hashsum.1: Fix counting error (left over from some previous edit).

[u/mdw/catacomb] / cc-sig.c

/* -*-c-*-
 *
 * $Id$
 *
 * Catcrypt signatures
 *
 * (c) 2004 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of Catacomb.
 *
 * Catacomb is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * Catacomb 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 Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with Catacomb; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Header files ------------------------------------------------------*/

#include <stdlib.h>

#include <mLib/report.h>

#include "rand.h"
#include "sha.h"
#include "has160.h"

#include "ec.h"
#include "ec-keys.h"
#include "dh.h"
#include "gdsa.h"
#include "gkcdsa.h"
#include "rsa.h"

#include "cc.h"

/*----- Main code ---------------------------------------------------------*/

/* --- RSA PKCS1 --- */

typedef struct rsap1_sigctx {
  sig s;
  rsa_privctx rp;
  pkcs1 p1;
} rsap1_sigctx;

static sig *rsap1_siginit(key *k, void *kd, const gchash *hc)
{
  rsap1_sigctx *rs = CREATE(rsap1_sigctx);
  rsa_privcreate(&rs->rp, kd, &rand_global);
  rs->p1.r = &rand_global;
  rs->p1.ep = hc->name;
  rs->p1.epsz = strlen(hc->name) + 1;
  rs->s.h = 0;
  return (&rs->s);
}

static int rsap1_sigdoit(sig *s, dstr *d)
{
  rsap1_sigctx *rs = (rsap1_sigctx *)s;
  size_t n;
  mp *m = rsa_sign(&rs->rp, MP_NEW,
		   GH_DONE(s->h, 0), GH_CLASS(s->h)->hashsz,
		   pkcs1_sigencode, &rs->p1);
  if (!m) return (-1);
  n = mp_octets(rs->rp.rp->n); dstr_ensure(d, n); mp_storeb(m, d->buf, n);
  d->len += n; mp_drop(m);
  return (0);
}

static const char *rsa_lengthcheck(mp *n)
{
  if (mp_bits(n) < 1024) return ("key too short");
  return (0);
}

static const char *rsap1_sigcheck(sig *s)
{
  rsap1_sigctx *rs = (rsap1_sigctx *)s;
  const char *e;
  if ((e = rsa_lengthcheck(rs->rp.rp->n)) != 0) return (e);
  return (0);
}

static void rsap1_sigdestroy(sig *s)
{
  rsap1_sigctx *rs = (rsap1_sigctx *)s;
  rsa_privdestroy(&rs->rp);
  DESTROY(rs);
}

static const sigops rsap1_sig = {
  rsa_privfetch, sizeof(rsa_priv),
  rsap1_siginit, rsap1_sigdoit, rsap1_sigcheck, rsap1_sigdestroy
};

typedef struct rsap1_vrfctx {
  sig s;
  rsa_pubctx rp;
  pkcs1 p1;
} rsap1_vrfctx;

static sig *rsap1_vrfinit(key *k, void *kd, const gchash *hc)
{
  rsap1_vrfctx *rv = CREATE(rsap1_vrfctx);
  rsa_pubcreate(&rv->rp, kd);
  rv->p1.r = &rand_global;
  rv->p1.ep = hc->name;
  rv->p1.epsz = strlen(hc->name) + 1;
  rv->s.h = 0;
  return (&rv->s);
}

static int rsap1_vrfdoit(sig *s, dstr *d)
{
  rsap1_vrfctx *rv = (rsap1_vrfctx *)s;
  mp *m = mp_loadb(MP_NEW, d->buf, d->len);
  int rc = rsa_verify(&rv->rp, m,
		      GH_DONE(s->h, 0), GH_CLASS(s->h)->hashsz,
		      0, pkcs1_sigdecode, &rv->p1);
  mp_drop(m);
  return (rc);
}

static const char *rsap1_vrfcheck(sig *s)
{
  rsap1_vrfctx *rv = (rsap1_vrfctx *)s;
  const char *e;
  if ((e = rsa_lengthcheck(rv->rp.rp->n)) != 0) return (e);
  return (0);
}

static void rsap1_vrfdestroy(sig *s)
{
  rsap1_vrfctx *rv = (rsap1_vrfctx *)s;
  rsa_pubdestroy(&rv->rp);
  DESTROY(rv);
}

static const sigops rsap1_vrf = {
  rsa_pubfetch, sizeof(rsa_pub),
  rsap1_vrfinit, rsap1_vrfdoit, rsap1_vrfcheck, rsap1_vrfdestroy
};

