ECDSA alternative support

Support for alternative implementation of ECDSA, at the higher layer

ChangeLog

@@ -36,6 +36,10 @@ Changes
    * Clarify ECDSA documentation and improve the sample code to avoid
      misunderstandings and potentially dangerous use of the API. Pointed out
      by Jean-Philippe Aumasson.
+   * Add support for alternative implementation for ECDSA, controlled by new
+     configuration flag MBEDTLS_ECDSA_ALT in config.h.
+     Alternative Ecdsa is supported for implementation of `mbedtls_ecdsa_sign`
+     and `mbedtls_ecdsa_verify`.
 
 = mbed TLS 2.5.0 branch released 2017-05-17
 

include/mbedtls/config.h

@@ -238,6 +238,7 @@
 //#define MBEDTLS_BLOWFISH_ALT
 //#define MBEDTLS_CAMELLIA_ALT
 //#define MBEDTLS_DES_ALT
+//#define MBEDTLS_ECDSA_ALT
 //#define MBEDTLS_XTEA_ALT
 //#define MBEDTLS_MD2_ALT
 //#define MBEDTLS_MD4_ALT

library/ecdsa.c

@@ -37,11 +37,10 @@
 #include "mbedtls/asn1write.h"
 
 #include <string.h>
-
+#include "mbedtls/platform.h"
 #if defined(MBEDTLS_ECDSA_DETERMINISTIC)
 #include "mbedtls/hmac_drbg.h"
 #endif
-
 /*
  * Derive a suitable integer for group grp from a buffer of length len
  * SEC1 4.1.3 step 5 aka SEC1 4.1.4 step 3
@@ -65,6 +64,8 @@ cleanup:
     return( ret );
 }
 
+#if !defined(MBEDTLS_ECDSA_ALT)
+
 /*
  * Compute ECDSA signature of a hashed message (SEC1 4.1.3)
  * Obviously, compared to SEC1 4.1.3, we skip step 4 (hash message)
@@ -154,43 +155,6 @@ cleanup:
     return( ret );
 }
 
-#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
-/*
- * Deterministic signature wrapper
- */
-int mbedtls_ecdsa_sign_det( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
-                    const mbedtls_mpi *d, const unsigned char *buf, size_t blen,
-                    mbedtls_md_type_t md_alg )
-{
-    int ret;
-    mbedtls_hmac_drbg_context rng_ctx;
-    unsigned char data[2 * MBEDTLS_ECP_MAX_BYTES];
-    size_t grp_len = ( grp->nbits + 7 ) / 8;
-    const mbedtls_md_info_t *md_info;
-    mbedtls_mpi h;
-
-    if( ( md_info = mbedtls_md_info_from_type( md_alg ) ) == NULL )
-        return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
-
-    mbedtls_mpi_init( &h );
-    mbedtls_hmac_drbg_init( &rng_ctx );
-
-    /* Use private key and message hash (reduced) to initialize HMAC_DRBG */
-    MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( d, data, grp_len ) );
-    MBEDTLS_MPI_CHK( derive_mpi( grp, &h, buf, blen ) );
-    MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &h, data + grp_len, grp_len ) );
-    mbedtls_hmac_drbg_seed_buf( &rng_ctx, md_info, data, 2 * grp_len );
-
-    ret = mbedtls_ecdsa_sign( grp, r, s, d, buf, blen,
-                      mbedtls_hmac_drbg_random, &rng_ctx );
-
-cleanup:
-    mbedtls_hmac_drbg_free( &rng_ctx );
-    mbedtls_mpi_free( &h );
-
-    return( ret );
-}
-#endif /* MBEDTLS_ECDSA_DETERMINISTIC */
 
 /*
  * Verify ECDSA signature of hashed message (SEC1 4.1.4)
@@ -278,6 +242,56 @@ cleanup:
     return( ret );
 }
 
+/*
+ * Generate key pair
+ */
+int mbedtls_ecdsa_genkey( mbedtls_ecdsa_context *ctx, mbedtls_ecp_group_id gid,
+                  int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
+{
+    return( mbedtls_ecp_group_load( &ctx->grp, gid ) ||
+            mbedtls_ecp_gen_keypair( &ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng ) );
+}
+
+#endif /* MBEDTLS_ECDSA_ALT */
+
+#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
+/*
+ * Deterministic signature wrapper
+ */
+int mbedtls_ecdsa_sign_det( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
+                    const mbedtls_mpi *d, const unsigned char *buf, size_t blen,
+                    mbedtls_md_type_t md_alg )
+{
+    int ret;
+    mbedtls_hmac_drbg_context rng_ctx;
+    unsigned char data[2 * MBEDTLS_ECP_MAX_BYTES];
+    size_t grp_len = ( grp->nbits + 7 ) / 8;
+    const mbedtls_md_info_t *md_info;
+    mbedtls_mpi h;
+
+    if( ( md_info = mbedtls_md_info_from_type( md_alg ) ) == NULL )
+        return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
+
+    mbedtls_mpi_init( &h );
+    mbedtls_hmac_drbg_init( &rng_ctx );
+
+    /* Use private key and message hash (reduced) to initialize HMAC_DRBG */
+    MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( d, data, grp_len ) );
+    MBEDTLS_MPI_CHK( derive_mpi( grp, &h, buf, blen ) );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &h, data + grp_len, grp_len ) );
+    mbedtls_hmac_drbg_seed_buf( &rng_ctx, md_info, data, 2 * grp_len );
+
+    ret = mbedtls_ecdsa_sign( grp, r, s, d, buf, blen,
+                      mbedtls_hmac_drbg_random, &rng_ctx );
+
+cleanup:
+    mbedtls_hmac_drbg_free( &rng_ctx );
+    mbedtls_mpi_free( &h );
+
+    return( ret );
+}
+#endif /* MBEDTLS_ECDSA_DETERMINISTIC */
+
 /*
  * Convert a signature (given by context) to ASN.1
  */
@@ -301,7 +315,6 @@ static int ecdsa_signature_to_asn1( const mbedtls_mpi *r, const mbedtls_mpi *s,
 
     return( 0 );
 }
-
 /*
  * Compute and write signature
  */
@@ -402,16 +415,6 @@ cleanup:
     return( ret );
 }
 
-/*
- * Generate key pair
- */
-int mbedtls_ecdsa_genkey( mbedtls_ecdsa_context *ctx, mbedtls_ecp_group_id gid,
-                  int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
-{
-    return( mbedtls_ecp_group_load( &ctx->grp, gid ) ||
-            mbedtls_ecp_gen_keypair( &ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng ) );
-}
-
 /*
  * Set context from an mbedtls_ecp_keypair
  */

library/version_features.c

@@ -93,6 +93,9 @@ static const char *features[] = {
 #if defined(MBEDTLS_DES_ALT)
     "MBEDTLS_DES_ALT",
 #endif /* MBEDTLS_DES_ALT */
+#if defined(MBEDTLS_ECDSA_ALT)
+    "MBEDTLS_ECDSA_ALT",
+#endif /* MBEDTLS_ECDSA_ALT */
 #if defined(MBEDTLS_XTEA_ALT)
     "MBEDTLS_XTEA_ALT",
 #endif /* MBEDTLS_XTEA_ALT */