From c80555d8359c736e01f9bd24ce37d4704f11950b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Manuel=20P=C3=A9gouri=C3=A9-Gonnard?=
 <manuel.pegourie-gonnard@arm.com>
Date: Thu, 20 Apr 2017 15:37:46 +0200
Subject: [PATCH] Add public function generating private keys

We need to separate the uses of the RNG for blinding and for key
generation for the sake of an upcoming security fix in deterministic
ECDSA.
---
 include/mbedtls/ecp.h | 16 ++++++++++++++++
 library/ecp.c         | 34 +++++++++++++++++++++++-----------
 2 files changed, 39 insertions(+), 11 deletions(-)

diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index 7b8ffff44..9c6db1952 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -595,6 +595,22 @@ int mbedtls_ecp_check_pubkey( const mbedtls_ecp_group *grp, const mbedtls_ecp_po
  */
 int mbedtls_ecp_check_privkey( const mbedtls_ecp_group *grp, const mbedtls_mpi *d );
 
+/**
+ * \brief           Generate a private key
+ *
+ * \param grp       ECP group
+ * \param d         Destination MPI (secret part)
+ * \param f_rng     RNG function
+ * \param p_rng     RNG parameter
+ *
+ * \return          0 if successful,
+ *                  or a MBEDTLS_ERR_ECP_XXX or MBEDTLS_MPI_XXX error code
+ */
+int mbedtls_ecp_gen_privkey( const mbedtls_ecp_group *grp,
+                     mbedtls_mpi *d,
+                     int (*f_rng)(void *, unsigned char *, size_t),
+                     void *p_rng );
+
 /**
  * \brief           Generate a keypair with configurable base point
  *
diff --git a/library/ecp.c b/library/ecp.c
index 75233f8ce..cb8e947db 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -1918,15 +1918,14 @@ int mbedtls_ecp_check_privkey( const mbedtls_ecp_group *grp, const mbedtls_mpi *
 }
 
 /*
- * Generate a keypair with configurable base point
+ * Generate a private key
  */
-int mbedtls_ecp_gen_keypair_base( mbedtls_ecp_group *grp,
-                     const mbedtls_ecp_point *G,
-                     mbedtls_mpi *d, mbedtls_ecp_point *Q,
+int mbedtls_ecp_gen_privkey( const mbedtls_ecp_group *grp,
+                     mbedtls_mpi *d,
                      int (*f_rng)(void *, unsigned char *, size_t),
                      void *p_rng )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
     size_t n_size = ( grp->nbits + 7 ) / 8;
 
 #if defined(ECP_MONTGOMERY)
@@ -1951,8 +1950,8 @@ int mbedtls_ecp_gen_keypair_base( mbedtls_ecp_group *grp,
         MBEDTLS_MPI_CHK( mbedtls_mpi_set_bit( d, 1, 0 ) );
         MBEDTLS_MPI_CHK( mbedtls_mpi_set_bit( d, 2, 0 ) );
     }
-    else
 #endif /* ECP_MONTGOMERY */
+
 #if defined(ECP_SHORTWEIERSTRASS)
     if( ecp_get_type( grp ) == ECP_TYPE_SHORT_WEIERSTRASS )
     {
@@ -1986,15 +1985,28 @@ int mbedtls_ecp_gen_keypair_base( mbedtls_ecp_group *grp,
         while( mbedtls_mpi_cmp_int( d, 1 ) < 0 ||
                mbedtls_mpi_cmp_mpi( d, &grp->N ) >= 0 );
     }
-    else
 #endif /* ECP_SHORTWEIERSTRASS */
-        return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );
 
 cleanup:
-    if( ret != 0 )
-        return( ret );
+    return( ret );
+}
 
-    return( mbedtls_ecp_mul( grp, Q, d, G, f_rng, p_rng ) );
+/*
+ * Generate a keypair with configurable base point
+ */
+int mbedtls_ecp_gen_keypair_base( mbedtls_ecp_group *grp,
+                     const mbedtls_ecp_point *G,
+                     mbedtls_mpi *d, mbedtls_ecp_point *Q,
+                     int (*f_rng)(void *, unsigned char *, size_t),
+                     void *p_rng )
+{
+    int ret;
+
+    MBEDTLS_MPI_CHK( mbedtls_ecp_gen_privkey( grp, d, f_rng, p_rng ) );
+    MBEDTLS_MPI_CHK( mbedtls_ecp_mul( grp, Q, d, G, f_rng, p_rng ) );
+
+cleanup:
+    return( ret );
 }
 
 /*