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Adding historic version of SSSS -- v0.5.
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‎HISTORY

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v0.5: (January 2006)
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- introduction of memory locking and tty echo suppression
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- a buffer overflow was fixed. It seems to be exploitable.
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v0.4: (October 2005)
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- the security level now can be chosen freely in the range
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8..1024 bits in steps of 8.
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v0.3: (July 2005)
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- separation of ssss into ssss-split and ssss-combine
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- introduction of a man page
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v0.2: (June 2005)
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- introduction of the diffusion layer
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v0.1: (May 2005)
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- initial release
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‎THANKS

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I would like to thank the following people for comments and code:
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Tam�s Tevesz (documentation)
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Stefan Schlesinger, Daniel Bielefeldt (error reporting)
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Olaf Mersmann (memory locking, echo suppression)
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Alex Popov (windows port)

‎doc.html

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>ssss: Shamir's Secret Sharing Scheme</title>
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</head>
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<body>
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<small>The following text is licensed under the
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<a href="http://www.gnu.org/licenses/gpl.html">
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GNU General Public License</a>. Copyright 2005, 2006 by
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B. Poettering.</small>
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<hr noshade="noshade"/>
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<h4>What is "Secret Sharing"?</h4>
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Citing from the <a href="http://en.wikipedia.org/">Wikipedia</a>
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article about <a
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href="http://en.wikipedia.org/wiki/Secret_sharing">Secret
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Sharing</a>:
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<blockquote>
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<p>
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In <a
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href="http://en.wikipedia.org/wiki/Cryptography">cryptography</a>, a
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<b>secret sharing scheme</b> is a method for distributing a <a
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href="http://en.wikipedia.org/wiki/Secrecy"><i>secret</i></a> amongst
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a group of participants, each of which is allocated a <i>share</i> of
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the secret. The secret can only be reconstructed when the shares are
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combined together; individual shares are of no use on their own.
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</p>
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<p>
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More formally, in a secret sharing scheme there is one <i>dealer</i>
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and <i>n</i> <i>players</i>. The dealer gives a secret to the players,
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but only when specific conditions are fulfilled. The dealer
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accomplishes this by giving each player a share in such a way that any
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group of <i>t</i> (for <i>threshold</i>) or more players can together
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reconstruct the secret but no group of less than <i>t</i> players
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can. Such a system is called a <i>(t,n)</i>-threshold scheme.
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</p>
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</blockquote>
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<p>
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A popular technique to implement threshold schemes uses <a
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href="http://en.wikipedia.org/wiki/Polynomial_interpolation">
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polynomial interpolation</a> ("Lagrange interpolation"). This
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method was invented by <a
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href="http://en.wikipedia.org/wiki/Adi_Shamir"> Adi Shamir</a> in
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1979. You can play around with a threshold scheme on the <a
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href="http://point-at-infinity.org/ssss/demo.html">demo page</a>.
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</p>
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<p>
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Note that Shamir's scheme is provable secure, that means: in a
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<i>(t,n)</i> scheme one can prove that it makes no difference
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whether an attacker has <i>t-1</i> valid shares at his disposal or
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none at all; as long as he has less than
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<i>t</i> shares, there is no better option than guessing to find
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out the secret.
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</p>
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<h4>Where is "Secret Sharing" used?</h4> Some popular examples are:
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<ul>
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<li>
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Good passwords are hard to memorize. A clever user could use a
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secret sharing scheme to generate a set of shares for a given
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password and store one share in his address book, one in his
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bank deposit safe, leave one share with a friend, etc. If one day he
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forgets his password, he can reconstruct it easily. Of
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course, writing passwords directly into the address book would
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pose a security risk, as it could be stolen by an "enemy". If
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a secret sharing scheme is used, the attacker has to steal
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many shares from different places.
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</li>
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<li>
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"A dealer could send <i>t</i> shares, all of which are
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necessary to recover the original secret, to a single
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recipient, using <i>t</i> different channels. An attacker
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would have to intercept all <i>t</i> shares to recover the
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secret, a task which may be more difficult than intercepting a
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single message" (<a
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href="http://en.wikipedia.org/wiki/Secret_sharing">Wikipedia</a>).
