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Merge #714: doc: document the length requirements of output parameter. 

4b48a43106 doc: document the length requirements of output parameter. (Rusty Russell)

Pull request description:

  It's subtle, since it is actually only touched by hashfp (though
  we assert it's non-NULL), but give explicit advice in the default
  case.

  Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

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Tim Ruffing 2020-02-10 12:06:17 +01:00
parent d72b9e2483 4b48a43106
commit 856a01d6ad
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1 changed files with 7 additions and 4 deletions
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11
include/secp256k1_ecdh.h
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@ -22,22 +22,25 @@ typedef int (*secp256k1_ecdh_hash_function)(
void *data void *data
); );
/** An implementation of SHA256 hash function that applies to compressed public key. */ /** An implementation of SHA256 hash function that applies to compressed public key.
* Populates the output parameter with 32 bytes. */
SECP256K1_API extern const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_sha256; SECP256K1_API extern const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_sha256;
/** A default ecdh hash function (currently equal to secp256k1_ecdh_hash_function_sha256). */ /** A default ecdh hash function (currently equal to secp256k1_ecdh_hash_function_sha256).
* Populates the output parameter with 32 bytes. */
SECP256K1_API extern const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_default; SECP256K1_API extern const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_default;
/** Compute an EC Diffie-Hellman secret in constant time /** Compute an EC Diffie-Hellman secret in constant time
* Returns: 1: exponentiation was successful * Returns: 1: exponentiation was successful
* 0: scalar was invalid (zero or overflow) * 0: scalar was invalid (zero or overflow)
* Args: ctx: pointer to a context object (cannot be NULL) * Args: ctx: pointer to a context object (cannot be NULL)
* Out: output: pointer to an array to be filled by the function * Out: output: pointer to an array to be filled by hashfp
* In: pubkey: a pointer to a secp256k1_pubkey containing an * In: pubkey: a pointer to a secp256k1_pubkey containing an
* initialized public key * initialized public key
* privkey: a 32-byte scalar with which to multiply the point * privkey: a 32-byte scalar with which to multiply the point
* hashfp: pointer to a hash function. If NULL, secp256k1_ecdh_hash_function_sha256 is used * hashfp: pointer to a hash function. If NULL, secp256k1_ecdh_hash_function_sha256 is used
* data: Arbitrary data pointer that is passed through * (in which case, 32 bytes will be written to output)
* data: Arbitrary data pointer that is passed through to hashfp
*/ */
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdh( SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdh(
const secp256k1_context* ctx, const secp256k1_context* ctx,