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| 1 | +# Maintained branches |
| 2 | + |
| 3 | +At any point in time, we have a number of maintained branches consisting of: |
| 4 | + |
| 5 | +- The [`master`](https://github.com/ARMmbed/mbedtls/tree/master) branch: |
| 6 | + this always contains the latest release, including all publicly available |
| 7 | + security fixes. |
| 8 | +- The [`development`](https://github.com/ARMmbed/mbedtls/tree/development) branch: |
| 9 | + this is where new features land, |
| 10 | + as well as bug fixes and security fixes. |
| 11 | +- One or more long-time support (LTS) branches: |
| 12 | + these only get bug fixes and security fixes. |
| 13 | + |
| 14 | +We use [Semantic Versioning](https://semver.org/). In particular, we maintain |
| 15 | +API compatibility in the `master` branch between major version changes. We |
| 16 | +also maintain ABI compatibility within LTS branches; see the next section for |
| 17 | +details. |
| 18 | + |
| 19 | +## Backwards Compatibility |
| 20 | + |
| 21 | +We maintain API compatibility in released versions of Mbed TLS. If you have |
| 22 | +code that's working and secure with Mbed TLS x.y.z and does not rely on |
| 23 | +undocumented features, then you should be able to re-compile it without |
| 24 | +modification with any later release x.y'.z' with the same major version |
| 25 | +number, and your code will still build, be secure, and work. |
| 26 | + |
| 27 | +There are rare exceptions: code that was relying on something that became |
| 28 | +insecure in the meantime (for example, crypto that was found to be weak) may |
| 29 | +need to be changed. In case security comes in conflict with backwards |
| 30 | +compatibility, we will put security first, but always attempt to provide a |
| 31 | +compatibility option. |
| 32 | + |
| 33 | +For the LTS branches, additionally we try very hard to also maintain ABI |
| 34 | +compatibility (same definition as API except with re-linking instead of |
| 35 | +re-compiling) and to avoid any increase in code size or RAM usage, or in the |
| 36 | +minimum version of tools needed to build the code. The only exception, as |
| 37 | +before, is in case those goals would conflict with fixing a security issue, we |
| 38 | +will put security first but provide a compatibility option. (So far we never |
| 39 | +had to break ABI compatibility in an LTS branch, but we occasionally had to |
| 40 | +increase code size for a security fix.) |
| 41 | + |
| 42 | +For contributors, see the [Backwards Compatibility section of |
| 43 | +CONTRIBUTING](CONTRIBUTING.md#cackwords-compatibility). |
| 44 | + |
| 45 | +## Current Branches |
| 46 | + |
| 47 | +The following branches are currently maintained: |
| 48 | + |
| 49 | +- [master](https://github.com/ARMmbed/mbedtls/tree/master) |
| 50 | +- [`development`](https://github.com/ARMmbed/mbedtls/) |
| 51 | +- [`mbedtls-2.28`](https://github.com/ARMmbed/mbedtls/tree/mbedtls-2.28) |
| 52 | + maintained until at least the end of 2024. |
| 53 | + |
| 54 | +Users are urged to always use the latest version of a maintained branch. |
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