Sandor W. Sklar
$Id: openssh-aix.html,v 1.15 2001/11/19 14:42:33 ssklar Exp ssklar $
This tutorial is designed for administrators of IBM RS/6000 systems who wish to improve the security and integrity of their servers running AIX 4.3, by replacing standard insecure network services with those provided by the OpenSSH implementation of the Secure Shell protocol.
Neither general network security, nor the use of the ssh client software is discussed in-depth; the primary focus of this tutorial is to detail the necessary components, steps, and configuration required to compile OpenSSH and its prerequisites from source and to deploy it across AIX systems.
The example system used in this tutorial is an RS/6000 running AIX 4.3.3 Maintenance Level 08. The source software was compiled with the IBM C for AIX version 5.0.1 compiler.
The latest stable version of each software package was used for this tutorial. As options and behavior of software may change across releases, always refer to the documentation included with the source distribution for the most recent information.
Sandor W. Sklar is a Unix Systems Administrator at Stanford University. He, his wife, and two children live in Northern California, and may be contacted at <ssklar@stanford.edu>.
AIX provides, as does most UNIX implementations, a large number of services, enabling remote users to log in interactively, transfer files to and from the server, and issue commands to the server in a non-interactive fashion. Unfortunately, most of the "daemons" (programs running on the server that fulfill requests for particular services) were designed during a time when security of systems and network traffic was an afterthought, if thought of at all.
The protocols behind such services as "telnet", "rsh", and "ftp" contain no provision for the encryption of traffic passed over the network; the methods used for authentication of users is in some protocols, extremely weak and easily forged; even worse is the transmission of user IDs and passwords from the client to the server in clear-text. Further, there is no guarantee that the data transferred through the network has not been intercepted by a third-party and possibly altered.
The Secure Shell (SSH) protocol was developed to "fix" the problems caused by these inherently insecure services.
In 1995, the original SSH protocol was developed by Tatu Ylönen, a researcher at the Helsinki University of Technology, in Finland. Along with developing the protocol, Ylönen also wrote an implementation for UNIX systems, distributing the source as free software, for unlimited use. As the popularity of the SSH software grew worldwide, Ylönen formed a company, SSH Communications Security, Ltd, in order to further development of the product (now licensed commercially, but with source available) and provide support.
In time, limitations and flaws were discovered in the original definition of the protocol. These problems could not be fixed without breaking compatibility with older versions, so a new protocol was defined, fixing the issues with the original SSH protocol. . As the various implementations of the protocol 2 software mature and gain features, the use of the older protocol 1-based software will fade. For now, though, implementations of both protocol 1 and protocol 2 are in widespread use around the world, and to provide service to the widest audience of clients, it is important for servers to support connections via both protocols.
The Secure Shell protocol (both protocols, but in different ways) "fixes" the following problems, most of which are inherent in the design of the various protocols that SSH can replace:
SSH uses several strong cryptographic methods of ensuring that both the client and the server are who they "say" they are. Unless both the server and the client agree that the user and host identities are valid, the connection is denied.
All data transmitted over the network between an ssh client and an ssh server is encrypted, with algorithms of varying strength. This ensures that, if the network traffic is "sniffed" (intercepted and read by an unauthorized party), the contents of the packets will be unreadable.
The SSH protocol assures the integrity of all data transmitted to and from a server. If a third-party attempts to alter the data packets, SSH will know that this occurred, and will alert the user.
The creation of OpenSSH, a completely free implementation of both protocol 1 and 2, was undertaken by the OpenBSD project, in order to provide a Secure Shell implementation unencumbered by restrictive licensing. First included with the release of OpenBSD 2.6, the quality and security of the code produced was excellent, and ported to other UNIX operating systems soon after.
Currently, the development of OpenSSH is divided between into two teams. One team does strictly OpenBSD-based development, aiming to produce code that is as clean, simple, and secure as possible. The other team takes the clean version and makes it portable, so that it will build and run on many operating systems, including AIX. The portable releases can be identified by the "p" in the version number; source distributions without the "p" will compile only on OpenBSD.
OpenSSH, like many other open source software applications, builds on the work and components of other applications to perform its tasks. This allows the developers of OpenSSH to focus on creating the stable and secure code that is at the core of the application, while relying on the expertise and ability of the developers of other applications to ensure that those components perform as designed.
Unfortunately, this model can make the deployment of OpenSSH a bit like a recipe: these numerous components need to be downloaded and compiled separately, and the various applications can use different systems for configuration, compilation, and installation of their code.
The following open source software projects are required to compile and deploy OpenSSH. The version numbers for each package listed is the most current stable version at the time of this tutorial. Check the project's website to find out about updated releases.
Project web site: <http://www.gnu.org/software/gzip/gzip.html
>
Source download: <ftp://ftp.gnu.org/gnu/gzip/gzip-1.2.4a.tar
>
Project web site: <http://www.gzip.org/zlib/
>
Source download: <http://www.info-zip.org/pub/infozip/zlib/zlib.tar.gz
>
Project web site: <http://www.aet.tu-cottbus.de/personen/jaenicke/postfix_tls/prngd.html
>
Source download: <ftp://ftp.aet.tu-cottbus.de/pub/postfix_tls/related/prngd/prngd-0.9.23.tar.gz
>
Project web site: <http://www.openssl.org
>
Source download: <http://www.openssl.org/source/openssl-0.9.6b.tar.gz
>
Project web site: <ftp://ftp.porcupine.org/pub/security/index.htm
l>
Source download: <ftp://ftp.porcupine.org/pub/security/tcp_wrappers_7.6.tar.gz
>
Project web site: <http://www.openssh.com/
>
Source download: <ftp://ftp5.usa.openbsd.org/pub/OpenBSD/OpenSSH/portable/openssh-3.0.1p1.tar.g
z>
GNU Zip (gzip) is an open source data compression program, similar to the standard UNIX compress/uncompress applications, but unencumbered by patents that might affect its status as free software.