/* --- RSA PSS --- */

static const gccipher *getmgf(key *k, const gchash *hc)
{
  dstr d = DSTR_INIT;
  const gccipher *gc;
  const char *mm;

  if ((mm = key_getattr(0, k, "mgf")) == 0) {
    dstr_putf(&d, "%s-mgf", hc->name);
    mm = d.buf;
  }
  if ((gc = gcipher_byname(mm)) == 0)
    die(EXIT_FAILURE, "unknown encryption scheme `%s'", mm);
  dstr_destroy(&d);
  return (gc);
}

typedef struct rsapss_sigctx {
  sig s;
  rsa_privctx rp;
  pss p;
} rsapss_sigctx;

static sig *rsapss_siginit(key *k, void *kd, const gchash *hc)
{
  rsapss_sigctx *rs = CREATE(rsapss_sigctx);
  rsa_privcreate(&rs->rp, kd, &rand_global);
  rs->p.r = &rand_global;
  rs->p.cc = getmgf(k, hc);
  rs->p.ch = hc;
  rs->p.ssz = hc->hashsz;
  rsa_privdestroy(&rs->rp);
  return (&rs->s);
}

static int rsapss_sigdoit(sig *s, dstr *d)
{
  rsapss_sigctx *rs = (rsapss_sigctx *)s;
  size_t n;
  mp *m = rsa_sign(&rs->rp, MP_NEW,
		   GH_DONE(s->h, 0), GH_CLASS(s->h)->hashsz,
		   pss_encode, &rs->p);
  if (!m) return (-1);
  n = mp_octets(rs->rp.rp->n); dstr_ensure(d, n); mp_storeb(m, d->buf, n);
  d->len += n;	mp_drop(m);
  return (0);
}

static const char *rsapss_sigcheck(sig *s)
{
  rsapss_sigctx *rs = (rsapss_sigctx *)s;
  const char *e;
  if ((e = rsa_lengthcheck(rs->rp.rp->n)) != 0) return (e);
  return (0);
}

static void rsapss_sigdestroy(sig *s)
{
  rsapss_sigctx *rs = (rsapss_sigctx *)s;
  rsa_privdestroy(&rs->rp);
  DESTROY(rs);
}

static const sigops rsapss_sig = {
  rsa_privfetch, sizeof(rsa_priv),
  rsapss_siginit, rsapss_sigdoit, rsapss_sigcheck, rsapss_sigdestroy
};

typedef struct rsapss_vrfctx {
  sig s;
  rsa_pubctx rp;
  pss p;
} rsapss_vrfctx;

static sig *rsapss_vrfinit(key *k, void *kd, const gchash *hc)
{
  rsapss_vrfctx *rv = CREATE(rsapss_vrfctx);
  rsa_pubcreate(&rv->rp, kd);
  rv->p.r = &rand_global;
  rv->p.cc = getmgf(k, hc);
  rv->p.ch = hc;
  rv->p.ssz = hc->hashsz;
  return (&rv->s);
}

static int rsapss_vrfdoit(sig *s, dstr *d)
{
  rsapss_vrfctx *rv = (rsapss_vrfctx *)s;
  mp *m = mp_loadb(MP_NEW, d->buf, d->len);
  int rc = rsa_verify(&rv->rp, m,
		      GH_DONE(s->h, 0), GH_CLASS(s->h)->hashsz,
		      0, pss_decode, &rv->p);
  mp_drop(m);
  return (rc);
}

