40-bit encryption

<h2 id="description">Description</h2>
<p>A typical home computer in 2004 could brute-force a 40-bit key in a little under two weeks, testing a million keys per second; modern computers are able to achieve this much faster.  Using free time on a large corporate network or a <a href="/facts/Botnet/bGspY7bJ">botnet</a> would reduce the time in proportion to the number of computers available.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> With dedicated hardware, a 40-bit key can be broken in seconds. The <a href="/facts/Electronic_Frontier_Foundation/vCy44tuo">Electronic Frontier Foundation</a>'s <a href="/facts/Deep_Crack/j3BIL9Gn">Deep Crack</a>, built by a group of enthusiasts for US$250,000 in 1998, could break a 56-bit <a href="/facts/Data_Encryption_Standard/STfBjTGb">Data Encryption Standard</a> (DES) key in days,<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> and would be able to break <a href="/facts/CDMF/cm9lMgyX">40-bit DES</a> encryption in about two seconds.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p><p>40-bit encryption was common in software released before 1999, especially those based on the <a href="/facts/RC2/kfXo2PEH">RC2</a> and <a href="/facts/RC4/HAR5kL0T">RC4</a> algorithms which had special "7-day" export review policies, when algorithms with larger key lengths could not legally be <a href="/facts/Export_of_cryptography_from_the_United_States/CH5yLRYo">exported</a> from the United States without a case-by-case license.  "In the early 1990s ... As a general policy, the State Department allowed exports of commercial encryption with 40-bit keys, although some software with DES could be exported to U.S.-controlled subsidiaries and financial institutions."<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a><a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> As a result, the "international" versions of <a href="/facts/Web_browser/2pfyymLs">web browsers</a> were designed to have an effective key size of 40 bits when using <a href="/facts/Secure_Sockets_Layer/pGy16TnA">Secure Sockets Layer</a> to protect <a href="/facts/E-commerce/7vxeea0Y">e-commerce</a>. Similar limitations were imposed on other software packages, including early versions of <a href="/facts/Wired_Equivalent_Privacy/LHqkdrCf">Wired Equivalent Privacy</a>. In 1992, <a href="/facts/IBM/QszA7nwd">IBM</a> designed the <a href="/facts/CDMF/cm9lMgyX">CDMF</a> algorithm to reduce the strength of <a href="/facts/56-bit_encryption/UuBPnA0C">56-bit</a> DES against brute force attack to 40 bits, in order to create exportable DES implementations.
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<h2 id="obsolescence">Obsolescence</h2>
<p>All 40-bit and 56-bit encryption algorithms are <a href="/facts/Obsolete/IrFKfFja">obsolete</a>, because they are vulnerable to brute force attacks, and therefore cannot be regarded as secure.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> As a result, virtually all Web browsers now use 128-bit keys, which are considered strong. Most <a href="/facts/Web_server/A4GS6thA">Web servers</a> will not communicate with a client unless it has 128-bit encryption capability installed on it.
</p><p>Public/private key pairs used in <a href="/facts/Asymmetric_encryption/gowoFTxS">asymmetric encryption</a> (public key cryptography), at least those based on prime factorization, must be much longer in order to be secure; see <a href="/facts/Key_size/1amrJ13L">key size</a> for more details.
</p><p>As a general rule, modern symmetric encryption algorithms such as <a href="/facts/Advanced_Encryption_Standard/HdXGBY2Q">AES</a> use key lengths of 128, 192 and 256 bits.
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<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/56-bit_encryption/UuBPnA0C">56-bit encryption</a></li>
<li><a href="/facts/Content_Scramble_System/vzPVMQvk">Content Scramble System</a></li></ul>
<h2 id="footnotes">Footnotes</h2>

<ul><li><a href="https://web.archive.org/web/20120918165854/http://w2.eff.org/Privacy/Crypto/Crypto_misc/DESCracker/HTML/19980716_eff_des_faq.html">"Frequently Asked Questions (FAQ) About the Electronic Frontier Foundation's "DES Cracker" Machine"</a>. Electronic Frontier Foundation. July 16, 1998. Archived from <a href="https://w2.eff.org/Privacy/Crypto/Crypto_misc/DESCracker/HTML/19980716_eff_des_faq.html">the original</a> on September 18, 2012. Retrieved March 23, 2012.</li>
<li>Grimmett, Jeanne J. (2001). <a href="https://web.archive.org/web/20190228095041/http://www.au.af.mil/au/awc/awcgate/crs/rl30273.pdf">Encryption Export Controls</a> (PDF) (Report). Congressional Research Service Report RL30273. Archived from <a href="http://www.au.af.mil/au/awc/awcgate/crs/rl30273.pdf">the original</a> (pdf) on February 28, 2019. Retrieved July 26, 2011.</li>
<li>Schneier, Bruce (1996). <i>Applied Cryptography</i> (Second ed.). John Wiley & Sons. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0-471-11709-9.</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Schneier 1996, p. 154. - Schneier, Bruce (1996). Applied Cryptography (Second ed.). John Wiley & Sons. ISBN 0-471-11709-9. <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>EFF-1998. - "Frequently Asked Questions (FAQ) About the Electronic Frontier Foundation's "DES Cracker" Machine". Electronic Frontier Foundation. July 16, 1998. Archived from the original on September 18, 2012. Retrieved March 23, 2012. <a href="https://web.archive.org/web/20120918165854/http://w2.eff.org/Privacy/Crypto/Crypto_misc/DESCracker/HTML/19980716_eff_des_faq.html" target="_blank">https://web.archive.org/web/20120918165854/http://w2.eff.org/Privacy/Crypto/Crypto_misc/DESCracker/HTML/19980716_eff_des_faq.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Schneier 1996, p. 153. - Schneier, Bruce (1996). Applied Cryptography (Second ed.). John Wiley & Sons. ISBN 0-471-11709-9. <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Grimmett 2001. - Grimmett, Jeanne J. (2001). Encryption Export Controls (PDF) (Report). Congressional Research Service Report RL30273. Archived from the original (pdf) on February 28, 2019. Retrieved July 26, 2011. <a href="https://web.archive.org/web/20190228095041/http://www.au.af.mil/au/awc/awcgate/crs/rl30273.pdf" target="_blank">https://web.archive.org/web/20190228095041/http://www.au.af.mil/au/awc/awcgate/crs/rl30273.pdf</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Schneier 1996, p. 615. - Schneier, Bruce (1996). Applied Cryptography (Second ed.). John Wiley & Sons. ISBN 0-471-11709-9. <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>University of California at Berkeley Public Information Office (January 29, 1997). "The only legally exportable cryptography level is totally insecure; UC Berkeley grad student breaks challenge cipher in hours". The Regents of the University of California. Retrieved December 14, 2015. This is the final proof of what we've known for years: 40-bit encryption technology is obsolete. <a href="http://www.berkeley.edu/news/media/releases/97legacy/code.html" target="_blank">http://www.berkeley.edu/news/media/releases/97legacy/code.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>Fitzmaurice, Ellen; Tamaki, Kevin (June 1, 1997). "Decoding the Encryption Debate: U.S. export restrictions and 'key recovery' policies are ineffectual as well as burdensome to business". Los  Angeles Times. Retrieved December 14, 2015. But recent advances in computing technology have rendered 40-bit encryption dangerously weak and export limits commercially obsolete. <a href="https://www.latimes.com/archives/la-xpm-1997-06-01-me-64597-story.html" target="_blank">https://www.latimes.com/archives/la-xpm-1997-06-01-me-64597-story.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
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40-bit encryption open-in-new

40-bit encryption