Though gzip is not a prerequisite for building OpenSSH, its use is required in decompressing the source bundles that will be used later in this tutorial. The gzip format is the most often for the distribution of free software on the Internet, and so its presence on an AIX system is "almost" a requirement.
Fortunately, the source for gzip is available in an uncompressed tape archive (tar) format. After downloading the tarball and saving it into /usr/local/src, execute the following commands:
tar xvf gzip-1.2.4a.tar cd gzip-1.2.4a ./configure && make check
When the auto-configuration and compilation is complete, the following lines will be output:
gzip test OK rm -f _gztest*
Now as root, run the command make install
, and the following
files will be installed into the subdirectories of /usr/local:
/usr/local/man/man1/gzip.1 /usr/local/man/man1/gzexe.1 /usr/local/man/man1/zdiff.1 /usr/local/man/man1/zgrep.1 /usr/local/man/man1/zmore.1 /usr/local/man/man1/znew.1 /usr/local/man/man1/zforce.1 /usr/local/man/man1/zcat.1 /usr/local/man/man1/zcmp.1 /usr/local/man/man1/gunzip.1 /usr/local/bin/gzip /usr/local/bin/zdiff /usr/local/bin/zgrep /usr/local/bin/zmore /usr/local/bin/znew /usr/local/bin/zforce /usr/local/bin/gzexe /usr/local/bin/zcmp /usr/local/bin/gunzip /usr/local/bin/zcat /usr/local/info/gzip.info
Zlib is a lossless, general-purpose compression library used by many open source software projects. The library uses the same compression algorithms used by the gzip program, which are more efficient than those used by UNIX compress.
After downloading the source for the latest version of zlib, and placing it into /usr/local/src, run the following commands:
gunzip -c zlib-1.1.3.tar.gz | tar xvf - cd zlib-1.1.3 vi Makefile
Edit the file "Makefile", adding "-qmaxmem=-1" to the end of the CFLAGS line, so that it appears as such:
CFLAGS=-O -qmaxmem=-1
Run the command make test
to compile and test the library.
When that process is complete, the last line displayed on the screen will be:
*** zlib test OK ***
As root, run the command make install
to install the following
components into subdirectories of /usr/local/src:
/usr/local/lib/libz.a /usr/local/include/zlib.h /usr/local/include/zconf.h
The "Psudo Random Number Generator Daemon", prngd, provides a source of entropy on platforms that do not include a /dev/random special file for that purpose. Entropy, or "randomness", is an integral part of any encryption process. Generating a quantity of true random data is critical in securing password, secret phrases, and other encrypted data. Many UNIX platform provide a kernel-level source of random data, via the /dev/random special file.
Unfortunately, AIX 4.3 does not include this source of randomness. On AIX and other systems lacking /dev/random, the prngd application can provide the entropy required by OpenSSH and other cryptographic software.
After downloading the source for the latest version of prngd into /usr/local/src, run the following commands:
gunzip -c prngd-0.9.23.tar.gz | tar xvf - cd prngd-0.9.23.tar.gz vi Makefile
Find the AIX 4.3 w/cc section in the Makefile; uncomment and add the flag "-qmaxmem=-1" to the CFLAGS line, so that it appears as such:
# AIX 4.3 w/cc ("Joerg Petersen <j.petersen@msh.de>) # Please also check out contrib/AIX-4.3/00README.aix-src CFLAGS=-O -DAIX43 -qmaxmem=-1 # SYSLIBS=
The source can then be compiled by issuing the make
command.
The prngd Makefile does not include a rule for installing the daemon; it must
be installed manually, by running the command:
mkdir /usr/local/sbin ; cp prngd /usr/local/sbin/ cp contrib/prngd.conf.aix43 /etc/prngd.conf
The longer the prngd daemon process is running, the better the quality of randomness it can provide to other applications that use entropy. Thus, this daemon should be run at startup and should never exit. There are numerous methods of running daemons at startup; this tutorial will present one using the AIX System Resource Controller (SRC). By using SRC, a consistent interface for starting, stopping, and querying the status of the "subsystem" will be made available.
To create a subsystem for controlling the prngd daemon, issue the command:
/usr/bin/mkssys -s prngd -p /usr/local/sbin/prngd -a '-f -c /etc/prngd.conf
-s /var/tmp/egd-seed /dev/egd-pool' -u 0 -S -n 15 -f 9 -R -G local
The prngd subsystem can now be started via the command startsrc -s
prngd
. To have the prngd subsystem start at system boot, run the
following command, which will add an entry to /etc/inittab:
/usr/sbin/mkitab "prngd:2:wait:startsrc -s prngd > /dev/console
2>&1"
OpenSSL is an open source implementation of the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols. The general-purpose cryptology libraries provided with OpenSSL are used by a number of encryption-related applications, including OpenSSH.
After downloading the latest source release of OpenSSL into /usr/local/src, run the following commands:
gunzip -c openssl-0.9.6b.tar.gz | tar xvf - cd openssl-0.9.6b ./config && make && make test
Note: OpenSSL is a large and complicated package; the compilation and testing can take a very long time, especially on slower systems. When the test suite has completed, text similar to the following will be printed to the screen:
OpenSSL 0.9.6b 9 Jul 2001 built on: Sat Nov 17 17:41:15 PST 2001 platform: aix43-cc options: bn(64,32) md2(int) rc4(ptr,char) des(idx,cisc,4,long) idea(int) blowfish(idx) compiler: cc -DDSO_DLFCN -DHAVE_DLFCN_H -O -DAIX -DB_ENDIAN -qmaxmem=16384 Target "test" is up to date.
