World Library  
Flag as Inappropriate
Email this Article




Developer(s) The OpenSSL Project
Stable release

1.0.2d (July 9, 2015 (2015-07-09)[1])
1.0.1p (July 9, 2015 (2015-07-09)[1])
1.0.0s (June 11, 2015 (2015-06-11)[1])

0.9.8zg (June 11, 2015 (2015-06-11)[1])
Written in C, assembly
Operating system Cross-platform
Type Security library
License Apache License 1.0 and four-clause BSD License
Website .org.opensslwww

In computer networking, OpenSSL is a software library to be used in applications that need to secure communications against eavesdropping or need to ascertain the identity of the party at the other end. It has found wide use in internet web servers, serving a majority of all web sites.

OpenSSL contains an open-source implementation of the SSL and TLS protocols. The core library, written in the C programming language, implements basic cryptographic functions and provides various utility functions. Wrappers allowing the use of the OpenSSL library in a variety of computer languages are available.

Versions are available for most Unix-like operating systems (including Solaris, Linux, Mac OS X and the various open-source BSD operating systems), OpenVMS and Microsoft Windows. IBM provides a port for the System i (OS/400).


  • Project history 1
  • Major version releases 2
  • Algorithms 3
  • FIPS 140-2 compliance 4
  • Licensing 5
  • Notable vulnerabilities 6
    • Timing attacks on RSA Keys 6.1
    • Denial of Service ASN.1 parsing 6.2
    • OCSP stapling vulnerability 6.3
    • ASN1 Bio vulnerability 6.4
    • SSL, TLS and DTLS Plaintext Recovery Attack 6.5
    • Predictable private keys (Debian-specific) 6.6
    • Heartbleed 6.7
    • CCS Injection Vulnerability 6.8
    • ClientHello sigalgs DoS 6.9
  • Forks 7
    • Agglomerated SSL 7.1
    • LibreSSL 7.2
    • BoringSSL 7.3
  • See also 8
  • References 9
  • External links 10

Project history

The OpenSSL project was founded in 1998 to invent a free set of encryption tools for the code used on the Internet. It is based on a fork of SSLeay by Eric Andrew Young and Tim Hudson, development of which unofficially ended on December 17, 1998, when Young and Hudson both started to work for RSA Security.

The OpenSSL project management team consists of four Europeans. The entire development group consists of 11 members, out of which 10 are volunteers; there is only one full-time employee, Stephen Henson, the lead developer.[2]

The project has a budget of less than $1 million a year and relies in part on donations. Steve Marquess, a former military consultant in Maryland started the foundation for donations and consultancy contracts and garnered sponsorship from the United States Department of Homeland Security and the United States Department of Defense.[2]

As of 2014 two thirds of all webservers use OpenSSL.[3]

Major version releases

OpenSSL release history[4][5]
Version Original release date Comment Last minor version
Old version, no longer supported: 0.9.1 December 23, 1998
  • Official start of the OpenSSL project
0.9.1c (December 23, 1998)
Old version, no longer supported: 0.9.2 March 22, 1999
  • Successor of 0.9.1c
0.9.2b (April 6, 1999)
Old version, no longer supported: 0.9.3 May 25, 1999
  • Successor of 0.9.2b
0.9.3a (May 27, 1999)
Old version, no longer supported: 0.9.4 August 9, 1999
  • Successor of 0.9.3a
0.9.4 (August 9, 1999)
Old version, no longer supported: 0.9.5 February 28, 2000
  • Successor of 0.9.4
0.9.5a (April 1, 2000)
Old version, no longer supported: 0.9.6 September 24, 2000
  • Successor of 0.9.5a
0.9.6m (March 17, 2004)
Old version, no longer supported: 0.9.7 December 31, 2002
  • Successor of 0.9.6m
0.9.7m (February 23, 2007)
Older version, yet still supported: 0.9.8 July 5, 2005
  • Successor of 0.9.7m
  • Support will end on December 31, 2015
0.9.8zg (June 11, 2015)
Older version, yet still supported: 1.0.0 March 29, 2010
  • Successor of 0.9.8n
  • Support will end on December 31, 2015
1.0.0s (June 11, 2015)
Older version, yet still supported: 1.0.1 March 14, 2012
  • Successor of 1.0.0l
  • Supported until December 31, 2016
  • RFC 6520 TLS/DTLS heartbeat support.
  • SCTP support.
  • RFC 5705 TLS key material exporter.
  • RFC 5764 DTLS-SRTP negotiation.
  • Next Protocol Negotiation.
  • PSS signatures in certificates, requests and certificate revocation lists (CRL)s.
  • Support for password based recipient info for CMS.
  • Support TLS v1.2 and TLS v1.1.
  • Preliminary FIPS capability for unvalidated 2.0 FIPS module.
  • Secure Remote Password protocol (SRP) support.
1.0.1p (July 9, 2015)
Current stable version: 1.0.2 January 22, 2015
  • Successor of 1.0.1l
  • Supported until December 31, 2019
  • Suite B support for TLS 1.2 and DTLS 1.2
  • Support for DTLS 1.2
  • TLS automatic elliptic curve (EC) curve selection.
  • API to set TLS supported signature algorithms and curves
  • SSL_CONF configuration API.
  • TLS Brainpool support.
  • ALPN support.
  • CMS support for RSA-PSS, RSA-OAEP, ECDH and X9.42 DH.
1.0.2d (July 9, 2015)
Future release: 1.1.0
  • Expected to release on April 28th 2016
Old version
Older version, still supported
Latest version
Latest preview version
Future release