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</li>
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<li>
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The director of a bank could generate shares for the bank's
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vault unlocking code and hand them out to his employees. Even
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if the director is not available, the vault can be opened, but only,
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when a certain number of employees do it together. Here secret
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sharing schemes allow the employment of not fully trusted
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people.
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</li>
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</ul>
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<h4>What is "ssss"? Where can I download "ssss"?</h4>
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<p>
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<b>ssss</b> is an implementation of Shamir's secret sharing
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scheme for UNIX systems, especially developed for linux
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machines. The code is licensed under the <a
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href="http://www.gnu.org/licenses/gpl.html">GNU GPL</a>.
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<b>ssss</b> does both: the generation of shares for a known
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secret and the reconstruction of a secret using user provided
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shares. The software was written in 2006 by B. Poettering, it
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links against the <a href="http://swox.com/gmp/">GNU libgmp</a>
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multiprecision library (version 4.1.4 works well) and requires
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the <tt>/dev/random</tt> entropy source. Please send bug reports
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to <b><tt>ssss AT point-at-infinity.org</tt></b>.
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</p>
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<p>There is a <a
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href="http://freshmeat.net/projects/ssss/">freshmeat page</a> for
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<b>ssss</b>. A <a
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href="http://packages.debian.org/unstable/utils/ssss">debian
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package</a> is also available. If you are the lucky owner of a
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debian system just run <tt>apt-get update &amp;&amp; apt-get
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install ssss</tt> to install <b>ssss</b>. Someone even ported (an
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outdated version of) <b>ssss</b> to <a
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href="http://www.seidlitz.ca/ssss/">Windows</a> (but with a
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lightly too sloppy random number generation, in my opinion).
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</p>
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<p>
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Download on the <a href="http://point-at-infinity.org/ssss">ssss homepage</a>.
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</p>
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<h4>How is "ssss" used? Is there an online demonstration?</h4>
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<p>The generation of shares given a
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known secret is shown first. A (3,5)-threshold scheme is used, that is:
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5 shares are generated, the secret can be reconstructed by any
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subset of size 3.
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</p>
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<pre>
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% ssss-split -t 3 -n 5
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Generating shares using a (3,5) scheme with dynamic security level.
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Enter the secret, at most 128 ASCII characters: my secret root password
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Using a 184 bit security level.
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1-1c41ef496eccfbeba439714085df8437236298da8dd824
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2-fbc74a03a50e14ab406c225afb5f45c40ae11976d2b665
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3-fa1c3a9c6df8af0779c36de6c33f6e36e989d0e0b91309
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4-468de7d6eb36674c9cf008c8e8fc8c566537ad6301eb9e
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5-4756974923c0dce0a55f4774d09ca7a4865f64f56a4ee0
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</pre>
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These shares can be combined to recreate the secret:
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<pre>
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% ssss-combine -t 3
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Enter 3 shares separated by newlines:
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Share [1/3]: 3-fa1c3a9c6df8af0779c36de6c33f6e36e989d0e0b91309
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Share [2/3]: 5-4756974923c0dce0a55f4774d09ca7a4865f64f56a4ee0
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Share [3/3]: 2-fbc74a03a50e14ab406c225afb5f45c40ae11976d2b665
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Resulting secret: my secret root password
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</pre>
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You can try it out on the
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<a href="http://point-at-infinity.org/ssss/demo.html">demo page</a>.
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<p>
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If larger secrets are to be shared a hybrid technique has to be
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applied: encrypt the secret with a block cipher (using openssl,
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gpg, etc) and apply secret sharing to just the key. See the man
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page for more information about this topic.
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</p>
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<h4>Where is the manpage?</h4>
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Read it as <a href="http://point-at-infinity.org/ssss/ssss.1.html">html</a> or
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<a href="http://point-at-infinity.org/ssss/ssss.1">*roff</a>!
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<form action="https://www.paypal.com/cgi-bin/webscr" method="post">
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<input name="cmd" value="_xclick" type="hidden">
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<input name="business" value="[email protected]" type="hidden">
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<input name="no_note" value="1" type="hidden">
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<input name="currency_code" value="EUR" type="hidden">
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<p>
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If you like this software, think about donating some money via
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<input src="https://www.paypal.com/en_US/i/btn/x-click-but7.gif" name="submit" alt="PayPal" type="image">.
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</p>
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</form>
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<hr>
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<small>
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<!-- hhmts start -->
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Last modified: Sun Jan 15 12:08:48 CET 2006
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<!-- hhmts end -->
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</small>
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</body>
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</html>

