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);
+