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8a7336e0bf
This fix also allows the creation and use of an 521 bit ECDH key which used to fail while creating the binding signature.
397 lines
11 KiB
C
397 lines
11 KiB
C
/* pksign.c - public key signing (well, actually using a secret key)
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* Copyright (C) 2001, 2002, 2003, 2004, 2010 Free Software Foundation, Inc.
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*
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* This file is part of GnuPG.
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*
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* GnuPG is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) any later version.
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*
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* GnuPG is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include <config.h>
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#include <errno.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <ctype.h>
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#include <assert.h>
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#include <unistd.h>
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#include <sys/stat.h>
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#include "agent.h"
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#include "i18n.h"
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static int
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do_encode_md (const byte * md, size_t mdlen, int algo, gcry_sexp_t * r_hash,
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int raw_value)
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{
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gcry_sexp_t hash;
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int rc;
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if (!raw_value)
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{
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const char *s;
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char tmp[16+1];
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int i;
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s = gcry_md_algo_name (algo);
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if (s && strlen (s) < 16)
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{
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for (i=0; i < strlen (s); i++)
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tmp[i] = tolower (s[i]);
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tmp[i] = '\0';
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}
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rc = gcry_sexp_build (&hash, NULL,
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"(data (flags pkcs1) (hash %s %b))",
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tmp, (int)mdlen, md);
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}
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else
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{
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gcry_mpi_t mpi;
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rc = gcry_mpi_scan (&mpi, GCRYMPI_FMT_USG, md, mdlen, NULL);
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if (! rc)
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{
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rc = gcry_sexp_build (&hash, NULL,
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"(data (flags raw) (value %m))",
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mpi);
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gcry_mpi_release (mpi);
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}
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}
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*r_hash = hash;
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return rc;
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}
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/* Return the number of bits of the Q parameter from the DSA key
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KEY. */
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static unsigned int
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get_dsa_qbits (gcry_sexp_t key)
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{
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gcry_sexp_t l1, l2;
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gcry_mpi_t q;
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unsigned int nbits;
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l1 = gcry_sexp_find_token (key, "private-key", 0);
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if (!l1)
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l1 = gcry_sexp_find_token (key, "protected-private-key", 0);
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if (!l1)
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l1 = gcry_sexp_find_token (key, "shadowed-private-key", 0);
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if (!l1)
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l1 = gcry_sexp_find_token (key, "public-key", 0);
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if (!l1)
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return 0; /* Does not contain a key object. */
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l2 = gcry_sexp_cadr (l1);
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gcry_sexp_release (l1);
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l1 = gcry_sexp_find_token (l2, "q", 1);
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gcry_sexp_release (l2);
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if (!l1)
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return 0; /* Invalid object. */
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q = gcry_sexp_nth_mpi (l1, 1, GCRYMPI_FMT_USG);
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gcry_sexp_release (l1);
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if (!q)
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return 0; /* Missing value. */
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nbits = gcry_mpi_get_nbits (q);
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gcry_mpi_release (q);
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return nbits;
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}
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/* Encode a message digest for use with an DSA algorithm. */
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static gpg_error_t
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do_encode_dsa (const byte *md, size_t mdlen, int dsaalgo, gcry_sexp_t pkey,
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gcry_sexp_t *r_hash)
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{
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gpg_error_t err;
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gcry_sexp_t hash;
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unsigned int qbits;
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int pkalgo;
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*r_hash = NULL;
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pkalgo = map_pk_openpgp_to_gcry (dsaalgo);
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if (pkalgo == GCRY_PK_ECDSA)
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qbits = gcry_pk_get_nbits (pkey);
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else if (pkalgo == GCRY_PK_DSA)
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qbits = get_dsa_qbits (pkey);
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else
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return gpg_error (GPG_ERR_WRONG_PUBKEY_ALGO);
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if (pkalgo == GCRY_PK_DSA && (qbits%8))
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{
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/* FIXME: We check the QBITS but print a message about the hash
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length. */
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log_error (_("DSA requires the hash length to be a"
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" multiple of 8 bits\n"));
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return gpg_error (GPG_ERR_INV_LENGTH);
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}
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/* Don't allow any Q smaller than 160 bits. We don't want someone
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to issue signatures from a key with a 16-bit Q or something like
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that, which would look correct but allow trivial forgeries. Yes,
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I know this rules out using MD5 with DSA. ;) */
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if (qbits < 160)
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{
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log_error (_("%s key uses an unsafe (%u bit) hash\n"),
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gcry_pk_algo_name (pkalgo), qbits);
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return gpg_error (GPG_ERR_INV_LENGTH);
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}
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/* Check if we're too short. Too long is safe as we'll
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* automatically left-truncate.