‎ssss.c

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/*
2-
* ssss version 0.4 - Copyright 2005 B. Poettering
2+
* ssss version 0.5 - Copyright 2005,2006 B. Poettering
33
*
44
* This program is free software; you can redistribute it and/or
55
* modify it under the terms of the GNU General Public License as
@@ -31,21 +31,26 @@
3131
* Compile with
3232
* "gcc -O2 -lgmp -o ssss-split ssss.c && ln ssss-split ssss-combine"
3333
*
34+
* Compile with -DNOMLOCK to obtain a version without memory locking.
35+
*
3436
* Report bugs to: ssss AT point-at-infinity.org
3537
*
3638
*/
3739

3840
#include <stdlib.h>
3941
#include <string.h>
42+
#include <errno.h>
4043
#include <fcntl.h>
4144
#include <unistd.h>
4245
#include <stdio.h>
4346
#include <stdint.h>
4447
#include <assert.h>
48+
#include <termios.h>
49+
#include <sys/mman.h>
4550

4651
#include <gmp.h>
4752

48-
#define VERSION "0.4"
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#define VERSION "0.5"
4954
#define RANDOM_SOURCE "/dev/random"
5055
#define MAXDEGREE 1024
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#define MAXTOKENLEN 128
@@ -77,25 +82,27 @@ int opt_threshold = -1;
7782
int opt_number = -1;
7883
char *opt_token = NULL;
7984

80-
int ttyoutput;
81-
8285
unsigned int degree;
8386
mpz_t poly;
8487
int cprng;
88+
struct termios echo_orig, echo_off;
8589

8690
#define mpz_lshift(A, B, l) mpz_mul_2exp(A, B, l)
8791
#define mpz_sizeinbits(A) (mpz_cmp_ui(A, 0) ? mpz_sizeinbase(A, 2) : 0)
8892

93+
/* emergency abort and warning functions */
94+
8995
void fatal(char *msg)
9096
{
91-
fprintf(stderr, "%sFATAL: %s.\n", ttyoutput ? "\a" : "", msg);
97+
tcsetattr(0, TCSANOW, &echo_orig);
98+
fprintf(stderr, "%sFATAL: %s.\n", isatty(2) ? "\a" : "", msg);
9299
exit(1);
93100
}
94101

95102
void warning(char *msg)
96103
{
97104
if (! opt_QUIET)
98-
fprintf(stderr, "%sWARNING: %s.\n", ttyoutput ? "\a" : "", msg);
105+
fprintf(stderr, "%sWARNING: %s.\n", isatty(2) ? "\a" : "", msg);
99106
}
100107

101108
/* field arithmetic routines */
@@ -110,6 +117,7 @@ int field_size_valid(int deg)
110117

