Call for testing: OpenSSH 8.2

Val Baranov val.baranov at
Tue Feb 11 06:06:16 AEDT 2020

AIX 7.1 SP5. "configure" OpenSSH 8.2p1

Command line:
./configure --prefix=/usr/local/openssh --with-ssl-dir=/usr/local/openssl --with-zlib=/usr/local/zlib --without-openssl-header-check --with-cflags=-q64 --with-ldflags=-q64

checking for getpagesize... (cached) yes
checking whether snprintf correctly terminates long strings... yes
checking whether snprintf understands %zu... yes
checking whether vsnprintf returns correct values on overflow... yes
checking whether snprintf can declare const char *fmt... yes
checking for (overly) strict mkstemp... no
checking if getaddrinfo seems to work... yes
checking whether AI_NUMERICSERV is declared... yes
checking for getpgrp... yes
checking if getpgrp accepts zero args... yes
configure: error: *** working libcrypto not found, check config.log


     Configure OpenSSH ver. 7.9p1 on the same host does not produce any errors:
checking for getpagesize... (cached) yes
checking whether snprintf correctly terminates long strings... yes
checking whether snprintf understands %zu... yes
checking whether vsnprintf returns correct values on overflow... yes
checking whether snprintf can declare const char *fmt... yes
checking for (overly) strict mkstemp... no
checking if getaddrinfo seems to work... yes
checking whether AI_NUMERICSERV is declared... yes
checking for getpgrp... yes
checking if getpgrp accepts zero args... yes
checking openssl/opensslv.h usability... yes
checking openssl/opensslv.h presence... yes
checking for openssl/opensslv.h... yes
              Host: powerpc-ibm-aix7.1.5.0
          Compiler: cc -qlanglvl=extc89
    Compiler flags: -g -q64
Preprocessor flags: -I/usr/local/ssl/include -I/usr/local/zlib/include
      Linker flags: -L/usr/local/ssl/lib -L/usr/local/zlib/lib  -q64 -blibpath:/usr/lib:/lib
         Libraries: -lcrypto -lz
(ended w/ no errors).

Is it something with "configure" specifically with OpenSSH 8.2?  My last build was for 7.9p1, did not try (yet) 8.0 or 8.1.

Pls advise.
Txs. Val

-----Original Message-----
From: openssh-unix-dev < at> On Behalf Of Damien Miller
Sent: Wednesday, February 5, 2020 6:29 PM
To: openssh-unix-dev at
Subject: Call for testing: OpenSSH 8.2


OpenSSH 8.2p1 is almost ready for release, so we would appreciate testing on as many platforms and systems as possible. This is a feature release.

Snapshot releases for portable OpenSSH are available from 

The OpenBSD version is available in CVS HEAD: 

Portable OpenSSH is also available via git using the instructions at
At  or via a mirror at Github: 

Running the regression tests supplied with Portable OpenSSH does not require installation and is a simply:

$ ./configure && make tests

Live testing on suitable non-production systems is also appreciated.
Please send reports of success or failure to openssh-unix-dev at Security bugs should be reported directly to openssh at

Below is a summary of changes. More detail may be found in the ChangeLog in the portable OpenSSH tarballs.

Thanks to the many people who contributed to this release.

Future deprecation notice

It is now possible[1] to perform chosen-prefix attacks against the
SHA-1 algorithm for less than USD$50K. For this reason, we will be disabling the "ssh-rsa" public key signature algorithm by default in a near-future release.

This algorithm is unfortunately still used widely despite the existence of better alternatives, being the only remaining public key signature algorithm specified by the original SSH RFCs.

The better alternatives include:

 * The RFC8332 RSA SHA-2 signature algorithms rsa-sha2-256/512. These
   algorithms have the advantage of using the same key type as
   "ssh-rsa" but use the safe SHA-2 hash algorithms. These have been
   supported since OpenSSH 7.2 and are already used by default if the
   client and server support them.

