Manuel Pégourié-Gonnard 7b7808cc76 Add tests for ECDSA verify with short r, s values
This is intended to test transcoding the signature to the format expected by
PSA (fixed-length encoding of r, s) when r and s have respectively:
- full length with initial null byte
- full length without initial null byte
- non-full length with initial null byte
- non-full length without initial null byte

The signatures were generated using:

programs/pkey/pk_sign tests/data_files/server5.key foo

where foo is an empty file, and with a variant of one of the following patches
applied:

diff --git a/library/ecdsa.c b/library/ecdsa.c
index abac015cebc6..e4a27b044516 100644
--- a/library/ecdsa.c
+++ b/library/ecdsa.c
@@ -305,7 +305,9 @@ static int ecdsa_sign_restartable( mbedtls_ecp_group *grp,
                 ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
                 goto cleanup;
             }
+            printf("\ngenerating r...\n");

+gen:
             MBEDTLS_MPI_CHK( mbedtls_ecp_gen_privkey( grp, pk, f_rng, p_rng ) );

 #if defined(MBEDTLS_ECP_RESTARTABLE)
@@ -317,6 +319,11 @@ mul:
             MBEDTLS_MPI_CHK( mbedtls_ecp_mul_restartable( grp, &R, pk, &grp->G,
                                                   f_rng, p_rng, ECDSA_RS_ECP ) );
             MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( pr, &R.X, &grp->N ) );
+
+            size_t bits = mbedtls_mpi_bitlen( pr );
+            printf("%zu ", bits);
+            if( bits != 255 )
+                goto gen;
         }
         while( mbedtls_mpi_cmp_int( pr, 0 ) == 0 );

or:

diff --git a/library/ecdsa.c b/library/ecdsa.c
index abac015cebc6..d704376e0c42 100644
--- a/library/ecdsa.c
+++ b/library/ecdsa.c
@@ -305,7 +305,9 @@ static int ecdsa_sign_restartable( mbedtls_ecp_group *grp,
                 ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
                 goto cleanup;
             }
+            printf("\ngenerating r...\n");

+gen:
             MBEDTLS_MPI_CHK( mbedtls_ecp_gen_privkey( grp, pk, f_rng, p_rng ) );

 #if defined(MBEDTLS_ECP_RESTARTABLE)
@@ -353,6 +355,11 @@ modn:
         MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( s, pk, &grp->N ) );
         MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( s, s, &e ) );
         MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( s, s, &grp->N ) );
+
+            size_t bits = mbedtls_mpi_bitlen( s );
+            printf("%zu ", bits);
+            if( bits != 247 )
+                goto gen;
     }
     while( mbedtls_mpi_cmp_int( s, 0 ) == 0 );

with the value edited manually between each run to get the desired bit length.
2018-11-22 13:37:14 -05:00
..