Attachment 2983 Details for Bug 2377 – allow CA signature operation to use keys hosted in ssh-agent

[patch] allow CA signature operation to use keys hosted in ssh-agent

keygen-ca-agent1.diff (text/plain), 9.86 KB, created by Damien Miller on 2017-05-25 12:29:32 AEST

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Creator: Damien Miller

Created: 2017-05-25 12:29:32 AEST

Size: 9.86 KB

patch

obsolete

>commit d060cc7b961a51deda464427a54b686970ece58d
>Author: Damien Miller <djm@mindrot.org>
>Date:   Thu May 25 12:05:01 2017 +1000
>
>    ability to use ssh-agent for CA operation
>
>diff --git a/authfd.c b/authfd.c
>index 8486e28b..7a2a3e41 100644
>--- a/authfd.c
>+++ b/authfd.c
>@@ -326,7 +326,7 @@ ssh_free_identitylist(struct ssh_identitylist *idl)
> 
> /* encode signature algoritm in flag bits, so we can keep the msg format */
> static u_int
>-agent_encode_alg(struct sshkey *key, const char *alg)
>+agent_encode_alg(const struct sshkey *key, const char *alg)
> {
> 	if (alg != NULL && key->type == KEY_RSA) {
> 		if (strcmp(alg, "rsa-sha2-256") == 0)
>@@ -339,7 +339,7 @@ agent_encode_alg(struct sshkey *key, const char *alg)
> 
> /* ask agent to sign data, returns err.h code on error, 0 on success */
> int
>-ssh_agent_sign(int sock, struct sshkey *key,
>+ssh_agent_sign(int sock, const struct sshkey *key,
>     u_char **sigp, size_t *lenp,
>     const u_char *data, size_t datalen, const char *alg, u_int compat)
> {
>diff --git a/authfd.h b/authfd.h
>index 0e98331d..805642ee 100644
>--- a/authfd.h
>+++ b/authfd.h
>@@ -38,7 +38,7 @@ int	ssh_remove_all_identities(int sock, int version);
> 
> int	ssh_decrypt_challenge(int sock, struct sshkey* key, BIGNUM *challenge,
> 	    u_char session_id[16], u_char response[16]);
>-int	ssh_agent_sign(int sock, struct sshkey *key,
>+int	ssh_agent_sign(int sock, const struct sshkey *key,
> 	    u_char **sigp, size_t *lenp,
> 	    const u_char *data, size_t datalen, const char *alg, u_int compat);
> 
>diff --git a/ssh-keygen.1 b/ssh-keygen.1
>index 786d37d5..492df3f4 100644
>--- a/ssh-keygen.1
>+++ b/ssh-keygen.1
>@@ -114,6 +114,8 @@
> .Fl s Ar ca_key
> .Fl I Ar certificate_identity
> .Op Fl h
>+.Op Fl U
>+.Op Fl D Ar pkcs11_provider
> .Op Fl n Ar principals
> .Op Fl O Ar option
> .Op Fl V Ar validity_interval
>@@ -558,6 +560,14 @@ The possible values are
> .Dq ed25519 ,
> or
> .Dq rsa .
>+.It Fl U
>+When used in combination with
>+.Fl s ,
>+this option indicates that a CA key resides in a
>+.Xr ssh-agent 1 .
>+See the
>+.Sx CERTIFICATES
>+section for more information.
> .It Fl u
> Update a KRL.
> When specified with
>@@ -705,6 +715,14 @@ to
> .Pp
> .Dl $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub
> .Pp
>+Similarly, it is possible for the CA key to be hosted in a
>+.Xr ssh-agent 1 .
>+This is indicated by the
>+.Fl U
>+flag and, again, the CA key must be identified by its public half.
>+.Pp
>+.Dl $ ssh-keygen -Us ca_key.pub -I key_id user_key.pub
>+.Pp
> In all cases,
> .Ar key_id
> is a "key identifier" that is logged by the server when the certificate
>diff --git a/ssh-keygen.c b/ssh-keygen.c
>index 7886582d..233a0975 100644
>--- a/ssh-keygen.c
>+++ b/ssh-keygen.c
>@@ -59,6 +59,7 @@
> #include "krl.h"
> #include "digest.h"
> #include "utf8.h"
>+#include "authfd.h"
> 
> #ifdef WITH_OPENSSL
> # define DEFAULT_KEY_TYPE_NAME "rsa"
>@@ -121,6 +122,9 @@ char *identity_comment = NULL;
> /* Path to CA key when certifying keys. */
> char *ca_key_path = NULL;
> 
>+/* Prefer to use agent keys for CA signing */
>+int prefer_agent = 0;
>+
> /* Certificate serial number */
> unsigned long long cert_serial = 0;
> 