 * The ssh-ed25519 signature algorithm. It has been supported in
   OpenSSH since release 6.5.

 * The RFC5656 ECDSA algorithms: ecdsa-sha2-nistp256/384/521. These
   have been supported by OpenSSH since release 5.7.

To check whether a server is using the weak ssh-rsa public key algorithm, for host authentication, try to connect to it after removing the ssh-rsa algorithm from ssh(1)'s allowed list:

    ssh -oHostBasedKeyTypes=-ssh-rsa user at host

If the host key verification fails and no other supported host key types are available, the the server software on that host should be upgraded.

[1] "SHA-1 is a Shambles: First Chosen-Prefix Collision on SHA-1 and
    Application to the PGP Web of Trust" Leurent, G and Peyrin, T


 * ssh(1), sshd(8), ssh-keygen(1): this release removes the "ssh-rsa"
   (RSA/SHA1) algorithm from those accepted for certificate signatures
   (i.e. the client and server CASignatureAlgorithms option) and will
   use the rsa-sha2-512 signature algorithm by default when the
   ssh-keygen(1) CA signs new certificates.

   Certificates are at special risk to the aforementioned SHA1
   collision vulnerability as an attacker has effectively unlimited
   time in which to craft a collision that yields them a valid
   certificate, far more than the relatively brief LoginGraceTime
   window that they have to forge a host key signature.

   OpenSSH releases prior to 7.2 do not support the newer RSA/SHA2
   algorithms and will refuse to accept certificates signed by an
   OpenSSH 8.2+ CA using RSA keys. Older clients/servers may use
   another CA key type such as ssh-ed25519 (supported since OpenSSH
   6.5) or one of the ecdsa-sha2-nistp256/384/521 types (supported
   since OpenSSH 5.7) instead if they cannot be upgraded.

Potentially-incompatible changes

This release includes a number of changes that may affect existing

 * ssh(1), sshd(8): the above removal of "ssh-rsa" from the accepted
   CASignatureAlgorithms list.

 * ssh(1), sshd(8): this release removes diffie-hellman-group14-sha1
   from the default key exchange proposal for both the client and

 * ssh-keygen(1): the command-line options related to the generation
   and screening of safe prime numbers used by the
   diffie-hellman-group-exchange-* key exchange algorithms have
   changed. Most options have been folded under the -O flag.

 * sshd(8): the sshd listener process title visible to ps(1) has
   changed to include information about the number of connections that
   are currently attempting authentication and the limits configured
   by MaxStartups.

Changes since OpenSSH 8.1

This release contains some significant new features.

FIDO/U2F Support

This release adds support for FIDO/U2F hardware authenticators to OpenSSH. U2F/FIDO are open standards for inexpensive two-factor authentication hardware that are widely used for website authentication.  In OpenSSH FIDO devices are supported by new public key types "ecdsa-sk" and "ed25519-sk", along with corresponding certificate types.

ssh-keygen(1) may be used to generate a FIDO token-backed key, after which they may be used much like any other key type supported by OpenSSH, so long as the hardware token is attached when the keys are used. FIDO token also generally require the user explicitly authorise operations by touching or tapping them.

Generating a FIDO key requires the token be attached, and will usually require the user tap the token to confirm the operation:

  $ ssh-keygen -t ecdsa-sk -f ~/.ssh/id_ecdsa_sk
  Generating public/private ecdsa-sk key pair.
  You may need to touch your security key to authorize key generation.
  Enter file in which to save the key (/home/djm/.ssh/id_ecdsa_sk): 
  Enter passphrase (empty for no passphrase): 
  Enter same passphrase again: 
  Your identification has been saved in /home/djm/.ssh/id_ecdsa_sk
  Your public key has been saved in /home/djm/.ssh/

This will yield a public and private key-pair. The private key file should be useless to an attacker who does not have access to the physical token. After generation, this key may be used like any other supported key in OpenSSH and may be listed in authorized_keys, added to ssh-agent(1), etc. The only additional stipulation is that the FIDO token that the key belongs to must be attached when the key is used.