static const char *rsapss_vrfcheck(sig *s)
{
  rsapss_vrfctx *rv = (rsapss_vrfctx *)s;
  const char *e;
  if ((e = rsa_lengthcheck(rv->rp.rp->n)) != 0) return (e);
  return (0);
}

static void rsapss_vrfdestroy(sig *s)
{
  rsapss_vrfctx *rv = (rsapss_vrfctx *)s;
  rsa_pubdestroy(&rv->rp);
  DESTROY(rv);
}

static const sigops rsapss_vrf = {
  rsa_pubfetch, sizeof(rsa_pub),
  rsapss_vrfinit, rsapss_vrfdoit, rsapss_vrfcheck, rsapss_vrfdestroy
};

/* --- DSA and ECDSA --- */

typedef struct dsa_sigctx {
  sig s;
  gdsa g;
} dsa_sigctx;

static void dsa_initcommon(dsa_sigctx *ds, const gchash *hc,
			   const char *ktag)
{
  ds->g.r = &rand_global;
  ds->g.h = hc;
  ds->g.u = MP_NEW;
  ds->s.h = 0;
}

static dsa_sigctx *dsa_doinit(key *k, const gprime_param *gp,
			      mp *y, const gchash *hc,
			      group *(*makegroup)(const gprime_param *),
			      const char *what)
{
  dsa_sigctx *ds = CREATE(dsa_sigctx);
  dstr t = DSTR_INIT;

  key_fulltag(k, &t);
  if ((ds->g.g = makegroup(gp)) == 0)
    die(EXIT_FAILURE, "bad %s group in key `%s'", what, t.buf);
  ds->g.p = G_CREATE(ds->g.g);
  if (G_FROMINT(ds->g.g, ds->g.p, y))
    die(EXIT_FAILURE, "bad public key in key `%s'", t.buf);
  dsa_initcommon(ds, hc, t.buf);
  dstr_destroy(&t);
  return (ds);
}

static dsa_sigctx *ecdsa_doinit(key *k, const char *cstr,
				ec *y, const gchash *hc)
{
  dsa_sigctx *ds = CREATE(dsa_sigctx);
  ec_info ei;
  const char *e;
  dstr t = DSTR_INIT;

  key_fulltag(k, &t);
  if ((e = ec_getinfo(&ei, cstr)) != 0)
    die(EXIT_FAILURE, "bad curve in key `%s': %s", t.buf, e);
  ds->g.g = group_ec(&ei);
  ds->g.p = G_CREATE(ds->g.g);
  if (G_FROMEC(ds->g.g, ds->g.p, y))
    die(EXIT_FAILURE, "bad public key in key `%s'", t.buf);
  dsa_initcommon(ds, hc, t.buf);
  dstr_destroy(&t);
  return (ds);
}

static sig *dsa_siginit(key *k, void *kd, const gchash *hc)
{
  dh_priv *dp = kd;
  dsa_sigctx *ds = dsa_doinit(k, &dp->dp, dp->y, hc, group_prime, "prime");
  ds->g.u = MP_COPY(dp->x);
  return (&ds->s);
}

static sig *bindsa_siginit(key *k, void *kd, const gchash *hc)
{
  dh_priv *dp = kd;
  dsa_sigctx *ds = dsa_doinit(k, &dp->dp, dp->y, hc, group_binary, "binary");
  ds->g.u = MP_COPY(dp->x);
  return (&ds->s);
}

static sig *ecdsa_siginit(key *k, void *kd, const gchash *hc)
{
  ec_priv *ep = kd;
  dsa_sigctx *ds = ecdsa_doinit(k, ep->cstr, &ep->p, hc);
  ds->g.u = MP_COPY(ep->x);
  return (&ds->s);
}

static int dsa_sigdoit(sig *s, dstr *d)
{
  dsa_sigctx *ds = (dsa_sigctx *)s;
  gdsa_sig ss = GDSA_SIG_INIT;
  size_t n = mp_octets(ds->g.g->r);

