Index: head/sbin/geom/class/eli/geli.8
===================================================================
--- head/sbin/geom/class/eli/geli.8
+++ head/sbin/geom/class/eli/geli.8
@@ -68,6 +68,7 @@
 .Nm
 .Cm attach
 .Op Fl Cdprv
+.Op Fl n Ar keyno
 .Op Fl j Ar passfile
 .Op Fl k Ar keyfile
 .Ar prov
@@ -407,6 +408,9 @@
 option for the
 .Cm detach
 subcommand.
+.It Fl n Ar keyno
+Specifies the index number of the Master Key copy to use (could be 0 or 1).
+If the index number is not provided all keys will be tested.
 .It Fl j Ar passfile
 Specifies a file which contains the passphrase component of the User Key
 (or part of it).
Index: head/sbin/geom/class/eli/geom_eli.c
===================================================================
--- head/sbin/geom/class/eli/geom_eli.c
+++ head/sbin/geom/class/eli/geom_eli.c
@@ -86,7 +86,7 @@
  *
  * init [-bdgPTv] [-a aalgo] [-B backupfile] [-e ealgo] [-i iterations] [-l keylen] [-J newpassfile] [-K newkeyfile] [-s sectorsize] [-V version] prov
  * label - alias for 'init'
- * attach [-Cdprv] [-j passfile] [-k keyfile] prov
+ * attach [-Cdprv] [-n keyno] [-j passfile] [-k keyfile] prov
  * detach [-fl] prov ...
  * stop - alias for 'detach'
  * onetime [-d] [-a aalgo] [-e ealgo] [-l keylen] prov
@@ -149,11 +149,12 @@
 		{ 'd', "detach", NULL, G_TYPE_BOOL },
 		{ 'j', "passfile", G_VAL_OPTIONAL, G_TYPE_STRING | G_TYPE_MULTI },
 		{ 'k', "keyfile", G_VAL_OPTIONAL, G_TYPE_STRING | G_TYPE_MULTI },
+		{ 'n', "keyno", "-1", G_TYPE_NUMBER },
 		{ 'p', "nopassphrase", NULL, G_TYPE_BOOL },
 		{ 'r', "readonly", NULL, G_TYPE_BOOL },
 		G_OPT_SENTINEL
 	    },
-	    "[-Cdprv] [-j passfile] [-k keyfile] prov"
+	    "[-Cdprv] [-n keyno] [-j passfile] [-k keyfile] prov"
 	},
 	{ "detach", 0, NULL,
 	    {
@@ -1129,7 +1130,7 @@
 	}
 
 	/* Decrypt Master Key. */
-	error = g_eli_mkey_decrypt(md, key, mkey, &nkey);
+	error = g_eli_mkey_decrypt_any(md, key, mkey, &nkey);
 	bzero(key, sizeof(key));
 	if (error != 0) {
 		bzero(md, sizeof(*md));
Index: head/stand/geli/geliboot.c
===================================================================
--- head/stand/geli/geliboot.c
+++ head/stand/geli/geliboot.c
@@ -121,14 +121,14 @@
 	int i;
 
 	if (ge->keybuf_slot >= 0) {
-		if (g_eli_mkey_decrypt(&ge->md, saved_keys[ge->keybuf_slot],
+		if (g_eli_mkey_decrypt_any(&ge->md, saved_keys[ge->keybuf_slot],
 		    mkey, &keynum) == 0) {
 			return (0);
 		}
 	}
 
 	for (i = 0; i < nsaved_keys; i++) {
-		if (g_eli_mkey_decrypt(&ge->md, saved_keys[i], mkey,
+		if (g_eli_mkey_decrypt_any(&ge->md, saved_keys[i], mkey,
 		    &keynum) == 0) {
 			ge->keybuf_slot = i;
 			return (0);
@@ -266,7 +266,7 @@
 
 	g_eli_crypto_hmac_final(&ctx, key, 0);
 
