Code review comment for lp:~rene-hummen/hipl/midauth-hipd

Looks good, aside from what Diego mentioned already (I'll approve as soon as the conflict is resolved). One minor point:

+/**
+ * Convert the opaque value in the CHALLENGE_REQUEST to the seed value I of a
+ * HIP puzzle.
+ *
+ * The opaque value plays a dual role in a CHALLENGE_REQUEST:
+ * i) it is a challenge that needs to be echoed back by the responder and
+ * ii) it is used to derive the seed value for a cryptographic puzzle. The
+ * puzzle is defined in RFC5201.
+ *
+ * @param opaque the nonce (challenge) in the CHALLENGE_REQUEST
+ * @param opaque_len the length of the nonce
+ * @param puzzle_value the puzzle value generated from the nonce
+ * @return zero on success, -1 in case of an error
+ */
+int hip_midauth_puzzle_seed(const uint8_t opaque[],
+ const unsigned int opaque_len,
+ uint8_t puzzle_value[PUZZLE_LENGTH])
+{
+ unsigned char sha_digest[SHA_DIGEST_LENGTH];
+

+ if (!puzzle_value) {
+ HIP_ERROR("Parameter puzzle_value is not allocated\n");
+ return -1;
+ }

This looks like it should never happen, i.e. an assertion would be more appropriate. Same for the opaque parameter.