111118
void field_init(int deg)
112119
{
120+
assert(field_size_valid(deg));
113121
mpz_init_set_ui(poly, 0);
114122
mpz_setbit(poly, deg);
115123
mpz_setbit(poly, irred_coeff[3 * (deg / 8 - 1) + 0]);
@@ -385,7 +393,7 @@ void split(void)
385393
unsigned int fmt_len;
386394
mpz_t x, y, coeff[opt_threshold];
387395
char buf[MAXLINELEN];
388-
int i;
396+
int deg, i;
389397
for(fmt_len = 1, i = opt_number; i >= 10; i /= 10, fmt_len++);
390398
if (! opt_quiet) {
391399
printf("Generating shares using a (%d,%d) scheme with ",
@@ -396,23 +404,27 @@ void split(void)
396404
printf("dynamic");
397405
printf(" security level.\n");
398406

399-
int deg = opt_security ? opt_security : MAXDEGREE;
407+
deg = opt_security ? opt_security : MAXDEGREE;
400408
fprintf(stderr, "Enter the secret, ");
401409
if (opt_hex)
402410
fprintf(stderr, "as most %d hex digits: ", deg / 4);
403411
else
404412
fprintf(stderr, "at most %d ASCII characters: ", deg / 8);
405413
}
414+
tcsetattr(0, TCSANOW, &echo_off);
406415
if (! fgets(buf, sizeof(buf), stdin))
407416
fatal("I/O error while reading secret");
417+
tcsetattr(0, TCSANOW, &echo_orig);
408418
buf[strcspn(buf, "\r\n")] = '\0';
409419

410420
if (! opt_security) {
411421
opt_security = opt_hex ? 4 * ((strlen(buf) + 1) & ~1): 8 * strlen(buf);
412-
422+
if (! field_size_valid(opt_security))
423+
fatal("security level invalid (secret too long?)");
413424
if (! opt_quiet)
414425
fprintf(stderr, "Using a %d bit security level.\n", opt_security);
415426
}
427+
416428
field_init(opt_security);
417429

418430
mpz_init(coeff[0]);
@@ -528,9 +540,31 @@ int main(int argc, char *argv[])
528540
{
529541
char *name;
530542
int i;
531-
if ((i = fileno(stderr)) < 0)
532-
fatal("couldn't determine fileno of stderr");
533-
ttyoutput = isatty(i);
543+
544+
#if ! NOMLOCK
545+
if (mlockall(MCL_CURRENT | MCL_FUTURE) < 0)
546+
switch(errno) {
547+
case ENOMEM:
548+
warning("couldn't get memory lock (ENOMEM, try to adjust RLIMIT_MEMLOCK!)");
549+
break;
550+
case EPERM:
551+
warning("couldn't get memory lock (EPERM, try UID 0!)");
552+
break;
553+
case ENOSYS:
554+
warning("couldn't get memory lock (ENOSYS, kernel doesn't allow page locking)");
555+
break;
556+
default:
557+
warning("couldn't get memory lock");
558+
break;
559+
}
560+
#endif
561+
562+
if (getuid() != geteuid())
563+
seteuid(getuid());
564+
565+
tcgetattr(0, &echo_orig);
566+
echo_off = echo_orig;
567+
echo_off.c_lflag &= ~ECHO;
534568

535569
opt_help = argc == 1;
536570
while((i = getopt(argc, argv, "vDhqQxs:t:n:w:")) != -1)

‎ssss.manpage.xml

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@@ -136,8 +136,19 @@ gpg -c &lt; file.plain &gt; file.encrypted
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</section>
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139+
<section name="Security">
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<p>
141+
<opt>ssss</opt> tries to lock its virtual address space into RAM for
142+
privacy reasons. But this may fail for two reasons: either the current uid
143+
doesn't permit page locking, or the RLIMIT_MEMLOCK is set too
144+
low. After printing a warning message <opt>ssss</opt> will run even without
145+
obtaining the desired mlock.
146+
</p>
147+
148+
</section>
149+
139150
<section name="Author">
140-
This software (v0.4) was written in 2005 by B. Poettering
151+
This software (v0.5) was written in 2006 by B. Poettering
141152
(ssss AT point-at-infinity.org). Find the newest version of
142153
ssss on the project's homepage: <url
143154
href="http://point-at-infinity.org/ssss/"/>.

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