On Tue, May 31, 2016 at 01:52:32PM +0200, Stephan Mueller wrote:

+ * NOTE: Technically you can use one buffer for holding the label_context and
+ *	 the outbuf in the example above. Howerver, multiple rounds of the
+ *	 KDF are to be expected with the input must always be the same.
+ *	 The first round would replace the input in case of one buffer, and the
+ *	 KDF would calculate a cryptographically strong result which, however,
+ *	 is not portable to other KDF implementations! Thus, always use
+ *	 different buffers for the label_context and the outbuf. A safe
+ *	 in-place operation can only be done when only one round of the KDF
+ *	 is executed (i.e. the size of the requested buffer is equal to the
+ *	 digestsize of the used MAC).

Why don't you put the result in a temporary buffer and then copy
it? These things are tiny, right?

Cheers,
-- 
Email: Herbert Xu [off-list ref]
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