New function pkcs1_decrypt, use in rsa_decrypt.

ChangeLog

+2012-04-09  Niels Möller  <nisse@lysator.liu.se>
+
+	* Makefile.in (hogweed_SOURCES): Added pkcs1-decrypt.c.
+	* rsa-decrypt.c (rsa_decrypt): Use pkcs1_decrypt.
+	* pkcs1-decrypt.c (pkcs1_decrypt): New file and function,
+	extracted from rsa_decrypt.
+
 2012-04-01  Niels Möller  <nisse@lysator.liu.se>
 
 	* salsa20.c (LE_SWAP32): Typo fix for big-endian case.

Makefile.in

@@ -99,7 +99,7 @@ hogweed_SOURCES = sexp.c sexp-format.c \
 		  bignum.c bignum-next-prime.c \
 		  bignum-random.c bignum-random-prime.c \
 		  sexp2bignum.c \
-		  pkcs1.c pkcs1-rsa-md5.c pkcs1-rsa-sha1.c \
+		  pkcs1.c pkcs1-decrypt.c pkcs1-rsa-md5.c pkcs1-rsa-sha1.c \
 		  pkcs1-rsa-sha256.c pkcs1-rsa-sha512.c \
 		  rsa.c rsa-sign.c rsa-verify.c \
 		  rsa-md5-sign.c rsa-md5-verify.c \

pkcs1-decrypt.c

+/* pkcs1-decrypt.c
+ *
+ */
+
+/* nettle, low-level cryptographics library
+ *
+ * Copyright (C) 2001, 2012 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.
+ */
+
+#if HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <string.h>
+
+#include "pkcs1.h"
+
+#include "bignum.h"
+#include "nettle-internal.h"
+
+int
+pkcs1_decrypt (unsigned key_size,
+	       const mpz_t m,
+	       unsigned *length, uint8_t *message)
+{
+  TMP_DECL(em, uint8_t, NETTLE_MAX_BIGNUM_BITS / 8);
+  uint8_t *terminator;
+  unsigned padding;
+  unsigned message_length;
+  
+  TMP_ALLOC(em, key_size);
+  nettle_mpz_get_str_256(key_size, em, 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;
+}
+	       

pkcs1.h

@@ -43,6 +43,7 @@ extern "C" {
 #define pkcs1_rsa_sha256_encode_digest nettle_pkcs1_rsa_sha256_encode_digest
 #define pkcs1_rsa_sha512_encode nettle_pkcs1_rsa_sha512_encode
 #define pkcs1_rsa_sha512_encode_digest nettle_pkcs1_rsa_sha512_encode_digest
+#define pkcs1_decrypt nettle_pkcs1_decrypt
 
 struct md5_ctx;
 struct sha1_ctx;
@@ -56,6 +57,11 @@ pkcs1_signature_prefix(unsigned size,
 		       const uint8_t *id,
 		       unsigned digest_size);
 
+int
+pkcs1_decrypt (unsigned key_size,
+	       const mpz_t m,
+	       unsigned *length, uint8_t *message);
+
 int
 pkcs1_rsa_md5_encode(mpz_t m, unsigned length, struct md5_ctx *hash);
 

rsa-decrypt.c

-/* rsa_decrypt.c
+/* rsa-decrypt.c
  *
  * The RSA publickey algorithm. PKCS#1 encryption.
  */
 
 /* nettle, low-level cryptographics library
  *
- * Copyright (C) 2001 Niels Möller
+ * Copyright (C) 2001, 2012 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
@@ -27,54 +27,22 @@
 # include "config.h"
 #endif
 
-#include <assert.h>
-#include <stdlib.h>
-#include <string.h>
-
 #include "rsa.h"
 
-#include "bignum.h"
-#include "nettle-internal.h"
+#include "pkcs1.h"
 
 int
 rsa_decrypt(const struct rsa_private_key *key,
 	    unsigned *length, uint8_t *message,
 	    const mpz_t gibberish)
 {
-  TMP_DECL(em, uint8_t, NETTLE_MAX_BIGNUM_BITS / 8);
-  uint8_t *terminator;
-  unsigned padding;
-  unsigned message_length;
-  
   mpz_t m;
+  int res;
 
   mpz_init(m);
   rsa_compute_root(key, m, gibberish);
 
-  TMP_ALLOC(em, key->size);
-  nettle_mpz_get_str_256(key->size, em, m);
+  res = pkcs1_decrypt (key->size, m, length, message);
   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;
+  return res;
 }