>@@ -1597,24 +1601,66 @@ load_pkcs11_key(char *path)
> #endif /* ENABLE_PKCS11 */
> }
> 
>+/* Signer for sshkey_certify that uses the agent */
>+static int
>+agent_signer(const struct sshkey *key, u_char **sigp, size_t *lenp,
>+    const u_char *data, size_t datalen,
>+    const char *alg, u_int compat, void *ctx)
>+{
>+	int *agent_fdp = (int *)ctx;
>+
>+	return ssh_agent_sign(*agent_fdp, key, sigp, lenp,
>+	    data, datalen, alg, compat);
>+}
>+
> static void
> do_ca_sign(struct passwd *pw, int argc, char **argv)
> {
>-	int r, i, fd;
>+	int r, i, fd, found, agent_fd = -1;
> 	u_int n;
> 	struct sshkey *ca, *public;
> 	char valid[64], *otmp, *tmp, *cp, *out, *comment, **plist = NULL;
> 	FILE *f;
>+	struct ssh_identitylist *agent_ids;
>+	size_t j;
> 
> #ifdef ENABLE_PKCS11
> 	pkcs11_init(1);
> #endif
> 	tmp = tilde_expand_filename(ca_key_path, pw->pw_uid);
> 	if (pkcs11provider != NULL) {
>+		/* If a PKCS#11 token was specified then try to use it */
> 		if ((ca = load_pkcs11_key(tmp)) == NULL)
> 			fatal("No PKCS#11 key matching %s found", ca_key_path);
>-	} else
>+	} else if (prefer_agent) {
>+		/*
>+		 * Agent signature requested. Try to use agent after making
>+		 * sure the public key specified is actually present in the
>+		 * agent.
>+		 */
>+		if ((r = sshkey_load_public(tmp, &ca, NULL)) != 0)
>+			fatal("Cannot load CA public key %s: %s",
>+			    tmp, ssh_err(r));
>+		if ((r = ssh_get_authentication_socket(&agent_fd)) != 0)
>+			fatal("Cannot use public key for CA signature: %s",
>+			    ssh_err(r));
>+		if ((r = ssh_fetch_identitylist(agent_fd, &agent_ids)) != 0)
>+			fatal("Retrieve agent key list: %s", ssh_err(r));
>+		found = 0;
>+		for (j = 0; j < agent_ids->nkeys; j++) {
>+			if (sshkey_equal(ca, agent_ids->keys[j])) {
>+				found = 1;
>+				break;
>+			}
>+		}
>+		if (!found)
>+			fatal("CA key %s not found in agent", tmp);
>+		ssh_free_identitylist(agent_ids);
>+		ca->flags |= SSHKEY_FLAG_EXT;
>+	} else {
>+		/* CA key is assumed to be a private key on the filesystem */
> 		ca = load_identity(tmp);
>+	}
> 	free(tmp);
> 
> 	if (key_type_name != NULL &&
>@@ -1664,8 +1710,16 @@ do_ca_sign(struct passwd *pw, int argc, char **argv)
> 		    &public->cert->signature_key)) != 0)
> 			fatal("key_from_private (ca key): %s", ssh_err(r));
> 
>-		if ((r = sshkey_certify(public, ca, key_type_name)) != 0)
>-			fatal("Couldn't certify key %s: %s", tmp, ssh_err(r));
>+		if (agent_fd != -1 && (ca->flags & SSHKEY_FLAG_EXT) != 0) {
>+			if ((r = sshkey_certify_custom(public, ca,
>+			    key_type_name, agent_signer, &agent_fd)) != 0)
>+				fatal("Couldn't certify key %s via agent: %s",
>+				    tmp, ssh_err(r));
>+		} else {
>+			if ((sshkey_certify(public, ca, key_type_name)) != 0)
>+				fatal("Couldn't certify key %s: %s",
>+				    tmp, ssh_err(r));
>+		}
> 
> 		if ((cp = strrchr(tmp, '.')) != NULL && strcmp(cp, ".pub") == 0)
> 			*cp = '\0';
>@@ -2261,8 +2315,9 @@ usage(void)
> 	    "       ssh-keygen -T output_file -f input_file [-v] [-a rounds] [-J num_lines]\n"
> 	    "                  [-j start_line] [-K checkpt] [-W generator]\n"
> #endif
>-	    "       ssh-keygen -s ca_key -I certificate_identity [-h] [-n principals]\n"
>-	    "                  [-O option] [-V validity_interval] [-z serial_number] file ...\n"
>+	    "       ssh-keygen -s ca_key -I certificate_identity [-h] [-U]\n"
>+	    "                  [-D pkcs11_provider] [-n principals] [-O option]\n"
>+	    "                  [-V validity_interval] [-z serial_number] file ...\n"
> 	    "       ssh-keygen -L [-f input_keyfile]\n"
> 	    "       ssh-keygen -A\n"
> 	    "       ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number]\n"
