From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Daniel Axtens <dja@axtens.net>

Date: Thu, 1 Oct 2020 20:23:48 +1000

Subject: [PATCH] pgp: factor out rsa_pad

rsa_pad does the PKCS#1 v1.5 padding for the RSA signature scheme.

We want to use it in other RSA signature verification applications.

I considered and rejected putting it in lib/crypto.c. That file doesn't

currently require any MPI functions, but rsa_pad does. That's not so

much of a problem for the grub kernel and modules, but crypto.c also

gets built into all the grub utilities. So - despite the utils not

using any asymmetric ciphers -  we would need to built the entire MPI

infrastructure in to them.

A better and simpler solution is just to spin rsa_pad out into its own

PKCS#1 v1.5 module.

Signed-off-by: Daniel Axtens <dja@axtens.net>

---

 grub-core/Makefile.core.def |  8 ++++++

 grub-core/commands/pgp.c    | 28 ++-------------------

 grub-core/lib/pkcs1_v15.c   | 59 +++++++++++++++++++++++++++++++++++++++++++++

 include/grub/pkcs1_v15.h    | 27 +++++++++++++++++++++

 4 files changed, 96 insertions(+), 26 deletions(-)

 create mode 100644 grub-core/lib/pkcs1_v15.c

 create mode 100644 include/grub/pkcs1_v15.h

diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def

index 809f11fea..99615c07b 100644

--- a/grub-core/Makefile.core.def

+++ b/grub-core/Makefile.core.def

@@ -2387,6 +2387,14 @@ module = {

   cppflags = '$(CPPFLAGS_GCRY)';

 };

+module = {

+  name = pkcs1_v15;

+  common = lib/pkcs1_v15.c;

+

+  cflags = '$(CFLAGS_GCRY) -Wno-redundant-decls -Wno-sign-compare';

+  cppflags = '$(CPPFLAGS_GCRY)';

+};

+

 module = {

   name = all_video;

   common = lib/fake_module.c;

diff --git a/grub-core/commands/pgp.c b/grub-core/commands/pgp.c

index d39846d8c..bb6543819 100644

--- a/grub-core/commands/pgp.c

+++ b/grub-core/commands/pgp.c

@@ -24,6 +24,7 @@

 #include <grub/file.h>

 #include <grub/command.h>

 #include <grub/crypto.h>

+#include <grub/pkcs1_v15.h>

 #include <grub/i18n.h>

 #include <grub/gcrypt/gcrypt.h>

 #include <grub/pubkey.h>

@@ -411,32 +412,7 @@ static int

 rsa_pad (gcry_mpi_t *hmpi, grub_uint8_t *hval,

 	 const gcry_md_spec_t *hash, struct grub_public_subkey *sk)

 {

-  grub_size_t tlen, emlen, fflen;

-  grub_uint8_t *em, *emptr;

-  unsigned nbits = gcry_mpi_get_nbits (sk->mpis[0]);

-  int ret;

-  tlen = hash->mdlen + hash->asnlen;

-  emlen = (nbits + 7) / 8;

-  if (emlen < tlen + 11)

-    return 1;

-

-  em = grub_malloc (emlen);

-  if (!em)

-    return 1;

-

-  em[0] = 0x00;

-  em[1] = 0x01;

-  fflen = emlen - tlen - 3;

-  for (emptr = em + 2; emptr < em + 2 + fflen; emptr++)

-    *emptr = 0xff;

-  *emptr++ = 0x00;

-  grub_memcpy (emptr, hash->asnoid, hash->asnlen);

-  emptr += hash->asnlen;

-  grub_memcpy (emptr, hval, hash->mdlen);

-

-  ret = gcry_mpi_scan (hmpi, GCRYMPI_FMT_USG, em, emlen, 0);

-  grub_free (em);

-  return ret;

+  return grub_crypto_rsa_pad(hmpi, hval, hash, sk->mpis[0]);

 }

 struct grub_pubkey_context

diff --git a/grub-core/lib/pkcs1_v15.c b/grub-core/lib/pkcs1_v15.c

new file mode 100644

index 000000000..dbacd563d

--- /dev/null

+++ b/grub-core/lib/pkcs1_v15.c

@@ -0,0 +1,59 @@

+/*

+ *  GRUB  --  GRand Unified Bootloader

+ *  Copyright (C) 2013  Free Software Foundation, Inc.

+ *

+ *  GRUB is free software: you can redistribute it and/or modify

+ *  it under the terms of the GNU General Public License as published by

+ *  the Free Software Foundation, either version 3 of the License, or

+ *  (at your option) any later version.

+ *

+ *  GRUB 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 General Public License for more details.

+ *

+ *  You should have received a copy of the GNU General Public License

+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.

+ */

+

+#include <grub/dl.h>

+#include <grub/gcrypt/gcrypt.h>

+

+GRUB_MOD_LICENSE ("GPLv3+");

+

+/*

+ * Given a hash value 'hval', of hash specification 'hash', perform

+ * the EMSA-PKCS1-v1_5 padding suitable for a key with modulus 'mod'

+ * (see RFC 8017 s 9.2) and place the result in 'hmpi'.

+ */

+gcry_err_code_t

+grub_crypto_rsa_pad (gcry_mpi_t * hmpi, grub_uint8_t * hval,

+		     const gcry_md_spec_t * hash, gcry_mpi_t mod)

+{

+  grub_size_t tlen, emlen, fflen;

+  grub_uint8_t *em, *emptr;

+  unsigned nbits = gcry_mpi_get_nbits (mod);

+  int ret;

+  tlen = hash->mdlen + hash->asnlen;

+  emlen = (nbits + 7) / 8;

+  if (emlen < tlen + 11)

+    return GPG_ERR_TOO_SHORT;

+

+  em = grub_malloc (emlen);

+  if (!em)

+    return 1;

+

+  em[0] = 0x00;

+  em[1] = 0x01;

+  fflen = emlen - tlen - 3;

+  for (emptr = em + 2; emptr < em + 2 + fflen; emptr++)

+    *emptr = 0xff;

+  *emptr++ = 0x00;

+  grub_memcpy (emptr, hash->asnoid, hash->asnlen);

+  emptr += hash->asnlen;

+  grub_memcpy (emptr, hval, hash->mdlen);

+

+  ret = gcry_mpi_scan (hmpi, GCRYMPI_FMT_USG, em, emlen, 0);

+  grub_free (em);

+  return ret;

+}

diff --git a/include/grub/pkcs1_v15.h b/include/grub/pkcs1_v15.h

new file mode 100644

index 000000000..5c338c84a

--- /dev/null

+++ b/include/grub/pkcs1_v15.h

@@ -0,0 +1,27 @@

+/*

+ *  GRUB  --  GRand Unified Bootloader

+ *  Copyright (C) 2013  Free Software Foundation, Inc.

+ *

+ *  GRUB is free software: you can redistribute it and/or modify

+ *  it under the terms of the GNU General Public License as published by

+ *  the Free Software Foundation, either version 3 of the License, or

+ *  (at your option) any later version.

+ *

+ *  GRUB 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 General Public License for more details.

+ *

+ *  You should have received a copy of the GNU General Public License

+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.

+ */

+

+/*

+ * Given a hash value 'hval', of hash specification 'hash', perform

+ * the EMSA-PKCS1-v1_5 padding suitable for a key with modulus 'mod'

+ * (See RFC 8017 s 9.2)

+ */

+gcry_err_code_t

+grub_crypto_rsa_pad (gcry_mpi_t * hmpi, grub_uint8_t * hval,

+		     const gcry_md_spec_t * hash, gcry_mpi_t mod);

+