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106 lines
5.4 KiB
106 lines
5.4 KiB
# Maintained branches
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At any point in time, we have a number of maintained branches, currently consisting of:
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- The [`master`](https://github.com/Mbed-TLS/mbedtls/tree/master) branch:
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this always contains the latest release, including all publicly available
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security fixes.
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- The [`development`](https://github.com/Mbed-TLS/mbedtls/tree/development) branch:
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this is where the current major version of Mbed TLS (version 3.x) is being
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prepared. It has API changes that make it incompatible with Mbed TLS 2.x,
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as well as all the new features and bug fixes and security fixes.
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- One or more long-time support (LTS) branches: these only get bug fixes and
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security fixes. Currently, the only supported LTS branch is:
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[`mbedtls-2.28`](https://github.com/Mbed-TLS/mbedtls/tree/mbedtls-2.28).
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We retain a number of historical branches, whose names are prefixed by `archive/`,
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such as [`archive/mbedtls-2.7`](https://github.com/Mbed-TLS/mbedtls/tree/archive/mbedtls-2.7).
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These branches will not receive any changes or updates.
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We use [Semantic Versioning](https://semver.org/). In particular, we maintain
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API compatibility in the `master` branch across minor version changes (e.g.
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the API of 3.(x+1) is backward compatible with 3.x). We only break API
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compatibility on major version changes (e.g. from 3.x to 4.0). We also maintain
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ABI compatibility within LTS branches; see the next section for details.
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## Backwards Compatibility for application code
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We maintain API compatibility in released versions of Mbed TLS. If you have
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code that's working and secure with Mbed TLS x.y.z and does not rely on
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undocumented features, then you should be able to re-compile it without
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modification with any later release x.y'.z' with the same major version
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number, and your code will still build, be secure, and work.
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Note that this guarantee only applies if you either use the default
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compile-time configuration (`mbedtls/mbedtls_config.h`) or the same modified
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compile-time configuration. Changing compile-time configuration options can
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result in an incompatible API or ABI, although features will generally not
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affect unrelated features (for example, enabling or disabling a
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cryptographic algorithm does not break code that does not use that
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algorithm).
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Note that new releases of Mbed TLS may extend the API. Here are some
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examples of changes that are common in minor releases of Mbed TLS, and are
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not considered API compatibility breaks:
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* Adding or reordering fields in a structure or union.
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* Removing a field from a structure, unless the field is documented as public.
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* Adding items to an enum.
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* Returning an error code that was not previously documented for a function
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when a new error condition arises.
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* Changing which error code is returned in a case where multiple error
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conditions apply.
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* Changing the behavior of a function from failing to succeeding, when the
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change is a reasonable extension of the current behavior, i.e. the
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addition of a new feature.
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There are rare exceptions where we break API compatibility: code that was
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relying on something that became insecure in the meantime (for example,
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crypto that was found to be weak) may need to be changed. In case security
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comes in conflict with backwards compatibility, we will put security first,
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but always attempt to provide a compatibility option.
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## Backward compatibility for the key store
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We maintain backward compatibility with previous versions of the
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PSA Crypto persistent storage since Mbed TLS 2.25.0, provided that the
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storage backend (PSA ITS implementation) is configured in a compatible way.
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We intend to maintain this backward compatibility throughout a major version
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of Mbed TLS (for example, all Mbed TLS 3.y versions will be able to read
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keys written under any Mbed TLS 3.x with x <= y).
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Mbed TLS 3.x can also read keys written by Mbed TLS 2.25.0 through 2.28.x
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LTS, but future major version upgrades (for example from 2.28.x/3.x to 4.y)
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may require the use of an upgrade tool.
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Note that this guarantee does not currently fully extend to drivers, which
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are an experimental feature. We intend to maintain compatibility with the
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basic use of drivers from Mbed TLS 2.28.0 onwards, even if driver APIs
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change. However, for more experimental parts of the driver interface, such
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as the use of driver state, we do not yet guarantee backward compatibility.
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## Long-time support branches
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For the LTS branches, additionally we try very hard to also maintain ABI
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compatibility (same definition as API except with re-linking instead of
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re-compiling) and to avoid any increase in code size or RAM usage, or in the
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minimum version of tools needed to build the code. The only exception, as
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before, is in case those goals would conflict with fixing a security issue, we
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will put security first but provide a compatibility option. (So far we never
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had to break ABI compatibility in an LTS branch, but we occasionally had to
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increase code size for a security fix.)
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For contributors, see the [Backwards Compatibility section of
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CONTRIBUTING](CONTRIBUTING.md#backwards-compatibility).
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## Current Branches
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The following branches are currently maintained:
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- [master](https://github.com/Mbed-TLS/mbedtls/tree/master)
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- [`development`](https://github.com/Mbed-TLS/mbedtls/)
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- [`mbedtls-2.28`](https://github.com/Mbed-TLS/mbedtls/tree/mbedtls-2.28)
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maintained until at least the end of 2024, see
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<https://github.com/Mbed-TLS/mbedtls/releases/tag/v2.28.2>.
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Users are urged to always use the latest version of a maintained branch.
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