FIDO tokens are most commonly connected via USB but may be attached via other means such as Bluetooth or NFC. In OpenSSH, communication with the token is managed via a middleware library, specified by the SecurityKeyProvider directive in ssh/sshd_config(5). OpenSSH includes a middleware with support for USB tokens that is may be enabled in portable OpenSSH via the --with-security-key-builtin configure flag (it is enabled automatically in OpenBSD). This internal middleware requires that libfido2 ( ) and its dependencies be installed. If the built-in middleware is enabled then it will be used by default.

Note: FIDO/U2F tokens are required to implement the ECDSA-P256 "ecdsa-sk" key type, but hardware support for Ed25519 "ed25519-sk" is less common. Similarly, not all hardware tokens support some of the optional features such as resident keys.

The protocol-level changes to support FIDO/U2F keys in SSH are documented in the PROTOCOL.u2f file in the OpenSSH source distribution.

There are a number of supporting changes to this feature:

 * ssh-keygen(1): add a "no-touch-required" option when generating
   FIDO-hosted keys, that disables their default behaviour of
   requiring a physical touch/tap on the token during authentication.
   Note: not all tokens support disabling the touch requirement.

 * sshd(8): add a sshd_config PubkeyAuthOptions directive that
   collects miscellaneous public key authentication-related options
   for sshd(8). At present it supports only a single option
   "no-touch-required". This causes sshd to skip its default check for
   FIDO/U2F keys that the signature was authorised by a touch or press
   event on the token hardware.

 * ssh(1), sshd(8), ssh-keygen(1): add a "no-touch-required" option
   for authorized_keys and a similar extension for certificates. This
   option disables the default requirement that FIDO key signatures
   attest that the user touched their key to authorize them, mirroring
   the similar PubkeyAuthOptions sshd_config option.

 * ssh-keygen(1): add support for the writing the FIDO attestation
   information that is returned when new keys are generated via the
   "-O write-attestation=/path" option. FIDO attestation certificates
   may be used to verify that a FIDO key is hosted in trusted
   hardware. OpenSSH does not currently make use of this information,
   beyond optionally writing it to disk.

FIDO2 resident keys

FIDO/U2F OpenSSH keys consist of two parts: a "key handle" part stored in the private key file on disk, and a per-device private key that is unique to each FIDO/U2F token and that cannot be exported. These are combined by the hardware at authentication time to derive the real key that is used to sign authentication challenges.

For tokens that are required to move between computers, it can be cumbersome to have to move the private key file first. To avoid this requirement, tokens implementing the newer FIDO2 standard support "resident keys", where it is possible to effectively retrieve the key handle part of the key from the hardware.

OpenSSH supports this feature, allowing resident keys to be generated using the ssh-keygen(1) "-O resident" flag. This will produce a public/private key pair as usual, but it will be possible to retrieve the private key part from the token later. This may be done using "ssh-keygen -K", which will download all available resident keys from the tokens attached to the host and write public/private key files for them. It is also possible to download and add resident keys directly to ssh-agent(1) without writing files to the file-system using "ssh-add -K".

Resident keys are indexed on the token by the application string and user ID. By default, OpenSSH uses an application string of "ssh:" and an empty user ID. If multiple resident keys on a single token are desired then it may be necessary to override one or both of these defaults using the ssh-keygen(1) "-O application=" or "-O user="
options. Note: OpenSSH will only download and use resident keys whose application string begins with "ssh:"

Storing both parts of a key on a FIDO token increases the likelihood of an attacker being able to use a stolen token device. For this reason, tokens should enforce PIN authentication before allowing download of keys, and users should set a PIN on their tokens before creating any resident keys.