-	error = g_eli_mkey_decrypt(&geli_e->md, key, mkey, &keynum);
+	error = g_eli_mkey_decrypt_any(&geli_e->md, key, mkey, &keynum);
 	if (error == -1) {
 		explicit_bzero(mkey, sizeof(mkey));
 		explicit_bzero(key, sizeof(key));
Index: head/sys/geom/eli/g_eli.h
===================================================================
--- head/sys/geom/eli/g_eli.h
+++ head/sys/geom/eli/g_eli.h
@@ -688,6 +688,8 @@
 
 void g_eli_mkey_hmac(unsigned char *mkey, const unsigned char *key);
 int g_eli_mkey_decrypt(const struct g_eli_metadata *md,
+    const unsigned char *key, unsigned char *mkey, unsigned keyp);
+int g_eli_mkey_decrypt_any(const struct g_eli_metadata *md,
     const unsigned char *key, unsigned char *mkey, unsigned *nkeyp);
 int g_eli_mkey_encrypt(unsigned algo, const unsigned char *key, unsigned keylen,
     unsigned char *mkey);
Index: head/sys/geom/eli/g_eli.c
===================================================================
--- head/sys/geom/eli/g_eli.c
+++ head/sys/geom/eli/g_eli.c
@@ -1086,7 +1086,7 @@
                                  memcpy(key, keybuf->kb_ents[i].ke_data,
                                      sizeof(key));
 
-                                 if (g_eli_mkey_decrypt(&md, key,
+                                 if (g_eli_mkey_decrypt_any(&md, key,
                                      mkey, &nkey) == 0 ) {
                                          explicit_bzero(key, sizeof(key));
                                          goto have_key;
@@ -1161,7 +1161,7 @@
                 /*
                  * Decrypt Master-Key.
                  */
-                error = g_eli_mkey_decrypt(&md, key, mkey, &nkey);
+                error = g_eli_mkey_decrypt_any(&md, key, mkey, &nkey);
                 bzero(key, sizeof(key));
                 if (error == -1) {
                         if (i == tries) {
Index: head/sys/geom/eli/g_eli_ctl.c
===================================================================
--- head/sys/geom/eli/g_eli_ctl.c
+++ head/sys/geom/eli/g_eli_ctl.c
@@ -60,8 +60,8 @@
 	const char *name;
 	u_char *key, mkey[G_ELI_DATAIVKEYLEN];
 	int *nargs, *detach, *readonly, *dryrun;
-	int keysize, error;
-	u_int nkey;
+	int keysize, error, nkey;
+	intmax_t *valp;
 
 	g_topology_assert();
 
@@ -81,6 +81,17 @@
 		return;
 	}
 
+	valp = gctl_get_paraml(req, "keyno", sizeof(*valp));
+	if (valp == NULL) {
+		gctl_error(req, "No '%s' argument.", "keyno");
+		return;
+	}
+	nkey = *valp;
+	if (nkey < -1 || nkey >= G_ELI_MAXMKEYS) {
+		gctl_error(req, "Invalid '%s' argument.", "keyno");
+		return;
+	}
+
 	readonly = gctl_get_paraml(req, "readonly", sizeof(*readonly));
 	if (readonly == NULL) {
 		gctl_error(req, "No '%s' argument.", "readonly");
@@ -129,7 +140,10 @@
 		return;
 	}
 
-	error = g_eli_mkey_decrypt(&md, key, mkey, &nkey);
+	if (nkey == -1)
+		error = g_eli_mkey_decrypt_any(&md, key, mkey, &nkey);
+	else
+		error = g_eli_mkey_decrypt(&md, key, mkey, nkey);
 	explicit_bzero(key, keysize);
 	if (error == -1) {
 		explicit_bzero(&md, sizeof(md));
@@ -981,7 +995,7 @@
 		return;
 	}
 
-	error = g_eli_mkey_decrypt(&md, key, mkey, &nkey);
+	error = g_eli_mkey_decrypt_any(&md, key, mkey, &nkey);
 	explicit_bzero(key, keysize);
 	if (error == -1) {
 		explicit_bzero(&md, sizeof(md));
Index: head/sys/geom/eli/g_eli_key.c
===================================================================
--- head/sys/geom/eli/g_eli_key.c
+++ head/sys/geom/eli/g_eli_key.c
@@ -103,52 +103,77 @@
 }
 