As root, run the command make install to install the following files:
/usr/local/ssl/man/man1/CA.pl.1
/usr/local/ssl/man/man1/asn1parse.1
/usr/local/ssl/man/man1/ca.1
/usr/local/ssl/man/man1/ciphers.1
/usr/local/ssl/man/man1/crl.1
/usr/local/ssl/man/man1/crl2pkcs7.1
/usr/local/ssl/man/man1/dgst.1
/usr/local/ssl/man/man1/dhparam.1
/usr/local/ssl/man/man1/dsa.1
/usr/local/ssl/man/man1/dsaparam.1
/usr/local/ssl/man/man1/enc.1
/usr/local/ssl/man/man1/gendsa.1
/usr/local/ssl/man/man1/genrsa.1
/usr/local/ssl/man/man1/nseq.1
/usr/local/ssl/man/man1/openssl.1
/usr/local/ssl/man/man1/passwd.1
/usr/local/ssl/man/man1/pkcs12.1
/usr/local/ssl/man/man1/pkcs7.1
/usr/local/ssl/man/man1/pkcs8.1
/usr/local/ssl/man/man1/rand.1
/usr/local/ssl/man/man1/req.1
/usr/local/ssl/man/man1/rsa.1
/usr/local/ssl/man/man1/rsautl.1
/usr/local/ssl/man/man1/s_client.1
/usr/local/ssl/man/man1/s_server.1
/usr/local/ssl/man/man1/sess_id.1
/usr/local/ssl/man/man1/smime.1
/usr/local/ssl/man/man1/speed.1
/usr/local/ssl/man/man1/spkac.1
/usr/local/ssl/man/man1/verify.1
/usr/local/ssl/man/man1/version.1
/usr/local/ssl/man/man1/x509.1
/usr/local/ssl/man/man3/BIO_ctrl.3
/usr/local/ssl/man/man3/BIO_f_base64.3
/usr/local/ssl/man/man3/BIO_f_buffer.3
/usr/local/ssl/man/man3/BIO_f_cipher.3
/usr/local/ssl/man/man3/BIO_f_md.3
/usr/local/ssl/man/man3/BIO_f_null.3
/usr/local/ssl/man/man3/BIO_f_ssl.3
/usr/local/ssl/man/man3/BIO_find_type.3
/usr/local/ssl/man/man3/BIO_new.3
/usr/local/ssl/man/man3/BIO_new_bio_pair.3
/usr/local/ssl/man/man3/BIO_push.3
/usr/local/ssl/man/man3/BIO_read.3
/usr/local/ssl/man/man3/BIO_s_accept.3
/usr/local/ssl/man/man3/BIO_s_bio.3
/usr/local/ssl/man/man3/BIO_s_connect.3
/usr/local/ssl/man/man3/BIO_s_fd.3
/usr/local/ssl/man/man3/BIO_s_file.3
/usr/local/ssl/man/man3/BIO_s_mem.3
/usr/local/ssl/man/man3/BIO_s_null.3
/usr/local/ssl/man/man3/BIO_s_socket.3
/usr/local/ssl/man/man3/BIO_set_callback.3
/usr/local/ssl/man/man3/BIO_should_retry.3
/usr/local/ssl/man/man3/BN_CTX_new.3
/usr/local/ssl/man/man3/BN_CTX_start.3
/usr/local/ssl/man/man3/BN_add.3
/usr/local/ssl/man/man3/BN_add_word.3
/usr/local/ssl/man/man3/BN_bn2bin.3
/usr/local/ssl/man/man3/BN_cmp.3
/usr/local/ssl/man/man3/BN_copy.3
/usr/local/ssl/man/man3/BN_generate_prime.3
/usr/local/ssl/man/man3/BN_mod_inverse.3
/usr/local/ssl/man/man3/BN_mod_mul_montgomery.3
/usr/local/ssl/man/man3/BN_mod_mul_reciprocal.3
/usr/local/ssl/man/man3/BN_new.3
/usr/local/ssl/man/man3/BN_num_bytes.3
/usr/local/ssl/man/man3/BN_rand.3
/usr/local/ssl/man/man3/BN_set_bit.3
/usr/local/ssl/man/man3/BN_zero.3
/usr/local/ssl/man/man3/CRYPTO_set_ex_data.3
/usr/local/ssl/man/man3/DH_generate_key.3
/usr/local/ssl/man/man3/DH_generate_parameters.3
/usr/local/ssl/man/man3/DH_get_ex_new_index.3
/usr/local/ssl/man/man3/DH_new.3
/usr/local/ssl/man/man3/DH_set_method.3
/usr/local/ssl/man/man3/DH_size.3
/usr/local/ssl/man/man3/DSA_SIG_new.3
/usr/local/ssl/man/man3/DSA_do_sign.3
/usr/local/ssl/man/man3/DSA_dup_DH.3
/usr/local/ssl/man/man3/DSA_generate_key.3
/usr/local/ssl/man/man3/DSA_generate_parameters.3
/usr/local/ssl/man/man3/DSA_get_ex_new_index.3
/usr/local/ssl/man/man3/DSA_new.3
/usr/local/ssl/man/man3/DSA_set_method.3
/usr/local/ssl/man/man3/DSA_sign.3
/usr/local/ssl/man/man3/DSA_size.3
/usr/local/ssl/man/man3/ERR_GET_LIB.3
/usr/local/ssl/man/man3/ERR_clear_error.3
/usr/local/ssl/man/man3/ERR_error_string.3
/usr/local/ssl/man/man3/ERR_get_error.3
/usr/local/ssl/man/man3/ERR_load_crypto_strings.3
/usr/local/ssl/man/man3/RAND_add.3
/usr/local/ssl/man/man3/ERR_load_strings.3
/usr/local/ssl/man/man3/ERR_print_errors.3
/usr/local/ssl/man/man3/ERR_put_error.3
/usr/local/ssl/man/man3/ERR_remove_state.3
/usr/local/ssl/man/man3/EVP_DigestInit.3
/usr/local/ssl/man/man3/EVP_EncryptInit.3
/usr/local/ssl/man/man3/EVP_OpenInit.3
/usr/local/ssl/man/man3/EVP_SealInit.3
/usr/local/ssl/man/man3/EVP_SignInit.3
/usr/local/ssl/man/man3/EVP_VerifyInit.3
/usr/local/ssl/man/man3/OPENSSL_VERSION_NUMBER.3
/usr/local/ssl/man/man3/OpenSSL_add_all_algorithms.3
/usr/local/ssl/man/man3/RAND_bytes.3
/usr/local/ssl/man/man3/RAND_cleanup.3
/usr/local/ssl/man/man3/RAND_egd.3
/usr/local/ssl/man/man3/RAND_load_file.3