  gdsa_sign(&ds->g, &ss, GH_DONE(ds->s.h, 0), 0);
  dstr_ensure(d, 2 * n);
  mp_storeb(ss.r, d->buf, n);
  mp_storeb(ss.s, d->buf + n, n);
  d->len += 2 * n;
  mp_drop(ss.r); mp_drop(ss.s);
  return (0);
}

static const char *dsa_sigcheck(sig *s)
{
  dsa_sigctx *ds = (dsa_sigctx *)s;
  const char *e;
  if ((e = G_CHECK(ds->g.g, &rand_global)) != 0)
    return (0);
  if (group_check(ds->g.g, ds->g.p))
    return ("public key not in subgroup");
  return (0);
}

static void dsa_sigdestroy(sig *s)
{
  dsa_sigctx *ds = (dsa_sigctx *)s;
  G_DESTROY(ds->g.g, ds->g.p);
  mp_drop(ds->g.u);
  G_DESTROYGROUP(ds->g.g);
  DESTROY(ds);
}

static const sigops dsa_sig = {
  dh_privfetch, sizeof(dh_priv),
  dsa_siginit, dsa_sigdoit, dsa_sigcheck, dsa_sigdestroy
};

static const sigops bindsa_sig = {
  dh_privfetch, sizeof(dh_priv),
  bindsa_siginit, dsa_sigdoit, dsa_sigcheck, dsa_sigdestroy
};

static const sigops ecdsa_sig = {
  ec_privfetch, sizeof(ec_priv),
  ecdsa_siginit, dsa_sigdoit, dsa_sigcheck, dsa_sigdestroy
};

static sig *dsa_vrfinit(key *k, void *kd, const gchash *hc)
{
  dh_pub *dp = kd;
  dsa_sigctx *ds = dsa_doinit(k, &dp->dp, dp->y, hc, group_prime, "prime");
  return (&ds->s);
}

static sig *bindsa_vrfinit(key *k, void *kd, const gchash *hc)
{
  dh_pub *dp = kd;
  dsa_sigctx *ds = dsa_doinit(k, &dp->dp, dp->y, hc, group_binary, "binary");
  return (&ds->s);
}

static sig *ecdsa_vrfinit(key *k, void *kd, const gchash *hc)
{
  ec_pub *ep = kd;
  dsa_sigctx *ds = ecdsa_doinit(k, ep->cstr, &ep->p, hc);
  return (&ds->s);
}

static int dsa_vrfdoit(sig *s, dstr *d)
{
  dsa_sigctx *ds = (dsa_sigctx *)s;
  gdsa_sig ss;
  size_t n = d->len/2;
  int rc;

  ss.r = mp_loadb(MP_NEW, d->buf, n);
  ss.s = mp_loadb(MP_NEW, d->buf + n, d->len - n);
  rc = gdsa_verify(&ds->g, &ss, GH_DONE(ds->s.h, 0));
  mp_drop(ss.r); mp_drop(ss.s);
  return (rc);
}

static const sigops dsa_vrf = {
  dh_pubfetch, sizeof(dh_pub),
  dsa_vrfinit, dsa_vrfdoit, dsa_sigcheck, dsa_sigdestroy
};

static const sigops bindsa_vrf = {
  dh_pubfetch, sizeof(dh_pub),
  bindsa_vrfinit, dsa_vrfdoit, dsa_sigcheck, dsa_sigdestroy
};

static const sigops ecdsa_vrf = {
  ec_pubfetch, sizeof(ec_pub),
  ecdsa_vrfinit, dsa_vrfdoit, dsa_sigcheck, dsa_sigdestroy
};

