libstrongswan agent plugin to use ssh-agent for RSA signatures
authorMartin Willi <martin@strongswan.org>
Tue, 2 Sep 2008 11:04:26 +0000 (11:04 -0000)
committerMartin Willi <martin@strongswan.org>
Tue, 2 Sep 2008 11:04:26 +0000 (11:04 -0000)
configure.in
src/libstrongswan/Makefile.am
src/libstrongswan/plugins/agent/Makefile.am [new file with mode: 0644]
src/libstrongswan/plugins/agent/agent_plugin.c [new file with mode: 0644]
src/libstrongswan/plugins/agent/agent_plugin.h [new file with mode: 0644]
src/libstrongswan/plugins/agent/agent_private_key.c [new file with mode: 0644]
src/libstrongswan/plugins/agent/agent_private_key.h [new file with mode: 0644]

index c3dd728..ea86c59 100644 (file)
@@ -572,6 +572,16 @@ AC_ARG_ENABLE(
 )
 
 AC_ARG_ENABLE(
+       [agent],
+       AS_HELP_STRING([--enable-agent],[enables the ssh-agent signing plugin. (default is NO).]),
+       [if test x$enableval = xyes; then
+               agent=true
+        else
+               agent=false
+       fi],
+)
+
+AC_ARG_ENABLE(
        [uci],
        AS_HELP_STRING([--enable-uci],[enable OpenWRT UCI configuration plugin (default is NO).]),
        [if test x$enableval = xyes; then
@@ -793,6 +803,9 @@ fi
 if test x$openssl = xtrue; then
        libstrongswan_plugins=${libstrongswan_plugins}" openssl"
 fi
+if test x$agent = xtrue; then
+       libstrongswan_plugins=${libstrongswan_plugins}" agent"
+fi
 if test x$gmp = xtrue; then
        libstrongswan_plugins=${libstrongswan_plugins}" gmp"
 fi
@@ -823,6 +836,7 @@ AM_CONDITIONAL(USE_MYSQL, test x$mysql = xtrue)
 AM_CONDITIONAL(USE_SQLITE, test x$sqlite = xtrue)
 AM_CONDITIONAL(USE_PADLOCK, test x$padlock = xtrue)
 AM_CONDITIONAL(USE_OPENSSL, test x$openssl = xtrue)
+AM_CONDITIONAL(USE_AGENT, test x$agent = xtrue)
 
 dnl charon plugins
 dnl ==============
@@ -900,6 +914,7 @@ AC_OUTPUT(
        src/libstrongswan/plugins/sqlite/Makefile
        src/libstrongswan/plugins/padlock/Makefile
        src/libstrongswan/plugins/openssl/Makefile
+       src/libstrongswan/plugins/agent/Makefile
        src/libstrongswan/fips/Makefile
        src/libcrypto/Makefile
        src/libfreeswan/Makefile
index 8976a79..08409d5 100644 (file)
@@ -156,6 +156,10 @@ if USE_OPENSSL
   SUBDIRS += plugins/openssl
 endif
 
+if USE_AGENT
+  SUBDIRS += plugins/agent
+endif
+
 if USE_INTEGRITY_TEST
   SUBDIRS += fips
 endif
diff --git a/src/libstrongswan/plugins/agent/Makefile.am b/src/libstrongswan/plugins/agent/Makefile.am
new file mode 100644 (file)
index 0000000..bc022aa
--- /dev/null
@@ -0,0 +1,12 @@
+
+INCLUDES = -I$(top_srcdir)/src/libstrongswan
+
+AM_CFLAGS = -rdynamic
+
+plugin_LTLIBRARIES = libstrongswan-agent.la
+
+libstrongswan_agent_la_SOURCES = agent_plugin.h agent_plugin.c \
+  agent_private_key.c agent_private_key.h
+
+libstrongswan_agent_la_LDFLAGS = -module
+
diff --git a/src/libstrongswan/plugins/agent/agent_plugin.c b/src/libstrongswan/plugins/agent/agent_plugin.c
new file mode 100644 (file)
index 0000000..474171a
--- /dev/null
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2008 Martin Willi