OpenSSL supports a number of different cryptographic algorithms:

AES, Blowfish, Camellia, SEED, CAST-128, DES, IDEA, RC2, RC4, RC5, Triple DES, GOST 28147-89[6]
Cryptographic hash functions
MD5, MD4, MD2, SHA-1, SHA-2, RIPEMD-160, MDC-2, GOST R 34.11-94[6]
Public-key cryptography
RSA, DSA, Diffie–Hellman key exchange, Elliptic curve, GOST R 34.10-2001[6]

(Perfect forward secrecy is supported using elliptic curve Diffie–Hellman since version 1.0.[7])

FIPS 140-2 compliance

As of December 2012, OpenSSL is one of two open source programs to be involved with validation under the FIPS 140-2 computer security standard by the National Institute of Standards and Technology's (NIST) Cryptographic Module Validation Program (CMVP).[8] (OpenSSL itself is not validated, but a component called the OpenSSL FIPS Object Module, based on OpenSSL, was created to provide many of the same capabilities).[9]

A certificate was first awarded in January 2006 but revoked in July 2006 "when questions were raised about the validated module’s interaction with outside software." The certification was reinstated in February 2007.[10]


OpenSSL is "dual licensed" under the OpenSSL License and the SSLeay License.[11] The OpenSSL License is Apache License 1.0 and SSLeay License bears some similarity to a 4-clause BSD License. The common usage of the term dual-license is that the user may pick which license they wish to use. However, OpenSSL documentation uses the term dual-license to mean that both licenses apply.

As the OpenSSL License is Apache License 1.0, but not Apache License 2.0, it requires the phrase "this product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit" to appear in advertising material and any redistributions (Sections 3 and 6 of the OpenSSL License). Due to this restriction, the OpenSSL License and the Apache License 1.0 are incompatible with the GPL.[12] Some GPL developers have added an OpenSSL exception to their licenses specifically allowing OpenSSL to be used with their system. GNU Wget and climm both use such exceptions.[13][14] Some packages (like Deluge) explicitly modify the GPL license by adding an extra section at the beginning of the license documenting the exception.[15] Other packages use the LGPL-licensed GnuTLS and MPL-licensed NSS, both of which perform the same task.

OpenSSL announced in August 2015 that it would require most contributors to sign a Contributor License Agreement (CLA), and that OpenSSL would eventually be relicensed under the terms of Apache License 2.0.[16]

Notable vulnerabilities

Timing attacks on RSA Keys

On March 14, 2003, a timing attack on RSA keys was discovered, which meant a vulnerability within OpenSSL versions 0.9.7a and 0.9.6. This vulnerability was assigned CAN-2003-0147 by the Common Vulnerabilities and Exposures project. RSA blinding was not turned on by default by OpenSSL, since it is not easily possible to when providing SSL or TLS using OpenSSL. Almost all SSL enabled Apaches were affected, along with many other applications of OpenSSL. Timing differences on the number of extra reductions along and use of Karatsuba and normal integer multiplication algorithms meant that it was possible for local and remote attackers to obtain the private key of the server.

Denial of Service ASN.1 parsing

OpenSSL 0.9.6k had a bug where certain ASN.1 sequences triggered a large amount of recursions on Windows machines, discovered on November 4, 2003. Windows could not handle large recursions correctly, so OpenSSL would crash as a result. Being able to send arbitrary large amounts of ASN.1 sequences would cause OpenSSL to crash as a result. A client certificate to a SSL/TLS enabled server could accept ASN.1 sequences and crash.

