+/*
+ * RSA "i15" engine. Integers are represented as 15-bit integers, so
+ * the code uses only 32-bit multiplication (no 64-bit result), which
+ * is vastly faster (and constant-time) on the ARM Cortex M0/M0+.
+ */
+
+/**
+ * \brief RSA public key engine "i15".
+ *
+ * \see br_rsa_public
+ *
+ * \param x operand to exponentiate.
+ * \param xlen length of the operand (in bytes).
+ * \param pk RSA public key.
+ * \return 1 on success, 0 on error.
+ */
+uint32_t br_rsa_i15_public(unsigned char *x, size_t xlen,
+ const br_rsa_public_key *pk);
+
+/**
+ * \brief RSA signature verification engine "i15".
+ *
+ * \see br_rsa_pkcs1_vrfy
+ *
+ * \param x signature buffer.
+ * \param xlen signature length (in bytes).
+ * \param hash_oid encoded hash algorithm OID (or `NULL`).
+ * \param hash_len expected hash value length (in bytes).
+ * \param pk RSA public key.
+ * \param hash_out output buffer for the hash value.
+ * \return 1 on success, 0 on error.
+ */
+uint32_t br_rsa_i15_pkcs1_vrfy(const unsigned char *x, size_t xlen,
+ const unsigned char *hash_oid, size_t hash_len,
+ const br_rsa_public_key *pk, unsigned char *hash_out);
+
+/**
+ * \brief RSA private key engine "i15".
+ *
+ * \see br_rsa_private
+ *
+ * \param x operand to exponentiate.
+ * \param sk RSA private key.
+ * \return 1 on success, 0 on error.
+ */
+uint32_t br_rsa_i15_private(unsigned char *x,
+ const br_rsa_private_key *sk);
+
+/**
+ * \brief RSA signature generation engine "i15".
+ *
+ * \see br_rsa_pkcs1_sign
+ *
+ * \param hash_oid encoded hash algorithm OID (or `NULL`).
+ * \param hash hash value.
+ * \param hash_len hash value length (in bytes).
+ * \param sk RSA private key.
+ * \param x output buffer for the hash value.
+ * \return 1 on success, 0 on error.
+ */
+uint32_t br_rsa_i15_pkcs1_sign(const unsigned char *hash_oid,
+ const unsigned char *hash, size_t hash_len,
+ const br_rsa_private_key *sk, unsigned char *x);
+