+ * Hochschule fuer Technik Rapperswil
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ *
+ * $Id$
+ */
+
+#include "agent_plugin.h"
+
+#include <library.h>
+#include "agent_private_key.h"
+
+typedef struct private_agent_plugin_t private_agent_plugin_t;
+
+/**
+ * private data of agent_plugin
+ */
+struct private_agent_plugin_t {
+
+       /**
+        * public functions
+        */
+       agent_plugin_t public;
+};
+
+/**
+ * Implementation of agent_plugin_t.agenttroy
+ */
+static void destroy(private_agent_plugin_t *this)
+{
+       lib->creds->remove_builder(lib->creds,
+                                                          (builder_constructor_t)agent_private_key_builder);
+       free(this);
+}
+
+/*
+ * see header file
+ */
+plugin_t *plugin_create()
+{
+       private_agent_plugin_t *this = malloc_thing(private_agent_plugin_t);
+       
+       this->public.plugin.destroy = (void(*)(plugin_t*))destroy;
+       
+       lib->creds->add_builder(lib->creds, CRED_PRIVATE_KEY, KEY_RSA,
+                                                       (builder_constructor_t)agent_private_key_builder);
+       return &this->public.plugin;
+}
+
diff --git a/src/libstrongswan/plugins/agent/agent_plugin.h b/src/libstrongswan/plugins/agent/agent_plugin.h
new file mode 100644 (file)
index 0000000..d12dd44
--- /dev/null
@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2008 Martin Willi
+ * Hochschule fuer Technik Rapperswil
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ */
+
+/**
+ * @defgroup agent_p agent
+ * @ingroup plugins
+ * 
+ * @defgroup agent_plugin agent_plugin
+ * @{ @ingroup agent_p
+ */
+
+#ifndef AGENT_PLUGIN_H_
+#define AGENT_PLUGIN_H_
+
+#include <plugins/plugin.h>
+
+typedef struct agent_plugin_t agent_plugin_t;
+
+/**
+ * Plugin to use private keys loaded in a ssh-agent.
+ */
+struct agent_plugin_t {
+
+       /**
+        * implements plugin interface
+        */
+       plugin_t plugin;
+};
+
+/**
+ * Create a agent_plugin instance.
+ */
+plugin_t *plugin_create();
+
+#endif /* AGENT_PLUGIN_H_ @}*/
diff --git a/src/libstrongswan/plugins/agent/agent_private_key.c b/src/libstrongswan/plugins/agent/agent_private_key.c
new file mode 100644 (file)
index 0000000..83f22b6
--- /dev/null
@@ -0,0 +1,540 @@
+/*
+ * Copyright (C) 2008 Martin Willi
+ * Hochschule fuer Technik Rapperswil
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ *
+ * $Id$
+ */
+
+#include "agent_private_key.h"
+
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <arpa/inet.h>
+#include <errno.h>
+
+#include <library.h>
+#include <chunk.h>
+#include <debug.h>
+#include <asn1/asn1.h>
+#include <asn1/oid.h>
+
+#ifndef UNIX_PATH_MAX
+#define UNIX_PATH_MAX 108
+#endif /* UNIX_PATH_MAX */
+
+typedef struct private_agent_private_key_t private_agent_private_key_t;
+typedef enum agent_msg_type_t agent_msg_type_t;
+
+/**
+ * Private data of a agent_private_key_t object.
+ */
+struct private_agent_private_key_t {
+       /**
+        * Public interface for this signer.