/usr/local/ssl/man/man3/RAND_set_rand_method.3
/usr/local/ssl/man/man3/RSA_blinding_on.3
/usr/local/ssl/man/man3/bio.3
/usr/local/ssl/man/man3/RSA_check_key.3
/usr/local/ssl/man/man3/RSA_generate_key.3
/usr/local/ssl/man/man3/RSA_get_ex_new_index.3
/usr/local/ssl/man/man3/RSA_new.3
/usr/local/ssl/man/man3/RSA_padding_add_PKCS1_type_1.3
/usr/local/ssl/man/man3/RSA_print.3
/usr/local/ssl/man/man3/RSA_private_encrypt.3
/usr/local/ssl/man/man3/RSA_public_encrypt.3
/usr/local/ssl/man/man3/RSA_set_method.3
/usr/local/ssl/man/man3/RSA_sign.3
/usr/local/ssl/man/man3/RSA_sign_ASN1_OCTET_STRING.3
/usr/local/ssl/man/man3/RSA_size.3
/usr/local/ssl/man/man3/blowfish.3
/usr/local/ssl/man/man3/bn.3
/usr/local/ssl/man/man3/bn_internal.3
/usr/local/ssl/man/man3/buffer.3
/usr/local/ssl/man/man3/crypto.3
/usr/local/ssl/man/man3/d2i_DHparams.3
/usr/local/ssl/man/man3/d2i_RSAPublicKey.3
/usr/local/ssl/man/man3/des.3
/usr/local/ssl/man/man3/dh.3
/usr/local/ssl/man/man3/dsa.3
/usr/local/ssl/man/man3/err.3
/usr/local/ssl/man/man3/evp.3
/usr/local/ssl/man/man3/hmac.3
/usr/local/ssl/man/man3/lh_stats.3
/usr/local/ssl/man/man3/lhash.3
/usr/local/ssl/man/man3/md5.3
/usr/local/ssl/man/man3/mdc2.3
/usr/local/ssl/man/man3/rand.3
/usr/local/ssl/man/man3/rc4.3
/usr/local/ssl/man/man3/ripemd.3
/usr/local/ssl/man/man3/rsa.3
/usr/local/ssl/man/man3/sha.3
/usr/local/ssl/man/man3/threads.3
/usr/local/ssl/man/man3/SSL_CIPHER_get_name.3
/usr/local/ssl/man/man3/SSL_CTX_add_extra_chain_cert.3
/usr/local/ssl/man/man3/SSL_CTX_add_session.3
/usr/local/ssl/man/man3/SSL_CTX_flush_sessions.3
/usr/local/ssl/man/man3/SSL_CTX_free.3
/usr/local/ssl/man/man3/SSL_CTX_get_ex_new_index.3
/usr/local/ssl/man/man3/SSL_CTX_get_verify_mode.3
/usr/local/ssl/man/man3/SSL_CTX_new.3
/usr/local/ssl/man/man3/SSL_CTX_load_verify_locations.3
/usr/local/ssl/man/man3/SSL_CTX_sess_number.3
/usr/local/ssl/man/man3/SSL_CTX_sess_set_cache_size.3
/usr/local/ssl/man/man3/SSL_CTX_sess_set_get_cb.3
/usr/local/ssl/man/man3/SSL_CTX_sessions.3
/usr/local/ssl/man/man3/SSL_CTX_set_cipher_list.3
/usr/local/ssl/man/man3/SSL_CTX_set_client_CA_list.3
/usr/local/ssl/man/man3/SSL_CTX_set_default_passwd_cb.3
/usr/local/ssl/man/man3/SSL_CTX_set_mode.3
/usr/local/ssl/man/man3/SSL_CTX_set_options.3
/usr/local/ssl/man/man3/SSL_CTX_set_session_cache_mode.3
/usr/local/ssl/man/man3/SSL_CTX_set_session_id_context.3
/usr/local/ssl/man/man3/SSL_CTX_set_ssl_version.3
/usr/local/ssl/man/man3/SSL_CTX_set_timeout.3
/usr/local/ssl/man/man3/SSL_CTX_set_verify.3
/usr/local/ssl/man/man3/SSL_CTX_use_certificate.3
/usr/local/ssl/man/man3/SSL_SESSION_free.3
/usr/local/ssl/man/man3/SSL_SESSION_get_ex_new_index.3
/usr/local/ssl/man/man3/SSL_SESSION_get_time.3
/usr/local/ssl/man/man3/SSL_accept.3
/usr/local/ssl/man/man3/SSL_clear.3
/usr/local/ssl/man/man3/SSL_connect.3
/usr/local/ssl/man/man3/SSL_free.3
/usr/local/ssl/man/man3/SSL_get_ciphers.3
/usr/local/ssl/man/man3/SSL_get_client_CA_list.3
/usr/local/ssl/man/man3/SSL_get_current_cipher.3
/usr/local/ssl/man/man3/SSL_get_error.3
/usr/local/ssl/man/man3/SSL_get_ex_data_X509_STORE_CTX_idx.3
/usr/local/ssl/man/man3/SSL_get_ex_new_index.3
/usr/local/ssl/man/man3/SSL_get_fd.3
/usr/local/ssl/man/man3/SSL_get_rbio.3
/usr/local/ssl/man/man3/SSL_get_peer_cert_chain.3
/usr/local/ssl/man/man3/SSL_get_peer_certificate.3
/usr/local/ssl/man/man3/SSL_get_session.3
/usr/local/ssl/man/man3/SSL_get_verify_result.3
/usr/local/ssl/man/man3/SSL_get_version.3
/usr/local/ssl/man/man3/SSL_library_init.3
/usr/local/ssl/man/man3/SSL_load_client_CA_file.3
/usr/local/ssl/man/man3/SSL_new.3
/usr/local/ssl/man/man3/SSL_pending.3
/usr/local/ssl/man/man3/SSL_read.3
/usr/local/ssl/man/man3/SSL_set_bio.3
/usr/local/ssl/man/man3/SSL_set_connect_state.3
/usr/local/ssl/man/man3/SSL_set_fd.3
/usr/local/ssl/man/man3/SSL_set_session.3
/usr/local/ssl/man/man3/SSL_set_shutdown.3
/usr/local/ssl/man/man3/SSL_set_verify_result.3
/usr/local/ssl/man/man3/SSL_shutdown.3
/usr/local/ssl/man/man3/SSL_write.3
/usr/local/ssl/man/man3/d2i_SSL_SESSION.3
/usr/local/ssl/man/man3/ssl.3
/usr/local/ssl/man/man5/config.5
/usr/local/ssl/man/man7/des_modes.7
/usr/local/ssl/bin/openssl
