1License Mixing 2============== 3 4libcurl can be built to use a fair amount of various third party libraries, 5libraries that are written and provided by other parties that are distributed 6using their own licenses. Even libcurl itself contains code that may cause 7problems to some. This document attempts to describe what licenses libcurl and 8the other libraries use and what possible dilemmas linking and mixing them all 9can lead to for end users. 10 11I am not a lawyer and this is not legal advice! 12 13One common dilemma is that [GPL](https://www.gnu.org/licenses/gpl.html) 14licensed code is not allowed to be linked with code licensed under the 15[Original BSD license](https://spdx.org/licenses/BSD-4-Clause.html) (with the 16announcement clause). You may still build your own copies that use them all, 17but distributing them as binaries would be to violate the GPL license - unless 18you accompany your license with an 19[exception](https://www.gnu.org/licenses/gpl-faq.html#GPLIncompatibleLibs). This 20particular problem was addressed when the [Modified BSD 21license](https://opensource.org/licenses/BSD-3-Clause) was created, which does 22not have the announcement clause that collides with GPL. 23 24## libcurl 25 26 Uses an [MIT style license](https://curl.haxx.se/docs/copyright.html) that is 27 very liberal. 28 29## OpenSSL 30 31 (May be used for SSL/TLS support) Uses an Original BSD-style license with an 32 announcement clause that makes it "incompatible" with GPL. You are not 33 allowed to ship binaries that link with OpenSSL that includes GPL code 34 (unless that specific GPL code includes an exception for OpenSSL - a habit 35 that is growing more and more common). If OpenSSL's licensing is a problem 36 for you, consider using another TLS library. 37 38## GnuTLS 39 40 (May be used for SSL/TLS support) Uses the 41 [LGPL](https://www.gnu.org/licenses/lgpl.html) license. If this is a problem 42 for you, consider using another TLS library. Also note that GnuTLS itself 43 depends on and uses other libs (libgcrypt and libgpg-error) and they too are 44 LGPL- or GPL-licensed. 45 46## WolfSSL 47 48 (May be used for SSL/TLS support) Uses the GPL license or a proprietary 49 license. If this is a problem for you, consider using another TLS library. 50 51## NSS 52 53 (May be used for SSL/TLS support) Is covered by the 54 [MPL](https://www.mozilla.org/MPL/) license, the GPL license and the LGPL 55 license. You may choose to license the code under MPL terms, GPL terms, or 56 LGPL terms. These licenses grant you different permissions and impose 57 different obligations. You should select the license that best meets your 58 needs. 59 60## mbedTLS 61 62 (May be used for SSL/TLS support) Uses the [Apache 2.0 63 license](https://opensource.org/licenses/Apache-2.0) or the GPL license. 64 You may choose to license the code under Apache 2.0 terms or GPL terms. 65 These licenses grant you different permissions and impose different 66 obligations. You should select the license that best meets your needs. 67 68## BoringSSL 69 70 (May be used for SSL/TLS support) As an OpenSSL fork, it has the same 71 license as that. 72 73## libressl 74 75 (May be used for SSL/TLS support) As an OpenSSL fork, it has the same 76 license as that. 77 78## c-ares 79 80 (Used for asynchronous name resolves) Uses an MIT license that is very 81 liberal and imposes no restrictions on any other library or part you may link 82 with. 83 84## zlib 85 86 (Used for compressed Transfer-Encoding support) Uses an MIT-style license 87 that shouldn't collide with any other library. 88 89## MIT Kerberos 90 91 (May be used for GSS support) MIT licensed, that shouldn't collide with any 92 other parts. 93 94## Heimdal 95 96 (May be used for GSS support) Heimdal is Original BSD licensed with the 97 announcement clause. 98 99## GNU GSS 100 101 (May be used for GSS support) GNU GSS is GPL licensed. Note that you may not 102 distribute binary curl packages that uses this if you build curl to also link 103 and use any Original BSD licensed libraries! 104 105## libidn 106 107 (Used for IDNA support) Uses the GNU Lesser General Public License [3]. LGPL 108 is a variation of GPL with slightly less aggressive "copyleft". This license 109 requires more requirements to be met when distributing binaries, see the 110 license for details. Also note that if you distribute a binary that includes 111 this library, you must also include the full LGPL license text. Please 112 properly point out what parts of the distributed package that the license 113 addresses. 114 115## OpenLDAP 116 117 (Used for LDAP support) Uses a Modified BSD-style license. Since libcurl uses 118 OpenLDAP as a shared library only, I have not heard of anyone that ships 119 OpenLDAP linked with libcurl in an app. 120 121## libssh2 122 123 (Used for scp and sftp support) libssh2 uses a Modified BSD-style license. 124