+        */
+       agent_private_key_t public;
+       
+       /**
+        * ssh-agent unix socket connection
+        */
+       int socket;
+       
+       /**
+        * key identity blob in ssh format
+        */
+       chunk_t key;
+       
+       /**
+        * keysize in bytes
+        */
+       size_t key_size;
+       
+       /**
+        * Keyid formed as a SHA-1 hash of a publicKey object
+        */
+       identification_t* keyid;
+
+       /**
+        * Keyid formed as a SHA-1 hash of a publicKeyInfo object
+        */
+       identification_t* keyid_info;
+       
+       /**
+        * reference count
+        */
+       refcount_t ref; 
+};
+
+/**
+ * Message types for ssh-agent protocol
+ */
+enum agent_msg_type_t {
+       SSH_AGENT_FAILURE = 5,
+       SSH_AGENT_SUCCESS =     6,
+       SSH_AGENT_ID_REQUEST = 11,
+       SSH_AGENT_ID_RESPONSE = 12,
+       SSH_AGENT_SIGN_REQUEST = 13,
+       SSH_AGENT_SIGN_RESPONSE = 14,
+};
+
+/**
+ * read a byte from a blob
+ */
+static u_char read_byte(chunk_t *blob)
+{
+       u_char val;
+
+       if (blob->len < sizeof(u_char))
+       {
+               return 0;
+       }
+       val = *(blob->ptr);
+       *blob = chunk_skip(*blob, sizeof(u_char));
+       return val;
+}
+
+/**
+ * read a u_int32_t from a blob
+ */
+static u_int32_t read_uint32(chunk_t *blob)
+{
+       u_int32_t val;
+
+       if (blob->len < sizeof(u_int32_t))
+       {
+               return 0;
+       }
+       val = ntohl(*(u_int32_t*)blob->ptr);
+       *blob = chunk_skip(*blob, sizeof(u_int32_t));
+       return val;
+}
+
+/**
+ * read a ssh-agent "string" length/value from a blob
+ */
+static chunk_t read_string(chunk_t *blob)
+{
+       int len;
+       chunk_t str;
+       
+       len = read_uint32(blob);
+       if (len > blob->len)
+       {
+               return chunk_empty;
+       }
+       str = chunk_create(blob->ptr, len);
+       *blob = chunk_skip(*blob, + len);
+       return str;
+}
+
+/**
+ * open socket connection to the ssh-agent
+ */
+static int open_connection(char *path)
+{
+       struct sockaddr_un addr;
+       int s;
+
+       s = socket(AF_UNIX, SOCK_STREAM, 0);
+       if (s == -1)
+       {
+               DBG1("opening ssh-agent socket %s failed: %s:", path, strerror(errno));
+               return -1;
+       }
+       
+       addr.sun_family = AF_UNIX;
+       addr.sun_path[UNIX_PATH_MAX - 1] = '\0';
+       strncpy(addr.sun_path, path, UNIX_PATH_MAX - 1);
+       
+       if (connect(s, (struct sockaddr*)&addr, SUN_LEN(&addr)) != 0)
+       {
+               DBG1("connecting to ssh-agent socket failed: %s", strerror(errno));
+               close(s);
+               return -1;
+       }
+       return s;
+}
+
+/** 
+ * Get the first usable key from the agent
+ */
+static bool read_key(private_agent_private_key_t *this)
+{
+       int len, count;
+       char buf[2048];
+       chunk_t blob = chunk_from_buf(buf), key, type, tmp;
+       
+       len = htonl(1);
+       write(this->socket, &len, sizeof(len));
+       buf[0] = SSH_AGENT_ID_REQUEST;
+       write(this->socket, &buf, 1);
+       
+       blob.len = read(this->socket, blob.ptr, blob.len);
+       
+       if (blob.len < sizeof(u_int32_t) + sizeof(u_char) ||
+               read_uint32(&blob) != blob.len ||
+               read_byte(&blob) != SSH_AGENT_ID_RESPONSE)
+       {
+               DBG1("received invalid ssh-agent identity response");
+               return FALSE;
+       }
+       count = read_uint32(&blob);
+       
+       while (blob.len)
+       {
+               key = read_string(&blob);
+               if (key.len)
+               {
+                       tmp = key;
+                       type = read_string(&tmp);
+                       read_string(&tmp);
+                       tmp = read_string(&tmp);
+                       if (type.len && strneq("ssh-rsa", type.ptr, type.len) &&
+                               tmp.len >= 512/8)
+                       {
+                               this->key = chunk_clone(key);
+                               this->key_size = tmp.len;
+                               if (tmp.ptr[0] == 0)
+                               {
+                                       this->key_size--;
+                               }
+                               return TRUE;
+                       }
+                       continue;
+               }
+               break;
+       }
+       return FALSE;
+}
+
+/**
+ * Implementation of agent_private_key.destroy.
