ECDH: output compressed point #446

1. 
   chfast commented at 10:52 pm on March 9, 2017: none
2. ecdh: allocate single buffer for compressed point 9fd8a92bf1
3. ecdh: extract shared secret hashing

   This commit separates finding shared secret for ECDH from hashing it.

   1478f233f6
4. ecdh: export secp256k1_ecdh_raw() function 9859f02f9e
5. 
   fanatid commented at 5:34 am on March 10, 2017: contributor

   Related: #352 #354
6. 
   chfast commented at 9:11 am on March 10, 2017: none

   Oh, thank. Good to know it is not only my issue. Any final conclusions how the API should look like?
7. chfast cross-referenced this on Mar 10, 2017 from issue Support custom hash functions in ECDH API by Kagami
8. 
   gmaxwell commented at 3:55 pm on March 11, 2017: contributor

   It is generally unsafe to use the raw point for almost any application. Following our design principle of being hard to abuse, we should not provide a function that directly does so.

   Instead, I think we can do is take a hasher function point, similar to how the signing takes a nonce function. Callers that need some other scheme for handling the nonce can pass a function pointer that accomplishes whatever they need, without creating an appearance that it’s generally okay to use the raw point for ECDH.

   There is a lot of reckless cryptography out there. We’re not going to change that, but we also don’t need to be a part of it.

9. 
   fanatid commented at 4:11 pm on March 11, 2017: contributor

   @gmaxwell IIRC I implemented hash function as argument in #354, but not receive any feedback… should I reopen that PR?
10. 
    chfast commented at 9:31 pm on March 11, 2017: none

    It doesn’t matter for me which version it will be. Is the one with the callback is to be accepted? Is the callback parameters as in the #354 fine?
11. fanatid cross-referenced this on Mar 12, 2017 from issue [ECDH API change] Support custom hash function by fanatid
12. 
    sipa commented at 1:00 am on March 22, 2017: contributor

    Closing in favor of #354.
13. sipa closed this on Mar 22, 2017

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Contributors
chfast fanatid gmaxwell sipa