X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/ba6e6b64033b1f9de49feccb5c9cd438354481f7..0f00dc4c8eb47e67bc0f148c2dd109f73a451e0a:/pub/rsa-gen.c

diff --git a/pub/rsa-gen.c b/pub/rsa-gen.c
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+/* -*-c-*-
+ *
+ * RSA parameter generation
+ *
+ * (c) 1999 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 <mLib/dstr.h>
+
+#include "grand.h"
+#include "mp.h"
+#include "mpint.h"
+#include "pgen.h"
+#include "rsa.h"
+#include "strongprime.h"
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @rsa_gen@ --- *
+ *
+ * Arguments:	@rsa_priv *rp@ = pointer to block to be filled in
+ *		@unsigned nbits@ = required modulus size in bits
+ *		@grand *r@ = random number source
+ *		@unsigned n@ = number of attempts to make
+ *		@pgen_proc *event@ = event handler function
+ *		@void *ectx@ = argument for the event handler
+ *
+ * Returns:	Zero if all went well, nonzero otherwise.
+ *
+ * Use:		Constructs a pair of strong RSA primes and other useful RSA
+ *		parameters.  A small encryption exponent is chosen if
+ *		possible.
+ */
+
+int rsa_gen(rsa_priv *rp, unsigned nbits, grand *r, unsigned n,
+	    pgen_proc *event, void *ectx)
+{
+  pgen_gcdstepctx g;
+  mp *phi = MP_NEW;
+
+  /* --- Bits of initialization --- */
+
+  rp->e = mp_fromulong(MP_NEW, 0x10001);
+  rp->d = MP_NEW;
+
+  /* --- Generate strong primes %$p$% and %$q$% --- *
+   *
+   * Constrain the GCD of @q@ to ensure that overly small private exponents
+   * are impossible.  Current results suggest that if %$d < n^{0.29}$% then
+   * it can be guessed fairly easily.  This implementation is rather more
+   * conservative about that sort of thing.
+   */
+
+again:
+  if ((rp->p = strongprime("p", MP_NEWSEC, nbits/2, r, n, event, ectx)) == 0)
+    goto fail_p;
+
+  /* --- Do painful fiddling with GCD steppers --- */
+
+  {
+    mp *q;
+    rabin rb;
+
+    if ((q = strongprime_setup("q", MP_NEWSEC, &g.jp, nbits / 2,
+			       r, n, event, ectx)) == 0)
+      goto fail_q;
+    g.r = mp_lsr(MP_NEW, rp->p, 1);
+    g.g = MP_NEW;
+    g.max = MP_256;
+    q = pgen("q", q, q, event, ectx, n, pgen_gcdstep, &g,
+		 rabin_iters(nbits/2), pgen_test, &rb);
+    pfilt_destroy(&g.jp);
+    mp_drop(g.r);
+    if (!q) {
+      mp_drop(g.g);
+      if (n)
+	goto fail_q;
+      mp_drop(rp->p);
+      goto again;
+    }
+    rp->q = q;
+  }
+
+  /* --- Ensure that %$p > q$% --- *
+   *
+   * Also ensure that %$p$% and %$q$% are sufficiently different to deter
+   * square-root-based factoring methods.
+   */
+
+  phi = mp_sub(phi, rp->p, rp->q);
+  if (MP_LEN(phi) * 4 < MP_LEN(rp->p) * 3 ||
+      MP_LEN(phi) * 4 < MP_LEN(rp->q) * 3) {
+    mp_drop(rp->p);
+    mp_drop(g.g);
+    if (n)
+      goto fail_q;
+    mp_drop(rp->q);
+    goto again;
+  }
+
+  if (MP_NEGP(phi)) {
+    mp *z = rp->p;
+    rp->p = rp->q;
+    rp->q = z;
+  }
+
+  /* --- Work out the modulus and the CRT coefficient --- */
+
+  rp->n = mp_mul(MP_NEW, rp->p, rp->q);
+  rp->q_inv = mp_modinv(MP_NEW, rp->q, rp->p);
+
+  /* --- Work out %$\varphi(n) = (p - 1)(q - 1)$% --- *
+   *
+   * Save on further multiplications by noting that %$n = pq$% is known and
+   * that %$(p - 1)(q - 1) = pq - p - q + 1$%.  To minimize the size of @d@
+   * (useful for performance reasons, although not very because an overly
+   * small @d@ will be rejected for security reasons) this is then divided by
+   * %$\gcd(p - 1, q - 1)$%.
+   */
+
+  phi = mp_sub(phi, rp->n, rp->p);
+  phi = mp_sub(phi, phi, rp->q);
+  phi = mp_add(phi, phi, MP_ONE);
+  phi = mp_lsr(phi, phi, 1);
+  mp_div(&phi, 0, phi, g.g);
+
+  /* --- Decide on a public exponent --- *
+   *
+   * Simultaneously compute the private exponent.
+   */
+
+  mp_gcd(&g.g, 0, &rp->d, phi, rp->e);
+  if (!MP_EQ(g.g, MP_ONE) && MP_LEN(rp->d) * 4 > MP_LEN(rp->n) * 3)
+    goto fail_e;
+
+  /* --- Work out exponent residues --- */
+
+  rp->dp = MP_NEW; phi = mp_sub(phi, rp->p, MP_ONE);
+  mp_div(0, &rp->dp, rp->d, phi);
+
+  rp->dq = MP_NEW; phi = mp_sub(phi, rp->q, MP_ONE);
+  mp_div(0, &rp->dq, rp->d, phi);
+
+  /* --- Done --- */
+
+  mp_drop(phi);
+  mp_drop(g.g);
+  return (0);
+
+  /* --- Tidy up when something goes wrong --- */
+
+fail_e:
+  mp_drop(g.g);
+  mp_drop(phi);
+  mp_drop(rp->n);
+  mp_drop(rp->q_inv);
+  mp_drop(rp->q);
+fail_q:
+  mp_drop(rp->p);
+fail_p:
+  mp_drop(rp->e);
+  if (rp->d)
+    mp_drop(rp->d);
+  return (-1);
+}
+
+/*----- That's all, folks -------------------------------------------------*/