+ */
+static bool sign(private_agent_private_key_t *this, signature_scheme_t scheme, 
+                                chunk_t data, chunk_t *signature)
+{
+       u_int32_t len, flags;
+       char buf[2048];
+       chunk_t blob = chunk_from_buf(buf);
+       
+       if (scheme != SIGN_DEFAULT && scheme != SIGN_RSA_EMSA_PKCS1_SHA1)
+       {
+               DBG1("signature scheme %N not supported by ssh-agent",
+                        signature_scheme_names, scheme);
+               return FALSE;
+       }
+       
+       len = htonl(1 + sizeof(u_int32_t) * 3 + this->key.len + data.len);
+       write(this->socket, &len, sizeof(len));
+       buf[0] = SSH_AGENT_SIGN_REQUEST;
+       write(this->socket, &buf, 1);
+       
+       len = htonl(this->key.len);
+       write(this->socket, &len, sizeof(len));
+       write(this->socket, this->key.ptr, this->key.len);
+       
+       len = htonl(data.len);
+       write(this->socket, &len, sizeof(len));
+       write(this->socket, data.ptr, data.len);
+       
+       flags = htonl(0);
+       write(this->socket, &flags, sizeof(flags));
+       
+       blob.len = read(this->socket, blob.ptr, blob.len);
+       if (blob.len < sizeof(u_int32_t) + sizeof(u_char) ||
+               read_uint32(&blob) != blob.len ||
+               read_byte(&blob) != SSH_AGENT_SIGN_RESPONSE)
+       {
+               DBG1("received invalid ssh-agent signature response");
+               return FALSE;
+       }
+       /* parse length */
+       blob = read_string(&blob);
+       /* skip sig type */
+       read_string(&blob);
+       /* parse length */
+       blob = read_string(&blob);
+       if (!blob.len)
+       {
+               DBG1("received invalid ssh-agent signature response");
+               return FALSE;
+       }
+       *signature =  chunk_clone(blob);
+       return TRUE;
+}
+
+/**
+ * Implementation of agent_private_key.destroy.
+ */
+static key_type_t get_type(private_agent_private_key_t *this)
+{
+       return KEY_RSA;
+}
+
+/**
+ * Implementation of agent_private_key.destroy.
+ */
+static bool decrypt(private_agent_private_key_t *this,
+                                       chunk_t crypto, chunk_t *plain)
+{
+       DBG1("private key decryption not supported by ssh-agent");
+       return FALSE;
+}
+
+/**
+ * Implementation of agent_private_key.destroy.
+ */
+static size_t get_keysize(private_agent_private_key_t *this)
+{
+       return this->key_size;
+}
+
+/**
+ * Implementation of agent_private_key.destroy.
+ */
+static identification_t* get_id(private_agent_private_key_t *this,
+                                                               id_type_t type)
+{
+       switch (type)
+       {
+               case ID_PUBKEY_INFO_SHA1:
+                       return this->keyid_info;
+               case ID_PUBKEY_SHA1:
+                       return this->keyid;
+               default:
+                       return NULL;
+       }
+}
+
+/**
+ * Implementation of agent_private_key.get_public_key.
