diff --git a/include/secp256k1_silentpayments.h b/include/secp256k1_silentpayments.h index 49e24a4df2..e72bcddab3 100644 --- a/include/secp256k1_silentpayments.h +++ b/include/secp256k1_silentpayments.h @@ -170,6 +170,33 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_silentpayments_create_o const unsigned char *label_tweak32 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4); +/** Create Silent Payment output private key (for spending receiver's funds). + * + * Given a shared_secret, a recipient's spend private key b_spend, and an + * output counter k, calculate the corresponding output private key d: + * + * d = (b_spend + sha256(shared_secret || ser_32(k))) mod n + * + * Returns: 1 if private key creation was successful. 0 if an error occured. + * Args: ctx: pointer to a context object + * Out: output_seckey: pointer to the resulting spending private key + * In: shared_secret33: shared secret, derived from either sender's + * or receiver's perspective with routines from above + * receiver_spend_seckey: pointer to the receiver's spend private key + * k: output counter (usually set to 0, should be increased for + * every additional output to the same recipient) + * label_tweak32: an optional 32-byte label tweak + * (not supported yet, must be set to NULL right now) + */ +SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_silentpayments_create_output_seckey( + const secp256k1_context *ctx, + unsigned char *output_seckey, + const unsigned char *shared_secret33, + const unsigned char *receiver_spend_seckey, + unsigned int k, + const unsigned char *label_tweak32 +) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4); + #ifdef __cplusplus } #endif diff --git a/src/modules/silentpayments/main_impl.h b/src/modules/silentpayments/main_impl.h index 8c3f3754da..519b33ddc8 100644 --- a/src/modules/silentpayments/main_impl.h +++ b/src/modules/silentpayments/main_impl.h @@ -239,4 +239,25 @@ int secp256k1_silentpayments_create_output_pubkey(const secp256k1_context *ctx, return 1; } +int secp256k1_silentpayments_create_output_seckey(const secp256k1_context *ctx, unsigned char *output_seckey, const unsigned char *shared_secret33, const unsigned char *receiver_spend_seckey, unsigned int k, const unsigned char *label_tweak32) { + unsigned char t_k[32]; + + /* Sanity check inputs */ + VERIFY_CHECK(ctx != NULL); + ARG_CHECK(output_seckey != NULL); + memset(output_seckey, 0, 32); + ARG_CHECK(shared_secret33 != NULL); + ARG_CHECK(receiver_spend_seckey != NULL); + ARG_CHECK(label_tweak32 == NULL); /* label tweaks are not supported yet */ + + /* Compute and return d = (b_spend + t_k) mod n */ + memcpy(output_seckey, receiver_spend_seckey, 32); + secp256k1_silentpayments_create_t_k(t_k, shared_secret33, k); + if (!secp256k1_ec_seckey_tweak_add(ctx, output_seckey, t_k)) { + return 0; + } + + return 1; +} + #endif