1 files changed, 75 insertions, 0 deletions
diff --git a/rsa-decrypt.c b/rsa-decrypt.c
new file mode 100644
index 00000000..a4cef7ad
--- /dev/null
+++ b/rsa-decrypt.c
@@ -0,0 +1,75 @@
+/* rsa_decrypt.c
+ *
+ * The RSA publickey algorithm. PKCS#1 encryption.
+ */
+
+/* nettle, low-level cryptographics library
+ *
+ * Copyright (C) 2001 Niels Möller
+ *  
+ * The nettle library is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or (at your
+ * option) any later version.
+ * 
+ * The nettle library is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
+ * License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with the nettle library; see the file COPYING.LIB.  If not, write to
+ * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA.
+ */
+
+#include "rsa.h"
+
+#include "bignum.h"
+
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+
+int
+rsa_decrypt(struct rsa_private_key *key,
+	    unsigned *length, uint8_t *message,
+	    const mpz_t gibberish)
+{
+  uint8_t *em;
+  uint8_t *terminator;
+  unsigned padding;
+  unsigned message_length;
+  
+  mpz_t m;
+
+  mpz_init(m);
+  rsa_compute_root(key, m, gibberish);
+
+  em = alloca(key->size);
+  nettle_mpz_get_str_256(key->size, em, m);
+  mpz_clear(m);
+
+  /* Check format */
+  if (em[0] || em[1] != 2)
+    return 0;
+
+  terminator = memchr(em + 2, 0, key->size - 2);
+
+  if (!terminator)
+    return 0;
+  
+  padding = terminator - (em + 2);
+  if (padding < 8)
+    return 0;
+
+  message_length = key->size - 3 - padding;
+
+  if (*length < message_length)
+    return 0;
+  
+  memcpy(message, terminator + 1, message_length);
+  *length = message_length;
+
+  return 1;
+}