Add ECDSA sign primitive
diff --git a/library/ecdsa.c b/library/ecdsa.c
index 09d14f9..a8f29c1 100644
--- a/library/ecdsa.c
+++ b/library/ecdsa.c
@@ -35,6 +35,67 @@
#include "polarssl/ecdsa.h"
+/*
+ * Compute ECDSA signature of a hashed message (SEC1 4.1.3)
+ * Obviously, compared to SEC1 4.1.3, we skip step 4 (hash message)
+ */
+int ecdsa_sign( const ecp_group *grp, mpi *r, mpi *s,
+ const mpi *d, const unsigned char *buf, size_t blen,
+ int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
+{
+ int ret, key_tries, sign_tries;
+ size_t n_size;
+ ecp_point R;
+ mpi k, e;
+
+ ecp_point_init( &R );
+ mpi_init( &k );
+ mpi_init( &e );
+
+ sign_tries = 0;
+ do
+ {
+ /*
+ * Steps 1-3: generate a suitable ephemeral keypair
+ */
+ key_tries = 0;
+ do
+ {
+ MPI_CHK( ecp_gen_keypair( grp, &k, &R, f_rng, p_rng ) );
+ MPI_CHK( mpi_copy( r, &R.X ) );
+
+ if( key_tries++ > 10 )
+ return( POLARSSL_ERR_ECP_GENERIC );
+ }
+ while( mpi_cmp_int( r, 0 ) == 0 );
+
+ /*
+ * Step 5: derive MPI from hashed message
+ */
+ n_size = (grp->nbits + 7) / 8;
+ MPI_CHK( mpi_read_binary( &e, buf, blen > n_size ? n_size : blen ) );
+
+ /*
+ * Step 6: compute s = (e + r * d) / k mod n
+ */
+ MPI_CHK( mpi_mul_mpi( s, r, d ) );
+ MPI_CHK( mpi_add_mpi( &e, &e, s ) );
+ MPI_CHK( mpi_inv_mod( s, &k, &grp->N ) );
+ MPI_CHK( mpi_mul_mpi( s, s, &e ) );
+ MPI_CHK( mpi_mod_mpi( s, s, &grp->N ) );
+
+ if( sign_tries++ > 10 )
+ return( POLARSSL_ERR_ECP_GENERIC );
+ }
+ while( mpi_cmp_int( s, 0 ) == 0 );
+
+cleanup:
+ ecp_point_free( &R );
+ mpi_free( &k );
+ mpi_free( &e );
+
+ return( ret );
+}
#if defined(POLARSSL_SELF_TEST)