Home > Articles > Operating Systems, Server > Solaris

Like this article? We recommend

Key Handling

Public-key cryptography is used in two places: server identification and two-factor authentication. This means that there are keys to be managed, protected, transported, and eventually destroyed. Key handling is the largest obstacle to the wide-scale deployment of OpenSSH. Because OpenSSH was designed as a point-to-point solution with no public-key infrastructure in place, all key operations must be done manually. This is not a problem for small deployments; however, the problem does not scale.

Because they are the foundation for systems security, keys must be handled with care. If private keys are divulged, security is compromised because the system appears to be secure when, in fact, it is not.

Host Keys

Server identification is accomplished by a host key pair. The openssh.server init script, which you can find on the Sun BluePrints website, generates a key set if it cannot find a host key. This key set is used to identify the server to the client. The private key remains private to ensure the integrity of the system. The client downloads the public key and compares it to its copy in known_hosts. If the key is different than it is expected to be, a warning message is printed and the connection is refused. The following is an example of this warning.

$ /opt/OBSDssh/bin/ssh some_host
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
Please contact your system administrator.
Add correct host key in /export/home/user/.ssh/known_hosts to get rid 
of this message.
Offending key in /export/home/user/.ssh/known_hosts:2
RSA host key for some_host has changed and you have requested strict checking.

The problem is how to get the public host key to the client in the first place. Another problem is what to do when the public host key has been regenerated due to loss, server upgrade, or compromise. Having multiple users call support because of the preceding warning message could create quite a support headache. Further, having users change keys manually would be even less desirable.

The client configuration option StrictHostKeyChecking controls how the client reacts to new hosts keys. If you set this option to yes, OpenSSH will not make connections to unknown servers. If you set the option to ask, OpenSSH will prompt users to accept a new host key if the server is unknown. If you set the option to no, OpenSSH will add new host keys without prompting users. The no option setting will allow connections to servers with modified host keys.

The easiest solution is to simply disable StrictHostKeyChecking by setting it to no. Blindly accepting new keys allows man-in-the-middle attacks and is not recommended. If your users can be trusted to act responsibly, then set the option to ask. Users can manually verify the host key by comparing the value in known_hosts to the value ssh_host_key.pub, ssh_host_dsa_key.pub, or ssh_host_rsa_key.pub depending on the protocol and public cryptographic system used to connect. If the values don't match, something odd has happened. This could be caused by an active attack or possibly just a server reinstallation. Respond according to your local policy.

Another solution is distribute a known_hosts file to users; however, it is difficult to do this in a secure fashion. You must decide how to securely collect public host keys and how to securely distribute the file to the users. Again, there are problems of scalability with any solution. Fortunately, changes to host keys should be infrequent.

The most secure method of gathering keys is to log in to every server and manually copy the public host key to a portable medium such as a floppy disk, CD-RW, or smartcard. For sites with a large number of machines, or during the first deployment of OpenSSH, this burden is significant. Alternatively, you can configure a client with StrictHostKeyChecking set to no, access every single host, copy the public host key, exit, and then compare the key with the value in known_hosts. Display a warning message for any server with a differing key. This can be automated using Korn shell, PERL, or some other scripting language.

Ssh-keyscan can also be used to generate a list of host keys. The risk is getting the host key of a compromised machine. None of the solutions are perfect. There are some serious tradeoffs between convience and security. At the minimum, set StrictHostKeyChecking to ask and train your users to check the host keys.

A novel use of ssh-keyscan is to regularly check for altered keys. At routine intervals, probe the servers and check if keys have been altered. This can provide warning of an intrusion or a non-logged installation.

With public host keys gathered, you must decide how to securely distribute the file to users. An easy solution is to integrate the file into the deployment packaging such as the OBSDssh package. The file can be placed on an ftp or http server. Also distribute a preferably signed hash (MD5 or SHA-1) of the file so the user can verify the integrity of the file. (OpenSSL has the capability of performing the hashes.)

For sites with a public-key infrastructure, a pretty good privacy installation, or a Gnu privacy-guard installation, distribute the file and its hash cryptographically signed.

With the hassle of users seeing an unfamiliar warning about a changed host key, there is the temptation to archive the public and private host key pairs onto a system. The key pairs would be replaced after a system was reinstalled or replaced. This is risky and not recommended. Any system storing the keys would be a tempting target and if it was comprised all keys within it would also be compromised. It is better to deal with the occasional host key change through user education and notices of reinstallation. If it is necessary to archive keys, store them offline, in encrypted format, and in secure storage such as a safe.

In the event of a server compromise, destroy host keys. An attacker with knowledge of the private portion of a host key could impersonate the host and perform a man-in-the-middle attack.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020