/* --- KCDSA and ECKCDSA --- */

static void kcdsa_privkey(dsa_sigctx *ds, mp *x)
  { ds->g.u = mp_modinv(MP_NEW, x, ds->g.g->r); }

static void kcdsa_sethash(dsa_sigctx *ds, const gchash *hc)
  { ds->s.h = gkcdsa_beginhash(&ds->g); }

static sig *kcdsa_siginit(key *k, void *kd, const gchash *hc)
{
  dh_priv *dp = kd;
  dsa_sigctx *ds = dsa_doinit(k, &dp->dp, dp->y, hc, group_prime, "prime");
  kcdsa_privkey(ds, dp->x);
  kcdsa_sethash(ds, hc);
  return (&ds->s);
}

static sig *binkcdsa_siginit(key *k, void *kd, const gchash *hc)
{
  dh_priv *dp = kd;
  dsa_sigctx *ds = dsa_doinit(k, &dp->dp, dp->y, hc, group_binary, "binary");
  kcdsa_privkey(ds, dp->x);
  kcdsa_sethash(ds, hc);
  return (&ds->s);
}

static sig *eckcdsa_siginit(key *k, void *kd, const gchash *hc)
{
  ec_priv *ep = kd;
  dsa_sigctx *ds = ecdsa_doinit(k, ep->cstr, &ep->p, hc);
  kcdsa_privkey(ds, ep->x);
  kcdsa_sethash(ds, hc);
  return (&ds->s);
}

static int kcdsa_sigdoit(sig *s, dstr *d)
{
  dsa_sigctx *ds = (dsa_sigctx *)s;
  gkcdsa_sig ss = GKCDSA_SIG_INIT;
  size_t hsz = ds->g.h->hashsz, n = mp_octets(ds->g.g->r);

  gkcdsa_sign(&ds->g, &ss, GH_DONE(ds->s.h, 0), 0);
  dstr_ensure(d, hsz + n);
  memcpy(d->buf, ss.r, hsz);
  mp_storeb(ss.s, d->buf + hsz, n);
  d->len += hsz + n;
  xfree(ss.r); mp_drop(ss.s);
  return (0);
}

static const sigops kcdsa_sig = {
  dh_privfetch, sizeof(dh_priv),
  kcdsa_siginit, kcdsa_sigdoit, dsa_sigcheck, dsa_sigdestroy
};

static const sigops binkcdsa_sig = {
  dh_privfetch, sizeof(dh_priv),
  binkcdsa_siginit, kcdsa_sigdoit, dsa_sigcheck, dsa_sigdestroy
};

static const sigops eckcdsa_sig = {
  ec_privfetch, sizeof(ec_priv),
  eckcdsa_siginit, kcdsa_sigdoit, dsa_sigcheck, dsa_sigdestroy
};

static sig *kcdsa_vrfinit(key *k, void *kd, const gchash *hc)
{
  dh_pub *dp = kd;
  dsa_sigctx *ds = dsa_doinit(k, &dp->dp, dp->y, hc, group_prime, "prime");
  kcdsa_sethash(ds, hc);
  return (&ds->s);
}

static sig *binkcdsa_vrfinit(key *k, void *kd, const gchash *hc)
{
  dh_pub *dp = kd;
  dsa_sigctx *ds = dsa_doinit(k, &dp->dp, dp->y, hc, group_binary, "binary");
  kcdsa_sethash(ds, hc);
  return (&ds->s);
}

static sig *eckcdsa_vrfinit(key *k, void *kd, const gchash *hc)
{
  ec_pub *ep = kd;
  dsa_sigctx *ds = ecdsa_doinit(k, ep->cstr, &ep->p, hc);
  kcdsa_sethash(ds, hc);
  return (&ds->s);
}

static int kcdsa_vrfdoit(sig *s, dstr *d)
{
  dsa_sigctx *ds = (dsa_sigctx *)s;
  gkcdsa_sig ss;
  size_t hsz = ds->g.h->hashsz, n = d->len - hsz;
  int rc;

  if (d->len < hsz)
    return (-1);
  ss.r = (octet *)d->buf;
  ss.s = mp_loadb(MP_NEW, d->buf + hsz, n);
  rc = gkcdsa_verify(&ds->g, &ss, GH_DONE(ds->s.h, 0));
  mp_drop(ss.s);
  return (rc);
}

