Add some convenience/helper functions for RSA.

src/platform/vboot_reference/crypto/rsa_utility.c

+/* Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * Utility functions for message digest functions.
+ */
+
+#include "padding.h"
+#include "rsa_utility.h"
+#include "utility.h"
+
+int RSAProcessedKeySize(int algorithm) {
+  int key_len = siglen_map[algorithm] * sizeof(uint32_t);  /* Key length in
+                                                            * bytes. */
+  /* Total size needed by a RSAPublicKey structure is =
+   *  2 * key_len bytes for the  n and rr arrays
+   *  + sizeof len + sizeof n0inv.
+   */
+  return (2 * key_len + sizeof(int) + sizeof(uint32_t));
+}
+
+RSAPublicKey* RSAPublicKeyFromBuf(uint8_t* buf, int len) {
+  RSAPublicKey* key = (RSAPublicKey*) Malloc(sizeof(RSAPublicKey));
+  MemcpyState st;
+  int key_len;
+
+  st.remaining_buf = buf;
+  st.remaining_len = len;
+
+  StatefulMemcpy(&st, &key->len, sizeof(key->len));
+  key_len = key->len * sizeof(uint32_t);  /* key length in bytes. */
+  key->n = (uint32_t*) Malloc(key_len);
+  key->rr = (uint32_t*) Malloc(key_len);
+
+  StatefulMemcpy(&st, &key->n0inv, sizeof(key->n0inv));
+  StatefulMemcpy(&st, key->n, key_len);
+  StatefulMemcpy(&st, key->rr, key_len);
+  if (st.remaining_len != 0) {  /* Underrun or overrun. */
+    Free(key->n);
+    Free(key->rr);
+    Free(key);
+    return NULL;
+  }
+
+  return key;
+}