>@@ -2320,8 +2375,8 @@ main(int argc, char **argv)
> 	if (gethostname(hostname, sizeof(hostname)) < 0)
> 		fatal("gethostname: %s", strerror(errno));
> 
>-	/* Remaining characters: UYdw */
>-	while ((opt = getopt(argc, argv, "ABHLQXceghiklopquvxy"
>+	/* Remaining characters: Ydw */
>+	while ((opt = getopt(argc, argv, "ABHLQUXceghiklopquvxy"
> 	    "C:D:E:F:G:I:J:K:M:N:O:P:R:S:T:V:W:Z:"
> 	    "a:b:f:g:j:m:n:r:s:t:z:")) != -1) {
> 		switch (opt) {
>@@ -2448,6 +2503,9 @@ main(int argc, char **argv)
> 		case 'D':
> 			pkcs11provider = optarg;
> 			break;
>+		case 'U':
>+			prefer_agent = 1;
>+			break;
> 		case 'u':
> 			update_krl = 1;
> 			break;
>diff --git a/sshkey.c b/sshkey.c
>index f9518bd7..b5ff8559 100644
>--- a/sshkey.c
>+++ b/sshkey.c
>@@ -2252,7 +2252,8 @@ sshkey_drop_cert(struct sshkey *k)
> 
> /* Sign a certified key, (re-)generating the signed certblob. */
> int
>-sshkey_certify(struct sshkey *k, struct sshkey *ca, const char *alg)
>+sshkey_certify_custom(struct sshkey *k, struct sshkey *ca, const char *alg,
>+    sshkey_certify_signer *signer, void *signer_ctx)
> {
> 	struct sshbuf *principals = NULL;
> 	u_char *ca_blob = NULL, *sig_blob = NULL, nonce[32];
>@@ -2341,8 +2342,8 @@ sshkey_certify(struct sshkey *k, struct sshkey *ca, const char *alg)
> 		goto out;
> 
> 	/* Sign the whole mess */
>-	if ((ret = sshkey_sign(ca, &sig_blob, &sig_len, sshbuf_ptr(cert),
>-	    sshbuf_len(cert), alg, 0)) != 0)
>+	if ((ret = signer(ca, &sig_blob, &sig_len, sshbuf_ptr(cert),
>+	    sshbuf_len(cert), alg, 0, signer_ctx)) != 0)
> 		goto out;
> 
> 	/* Append signature and we are done */
>@@ -2358,6 +2359,22 @@ sshkey_certify(struct sshkey *k, struct sshkey *ca, const char *alg)
> 	return ret;
> }
> 
>+static int
>+default_key_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
>+    const u_char *data, size_t datalen,
>+    const char *alg, u_int compat, void *ctx)
>+{
>+	if (ctx != NULL)
>+		return SSH_ERR_INVALID_ARGUMENT;
>+	return sshkey_sign(key, sigp, lenp, data, datalen, alg, compat);
>+}
>+
>+int
>+sshkey_certify(struct sshkey *k, struct sshkey *ca, const char *alg)
>+{
>+	return sshkey_certify_custom(k, ca, alg, default_key_sign, NULL);
>+}
>+
> int
> sshkey_cert_check_authority(const struct sshkey *k,
>     int want_host, int require_principal,
>diff --git a/sshkey.h b/sshkey.h
>index b0b5b274..f0440291 100644
>--- a/sshkey.h
>+++ b/sshkey.h
>@@ -136,13 +136,19 @@ int	 sshkey_type_is_cert(int);
> int	 sshkey_type_plain(int);
> int	 sshkey_to_certified(struct sshkey *);
> int	 sshkey_drop_cert(struct sshkey *);
>-int	 sshkey_certify(struct sshkey *, struct sshkey *, const char *);
> int	 sshkey_cert_copy(const struct sshkey *, struct sshkey *);
> int	 sshkey_cert_check_authority(const struct sshkey *, int, int,
>     const char *, const char **);
> size_t	 sshkey_format_cert_validity(const struct sshkey_cert *,
>     char *, size_t) __attribute__((__bounded__(__string__, 2, 3)));
> 
>+int	 sshkey_certify(struct sshkey *, struct sshkey *, const char *);
>+/* Variant allowing use of a custom signature function (e.g. for ssh-agent) */
>+typedef int sshkey_certify_signer(const struct sshkey *, u_char **, size_t *,
>+    const u_char *, size_t, const char *, u_int, void *);
>+int	 sshkey_certify_custom(struct sshkey *, struct sshkey *, const char *,
>+    sshkey_certify_signer *, void *);
>+
> int		 sshkey_ecdsa_nid_from_name(const char *);
> int		 sshkey_curve_name_to_nid(const char *);
> const char *	 sshkey_curve_nid_to_name(int);

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Attachments on bug 2377: 2690 | 2692 | 2887 | 2983