static const sigops kcdsa_vrf = {
  dh_pubfetch, sizeof(dh_pub),
  kcdsa_vrfinit, kcdsa_vrfdoit, dsa_sigcheck, dsa_sigdestroy
};

static const sigops binkcdsa_vrf = {
  dh_pubfetch, sizeof(dh_pub),
  binkcdsa_vrfinit, kcdsa_vrfdoit, dsa_sigcheck, dsa_sigdestroy
};

static const sigops eckcdsa_vrf = {
  ec_pubfetch, sizeof(ec_pub),
  eckcdsa_vrfinit, kcdsa_vrfdoit, dsa_sigcheck, dsa_sigdestroy
};

/* --- Symmetric message authentication --- */

typedef struct mac_ctx {
  sig s;
  const gcmac *mc;
  gmac *m;
  key_packdef kp;
  key_bin kb;
} mac_ctx;

static sig *mac_init(key *k, void *kd, const gchash *hc)
{
  mac_ctx *m;
  dstr d = DSTR_INIT;
  int err;
  const char *mm;

  m = CREATE(mac_ctx);

  key_fulltag(k, &d);
  m->kp.e = KENC_BINARY;
  m->kp.p = &m->kb;
  m->kp.kd = 0;

  if ((mm = key_getattr(0 /*yik*/, k, "mac")) == 0) {
    dstr_putf(&d, "%s-hmac", hc->name);
    mm = d.buf;
  }
  if ((m->mc = gmac_byname(mm)) == 0)
    die(EXIT_FAILURE, "unknown message authentication scheme `%s'", mm);
  dstr_reset(&d);

  if ((err = key_unpack(&m->kp, kd, &d)) != 0) {
    die(EXIT_FAILURE, "failed to unpack symmetric key `%s': %s",
	d.buf, key_strerror(err));
  }
  dstr_destroy(&d);

  if (keysz(m->kb.sz, m->mc->keysz) != m->kb.sz) {
    die(EXIT_FAILURE, "bad key size %lu for `%s'",
	(unsigned long)m->kb.sz, m->mc->name);
  }
  m->m = GM_KEY(m->mc, m->kb.k, m->kb.sz);
  m->s.h = GM_INIT(m->m);
  return (&m->s);
}

static int mac_sigdoit(sig *s, dstr *d)
{
  mac_ctx *m = (mac_ctx *)s;

  dstr_ensure(d, m->mc->hashsz);
  GH_DONE(m->s.h, d->buf);
  d->len += m->mc->hashsz;
  return (0);
}

static int mac_vrfdoit(sig *s, dstr *d)
{
  mac_ctx *m = (mac_ctx *)s;
  const octet *t;

  t = GH_DONE(m->s.h, 0);
  if (d->len != m->mc->hashsz || memcmp(d->buf, t, d->len) != 0)
    return (-1);
  return (0);
}

static const char *mac_check(sig *s) { return (0); }

static void mac_destroy(sig *s)
{
  mac_ctx *m = (mac_ctx *)s;
  GM_DESTROY(m->m);
  key_unpackdone(&m->kp);
}

static const sigops mac_sig = {
  0, 0,
  mac_init, mac_sigdoit, mac_check, mac_destroy
};

static const sigops mac_vrf = {
  0, 0,
  mac_init, mac_vrfdoit, mac_check, mac_destroy
};

/* --- The switch table --- */

const struct sigtab sigtab[] = {
  { "rsapkcs1",	&rsap1_sig,	&rsap1_vrf,	&sha },
  { "rsapss",	&rsapss_sig,	&rsapss_vrf,	&sha },
  { "dsa",	&dsa_sig,	&dsa_vrf,	&sha },
  { "bindsa",	&bindsa_sig,	&bindsa_vrf,	&sha },
  { "ecdsa",	&ecdsa_sig,	&ecdsa_vrf,	&sha },
  { "kcdsa",	&kcdsa_sig,	&kcdsa_vrf,	&has160 },
  { "binkcdsa",	&binkcdsa_sig,	&binkcdsa_vrf,	&has160 },
  { "eckcdsa",	&eckcdsa_sig,	&eckcdsa_vrf,	&has160 },
  { "mac",	&mac_sig,	&mac_vrf,	&rmd160 },
  { 0,		0,		0 }
};

