign_commit && do_sign_commit(&buffer, sign_commit))
+		return -1;
+
 	result = write_sha1_file(buffer.buf, buffer.len, commit_type, ret);
 	strbuf_release(&buffer);
 	return result;
diff --git a/commit.h b/commit.h
index 009b113e5b..f92916e0a3 100644
--- a/commit.h
+++ b/commit.h
@@ -183,6 +183,9 @@ struct commit_list *reduce_heads(struct commit_list *heads);
 
 extern int commit_tree(const char *msg, unsigned char *tree,
 		struct commit_list *parents, unsigned char *ret,
-		const char *author);
+		       const char *author, const char *sign_commit);
+
+extern int parse_signed_commit(const unsigned char *sha1,
+			       struct strbuf *message, struct strbuf *signature);
 
 #endif /* COMMIT_H */
diff --git a/gpg-interface.c b/gpg-interface.c
new file mode 100644
index 0000000000..ff232c8c5d
--- /dev/null
+++ b/gpg-interface.c
@@ -0,0 +1,138 @@
+#include "cache.h"
+#include "run-command.h"
+#include "strbuf.h"
+#include "gpg-interface.h"
+#include "sigchain.h"
+
+static char *configured_signing_key;
+
+void set_signing_key(const char *key)
+{
+	free(configured_signing_key);
+	configured_signing_key = xstrdup(key);
+}
+
+int git_gpg_config(const char *var, const char *value, void *cb)
+{
+	if (!strcmp(var, "user.signingkey")) {
+		if (!value)
+			return config_error_nonbool(var);
+		set_signing_key(value);
+	}
+	return 0;
+}
+
+const char *get_signing_key(void)
+{
+	if (configured_signing_key)
+		return configured_signing_key;
+	return git_committer_info(IDENT_ERROR_ON_NO_NAME|IDENT_NO_DATE);
+}
+
+/*
+ * Create a detached signature for the contents of "buffer" and append
+ * it after "signature"; "buffer" and "signature" can be the same
+ * strbuf instance, which would cause the detached signature appended
+ * at the end.
+ */
+int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
+{
+	struct child_process gpg;
+	const char *args[4];
+	ssize_t len;
+	size_t i, j, bottom;
+
+	memset(&gpg, 0, sizeof(gpg));
+	gpg.argv = args;
+	gpg.in = -1;
+	gpg.out = -1;
+	args[0] = "gpg";
+	args[1] = "-bsau";
+	args[2] = signing_key;
+	args[3] = NULL;
+
+	if (start_command(&gpg))
+		return error(_("could not run gpg."));
+
+	/*
+	 * When the username signingkey is bad, program could be terminated
+	 * because gpg exits without reading and then write gets SIGPIPE.
+	 */
+	sigchain_push(SIGPIPE, SIG_IGN);
+
+	if (write_in_full(gpg.in, buffer->buf, buffer->len) != buffer->len) {
+		close(gpg.in);
+		close(gpg.out);
+		finish_command(&gpg);
+		return error(_("gpg did not accept the data"));
+	}
+	close(gpg.in);
+
+	bottom = signature->len;
+	len = strbuf_read(signature, gpg.out, 1024);
+	close(gpg.out);
+
+	sigchain_pop(SIGPIPE);
+
+	if (finish_command(&gpg) || !len || len < 0)
+		return error(_("gpg failed to sign the data"));
+
+	/* Strip CR from the line endings, in case we are on Windows. */
+	for (i = j = bottom; i < signature->len; i++)
+		if (signature->buf[i] != '\r') {
+			if (i != j)
+				signature->buf[j] = signature->buf[i];
+			j++;
+		}
+	strbuf_setlen(signature, j);
+
+	return 0;
+}
+
+/*
+ * Run "gpg" to see if the payload matches the detached signature.
+ * gpg_output_to tells where the output from "gpg" should go:
+ *   < 0: /dev/null
+ *   = 0: standard error of the calling process
+ *   > 0: the specified file descriptor
+ */
+int verify_signed_buffer(const char *payload, size_t payload_size,
+			 const char *signature, size_t signature_size,
+			 struct strbuf *gpg_output)
+{
+	struct child_process gpg;
+	const char *args_gpg[] = {"gpg", "--verify", "FILE", "-", NULL};
+	char path[PATH_MAX];
+	int fd, ret;
+
+	fd = git_mkstemp(path, PATH_MAX, ".git_vtag_tmpXXXXXX");
+	if (fd < 0)
+		return error("could not create temporary file '%s': %s",
+			     path, strerror(errno));
+	if (write_in_full(fd, signature, signature_size) < 0)
+		return error("failed writing detached signature to '%s': %s",
+			     path, strerror(errno));
+	close(fd);
+
+	memset(&gpg, 0, sizeof(gpg));
+	gpg.argv = args_gpg;
+	gpg.in = -1;
+	if (gpg_output)
+		gpg.err = -1;
+	args_gpg[2] = path;
+	if (start_command(&gpg)) {
+		unlink(path);
+		return error("could not run gpg.");
+	}
+
+	write_in_full(gpg.in, payload, payload_size);
+	close(gpg.in);
+
+	if (gpg_output)
+		strbuf_read(gpg_output, gpg.err, 0);
+	ret = finish_command(&gpg);
+
+	unlink_or_warn(path);
+
+	return ret;
+}
diff --git a/gpg-interface.h b/gpg-interface.h
new file mode 100644
index 0000000000..b9c36088ce
--- /dev/null
+++ b/gpg-interface.h
@@ -0,0 +1,10 @@
+#ifndef GPG_INTERFACE_H
+#define GPG_INTERFACE_H
+
+extern int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key);
+extern int verify_signed_buffer(const char *payload, size_t payload_size, const char *signature, size_t signature_size, struct strbuf *gpg_output);
+extern int git_gpg_config(const char *, const char *, void *);
+extern void set_signing_key(const char *);
+extern const char *get_signing_key(void);
+
+#endif
diff --git a/log-tree.c b/log-tree.c
index e7694a3a4c..142ba51427 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -8,6 +8,7 @@
 #include "refs.h"
 #include "string-list.h"
 #include "color.h"
+#include "gpg-interface.h"
 