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*
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* This check would require the use of SHA512 with ECDSA 512. I
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* think this is overkill to fail in this case. Therefore, relax
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* the check, but only for ECDSA keys. We may need to adjust it
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* later for general case. (Note that the check is really a bug for
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* ECDSA 521 as the only hash that matches it is SHA 512, but 512 <
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* 521 ).
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*/
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if (mdlen < ((pkalgo==GCRY_PK_ECDSA && qbits > 521) ? 512 : qbits)/8)
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{
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log_error (_("a %zu bit hash is not valid for a %u bit %s key\n"),
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mdlen*8,
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gcry_pk_get_nbits (pkey),
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gcry_pk_algo_name (pkalgo));
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/* FIXME: we need to check the requirements for ECDSA. */
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if (mdlen < 20 || pkalgo == GCRY_PK_DSA)
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return gpg_error (GPG_ERR_INV_LENGTH);
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}
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/* Truncate. */
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if (mdlen > qbits/8)
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mdlen = qbits/8;
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/* Create the S-expression. We need to convert to an MPI first
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because we want an unsigned integer. Using %b directly is not
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possible because libgcrypt assumes an mpi and uses
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GCRYMPI_FMT_STD for parsing and thus possible yielding a negative
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value. */
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{
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gcry_mpi_t mpi;
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err = gcry_mpi_scan (&mpi, GCRYMPI_FMT_USG, md, mdlen, NULL);
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if (!err)
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{
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err = gcry_sexp_build (&hash, NULL,
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"(data (flags raw) (value %m))", mpi);
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gcry_mpi_release (mpi);
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}
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}
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if (!err)
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*r_hash = hash;
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return err;
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}
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/* Special version of do_encode_md to take care of pkcs#1 padding.
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For TLS-MD5SHA1 we need to do the padding ourself as Libgrypt does
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not know about this special scheme. Fixme: We should have a
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pkcs1-only-padding flag for Libgcrypt. */
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static int
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do_encode_raw_pkcs1 (const byte *md, size_t mdlen, unsigned int nbits,
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gcry_sexp_t *r_hash)
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{
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int rc;
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gcry_sexp_t hash;
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unsigned char *frame;
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size_t i, n, nframe;
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nframe = (nbits+7) / 8;
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if ( !mdlen || mdlen + 8 + 4 > nframe )
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{
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/* Can't encode this hash into a frame of size NFRAME. */
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return gpg_error (GPG_ERR_TOO_SHORT);
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}
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frame = xtrymalloc (nframe);
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if (!frame)
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return gpg_error_from_syserror ();
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/* Assemble the pkcs#1 block type 1. */
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n = 0;
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frame[n++] = 0;
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frame[n++] = 1; /* Block type. */
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i = nframe - mdlen - 3 ;
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assert (i >= 8); /* At least 8 bytes of padding. */
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memset (frame+n, 0xff, i );
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n += i;
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frame[n++] = 0;
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memcpy (frame+n, md, mdlen );
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n += mdlen;
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assert (n == nframe);
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/* Create the S-expression. */
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rc = gcry_sexp_build (&hash, NULL,
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"(data (flags raw) (value %b))",
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(int)nframe, frame);
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xfree (frame);
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*r_hash = hash;
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return rc;
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}
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/* SIGN whatever information we have accumulated in CTRL and return
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the signature S-expression. LOOKUP is an optional function to
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provide a way for lower layers to ask for the caching TTL. If a
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CACHE_NONCE is given that cache item is first tried to get a
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passphrase. */
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int
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agent_pksign_do (ctrl_t ctrl, const char *cache_nonce,
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const char *desc_text,
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gcry_sexp_t *signature_sexp,
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cache_mode_t cache_mode, lookup_ttl_t lookup_ttl)
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{
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gcry_sexp_t s_skey = NULL, s_sig = NULL;
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unsigned char *shadow_info = NULL;
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unsigned int rc = 0; /* FIXME: gpg-error? */
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if (! ctrl->have_keygrip)
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return gpg_error (GPG_ERR_NO_SECKEY);
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rc = agent_key_from_file (ctrl, cache_nonce, desc_text, ctrl->keygrip,
