113 lines
3.4 KiB
ReStructuredText
113 lines
3.4 KiB
ReStructuredText
-----------------
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The SHA256 class
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-----------------
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.. cpp:class:: emsha::SHA256
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SHA256 is an implementation of the :cpp:class:`emsha::Hash` interface
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implementing the SHA-256 cryptographic hash algorithm
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.. cpp:function:: SHA256::SHA256()
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A SHA256 context does not need any special construction. It can be
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declared and immediately start being used.
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.. cpp:function:: SHA256::~SHA256()
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The SHA256 destructor will clear out its internal message buffer;
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all of the members are local and not resource handles, so cleanup
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is minimal.
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.. cpp:function:: emsha::EMSHA_RESULT SHA256::reset(void)
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reset clears the internal state of the `SHA256` context and returns
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it to its initial state. It should always return ``EMSHA_ROK``.
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.. cpp:function:: emsha::EMSHA_RESULT SHA256::update(const uint8_t *m, uint32_t ml)
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update writes data into the context. While there is an upper limit
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on the size of data that SHA-256 can operate on, this package is
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designed for small systems that will not approach that level of
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data (which is on the order of 2 exabytes), so it is not thought to
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be a concern.
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**Inputs**:
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+ ``m``: a byte array containing the message to be written. It must
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not be NULL (unless the message length is zero).
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+ ``ml``: the message length, in bytes.
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**Return values**:
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* ``EMSHA_NULLPTR`` is returned if ``m`` is NULL and ``ml`` is nonzero.
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* ``EMSHA_INVALID_STATE`` is returned if the `update` is called
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after a call to `finalize`.
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* ``SHA256_INPUT_TOO_LONG`` is returned if too much data has been
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written to the context.
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+ ``EMSHA_ROK`` is returned if the data was successfully added to
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the SHA-256 context.
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.. cpp:function:: emsha::EMSHA_RESULT SHA256::finalize(uint8_t *d)
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``finalize`` completes the digest. Once this method is called, the
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context cannot be updated unless the context is reset.
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**Inputs**:
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* d: a byte buffer that must be at least ``SHA256.size()`` in
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length.
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**Outputs**:
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* ``EMSHA_NULLPTR`` is returned if ``d`` is the null pointer.
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* ``EMSHA_INVALID_STATE`` is returned if the SHA-256 context is in
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an invalid state, such as if there were errors in previous
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updates.
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* ``EMSHA_ROK`` is returned if the context was successfully
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finalised and the digest copied to ``d``.
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.. cpp:function:: emsha::EMSHA_RESULT SHA256::result(uint8_t *d)
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``result`` copies the result from the SHA-256 context into the
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buffer pointed to by ``d``, running finalize if needed. Once
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called, the context cannot be updated until the context is reset.
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**Inputs**:
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* ``d``: a byte buffer that must be at least ``SHA256.size()`` in
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length.
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**Outputs**:
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* ``EMSHA_NULLPTR`` is returned if ``d`` is the null pointer.
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* ``EMSHA_INVALID_STATE`` is returned if the SHA-256 context is in
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an invalid state, such as if there were errors in previous
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updates.
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* ``EMSHA_ROK`` is returned if the context was successfully
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finalised and the digest copied to ``d``.
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.. cpp:function:: uint32_t SHA256::size(void)
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``size`` returns the output size of SHA256, e.g.
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the size that the buffers passed to ``finalize``
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and ``result`` should be.
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**Outputs**:
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* a ``uint32_t`` representing the expected size of buffers passed
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to ``result`` and ``finalize``.
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