 struct decoration name_decoration = { "object names" };
 
@@ -403,6 +404,41 @@ void log_write_email_headers(struct rev_info *opt, struct commit *commit,
 	*extra_headers_p = extra_headers;
 }
 
+static void show_signature(struct rev_info *opt, struct commit *commit)
+{
+	struct strbuf payload = STRBUF_INIT;
+	struct strbuf signature = STRBUF_INIT;
+	struct strbuf gpg_output = STRBUF_INIT;
+	int status;
+	const char *color, *reset, *bol, *eol;
+
+	if (parse_signed_commit(commit->object.sha1, &payload, &signature) <= 0)
+		goto out;
+
+	status = verify_signed_buffer(payload.buf, payload.len,
+				      signature.buf, signature.len,
+				      &gpg_output);
+	if (status && !gpg_output.len)
+		strbuf_addstr(&gpg_output, "No signature\n");
+
+	color = diff_get_color_opt(&opt->diffopt,
+				   status ? DIFF_WHITESPACE : DIFF_FRAGINFO);
+	reset = diff_get_color_opt(&opt->diffopt, DIFF_RESET);
+
+	bol = gpg_output.buf;
+	while (*bol) {
+		eol = strchrnul(bol, '\n');
+		printf("%s%.*s%s%s", color, (int)(eol - bol), bol, reset,
+		       *eol ? "\n" : "");
+		bol = (*eol) ? (eol + 1) : eol;
+	}
+
+ out:
+	strbuf_release(&gpg_output);
+	strbuf_release(&payload);
+	strbuf_release(&signature);
+}
+
 void show_log(struct rev_info *opt)
 {
 	struct strbuf msgbuf = STRBUF_INIT;
@@ -514,6 +550,9 @@ void show_log(struct rev_info *opt)
 		}
 	}
 
+	if (opt->show_signature)
+		show_signature(opt, commit);
+
 	if (!commit->buffer)
 		return;
 
diff --git a/notes-cache.c b/notes-cache.c
index 4c8984ede1..c36a960bc3 100644
--- a/notes-cache.c
+++ b/notes-cache.c
@@ -56,7 +56,7 @@ int notes_cache_write(struct notes_cache *c)
 
 	if (write_notes_tree(&c->tree, tree_sha1))
 		return -1;
-	if (commit_tree(c->validity, tree_sha1, NULL, commit_sha1, NULL) < 0)
+	if (commit_tree(c->validity, tree_sha1, NULL, commit_sha1, NULL, NULL) < 0)
 		return -1;
 	if (update_ref("update notes cache", c->tree.ref, commit_sha1, NULL,
 		       0, QUIET_ON_ERR) < 0)
diff --git a/notes-merge.c b/notes-merge.c
index e9e4199311..61cf18eeab 100644
--- a/notes-merge.c
+++ b/notes-merge.c
@@ -546,7 +546,7 @@ void create_notes_commit(struct notes_tree *t, struct commit_list *parents,
 		/* else: t->ref points to nothing, assume root/orphan commit */
 	}
 