/usr/local/ssl/bin/c_rehash
/usr/local/ssl/lib/libcrypto.a
/usr/local/ssl/lib/libssl.a
/usr/local/ssl/include/openssl/e_os.h
/usr/local/ssl/include/openssl/e_os2.h
/usr/local/ssl/include/openssl/crypto.h
/usr/local/ssl/include/openssl/tmdiff.h
/usr/local/ssl/include/openssl/opensslv.h
/usr/local/ssl/include/openssl/opensslconf.h
/usr/local/ssl/include/openssl/ebcdic.h
/usr/local/ssl/include/openssl/symhacks.h
/usr/local/ssl/include/openssl/md2.h
/usr/local/ssl/include/openssl/md4.h
/usr/local/ssl/include/openssl/md5.h
/usr/local/ssl/include/openssl/sha.h
/usr/local/ssl/include/openssl/mdc2.h
/usr/local/ssl/include/openssl/hmac.h
/usr/local/ssl/include/openssl/ripemd.h
/usr/local/ssl/include/openssl/des.h
/usr/local/ssl/include/openssl/rc2.h
/usr/local/ssl/include/openssl/rc4.h
/usr/local/ssl/include/openssl/rc5.h
/usr/local/ssl/include/openssl/idea.h
/usr/local/ssl/include/openssl/blowfish.h
/usr/local/ssl/include/openssl/cast.h
/usr/local/ssl/include/openssl/bn.h
/usr/local/ssl/include/openssl/rsa.h
/usr/local/ssl/include/openssl/dsa.h
/usr/local/ssl/include/openssl/dh.h
/usr/local/ssl/include/openssl/dso.h
/usr/local/ssl/include/openssl/buffer.h
/usr/local/ssl/include/openssl/bio.h
/usr/local/ssl/include/openssl/stack.h
/usr/local/ssl/include/openssl/safestack.h
/usr/local/ssl/include/openssl/lhash.h
/usr/local/ssl/include/openssl/rand.h
/usr/local/ssl/include/openssl/err.h
/usr/local/ssl/include/openssl/objects.h
/usr/local/ssl/include/openssl/obj_mac.h
/usr/local/ssl/include/openssl/evp.h
/usr/local/ssl/include/openssl/asn1.h
/usr/local/ssl/include/openssl/asn1_mac.h
/usr/local/ssl/include/openssl/pem.h
/usr/local/ssl/include/openssl/pem2.h
/usr/local/ssl/include/openssl/x509.h
/usr/local/ssl/include/openssl/x509_vfy.h
/usr/local/ssl/include/openssl/x509v3.h
/usr/local/ssl/include/openssl/conf.h
/usr/local/ssl/include/openssl/conf_api.h
/usr/local/ssl/include/openssl/txt_db.h
/usr/local/ssl/include/openssl/pkcs7.h
/usr/local/ssl/include/openssl/pkcs12.h
/usr/local/ssl/include/openssl/comp.h
/usr/local/ssl/include/openssl/ssl.h
/usr/local/ssl/include/openssl/ssl2.h
/usr/local/ssl/include/openssl/ssl3.h
/usr/local/ssl/include/openssl/ssl23.h
/usr/local/ssl/include/openssl/tls1.h
/usr/local/ssl/misc/CA.sh
/usr/local/ssl/misc/CA.pl
/usr/local/ssl/misc/der_chop
/usr/local/ssl/misc/c_hash
/usr/local/ssl/misc/c_info
/usr/local/ssl/misc/c_issuer
/usr/local/ssl/misc/c_name
/usr/local/ssl/openssl.cnf
TCP Wrappers provides a simple application, tcpd, that can be used to limit access to various network services based on the IP address of the client. It is often used, and in fact, was designed for "wrapping" services spawned by inetd. The package also provides a library, libwrap.a, that applications, including OpenSSH, can link to and gain the access controls that TCP Wrappers provides. While it is not necessary for deploying OpenSSH, TCP Wrappers adds another level of access control and logging capability that an administrator might appreciate.
To build TCP Wrappers, issue the following commands after downloading the source distribution into /usr/local/src:
gunzip -c tcp_wrappers_7.6.tar.gz | tar xvf -
cd tcp_wrappers_7.6
vi Makefile
Before compiling the source, several changes will need to be made to the file "Makefile":
# SysV.4 Solaris 2.x OSF AIX
REAL_DAEMON_DIR=/usr/sbin
#STYLE = -DPROCESS_OPTIONS # Enable language extensions.
FACILITY= LOG_MAIL # LOG_MAIL is what most sendmail daemons use
to
FACILITY= LOG_LOCAL7 # tcpd messages will to facility local7
TABLES = -DHOSTS_DENY=\"/etc/hosts.deny\" -DHOSTS_ALLOW=\"/etc/hosts.allow\"
to
TABLES = -DHOSTS_DENY=\"/etc/tcpd.conf\" -DHOSTS_ALLOW=\"/etc/tcpd.conf\"
-qmaxmem=-1
to the CFLAGS block:
CFLAGS = -O -DFACILITY=$(FACILITY) $(ACCESS) $(PARANOID) $(NETGROUP) \
$(BUGS) $(SYSTYPE) $(AUTH) $(UMASK) \
-DREAL_DAEMON_DIR=\"$(REAL_DAEMON_DIR)\" $(STYLE) $(KILL_OPT) \
-DSEVERITY=$(SEVERITY) -DRFC931_TIMEOUT=$(RFC931_TIMEOUT) \
$(UCHAR) $(TABLES) $(STRINGS) $(TLI) $(EXTRA_CFLAGS) $(DOT) \
$(VSYSLOG) $(HOSTNAME) -qmaxmem=-1
After saving the above changes to the Makefile, run the command make
aix
to compile the source.