OCSP stapling vulnerability

When creating a handshake, the client could send an incorrectly formatted ClientHello message, leading to OpenSSL parsing more than the end of the message. Titled CVE-2011-0014, this affected all OpenSSL versions 0.9.8h to 0.9.8q and OpenSSL 1.0.0 to 1.0.0c. Since the parsing could lead to a read on an incorrect memory address, it was possible for the attacker to cause a DDOS. It was also possible that some applications expose the contents of parsed OCSP extensions, leading to an attacker being able to read the contents of memory that came after the ClientHello.[17]

ASN1 Bio vulnerability

When using BIO or FILE based functions to read untrusted DER format data, OpenSSL is vulnerable. The CVE assigned this CVE-2012-2110, as this was discovered on April 19, 2012. While not directly affecting the SSL/TLS code of OpenSSL, any application that was using ASN1 functions (particularly d2i_X509 and d2i_PKCS12) were also not affected.[18]

SSL, TLS and DTLS Plaintext Recovery Attack

In handling CBC cipher-suites in SSL, TLS, and DTLS, OpenSSL was found to be vulnerable to a timing attack which arises during the MAC processing. This was found by Nadhem Alfardan and Kenny Paterson, who published their findings on February 5, 2013, given the name CVE-2013-0169. All versions of OpenSSL were affected, and it was only partially mitigated by the use of the OpenSSL FIPS Object Module and the FIPS mode of operation is enabled.

Predictable private keys (Debian-specific)

OpenSSL's pseudo-random number generator acquires entropy using complex programming methods described as poor coding practice. In order to keep associated warnings from being issued by the Valgrind analysis tool, a maintainer of the Debian distribution applied a patch to the Debian's variant of the OpenSSL suite, which inadvertently broke its random number generator by limiting the overall number of private keys it could generate to 32,768.[19][20] The broken version was included in the Debian release of September 17, 2006 (version 0.9.8c-1), also compromising other Debian-based distributions, for example Ubuntu. Any key generated with the broken random number generator was compromised, as well as the data encrypted with such keys; moreover, ready-to-use exploits are easily available.[21]

The error was reported by Debian on May 13, 2008. On the Debian 4.0 distribution (etch), these problems were fixed in version 0.9.8c-4etch3, while fixes for the Debian 5.0 distribution (lenny) were provided in version 0.9.8g-9.[22]


A logo representing the Heartbleed bug

OpenSSL versions 1.0.1 through 1.0.1f had a severe memory handling bug in their implementation of the TLS Heartbeat Extension that could be used to reveal up to 64 KB of the application's memory with every heartbeat.[23][24] By reading the memory of the web server, attackers could access sensitive data, including the server's private key.[25] This could allow attackers to decode earlier eavesdropped communications if the encryption protocol used does not ensure Perfect Forward Secrecy. Knowledge of the private key could also allow an attacker to mount a man-in-the-middle attack against any future communications.[26] The vulnerability might also reveal unencrypted parts of other users' sensitive requests and responses, including session cookies and passwords, which might allow attackers to hijack the identity of another user of the service.[27]

At its disclosure on April 7, 2014, around 17% or half a million of the Internet's secure web servers certified by trusted authorities were believed to have been vulnerable to the attack.[28] However, Heartbleed can affect both the server and client.

CCS Injection Vulnerability

CCS Injection Vulnerability (CVE-2014-0224) is a security bypass vulnerability that exists in OpenSSL. The vulnerability is due to a weakness in OpenSSL methods used for keying material.[29]

This vulnerability can be exploited through the use of a man-in-the-middle attack,[30] where an attacker may be able to decrypt and modify traffic in transit. A remote unauthenticated attacker could exploit this vulnerability by using a specially crafted handshake to force the use of weak keying material. Successful exploitation could lead to a security bypass condition where an attacker could gain access to potentially sensitive information. The attack can only be performed between a vulnerable client and server.

OpenSSL clients are vulnerable in all versions of OpenSSL before the versions 0.9.8za, 1.0.0m and 1.0.1h. Servers are only known to be vulnerable in OpenSSL 1.0.1 and 1.0.2-beta1. Users of OpenSSL servers earlier than 1.0.1 are advised to upgrade as a precaution.[31]

ClientHello sigalgs DoS

This vulnerability allows anyone to take a certificate, read its contents and modify it accurately to abuse the vulnerability causing a certificate to crash a client or server. A client connects to an OpenSSL 1.0.2 server and renegotiates with an invalid signature algorithms extension a NULL pointer dereference will occur. This can cause a DoS attack against the server.

A Stanford Security researcher, David Ramos had a private exploit and presented it before the OpenSSL team where they patched the issue.