Other New Features

 * sshd(8): add an Include sshd_config keyword that allows including
   additional configuration files via glob(3) patterns. bz2468

 * ssh(1)/sshd(8): make the LE (low effort) DSCP code point available
   via the IPQoS directive; bz2986,

 * ssh(1): when AddKeysToAgent=yes is set and the key contains no
   comment, add the key to the agent with the key's path as the
   comment. bz2564
 * ssh-keygen(1), ssh-agent(1): expose PKCS#11 key labels and X.509
   subjects as key comments, rather than simply listing the PKCS#11
   provider library path. PR138

 * ssh-keygen(1): allow PEM export of DSA and ECDSA keys; bz3091

 * ssh(1), sshd(8): make zlib compile-time optional, available via the ZLIB flag on OpenBSD or via the --with-zlib configure
   option for OpenSSH portable.

 * sshd(8): when clients get denied by MaxStartups, send a
   notification prior to the SSH2 protocol banner according to
   RFC4253 section 4.2.

 * ssh(1), ssh-agent(1): when invoking the $SSH_ASKPASS prompt
   program, pass a hint to the program to describe the type of
   desired prompt.  The possible values are "confirm" (indicating
   that a yes/no confirmation dialog with no text entry should be
   shown), "none" (to indicate an informational message only), or
   blank for the original ssh-askpass behaviour of requesting a

 * ssh(1): allow forwarding a different agent socket to the path
   specified by $SSH_AUTH_SOCK, by extending the existing ForwardAgent
   option to accepting an explicit path or the name of an environment
   variable in addition to yes/no.
 * ssh-keygen(1): add a new signature operations "find-principals" to
   look up the principal associated with a signature from an allowed-
   signers file.
 * sshd(8): expose the number of currently-authenticating connections
   along with the MaxStartups limit in the process title visible to


 * sshd(8): make ClientAliveCountMax=0 have sensible semantics: it
   will now disable connection killing entirely rather than the
   current behaviour of instantly killing the connection after the
   first liveness test regardless of success. bz2627
 * sshd(8): clarify order of AllowUsers / DenyUsers vs AllowGroups /
   DenyGroups in the sshd(8) manual page. bz1690

 * sshd(8): better describe HashKnownHosts in the manual page. bz2560

 * sshd(8): clarify that that permitopen=/PermitOpen do no name or
   address translation in the manual page. bz3099

 * sshd(8): allow the UpdateHostKeys feature to function when
   multiple known_hosts files are in use. When updating host keys,
   ssh will now search subsequent known_hosts files, but will add
   updated host keys to the first specified file only. bz2738
 * All: replace all calls to signal(2) with a wrapper around
   sigaction(2). This wrapper blocks all other signals during the
   handler preventing races between handlers, and sets SA_RESTART
   which should reduce the potential for short read/write operations.
 * sftp(1): fix a race condition in the SIGCHILD handler that could
   turn in to a kill(-1); bz3084

 * sshd(8): fix a case where valid (but extremely large) SSH channel
   IDs were being incorrectly rejected. bz3098

 * ssh(1): when checking host key fingerprints as answers to new
   hostkey prompts, ignore whitespace surrounding the fingerprint

 * All: wait for file descriptors to be readable or writeable during
   non-blocking connect, not just readable. Prevents a timeout when
   the server doesn't immediately send a banner (e.g. multiplexers
   like sslh)
 * sshd_config(5): document the sntrup4591761x25519-sha512 at
   key exchange algorithm. PR#151


 * sshd(8): multiple adjustments to the Linux seccomp sandbox:
   - Non-fatally deny IPC syscalls in sandbox
   - Allow clock_gettime64() in sandbox (MIPS / glibc >= 2.31)
   - Allow clock_nanosleep_time64 in sandbox (ARM) bz3100
   - Allow clock_nanosleep() in sandbox (recent glibc) bz3093

 * Explicit check for memmem declaration and fix up declaration if the
   system headers lack it. bz3102
OpenSSH is brought to you by Markus Friedl, Niels Provos, Theo de Raadt, Kevin Steves, Damien Miller, Darren Tucker, Jason McIntyre, Tim Rice and Ben Lindstrom.

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