-	if (commit_tree(msg, tree_sha1, parents, result_sha1, NULL))
+	if (commit_tree(msg, tree_sha1, parents, result_sha1, NULL, NULL))
 		die("Failed to commit notes tree to database");
 }
 
diff --git a/pretty.c b/pretty.c
index f45eb54e4c..392d656595 100644
--- a/pretty.c
+++ b/pretty.c
@@ -9,6 +9,7 @@
 #include "notes.h"
 #include "color.h"
 #include "reflog-walk.h"
+#include "gpg-interface.h"
 
 static char *user_format;
 static struct cmt_fmt_map {
@@ -640,6 +641,12 @@ struct format_commit_context {
 	const struct pretty_print_context *pretty_ctx;
 	unsigned commit_header_parsed:1;
 	unsigned commit_message_parsed:1;
+	unsigned commit_signature_parsed:1;
+	struct {
+		char *gpg_output;
+		char good_bad;
+		char *signer;
+	} signature;
 	char *message;
 	size_t width, indent1, indent2;
 
@@ -822,6 +829,59 @@ static void rewrap_message_tail(struct strbuf *sb,
 	c->indent2 = new_indent2;
 }
 
+static struct {
+	char result;
+	const char *check;
+} signature_check[] = {
+	{ 'G', ": Good signature from " },
+	{ 'B', ": BAD signature from " },
+};
+
+static void parse_signature_lines(struct format_commit_context *ctx)
+{
+	const char *buf = ctx->signature.gpg_output;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(signature_check); i++) {
+		const char *found = strstr(buf, signature_check[i].check);
+		const char *next;
+		if (!found)
+			continue;
+		ctx->signature.good_bad = signature_check[i].result;
+		found += strlen(signature_check[i].check);
+		next = strchrnul(found, '\n');
+		ctx->signature.signer = xmemdupz(found, next - found);
+		break;
+	}
+}
+
+static void parse_commit_signature(struct format_commit_context *ctx)
+{
+	struct strbuf payload = STRBUF_INIT;
+	struct strbuf signature = STRBUF_INIT;
+	struct strbuf gpg_output = STRBUF_INIT;
+	int status;
+
+	ctx->commit_signature_parsed = 1;
+
+	if (parse_signed_commit(ctx->commit->object.sha1,
+				&payload, &signature) <= 0)
+		goto out;
+	status = verify_signed_buffer(payload.buf, payload.len,
+				      signature.buf, signature.len,
+				      &gpg_output);
+	if (status && !gpg_output.len)
+		goto out;
+	ctx->signature.gpg_output = strbuf_detach(&gpg_output, NULL);
+	parse_signature_lines(ctx);
+
+ out:
+	strbuf_release(&gpg_output);
+	strbuf_release(&payload);
+	strbuf_release(&signature);
+}
+
+
 static size_t format_commit_one(struct strbuf *sb, const char *placeholder,
 				void *context)
 {
@@ -974,6 +1034,30 @@ static size_t format_commit_one(struct strbuf *sb, const char *placeholder,
 		return 0;
 	}
 
+	if (placeholder[0] == 'G') {
+		if (!c->commit_signature_parsed)
+			parse_commit_signature(c);
+		switch (placeholder[1]) {
+		case 'G':
+			if (c->signature.gpg_output)
+				strbuf_addstr(sb, c->signature.gpg_output);
+			break;
+		case '?':
+			switch (c->signature.good_bad) {
+			case 'G':
+			case 'B':
+				strbuf_addch(sb, c->signature.good_bad);
+			}
+			break;
+		case 'S':
+			if (c->signature.signer)
+				strbuf_addstr(sb, c->signature.signer);
+			break;
+		}
+		return 2;
+	}
+
+
 	/* For the rest we have to parse the commit header. */
 	if (!c->commit_header_parsed)
 		parse_commit_header(c);
@@ -1114,6 +1198,8 @@ void format_commit_message(const struct commit *commit,
 
