OpenSSL

OpenSSL is a software library for applications that secure communications over computer networks against eavesdropping or need to identify the party at the other end. It is widely used by Internet servers, including the majority of HTTPS websites.

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.

The OpenSSL Software Foundation (OSF) represents the OpenSSL project in most legal capacities including contributor license agreements, managing donations, and so on. OpenSSL Software Services (OSS) also represents the OpenSSL project, for Support Contracts.

OpenSSL is available for most Unix-like operating systems (including Linux, macOS, and BSD) and Microsoft Windows.

Project history 

The OpenSSL project was founded in 1998 to provide 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, which unofficially ended development on December 17, 1998, when Young and Hudson both went to work for RSA Security.  The initial founding members were Mark Cox, Ralf Engelschall, Stephen Henson, Ben Laurie, and Paul Sutton.

, the OpenSSL management committee consisted of 7 people and there are 17 developers with commit access (many of whom are also part of the OpenSSL management committee). 
There are only two full-time employees (fellows) and the remainder are volunteers.

The project has a budget of less than one million USD per year and relies primarily on donations. Development of TLS 1.3 is sponsored by Akamai.

Major version releases

Algorithms 

OpenSSL supports a number of different cryptographic algorithms:
 Ciphers
 AES, Blowfish, Camellia, Chacha20, Poly1305,  SEED, CAST-128, DES, IDEA, RC2, RC4, RC5, Triple DES, GOST 28147-89, SM4
 Cryptographic hash functions
 MD5, MD4, MD2, SHA-1, SHA-2, SHA-3, RIPEMD-160, MDC-2, GOST R 34.11-94, BLAKE2, Whirlpool, SM3
 Public-key cryptography
 RSA, DSA, Diffie–Hellman key exchange,  Elliptic curve, X25519, Ed25519, X448, Ed448, GOST R 34.10-2001, SM2

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

FIPS 140-2 compliance 

, OpenSSL is one of two open source programs involved in validation under the FIPS 140-2 computer security standard by the National Institute of Standards and Technology's (NIST) Cryptographic Module Validation Program (CMVP). (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).

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.

Licensing 

OpenSSL is double licensed under the OpenSSL License and the SSLeay License, which means that the terms of both licenses apply. The OpenSSL License is Apache License 1.0 and SSLeay License bears some similarity to a 4-clause BSD License.

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.
Some GPL developers have added an OpenSSL exception to their licenses that specifically permits using OpenSSL with their system. GNU Wget and climm both use such exceptions. Some packages (like Deluge) explicitly modify the GPL license by adding an extra section at the beginning of the license documenting the exception. Other packages use the LGPL-licensed GnuTLS and MPL-licensed NSS, which both 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. This process commenced in March 2017, and was complete in 2018.

Notable vulnerabilities

Timing attacks on RSA Keys 

On March 14, 2003, a timing attack on RSA keys was discovered, indicating a vulnerability within OpenSSL versions 0.9.7a and 0.9.6. This vulnerability was assigned the identifier CAN-2003-0147 by the Common Vulnerabilities and Exposures (CVE) 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.

Denial of Service ASN.1 parsing 

OpenSSL 0.9.6k had a bug where certain ASN.1 sequences triggered a large number 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 numbers of ASN.1 sequences would cause OpenSSL to crash as a result.

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. Assigned the identifier CVE-2011-0014 by the CVE project, 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 DoS. 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.

ASN.1 BIO vulnerability 

When using Basic Input/Output (BIO) or FILE based functions to read untrusted DER format data, OpenSSL is vulnerable. This vulnerability was discovered on April 19, 2012, and was assigned the CVE identifier CVE-2012-2110. While not directly affecting the SSL/TLS code of OpenSSL, any application that was using ASN.1 functions (particularly d2i_X509 and d2i_PKCS12) were also not affected.

SSL, TLS and DTLS Plaintext Recovery Attack 

In handling CBC cipher-suites in SSL, TLS, and DTLS, OpenSSL was found vulnerable to a timing attack during the MAC processing. Nadhem Alfardan and Kenny Paterson discovered the problem, and published their findings on February 5, 2013. The vulnerability was assigned the CVE identifier CVE-2013-0169.

Predictable private keys (Debian-specific) 

OpenSSL's pseudo-random number generator acquires entropy using complex programming methods. To keep the Valgrind analysis tool from issuing associated warnings, 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. 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. Ready-to-use exploits are easily available.

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.

Heartbleed 

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 (CVE-2014-0160). By reading the memory of the web server, attackers could access sensitive data, including the server's private key. 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. 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.

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. 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.

This vulnerability can be exploited through the use of a man-in-the-middle attack, 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.

ClientHello sigalgs DoS 

This vulnerability (CVE-2015-0291) 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. If a client connects to an OpenSSL 1.0.2 server and renegotiates with an invalid signature algorithms extension, a null-pointer dereference occurs. 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.

Key Recovery Attack on Diffie Hellman small subgroups 

This vulnerability (CVE-2016-0701) allows, when some particular circumstances are met, to recover the OpenSSL server's private Diffie–Hellman key. An Adobe System Security researcher, Antonio Sanso, privately reported the vulnerability.

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

Forks

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.  It has since been deprecated in light of the LibreSSL fork circa 2016.

LibreSSL 

In April 2014 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. In the first week of pruning the OpenSSL's codebase, more than 90,000 lines of C code had been removed from the fork.

BoringSSL 

In June 2014, Google announced its own fork of OpenSSL dubbed BoringSSL. Google plans to co-operate with OpenSSL and LibreSSL developers. Google has since developed a new library, Tink, based on BoringSSL.

See also 

 Comparison of TLS implementations
 Comparison of cryptography libraries
 LibreSSL
List of free and open-source software packages
 POSSE project
 wolfSSL

References

External links  

 
 OpenSSL Manpages
 OpenSSL Programming Guide
 The OpenSSL License and the GPL by Mark McLoughlin
 OpenSSL programming tutorial
 OpenSSL Community Wiki

Category:1998 software
Category:C libraries
Category:Cryptographic software
Category:Free security software
Category:Transport Layer Security implementation