OpenSSL classified the bug as a high-severity issue, noting version 1.0.2 was found vulnerable.[32]


Agglomerated SSL

In 2009, after frustrations with the original OpenSSL API, Marco Peereboom, an OpenBSD developer at the time, forked the original API by creating Agglomerated SSL (assl), which reuses OpenSSL API under the hood, but provides a much simpler external interface.[33]


In the wake of Heartbleed, members of the OpenBSD project forked OpenSSL starting with the 1.0.1g branch, to create a project named LibreSSL.[34] In the first week of pruning the OpenSSL's codebase, more than 90,000 lines of C code had been removed from the fork.[35]


In June 2014, Google announced its own fork of OpenSSL dubbed BoringSSL. Google plans to co-operate with OpenSSL and LibreSSL developers.[36][37]

See also


  1. ^ a b c d "OpenSSL: News, Project Newsflash". Retrieved July 10, 2015. 
  2. ^ a b Yadron, Danny (11 April 2014). "Internet Security Relies on Very Few". Retrieved 14 April 2014. 
  3. ^ "Critical crypto bug in OpenSSL opens two-thirds of the Web to eavesdropping". 
  4. ^ "OpenSSL – Changelog". OpenSSL Software Foundation. Retrieved 17 September 2015. 
  5. ^ "OpenSSL – Release Strategy". OpenSSL Software Foundation. Retrieved 17 September 2015. 
  6. ^ a b c "GOST engine OpenSSL 1.0.0 README". 
  7. ^ "Protecting data for the long term with forward secrecy". Retrieved 2012-11-05. 
  8. ^ Validated FIPS 140-1 and FIPS 140-2 Cryptographic Modules. NIST. Retrieved 2012-12-19.
  9. ^ "Important Notes about OpenSSL and FIPS 140-2". 
  10. ^ "NIST recertifies open source encryption module". 
  11. ^ "OpenSSL: Source, License". 
  12. ^ "Licenses – Free Software Foundation". 
  13. ^ "WGET 1.10.2 for Windows (win32)". 
  14. ^ "Releases of source and binaries". Retrieved 30 November 2010. 
  15. ^ "Deluge LICENSE file". Retrieved 24 January 2013. 
  16. ^ Salz, Rich (1 August 2015). "License Agreements and Changes Are Coming". Retrieved 23 August 2015. 
  17. ^ "OpenSSL Updates Fix Critical Security Vulnerabilities [09 Aug 2014]". Retrieved 25 Aug 2014. 
  18. ^ "ASN1 BIO vulnerability". OpenSSL. 
  19. ^ "research!rsc: Lessons from the Debian/OpenSSL Fiasco". Retrieved 2015-08-12. 
  20. ^ "SSLkeys - Debian Wiki". Retrieved 2015-06-19. 
  21. ^ "Debian OpenSSL – Predictable PRNG Bruteforce SSH Exploit Python – Exploits Database". Retrieved 2015-08-12. 
  22. ^ "DSA-1571-1 openssl – predictable random number generator".  
  23. ^ (7 April 2014). "OpenSSL Security Advisory [07 Apr 2014]". Retrieved 9 April 2014. 
  24. ^ OpenSSL (2014-04-07). "TLS heartbeat read overrun (CVE-2014-0160)". Retrieved 2014-04-08. 
  25. ^ Codenomicon Ltd (2014-04-08). "Heartbleed Bug". Retrieved 2014-04-08. 
  26. ^ "Man in Middle Attacks [04 Jun 2014]". Retrieved 25 Aug 2014. 
  27. ^ "Why Heartbleed is dangerous? Exploiting CVE-2014-0160". 2014. 
  28. ^ Mutton, Paul (8 April 2014). "Half a million widely trusted websites vulnerable to Heartbleed bug". Netcraft Ltd. Retrieved 8 April 2014. 
  29. ^ "OpenSSL continues to bleed out more flaws – more critical vulnerabilities found". Cyberoam Threat Research Labs. 2014. 
  30. ^ "CVE-2014-0224". CVE. 2014. 
  31. ^ "OpenSSL Security Advisory [05 Jun 2014]". OpenSSL. 2014. 
  32. ^ "OpenSSL Patches Severe Denial-of-Service Vulnerability [20 March 2015]". Brandon Stosh. 2015. 
  33. ^ "security/assl: assl-1.5.0p0v0 – hide awful SSL API in a sane interface".  
  34. ^ "OpenBSD has started a massive strip-down and cleanup of OpenSSL". OpenBSD journal. 2014-04-15. 
  35. ^ "OpenBSD forks, prunes, fixes OpenSSL". ZDNet. 21 April 2014. Retrieved 21 April 2014. 
  36. ^ "'"Google unveils independent 'fork' of OpenSSL called 'BoringSSL. Ars Technica. 2014-06-21. 
  37. ^ "BoringSSL". Adam Langley's Weblog. 2014-06-20. 

External links

  • Official website
  • The OpenSSL License and the GPL by Mark McLoughlin
  • Use OpenSSL easily with PKCS#11 enabled smartcards
  • OpenSSL for windows 32-bit and x64 version
  • OpenSSL for OpenVMS on Dec Alpha, IA-64 and VAX architectures
  • OpenSSL programming tutorial
  • OpenSSL Community Wiki
  • LibreSSL homepage
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Hawaii eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.