 	if (context.message != commit->buffer)
 		free(context.message);
+	free(context.signature.gpg_output);
+	free(context.signature.signer);
 }
 
 static void pp_header(const struct pretty_print_context *pp,
diff --git a/revision.c b/revision.c
index 8764dde381..064e351084 100644
--- a/revision.c
+++ b/revision.c
@@ -1469,6 +1469,8 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 		revs->show_notes = 1;
 		revs->show_notes_given = 1;
 		revs->notes_opt.use_default_notes = 1;
+	} else if (!strcmp(arg, "--show-signature")) {
+		revs->show_signature = 1;
 	} else if (!prefixcmp(arg, "--show-notes=") ||
 		   !prefixcmp(arg, "--notes=")) {
 		struct strbuf buf = STRBUF_INIT;
diff --git a/revision.h b/revision.h
index 6aa53d1aa7..b8e9223954 100644
--- a/revision.h
+++ b/revision.h
@@ -110,6 +110,7 @@ struct rev_info {
 			show_merge:1,
 			show_notes:1,
 			show_notes_given:1,
+			show_signature:1,
 			pretty_given:1,
 			abbrev_commit:1,
 			abbrev_commit_given:1,
diff --git a/t/t7510-signed-commit.sh b/t/t7510-signed-commit.sh
new file mode 100755
index 0000000000..30401ced07
--- /dev/null
+++ b/t/t7510-signed-commit.sh
@@ -0,0 +1,71 @@
+#!/bin/sh
+
+test_description='signed commit tests'
+. ./test-lib.sh
+. "$TEST_DIRECTORY/lib-gpg.sh"
+
+test_expect_success GPG 'create signed commits' '
+	echo 1 >file && git add file &&
+	test_tick && git commit -S -m initial &&
+	git tag initial &&
+	git branch side &&
+
+	echo 2 >file && test_tick && git commit -a -S -m second &&
+	git tag second &&
+
+	git checkout side &&
+	echo 3 >elif && git add elif &&
+	test_tick && git commit -m "third on side" &&
+
+	git checkout master &&
+	test_tick && git merge -S side &&
+	git tag merge &&
+
+	echo 4 >file && test_tick && git commit -a -m "fourth unsigned" &&
+	git tag fourth-unsigned &&
+
+	test_tick && git commit --amend -S -m "fourth signed"
+'
+
+test_expect_success GPG 'show signatures' '
+	(
+		for commit in initial second merge master
+		do
+			git show --pretty=short --show-signature $commit >actual &&
+			grep "Good signature from" actual || exit 1
+			! grep "BAD signature from" actual || exit 1
+			echo $commit OK
+		done
+	) &&
+	(
+		for commit in merge^2 fourth-unsigned
+		do
+			git show --pretty=short --show-signature $commit >actual &&
+			grep "Good signature from" actual && exit 1
+			! grep "BAD signature from" actual || exit 1
+			echo $commit OK
+		done
+	)
+'
+
+test_expect_success GPG 'detect fudged signature' '
+	git cat-file commit master >raw &&
+
+	sed -e "s/fourth signed/4th forged/" raw >forged1 &&
+	git hash-object -w -t commit forged1 >forged1.commit &&
+	git show --pretty=short --show-signature $(cat forged1.commit) >actual1 &&
+	grep "BAD signature from" actual1 &&
+	! grep "Good signature from" actual1
+'
+
+test_expect_success GPG 'detect fudged signature with NUL' '
+	git cat-file commit master >raw &&
+	cat raw >forged2 &&
+	echo Qwik | tr "Q" "\000" >>forged2 &&
+	git hash-object -w -t commit forged2 >forged2.commit &&
+	git show --pretty=short --show-signature $(cat forged2.commit) >actual2 &&
+	grep "BAD signature from" actual2 &&
+	! grep "Good signature from" actual2
+'
+
+test_done
diff --git a/tag.c b/tag.c
index 7d38cc0f4d..3aa186df62 100644
--- a/tag.c
+++ b/tag.c
@@ -139,6 +139,11 @@ int parse_tag(struct tag *item)
 	return ret;
 }
 
+/*
+ * Look at a signed tag object, and return the offset where
+ * the embedded detached signature begins, or the end of the
+ * data when there is no such signature.
+ */
 size_t parse_signature(const char *buf, unsigned long size)
 {
 	char *eol;