PK: declare restartable sign/verify functions

For RSA, we could either have the function return an error code like
NOT_IMPLEMENTED or just run while disregarding ecp_max_ops. IMO the second
option makes more sense, as otherwise the caller would need to check whether
the key is EC or RSA before deciding to call either sign() or
sign_restartable(), and having to do this kind of check feels contrary to the
goal of the PK layer.

include/mbedtls/pk.h

@@ -284,6 +284,33 @@ int mbedtls_pk_verify( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
                const unsigned char *hash, size_t hash_len,
                const unsigned char *sig, size_t sig_len );
 
+/**
+ * \brief           Restartable version of \c mbedtls_pk_verify()
+ *
+ * \note            Performs the same job as \c mbedtls_pk_verify(), but can
+ *                  return early and restart according to the limit set with
+ *                  \c mbedtls_ecp_set_max_ops() to reduce blocking for ECC
+ *                  operations. For RSA, same as \c mbedtls_pk_verify().
+ *
+ * \param ctx       PK context to use
+ * \param md_alg    Hash algorithm used (see notes)
+ * \param hash      Hash of the message to sign
+ * \param hash_len  Hash length or 0 (see notes)
+ * \param sig       Signature to verify
+ * \param sig_len   Signature length
+ * \param rs_ctx    Restart context: for ECC, must be NULL (no restart) or a
+ *                  pointer to a \c mbedtls_ecdsa_restart_ctx. Ignored for RSA.
+ *
+ * \return          See \c mbedtls_pk_verify(), or
+ *                  MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of
+ *                  operations was reached: see \c mbedtls_ecp_set_max_ops().
+ */
+int mbedtls_pk_verify_restartable( mbedtls_pk_context *ctx,
+               mbedtls_md_type_t md_alg,
+               const unsigned char *hash, size_t hash_len,
+               const unsigned char *sig, size_t sig_len,
+               void *rs_ctx );
+
 /**
  * \brief           Verify signature, with options.
  *                  (Includes verification of the padding depending on type.)
@@ -347,6 +374,36 @@ int mbedtls_pk_sign( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
              unsigned char *sig, size_t *sig_len,
              int (*f_rng)(void *, unsigned char *, size_t), void *p_rng );
 
+/**
+ * \brief           Restartable version of \c mbedtls_pk_sign()
+ *
+ * \note            Performs the same job as \c mbedtls_pk_sign(), but can
+ *                  return early and restart according to the limit set with
+ *                  \c mbedtls_ecp_set_max_ops() to reduce blocking for ECC
+ *                  operations. For RSA, same as \c mbedtls_pk_sign().
+ *
+ * \param ctx       PK context to use - must hold a private key
+ * \param md_alg    Hash algorithm used (see notes)
+ * \param hash      Hash of the message to sign
+ * \param hash_len  Hash length or 0 (see notes)
+ * \param sig       Place to write the signature
+ * \param sig_len   Number of bytes written
+ * \param f_rng     RNG function
+ * \param p_rng     RNG parameter
+ * \param rs_ctx    Restart context: for ECC, must be NULL (no restart) or a
+ *                  pointer to a \c mbedtls_ecdsa_restart_ctx. Ignored for RSA.
+ *
+ * \return          See \c mbedtls_pk_sign(), or
+ *                  MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of
+ *                  operations was reached: see \c mbedtls_ecp_set_max_ops().
+ */
+int mbedtls_pk_sign_restartable( mbedtls_pk_context *ctx,
+             mbedtls_md_type_t md_alg,
+             const unsigned char *hash, size_t hash_len,
+             unsigned char *sig, size_t *sig_len,
+             int (*f_rng)(void *, unsigned char *, size_t), void *p_rng,
+             void *rs_ctx );
+
 /**
  * \brief           Decrypt message (including padding if relevant).
  *

library/pk.c

@@ -176,12 +176,16 @@ static inline int pk_hashlen_helper( mbedtls_md_type_t md_alg, size_t *hash_len
 }
 
 /*
- * Verify a signature
+ * Verify a signature (restartable)
  */
-int mbedtls_pk_verify( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
+int mbedtls_pk_verify_restartable( mbedtls_pk_context *ctx,
+               mbedtls_md_type_t md_alg,
                const unsigned char *hash, size_t hash_len,
-               const unsigned char *sig, size_t sig_len )
+               const unsigned char *sig, size_t sig_len,
+               void *rs_ctx )
 {
+    (void) rs_ctx; // XXX temporary
+
     if( ctx == NULL || ctx->pk_info == NULL ||
         pk_hashlen_helper( md_alg, &hash_len ) != 0 )
         return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );
@@ -193,6 +197,17 @@ int mbedtls_pk_verify( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
                                        sig, sig_len ) );
 }
 
+/*
+ * Verify a signature
+ */
+int mbedtls_pk_verify( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
+               const unsigned char *hash, size_t hash_len,
+               const unsigned char *sig, size_t sig_len )
+{
+    return( mbedtls_pk_verify_restartable( ctx, md_alg, hash, hash_len,
+                                           sig, sig_len, NULL ) );
+}
+
 /*
  * Verify a signature with options
  */
@@ -252,13 +267,17 @@ int mbedtls_pk_verify_ext( mbedtls_pk_type_t type, const void *options,
 }
 
 /*
- * Make a signature
+ * Make a signature (restartable)
  */
-int mbedtls_pk_sign( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
+int mbedtls_pk_sign_restartable( mbedtls_pk_context *ctx,
+             mbedtls_md_type_t md_alg,
              const unsigned char *hash, size_t hash_len,
              unsigned char *sig, size_t *sig_len,
-             int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
+             int (*f_rng)(void *, unsigned char *, size_t), void *p_rng,
+             void *rs_ctx )
 {
+    (void) rs_ctx; // XXX temporary
+
     if( ctx == NULL || ctx->pk_info == NULL ||
         pk_hashlen_helper( md_alg, &hash_len ) != 0 )
         return( MBEDTLS_ERR_PK_BAD_INPUT_DATA );
@@ -270,6 +289,18 @@ int mbedtls_pk_sign( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
                                      sig, sig_len, f_rng, p_rng ) );
 }
 
+/*
+ * Make a signature
+ */
+int mbedtls_pk_sign( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
+             const unsigned char *hash, size_t hash_len,
+             unsigned char *sig, size_t *sig_len,
+             int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
+{
+    return( mbedtls_pk_sign_restartable( ctx, md_alg, hash, hash_len,
+                                         sig, sig_len, f_rng, p_rng, NULL ) );
+}
+
 /*
  * Decrypt message
  */