 /*
- * Find and decrypt Master Key encrypted with 'key'.
- * Return decrypted Master Key number in 'nkeyp' if not NULL.
+ * Find and decrypt Master Key encrypted with 'key' at slot 'nkey'.
  * Return 0 on success, > 0 on failure, -1 on bad key.
  */
 int
 g_eli_mkey_decrypt(const struct g_eli_metadata *md, const unsigned char *key,
-    unsigned char *mkey, unsigned *nkeyp)
+    unsigned char *mkey, unsigned nkey)
 {
 	unsigned char tmpmkey[G_ELI_MKEYLEN];
 	unsigned char enckey[SHA512_MDLEN];	/* Key for encryption. */
 	const unsigned char *mmkey;
-	int bit, error, nkey;
+	int bit, error;
 
-	if (nkeyp != NULL)
-		*nkeyp = -1;
+	if (nkey > G_ELI_MKEYLEN)
+		return (-1);
 
 	/*
 	 * The key for encryption is: enckey = HMAC_SHA512(Derived-Key, 1)
 	 */
 	g_eli_crypto_hmac(key, G_ELI_USERKEYLEN, "\x01", 1, enckey, 0);
 
-	mmkey = md->md_mkeys;
-	for (nkey = 0; nkey < G_ELI_MAXMKEYS; nkey++, mmkey += G_ELI_MKEYLEN) {
-		bit = (1 << nkey);
-		if (!(md->md_keys & bit))
-			continue;
-		bcopy(mmkey, tmpmkey, G_ELI_MKEYLEN);
-		error = g_eli_crypto_decrypt(md->md_ealgo, tmpmkey,
-		    G_ELI_MKEYLEN, enckey, md->md_keylen);
-		if (error != 0) {
-			explicit_bzero(tmpmkey, sizeof(tmpmkey));
-			explicit_bzero(enckey, sizeof(enckey));
-			return (error);
-		}
-		if (g_eli_mkey_verify(tmpmkey, key)) {
-			bcopy(tmpmkey, mkey, G_ELI_DATAIVKEYLEN);
-			explicit_bzero(tmpmkey, sizeof(tmpmkey));
-			explicit_bzero(enckey, sizeof(enckey));
-			if (nkeyp != NULL)
-				*nkeyp = nkey;
-			return (0);
-		}
+	mmkey = md->md_mkeys + G_ELI_MKEYLEN * nkey;
+	bit = (1 << nkey);
+	if (!(md->md_keys & bit))
+		return (-1);
+	bcopy(mmkey, tmpmkey, G_ELI_MKEYLEN);
+	error = g_eli_crypto_decrypt(md->md_ealgo, tmpmkey,
+	    G_ELI_MKEYLEN, enckey, md->md_keylen);
+	if (error != 0) {
+		explicit_bzero(tmpmkey, sizeof(tmpmkey));
+		explicit_bzero(enckey, sizeof(enckey));
+		return (error);
 	}
+	if (g_eli_mkey_verify(tmpmkey, key)) {
+		bcopy(tmpmkey, mkey, G_ELI_DATAIVKEYLEN);
+		explicit_bzero(tmpmkey, sizeof(tmpmkey));
+		explicit_bzero(enckey, sizeof(enckey));
+		return (0);
+	}
 	explicit_bzero(enckey, sizeof(enckey));
 	explicit_bzero(tmpmkey, sizeof(tmpmkey));
+
 	return (-1);
+}
+
+/*
+ * Find and decrypt Master Key encrypted with 'key'.
+ * Return decrypted Master Key number in 'nkeyp' if not NULL.
+ * Return 0 on success, > 0 on failure, -1 on bad key.
+ */
+int
+g_eli_mkey_decrypt_any(const struct g_eli_metadata *md,
+    const unsigned char *key, unsigned char *mkey, unsigned *nkeyp)
+{
+	int error, nkey;
+
+	if (nkeyp != NULL)
+		*nkeyp = -1;
+
+	error = -1;
+	for (nkey = 0; nkey < G_ELI_MAXMKEYS; nkey++) {
+		error = g_eli_mkey_decrypt(md, key, mkey, nkey);
+		if (error == 0) {
+			if (nkeyp != NULL)
+				*nkeyp = nkey;
+			break;
+		} else if (error > 0) {
+			break;
+		}
+	}
+
+	return (error);
 }
 
 /*