The Makefile for TCP Wrappers does not include an install target. To place the files in the proper locations, enter the following commands as root:
cp tcpdchk safe_finger try-from tcpdmatch tcpd /usr/local/sbin/ cp libwrap.a /usr/local/lib/ cp hosts_access.3 /usr/local/man/man3/ cp hosts_access.5 hosts_options.5 /usr/local/man/man5/ cp tcpd.8 tcpdchk.8 tcpdmatch.8 /usr/local/man/man8/ mkdir -p /usr/local/share/tcpd/ cp Banners.Makefile /usr/local/share/tcpd/ mkdir /usr/local/include/ cp tcpd.h /usr/local/include/ touch /etc/tcpd.conf
Configuration of TCP Wrappers will not be detailed in this tutorial. See the included README and man pages for instructions on usage and configuration settings.
Now that all of the prerequisites are in place, the OpenSSH source can be compiled. After downloading the latest version the OpenSSH source into /usr/local/src, extract the contents with the commands:
gunzip -c openssh-3.0.1p1.tar.gz | tar xvf - cd openssh-3.0.1p1
There are a number of options that must be defined at compile-time, and other
options that can have their default values set during compilation. For a list
and description of all of the compile-time configuration options, type the command
./configure --help
in the source directory. For this tutorial,
the following options will be specified:
./configure --sysconfdir=/etc/ssh --with-cflags="-qmaxmem=-1"
--with-tcp-wrappers --with-xauth=/usr/bin/X11/xauth --with-prngd-socket=/dev/egd-pool
--with-ipv4-default --with-pid-dir=/var/tmp
When configuration completes, a summary of the options will be printed to the screen, similar to:
OpenSSH has been configured with the following options:
User binaries: /usr/local/bin
System binaries: /usr/local/sbin
Configuration files: /etc/ssh
Askpass program: /usr/local/libexec/ssh-askpass
Manual pages: /usr/local/man/manX
PID file: /var/tmp
sshd default user PATH: /usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin
Random number collection: PRNGD/EGD (socket /dev/egd-pool)
Manpage format: man
PAM support: no
KerberosIV support: no
Smartcard support: no
AFS support: no
S/KEY support: no
TCP Wrappers support: yes
MD5 password support: no
IP address in $DISPLAY hack: no
Use IPv4 by default hack: yes
Translate v4 in v6 hack: no
Host: powerpc-ibm-aix4.3.3.0
Compiler: cc
Compiler flags: -g -qmaxmem=-1
Preprocessor flags: -I/usr/local/ssl/include -I/usr/local/include
Linker flags: -L/usr/local/ssl/lib -L/usr/local/lib -blibpath:/usr/lib:/lib:/usr/local/lib
Libraries: -lwrap -lz -lcrypto
Issue the command make
to compile the source. When the
build is complete, run the command make install
as root,
to install the various files in their proper places.
The following files will be installed into /usr/local:
/usr/local/man/man1/ssh.1
/usr/local/man/man1/scp.1
/usr/local/man/man1/ssh-add.1
/usr/local/man/man1/ssh-agent.1
/usr/local/man/man1/ssh-keygen.1
/usr/local/man/man1/ssh-keyscan.1
/usr/local/man/man1/sftp.1
/usr/local/man/man8/sshd.8
/usr/local/man/man8/sftp-server.8
/usr/local/bin/ssh
/usr/local/bin/scp
/usr/local/bin/ssh-add
/usr/local/bin/ssh-agent
/usr/local/bin/ssh-keygen
/usr/local/bin/ssh-keyscan
/usr/local/bin/sftp
/usr/local/sbin/sshd
/usr/local/share/Ssh.bin
/usr/local/libexec/sftp-server
The directory /etc/ssh will also be created, with the contents:
/etc/ssh/ssh_config
/etc/ssh/sshd_config
/etc/ssh/ssh_prng_cmds
/etc/ssh/moduli
/etc/ssh/ssh_host_key
/etc/ssh/ssh_host_key.pub
/etc/ssh/ssh_host_dsa_key
/etc/ssh/ssh_host_dsa_key.pub
/etc/ssh/ssh_host_rsa_key
/etc/ssh/ssh_host_rsa_key.pub
As part of the install process, host keys will be generated and placed in /etc/ssh. There are three types of host keys, each comprised of two files (a "key pair"): a "secret" portion, whose contents should not be accessable by any user other then root, and a "public" portion, whose contents are transferred to the client system each time a connection is initiated.
At the start of each new connection to a server, client compares the public portion of the server's host key to one from a previous connection, saved in a file in the user's home directory. If the current version and previous versions are not identical, the client will be issued a warning that the server they have connected to may have been spoofed or compromised, and should not be trusted. For this reason, it is important to back up the server keys, and ensure that those files are not replaced during an upgrade of the OpenSSH software.
The three types of key pairs are:
ssh_host_key
and ssh_host_key.pub
This pair of files contains the host key that will be used when clients connect to the server using version 1 of the Secure Shell protocol. This key pair uses the Rivest-Shamir-Adleman (RSA) algorithm for encryption.
ssh_host_dsa_key
and ssh_host_dsa_key.pub
This key pair contains the host key used for clients connecting via version 2 of the Secure Shell protocol. It uses the Digital Signature Algorithm (DSA) public-key algorithm for encryption.
ssh_host_rsa_key
and ssh_host_rsa_key.pub
This key pair is also used with clients connecting with version 2 of the Secure Shell protocol. It also uses the RSA algorithm for encryption, and is most commonly used with key pairs that have been converted from the protocol 1 version for use with protocol 2.
