Using sipa's secp256k1 library to find a public key from a private key

[fatefree]

I am trying to create a proof of concept using sipa's secp256k1 library (https://github.com/bitcoin/secp256k1) to find the public key of a given private key. However the code does not have much documentation so I am having trouble following it.

I believe the appropriate method to use is:

secp256k1_ecdsa_pubkey_create(unsigned char *pubkey, int *pubkeylen, const unsigned char *seckey, int compressed)

However I'm not sure exactly how it should be called. If anyone is familiar with using this, I would appreciate any direction.

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[piotr_n]

I think you want to use secp256k1_ecmult_gen() followed by secp256k1_ge_set_gej()
The XY returned by the second function is the public key.

[gmaxwell]

I think you want to use secp256k1_ecmult_gen() followed by secp256k1_ge_set_gej()
The XY returned by the second function is the public key.

Absolutely not. Those are not public functions.

secp256k1_ecdsa_pubkey_create(unsigned char *pubkey, int *pubkeylen, const unsigned char *seckey, int compressed)

Is correct... there is more information in the header that defines it.