+ */
+static public_key_t* get_public_key(private_agent_private_key_t *this)
+{
+       chunk_t key, n, e, encoded;
+       public_key_t *public;
+       
+       key = this->key;
+       read_string(&key);
+       e = read_string(&key);
+       n = read_string(&key);
+       encoded = asn1_wrap(ASN1_SEQUENCE, "mm", 
+                                       asn1_wrap(ASN1_INTEGER, "c", n),
+                                       asn1_wrap(ASN1_INTEGER, "c", e));
+
+       public = lib->creds->create(lib->creds, CRED_PUBLIC_KEY, KEY_RSA, 
+                                                               BUILD_BLOB_ASN1_DER, encoded, BUILD_END);
+       free(encoded.ptr);
+       return public;
+}
+
+/**
+ * Implementation of agent_private_key.belongs_to.
+ */
+static bool belongs_to(private_agent_private_key_t *this, public_key_t *public)
+{
+       identification_t *keyid;
+
+       if (public->get_type(public) != KEY_RSA)
+       {
+               return FALSE;
+       }
+       keyid = public->get_id(public, ID_PUBKEY_SHA1);
+       if (keyid && keyid->equals(keyid, this->keyid))
+       {
+               return TRUE;
+       }
+       keyid = public->get_id(public, ID_PUBKEY_INFO_SHA1);
+       if (keyid && keyid->equals(keyid, this->keyid_info))
+       {
+               return TRUE;
+       }
+       return FALSE;
+}
+
+/**
+ * Build the RSA key identifier from n and e using SHA1 hashed publicKey(Info).
+ */
+static bool build_ids(private_agent_private_key_t *this)
+{
+       chunk_t publicKeyInfo, publicKey, hash, key, n, e;
+       hasher_t *hasher;
+       
+       key = this->key;
+       e = read_string(&key);
+       n = read_string(&key);
+       
+       hasher = lib->crypto->create_hasher(lib->crypto, HASH_SHA1);
+       if (hasher == NULL)
+       {
+               DBG1("SHA1 hash algorithm not supported, unable to use RSA");
+               return FALSE;
+       }
+       publicKey = asn1_wrap(ASN1_SEQUENCE, "cc", n, e);
+       hasher->allocate_hash(hasher, publicKey, &hash);
+       this->keyid = identification_create_from_encoding(ID_PUBKEY_SHA1, hash);
+       chunk_free(&hash);
+       
+       publicKeyInfo = asn1_wrap(ASN1_SEQUENCE, "cm",
+                                               asn1_algorithmIdentifier(OID_RSA_ENCRYPTION),
+                                               asn1_bitstring("m", publicKey));
+       hasher->allocate_hash(hasher, publicKeyInfo, &hash);
+       this->keyid_info = identification_create_from_encoding(ID_PUBKEY_INFO_SHA1, hash);
+       chunk_free(&hash);
+       
+       hasher->destroy(hasher);
+       chunk_free(&publicKeyInfo);
+       return TRUE;
+}
+
+/**
+ * Implementation of private_key_t.get_encoding.
+ */
+static chunk_t get_encoding(private_agent_private_key_t *this)
+{
+       return chunk_empty;
+}
+
+/**
+ * Implementation of agent_private_key.get_ref.
+ */
+static private_agent_private_key_t* get_ref(private_agent_private_key_t *this)
+{
+       ref_get(&this->ref);
+       return this;
+}
+
+/**
+ * Implementation of agent_private_key.destroy.