If the file containing the public half of a key pair is damaged, it can easily
be regenerated from the secret half, with the ssh-keygen
utility.
If the private half is damaged or compromised by a security breach, the entire
key pair is useless, and must be regenerated. If this occurs, all users of the
system must be told that there is a new host key, and they will have to delete
the public portion of the old server key from their ~/.ssh/known_hosts
or known_hosts2
file. If they don't, they will receive a warning
message each time they connect to the server, or, depending on their local configuration,
they will not be able to connect at all.
Secure Shell server (sshd) options are defined in the file /etc/ssh/sshd_config
.
A default file is placed into that location during the install process. For
a list and description of all the possible options, see the sshd(8) man page.
A few of the more common options, and their recommended settings are:
DenyGroups
This keyword can be followed by a number of group names, separated by spaces. Users whose primary group or supplementary group list matches one of the patterns aren't allowed to log in. `*' and `?' can be used as wildcards in the patterns. Only group names are valid; a numerical group ID is not recognized. By default login is allowed regardless of the group list.
DenyUsers
This keyword can be followed by a number of user names, separated by spaces. Login is disallowed for user names that match one of the patterns. `*' and `?' can be used as wildcards in the patterns. Only user names are valid; a numerical user ID is not recognized. By default login is allowed regardless of the user name.
HostbasedAuthentication
Specifies whether rhosts or /etc/hosts.equiv authentication together with successful public key client host authentication is allowed (hostbased authentication). This option is similar to RhostsRSAAuthentication and applies to protocol version 2 only. The default is ``no''.
IgnoreRhosts
Specifies that .rhosts and .shosts files will not be used in RhostsAuthentication, RhostsRSAAuthentication or HostbasedAuthentication. /etc/hosts.equiv and /etc/shosts.equiv are still used. The default is ``yes''.
LogLevel
Gives the verbosity level that is used when logging messages from sshd. The possible values are: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. The default is INFO. Logging with level DEBUG violates the privacy of users and is not recommended.
PermitRootLogin
Specifies whether root can login using ssh(1). The argument must be ``yes'', ``without-password'', ``forced-commands-only'' or ``no''. The default is ``yes''. If this option is set to ``without-password'' password authentication is disabled for root. If this option is set to ``forced-commands-only'' root login with public key authentication will be allowed, but only if the command option has been specified (which may be useful for taking remote backups even if root login is normally not allowed). All other authentication methods are disabled for root. If this option is set to ``no'' root is not allowed to login.
Protocol
Specifies the protocol versions sshd should support. The possible values are ``1'' and ``2''. Multiple versions must be comma- separated. The default is ``2,1''.
RhostsAuthentication
Specifies whether authentication using rhosts or /etc/hosts.equiv files is sufficient. Normally, this method should not be permitted because it is insecure. RhostsRSAAuthentication should be used instead, because it performs RSA-based host authentication in addition to normal rhosts or /etc/hosts.equiv authentication. The default is ``no''. This option applies to protocol version 1 only.
RhostsRSAAuthentication
Specifies whether rhosts or /etc/hosts.equiv authentication together with successful RSA host authentication is allowed. The default is ``no''. This option applies to protocol version 1 on- ly.
StrictModes
Specifies whether sshd should check file modes and ownership of the user's files and home directory before accepting login. This is normally desirable because novices sometimes accidentally leave their directory or files world-writable. The default is ``yes''.
Subsystem
Configures an external subsystem (e.g., file transfer daemon). Arguments should be a subsystem name and a command to execute upon subsystem request. The command sftp-server(8) implements the``sftp'' file transfer subsystem. By default no subsystems are defined. Note that this option applies to protocol version 2 only.
SyslogFacility
Gives the facility code that is used when logging messages from sshd. The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The default is AUTH.
X11Forwarding
Specifies whether X11 forwarding is permitted. The default is ``no''. Note that disabling X11 forwarding does not improve security in any way, as users can always install their own for- warders. X11 forwarding is automatically disabled if UseLogin is enabled.
It is useful to set options even if the setting is to the default value, as defaults can change between version releases. Using the above options, the /etc/ssh/sshd_config configuration file would be:
############################################################# # # /etc/ssh/sshd_config # # configuration file for the OpenSSH ssh daemon # ############################################################ # deny connections from members of these groups: DenyGroups uucp, mail, nobody, nogroup # deny connections from these users: DenyUsers daemon, bin, sys, adm, uucp, guest, nobody, lpd # allow host-based authentication (.rhosts and /etc/hosts.equiv) # if the host key exchange was successful. I realize that this # is reducing the security of my server. [ protocol 2 only] HostbasedAuthentication yes # permit the use of user .rhosts and .shosts files. Again, I # release that I am reducing the security of my server in favor # of functionality for clients: IgnoreRhosts no # messages logged to syslog from sshd will be at priority INFO: LogLevel INFO # root will not be permitted to log in interactively, but can # run commands remotely ... PermitRootLogin forced-commands-only # accept protocol 2 connections first, then fall back to protocol 1 Protocol 2,1 # straight .rhosts authentication will not be permitted, as this is # exactly the same as "rsh/rcp" ... RhostsAuthentication no # however, .rhosts authentication with successful RSA host # authentication will be permitted [protocol 1 only]: RhostsRSAAuthentication yes # ensure that the permissions on a user's ssh-related files are # set properly; deny connections if they are not: StrictModes yes # define the subsystem "sftp" to enable the secure replacement for # the ftp protocol: Subsystem sftp /usr/local/libexec/sftp-server # have syslogd dispatch sshd messages to the AUTH facility ... SyslogFacility AUTH # permit the forwarding of X11 connections. This doesn't decrease # security at all ... X11Forwarding yes ############################################################
As with most programs that are to be run upon system startup, there are a number of ways to accomplish this goal. This tutorial presents one possibility, again using the System Resource Controller (SRC) feature of AIX. Using the SRC provides a method of controlling the daemon consistent with other subsystems present on AIX systems.