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&shadow_info, cache_mode, lookup_ttl,
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&s_skey, NULL);
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if (rc)
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{
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log_error ("failed to read the secret key\n");
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goto leave;
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}
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if (!s_skey)
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{
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/* Divert operation to the smartcard */
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unsigned char *buf = NULL;
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size_t len = 0;
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rc = divert_pksign (ctrl,
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ctrl->digest.value,
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ctrl->digest.valuelen,
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ctrl->digest.algo,
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shadow_info, &buf);
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if (rc)
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{
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log_error ("smartcard signing failed: %s\n", gpg_strerror (rc));
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goto leave;
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}
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len = gcry_sexp_canon_len (buf, 0, NULL, NULL);
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assert (len);
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rc = gcry_sexp_sscan (&s_sig, NULL, (char*)buf, len);
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xfree (buf);
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if (rc)
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{
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log_error ("failed to convert sigbuf returned by divert_pksign "
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"into S-Exp: %s", gpg_strerror (rc));
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goto leave;
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}
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}
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else
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{
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/* No smartcard, but a private key */
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gcry_sexp_t s_hash = NULL;
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int dsaalgo;
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/* Put the hash into a sexp */
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if (ctrl->digest.algo == MD_USER_TLS_MD5SHA1)
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rc = do_encode_raw_pkcs1 (ctrl->digest.value,
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ctrl->digest.valuelen,
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gcry_pk_get_nbits (s_skey),
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&s_hash);
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else if ( (dsaalgo = agent_is_dsa_key (s_skey)) )
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rc = do_encode_dsa (ctrl->digest.value,
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ctrl->digest.valuelen,
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dsaalgo, s_skey,
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&s_hash);
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else
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rc = do_encode_md (ctrl->digest.value,
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ctrl->digest.valuelen,
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ctrl->digest.algo,
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&s_hash,
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ctrl->digest.raw_value);
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if (rc)
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goto leave;
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if (DBG_CRYPTO)
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{
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log_debug ("skey:\n");
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gcry_sexp_dump (s_skey);
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log_debug ("hash:\n");
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gcry_sexp_dump (s_hash);
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}
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/* sign */
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rc = gcry_pk_sign (&s_sig, s_hash, s_skey);
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gcry_sexp_release (s_hash);
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if (rc)
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{
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log_error ("signing failed: %s\n", gpg_strerror (rc));
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goto leave;
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}
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if (DBG_CRYPTO)
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{
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log_debug ("result:\n");
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gcry_sexp_dump (s_sig);
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}
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}
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leave:
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*signature_sexp = s_sig;
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gcry_sexp_release (s_skey);
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xfree (shadow_info);
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return rc;
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}
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/* SIGN whatever information we have accumulated in CTRL and write it
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back to OUTFP. If a CACHE_NONCE is given that cache item is first
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tried to get a passphrase. */
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int
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agent_pksign (ctrl_t ctrl, const char *cache_nonce, const char *desc_text,
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membuf_t *outbuf, cache_mode_t cache_mode)
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{
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gcry_sexp_t s_sig = NULL;
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char *buf = NULL;
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size_t len = 0;
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int rc = 0;
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rc = agent_pksign_do (ctrl, cache_nonce, desc_text, &s_sig, cache_mode, NULL);
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if (rc)
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goto leave;
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len = gcry_sexp_sprint (s_sig, GCRYSEXP_FMT_CANON, NULL, 0);
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assert (len);
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buf = xmalloc (len);
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len = gcry_sexp_sprint (s_sig, GCRYSEXP_FMT_CANON, buf, len);
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assert (len);
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put_membuf (outbuf, buf, len);
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leave:
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gcry_sexp_release (s_sig);
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xfree (buf);
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return rc;
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}
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