+ */
+static void destroy(private_agent_private_key_t *this)
+{
+       if (ref_put(&this->ref))
+       {
+               close(this->socket);
+               DESTROY_IF(this->keyid);
+               DESTROY_IF(this->keyid_info);
+               free(this->key.ptr);
+               free(this);
+       }
+}
+
+/**
+ * Internal constructor
+ */
+static agent_private_key_t *agent_private_key_create(char *path)
+{
+       private_agent_private_key_t *this = malloc_thing(private_agent_private_key_t);
+       
+       this->public.interface.get_type = (key_type_t (*)(private_key_t *this))get_type;
+       this->public.interface.sign = (bool (*)(private_key_t *this, signature_scheme_t scheme, chunk_t data, chunk_t *signature))sign;
+       this->public.interface.decrypt = (bool (*)(private_key_t *this, chunk_t crypto, chunk_t *plain))decrypt;
+       this->public.interface.get_keysize = (size_t (*) (private_key_t *this))get_keysize;
+       this->public.interface.get_id = (identification_t* (*) (private_key_t *this,id_type_t))get_id;
+       this->public.interface.get_public_key = (public_key_t* (*)(private_key_t *this))get_public_key;
+       this->public.interface.belongs_to = (bool (*) (private_key_t *this, public_key_t *public))belongs_to;
+       this->public.interface.get_encoding = (chunk_t(*)(private_key_t*))get_encoding;
+       this->public.interface.get_ref = (private_key_t* (*)(private_key_t *this))get_ref;
+       this->public.interface.destroy = (void (*)(private_key_t *this))destroy;
+       
+       this->socket = open_connection(path);
+       if (this->socket < 0)
+       {
+               free(this);
+               return NULL;
+       }
+       this->keyid = NULL;
+       this->keyid_info = NULL;
+       this->ref = 1;
+       if (!read_key(this) || !build_ids(this))
+       {
+               destroy(this);
+               return NULL;
+       }
+       return &this->public;
+}
+
+typedef struct private_builder_t private_builder_t;
+/**
+ * Builder implementation for key loading/generation
+ */
+struct private_builder_t {
+       /** implements the builder interface */
+       builder_t public;
+       /** loaded/generated private key */
+       agent_private_key_t *key;
+};
+
+/**
+ * Implementation of builder_t.build
+ */
+static agent_private_key_t *build(private_builder_t *this)
+{
+       agent_private_key_t *key = this->key;
+       
+       free(this);
+       return key;
+}
+
+/**
+ * Implementation of builder_t.add
+ */
+static void add(private_builder_t *this, builder_part_t part, ...)
+{
+       va_list args;
+       
+       if (this->key)
+       {
+               DBG1("ignoring surplus build part %N", builder_part_names, part);
+               return;
+       }
+       
+       switch (part)
+       {
+               case BUILD_AGENT_SOCKET:
+               {
+                       va_start(args, part);
+                       this->key = agent_private_key_create(va_arg(args, char*));
+                       va_end(args);
+                       break;
+               }
+               default:
+                       DBG1("ignoring unsupported build part %N", builder_part_names, part);
+                       break;
+       }
+}
+
+/**
+ * Builder construction function
+ */
+builder_t *agent_private_key_builder(key_type_t type)
+{
+       private_builder_t *this;
+       
+       if (type != KEY_RSA)
+       {
+               return NULL;
+       }
+       
+       this = malloc_thing(private_builder_t);
+       
+       this->key = NULL;
+       this->public.add = (void(*)(builder_t *this, builder_part_t part, ...))add;
+       this->public.build = (void*(*)(builder_t *this))build;
+       
+       return &this->public;
+}
+
diff --git a/src/libstrongswan/plugins/agent/agent_private_key.h b/src/libstrongswan/plugins/agent/agent_private_key.h
new file mode 100644 (file)
index 0000000..4d678dd
--- /dev/null
@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2008 Martin Willi
+ * Hochschule fuer Technik Rapperswil
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ */
+
+/**
+ * @defgroup agent_private_key agent_private_key
+ * @{ @ingroup agent_p
+ */
+
+#ifndef AGENT_PRIVATE_KEY_H_
+#define AGENT_PRIVATE_KEY_H_
+
+#include <credentials/keys/private_key.h>
+
+typedef struct agent_private_key_t agent_private_key_t;
+
+/**
+ * private_key_t implementation using an ssh-agent.
+ */
+struct agent_private_key_t {
+
+       /**
+        * Implements private_key_t interface
+        */
+       private_key_t interface;
+};
+
+/**
+ * Create the builder for a private key.
+ *
+ * @param type         type of the key
+ * @return                     builder instance
+ */
+builder_t *agent_private_key_builder(key_type_t type);
+
+#endif /*AGENT_PRIVATE_KEY_H_ @}*/
+