Adding point and an integer? Is this valid? #11

1. 
   genjix commented at 1:13 am on May 8, 2014: none

   https://github.com/bitcoin/secp256k1/blob/master/include/secp256k1.h#L113

   int secp256k1_ecdsa_pubkey_tweak_add(unsigned char *pubkey, int pubkeylen, const unsigned char *tweak);

   Looking at the source code for this function, it seems like tweak is a 32 byte number. Is this valid?

   What is the way to add 2 points together then if this function doesn’t work.

2. 
   gmaxwell commented at 1:16 am on May 8, 2014: contributor

   This function is the sister of the privkey_tweak_add, it adds G*tweak in order to perform the the same operation as privkey_tweak_add and then converting it into a pubkey.
3. 
   genjix commented at 1:26 am on May 8, 2014: none

   Ah ok, thanks. So what is the recommended way to add 2 points?

   I see:

   Create point: void static secp256k1_gej_set_xy(secp256k1_gej_t *r, const secp256k1_fe_t *x, const secp256k1_fe_t *y);

   Add both points: void static secp256k1_gej_add(secp256k1_gej_t *r, const secp256k1_gej_t *a, const secp256k1_gej_t *b);

   And then finally convert the jacobian point back into a cartesian value (0x04, x, y) as used in Bitcoin.

   (using x/z^2 and y/z^3 as it says in group.h)

4. 
   genjix commented at 4:42 pm on May 8, 2014: none

   moving to new thread.
5. genjix closed this on May 8, 2014

   ---

Contributors
genjix gmaxwell