/* --- @getsig@ --- *
 *
 * Arguments:	@key *k@ = the key to load
 *		@const char *app@ = application name
 *		@int wantpriv@ = nonzero if we want to sign
 *
 * Returns:	A signature-making thing.
 *
 * Use:		Loads a key and starts hashing.
 */

sig *getsig(key *k, const char *app, int wantpriv)
{
  const char *salg, *halg = 0;
  dstr d = DSTR_INIT;
  dstr t = DSTR_INIT;
  char *p = 0;
  const char *q;
  sig *s;
  size_t n;
  const struct sigtab *st;
  const sigops *so;
  const gchash *ch;
  void *kd;
  int e;
  key_packdef *kp;

  /* --- Setup stuff --- */

  key_fulltag(k, &t);

  /* --- Get the signature algorithm --- *
   *
   * Take the attribute if it's there; otherwise use the key type.
   */

  n = strlen(app);
  if ((q = key_getattr(0, k, "sig")) != 0) {
    dstr_puts(&d, q);
    p = d.buf;
  } else if (strncmp(k->type, app, n) == 0 && k->type[n] == '-') {
    dstr_puts(&d, k->type);
    p = d.buf + n + 1;
  } else
    die(EXIT_FAILURE, "no signature algorithm for key `%s'", t.buf);

  /* --- Grab the hash algorithm --- *
   *
   * Grab it from the signature algorithm if it's there.  But override that
   * from the attribute.
   */

  salg = p;
  if ((p = strchr(p, '/')) != 0) {
    *p++ = 0;
    halg = p;
  }
  if ((q = key_getattr(0, k, "hash")) != 0)
    halg = q;

  /* --- Look up the algorithms in the table --- */

  for (st = sigtab; st->name; st++) {
    if (strcmp(st->name, salg) == 0)
      goto s_found;
  }
  die(EXIT_FAILURE, "signature algorithm `%s' not found in key `%s'",
      salg, t.buf);
s_found:;
  if (!halg)
    ch = st->ch;
  else {
    if ((ch = ghash_byname(halg)) == 0) {
      die(EXIT_FAILURE, "hash algorithm `%s' not found in key `%s'",
	  halg, t.buf);
    }
  }
  so = wantpriv ? st->signops : st->verifyops;

  /* --- Load the key --- */

  if (!so->kf) {
    kd = k->k;
    key_incref(kd);
    kp = 0;
  } else {
    kd = xmalloc(so->kdsz);
    kp = key_fetchinit(so->kf, 0, kd);
    if ((e = key_fetch(kp, k)) != 0) {
      die(EXIT_FAILURE, "error fetching key `%s': %s",
	  t.buf, key_strerror(e));
    }
  }
  s = so->init(k, kd, ch);
  if (!s->h)
    s->h = GH_INIT(ch);
  s->kp = kp;
  s->ops = so;
  s->kd = kd;
  s->ch = ch;

  /* --- Free stuff up --- */

  dstr_destroy(&d);
  dstr_destroy(&t);
  return (s);
}

/* --- @freesig@ --- *
 *
 * Arguments:	@sig *s@ = signature-making thing
 *
 * Returns:	---
 *
 * Use:		Frees up a signature-making thing
 */

void freesig(sig *s)
{
  GH_DESTROY(s->h);
  if (!s->ops->kf)
    key_drop(s->kd);
  else {
    key_fetchdone(s->kp);
    xfree(s->kd);
  }
  s->ops->destroy(s);
}

/*----- That's all, folks -------------------------------------------------*/