Add and document an RSA-specific error code for unsupported exports
E.g., a private key on an external chip might not be exportable to RAM.
#define MBEDTLS_ERR_RSA_VERIFY_FAILED -0x4380 /**< The PKCS#1 verification failed. */
#define MBEDTLS_ERR_RSA_OUTPUT_TOO_LARGE -0x4400 /**< The output buffer for decryption is not large enough. */
#define MBEDTLS_ERR_RSA_RNG_FAILED -0x4480 /**< The random generator failed to generate non-zeros. */
+#define MBEDTLS_ERR_RSA_EXPORT_UNSUPPORTED -0x4500 /**< The requested parameter export is not possible/allowed. */
/*
* RSA constants
@@ -446,6 +447,21 @@ int mbedtls_rsa_check_crt( const mbedtls_rsa_context *ctx,
* \param E MPI to hold the public exponent, or NULL
*
* \return 0 if successful, non-zero error code otherwise.
+ * In particular, if exporting the requested parameters
+ * cannot be done because of a lack of functionality
+ * or because of security policies, the error code
+ * MBEDTLS_ERR_RSA_EXPORT_UNSUPPORTED is returned.
+ * In this case, the RSA context stays intact and can
+ * be continued to be used.
+ *
+ * \note Two reasons for returning MBEDTLS_ERR_RSA_EXPORT_UNSUPPORTED
+ * would be the following: Firstly, it might be that an
+ * alternative RSA implementation is in use which stores
+ * the key externally, and which either cannot or should not
+ * export it into RAM. Alternatively, an implementation
+ * (regardless of SW or HW) might not support deducing e.g.
+ * P, Q from N, D, E if the former are not part of the
+ * implementation.
*
*/
int mbedtls_rsa_export( const mbedtls_rsa_context *ctx,
@@ -475,6 +491,24 @@ int mbedtls_rsa_export( const mbedtls_rsa_context *ctx,
* pointed to by N, P, Q, D, E are fully written, with
* additional unused space filled leading by 0-bytes.
*
+ * \return 0 if successful, non-zero error code otherwise.
+ * In particular, if exporting the requested parameters
+ * cannot be done because of a lack of functionality
+ * or because of security policies, the error code
+ * MBEDTLS_ERR_RSA_EXPORT_UNSUPPORTED is returned.
+ * In this case, the RSA context stays intact and can
+ * be continued to be used.
+ *
+ * \note Two reasons for returning MBEDTLS_ERR_RSA_EXPORT_UNSUPPORTED
+ * would be the following: Firstly, it might be that an
+ * alternative RSA implementation is in use which stores
+ * the key externally, and which either cannot or should not
+ * export it into RAM. Alternatively, an implementation
+ * (regardless of SW or HW) might not support deducing e.g.
+ * P, Q from N, D, E if the former are not part of the
+ * implementation.
+ *
+ *
*/
int mbedtls_rsa_export_raw( const mbedtls_rsa_context *ctx,
unsigned char *N, size_t N_len,