To create a subsystem that will control the sshd daemon, issue the following command as root:
/usr/bin/mkssys -s sshd -p /usr/local/sbin/sshd -a '-D' -u 0 -S -n 15 -f 9 -R -G local
The above command will create a new subsystem named "sshd". The program that will be started by this subsystem is /usr/local/sbin/sshd, with the "-D" argument. The program will be run as root, and will use signals for communication with the SRC. When requested to stop, the daemon will be sent the TERM signal, and if that fails, the KILL signal. The subsystem will be restarted if it stops abnormally, and it will be included in the SRC group named "local".
To have the subsystem started at system boot, run the following command to add an entry to /etc/inittab, after the "prngd" entry:
/usr/sbin/mkitab -i prngd "sshd:2:wait:startsrc -s sshd > /dev/console 2>&1"
Replacing the use of the insecure telnet protocol with the much more secure ssh protocol is simple. Users will have to substitute the use of an ssh client for their telnet client. When connecting via telnet, the user will enter:
$ telnet earth
They will then be prompted to enter their user name and password:
Trying 123.456.789.012 ... Connected to earth.galaxy.com Escape character is '^]
AIX Version 4 (C) Copyrights by IBM and by others 1982, 1996. login: user user's Password: ******
If the user account specified and the password is correct, the user will then be logged in. To perform the same action using ssh, the user will type:
$ ssh earth user@earth's password: ******
As with telnet, the user will then be logged in if the user account and password specified are valid. The difference, though, is that all network traffic between the client and the server, including the user name and password, will be encrypted, and thus, immune from packet sniffing attacks. SSH clients usually use the name of the user that is logged in on the client system when connecting to the remote system. If the end user wishes to use a different user account, they will need to add that account name before the host name, connected with an "@" sign:
$ ssh user@earth
The telnet service should be disabled on the server, by either deleting or commenting out the telnet entry in /etc/inetd.conf.
The "r" services are those that use only the file /etc/hosts.equiv and the "~/.rhosts" files within users home directories to perform authentication. These services include rsh, rlogin, and rcp. All of these services can be replaced by OpenSSH, exponentially increasing the overall security of the server. Several "layers" of security may be imposed on the use of these services, depending on the options set in the /etc/ssh/sshd_config file by the server's administrator.
The OpenSSH distribution includes both the client and server programs necessary to replace the insecure "r" commands. For the examples presented in the following table, it is assumed that:
Insecure command | Secure equivalent | Action performed | Security advantage |
rsh earth rlogin earth |
ssh earth slogin earth |
provides the user with an interactive login session on the server named earth, without having to enter a password. | The host key of the client system is checked against the server's known hosts file. If they do not match, the connection is refused. All communications between the server and the client are encrypted. |
rsh earth uptime |
ssh earth uptime |
executes the uptime command on the server named earth, without having to enter a password. | |
rcp earth:/etc/passwd /tmp/earth-passwd |
scp earth:/etc/passwd /tmp/earth-passwd |
copies the file /etc/passwd from the server named earth and saves it on the local system as /tmp/earth-passwd, without the user needing to enter a password. |
The "rexec" command, though similarly named, uses a different but also insecure method of authorizing a remote user to run a command on a server without entering her password. Instead of the .rhosts file, a .netrc file in the user's home directory on the client system contains the user name and password. This data, and all other data transferred over the network is sent in clear-text. By using the ssh client's ability to execute commands, use of the rexec service can be avoided, and the daemon that provides this service can be disabled on the server.
In order to take advantage of the increased security provided by the OpenSSH replacements, the "login", "shell", and "exec" services should be commented out or deleted from the server's /etc/inetd.conf.
For those systems that are required to provide an interactive file transfer service, the sftp-server is included with the OpenSSH distribution. Using the same authentication and encryption methods as ssh, users can use the sftp client program to connect to and transfer files to and from remote servers. Operation of the sftp program is similar to standard ftp clients, though the sftp-server program lacks some of the "bells and whistles" of the ftpd daemon.
If the features provided by the sftpd-server program meet the requirements for your FTP service, the standard ftpd daemon should be disabled by commenting out or deleting the "ftp" entry in /etc/inetd.conf.
The Secure Shell protocol is a flexible and powerful tool; this tutorial has only scratched the surface of its capabilities. SSH can be used in many different ways, including but not limited to: securing remote X11 sessions, providing encryption for services not designed with such protection, the use of public keys to provide seamless login and the secure execution of specific commands, and so on.
OpenSSH can be extended to include Kerberos authentication, AFS token passing, Smart Card support, and a number of other related technologies. For more information about using these and other features with OpenSSH, refer to the items listed in the references and resources section.
The web site for the OpenSSH project, <http://www.openssh.com>, is the primary source for information about new releases of OpenSSH. It also contains a Frequently Asked Questions page, a form for reporting bugs, and an archive of the various OpenSSH related mailing lists.
SSH, The Secure Shell: The Definitive Guide, by Daniel J. Barrett and Richard E. Silverman, published by O'Reilly & Associates, is, as the title states, the definitive guide to the Secure Shell protocol, providing in-depth explanations about almost everything SSH-related. The book also has a website, <http://www.snailbook.com>, containing news, an FAQ, and discussion forums dedicated to SSH.
A number of Internet Drafts (working documents of the Internet Engineering Task Force, IETF) related to Secure Shell have been published: they can be found at the web site <http://www.ietf.org/html.charters/secsh-charter.html>.
A general discussion mailing list for discussion of Secure Shell is hosted by Security Focus. To subscribe to this list, send an empty message to <secureshell-subscribe@securityfocus.com>. A read-only list for announcements of updates to OpenSSH and related software can be subscribed to by sending a message containing only the word "SUBSCRIBE" in the body, to <openssh-unix-announce-request@mindrot.org>.
$Id: openssh-aix.html,v 1.15 2001/11/19 14:42:33 ssklar Exp ssklar $