wip: Add initial Modular Exponentiation for bignum

Author: AnthonyGrondin

esp-mbedtls-sys/headers/esp32c3/config.h

@@ -3609,6 +3609,8 @@
 /* MPI / BIGNUM options */
 //#define MBEDTLS_MPI_WINDOW_SIZE            2 /**< Maximum window size used. */
 //#define MBEDTLS_MPI_MAX_SIZE            1024 /**< Maximum number of bytes for usable MPIs. */
+#define MBEDTLS_MPI_EXP_MOD_ALT
+// #define MBEDTLS_MPI_MUL_MPI_ALT
 
 /* CTR_DRBG options */
 //#define MBEDTLS_CTR_DRBG_ENTROPY_LEN               48 /**< Amount of entropy used per seed by default (48 with SHA-512, 32 with SHA-256) */

esp-mbedtls-sys/headers/esp32s3/config.h

@@ -3610,8 +3610,8 @@
 //#define MBEDTLS_MPI_WINDOW_SIZE            2 /**< Maximum window size used. */
 //#define MBEDTLS_MPI_MAX_SIZE            1024 /**< Maximum number of bytes for usable MPIs. */
 // #define MBEDTLS_BIGNUM_ALT
-// #define MBEDTLS_MPI_EXP_MOD_ALT
-#define MBEDTLS_MPI_MUL_MPI_ALT
+#define MBEDTLS_MPI_EXP_MOD_ALT
+// #define MBEDTLS_MPI_MUL_MPI_ALT
 
 /* CTR_DRBG options */
 //#define MBEDTLS_CTR_DRBG_ENTROPY_LEN               48 /**< Amount of entropy used per seed by default (48 with SHA-512, 32 with SHA-256) */

esp-mbedtls/Cargo.toml

@@ -13,6 +13,7 @@ esp32-hal = { version = "0.16.0", optional = true }
 esp32c3-hal = { version = "0.13.0", optional = true }
 esp32s2-hal = { version = "0.13.0", optional = true }
 esp32s3-hal = { version = "0.13.0", optional = true }
+cfg-if = "1.0.0"
 
 [features]
 async = ["dep:embedded-io-async"]