3 * RSA parameter generation
5 * (c) 1999 Straylight/Edgeware
8 /*----- Licensing notice --------------------------------------------------*
10 * This file is part of Catacomb.
12 * Catacomb is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU Library General Public License as
14 * published by the Free Software Foundation; either version 2 of the
15 * License, or (at your option) any later version.
17 * Catacomb is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU Library General Public License for more details.
22 * You should have received a copy of the GNU Library General Public
23 * License along with Catacomb; if not, write to the Free
24 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
28 /*----- Header files ------------------------------------------------------*/
30 #include <mLib/dstr.h>
37 #include "strongprime.h"
39 /*----- Main code ---------------------------------------------------------*/
41 /* --- @rsa_gen@ --- *
43 * Arguments: @rsa_priv *rp@ = pointer to block to be filled in
44 * @unsigned nbits@ = required modulus size in bits
45 * @grand *r@ = random number source
46 * @unsigned n@ = number of attempts to make
47 * @pgen_proc *event@ = event handler function
48 * @void *ectx@ = argument for the event handler
50 * Returns: Zero if all went well, nonzero otherwise.
52 * Use: Constructs a pair of strong RSA primes and other useful RSA
53 * parameters. A small encryption exponent is chosen if
57 int rsa_gen(rsa_priv
*rp
, unsigned nbits
, grand
*r
, unsigned n
,
58 pgen_proc
*event
, void *ectx
)
63 /* --- Bits of initialization --- */
65 rp
->e
= mp_fromulong(MP_NEW
, 0x10001);
68 /* --- Generate strong primes %$p$% and %$q$% --- *
70 * Constrain the GCD of @q@ to ensure that overly small private exponents
71 * are impossible. Current results suggest that if %$d < n^{0.29}$% then
72 * it can be guessed fairly easily. This implementation is rather more
73 * conservative about that sort of thing.
76 if ((rp
->p
= strongprime("p", MP_NEWSEC
, nbits
/2, r
, n
, event
, ectx
)) == 0)
79 /* --- Do painful fiddling with GCD steppers --- *
81 * Also, arrange that %$q \ge \lceil 2^{N-1}/p \rceil$%, so that %$p q$%
82 * has the right length.
87 mp
*t
= MP_NEW
, *u
= MP_NEW
;
90 if ((q
= strongprime_setup("q", MP_NEWSEC
, &g
.jp
, nbits
/ 2,
91 r
, n
, event
, ectx
)) == 0)
93 t
= mp_lsl(t
, MP_ONE
, nbits
- 1);
94 mp_div(&t
, &u
, t
, rp
->p
);
95 if (!MP_ZEROP(u
)) t
= mp_add(t
, t
, MP_ONE
);
96 if (MP_CMP(q
, <, t
)) q
= mp_leastcongruent(q
, t
, q
, g
.jp
.m
);
99 g
.r
= mp_lsr(MP_NEW
, rp
->p
, 1);
102 q
= pgen("q", q
, q
, event
, ectx
, n
, pgen_gcdstep
, &g
,
103 rabin_iters(nbits
/2), pgen_test
, &rb
);
104 pfilt_destroy(&g
.jp
);
113 /* --- Ensure that %$p > q$% --- *
115 * Also ensure that %$p$% and %$q$% are sufficiently different to deter
116 * square-root-based factoring methods.
119 phi
= mp_sub(phi
, rp
->p
, rp
->q
);
120 if (MP_LEN(phi
) * 4 < MP_LEN(rp
->p
) * 3 ||
121 MP_LEN(phi
) * 4 < MP_LEN(rp
->q
) * 3) {
133 /* --- Work out the modulus and the CRT coefficient --- */
135 rp
->n
= mp_mul(MP_NEW
, rp
->p
, rp
->q
);
136 rp
->q_inv
= mp_modinv(MP_NEW
, rp
->q
, rp
->p
);
138 /* --- Work out %$\varphi(n) = (p - 1)(q - 1)$% --- *
140 * Save on further multiplications by noting that %$n = pq$% is known and
141 * that %$(p - 1)(q - 1) = pq - p - q + 1$%. To minimize the size of @d@
142 * (useful for performance reasons, although not very because an overly
143 * small @d@ will be rejected for security reasons) this is then divided by
144 * %$\gcd(p - 1, q - 1)$%.
147 phi
= mp_sub(phi
, rp
->n
, rp
->p
);
148 phi
= mp_sub(phi
, phi
, rp
->q
);
149 phi
= mp_add(phi
, phi
, MP_ONE
);
150 phi
= mp_lsr(phi
, phi
, 1);
151 mp_div(&phi
, 0, phi
, g
.g
);
153 /* --- Decide on a public exponent --- *
155 * Simultaneously compute the private exponent.
158 mp_gcd(&g
.g
, 0, &rp
->d
, phi
, rp
->e
);
159 if (!MP_EQ(g
.g
, MP_ONE
) && MP_LEN(rp
->d
) * 4 > MP_LEN(rp
->n
) * 3)
161 if (mp_bits(rp
->n
) != nbits
)
164 /* --- Work out exponent residues --- */
166 rp
->dp
= MP_NEW
; phi
= mp_sub(phi
, rp
->p
, MP_ONE
);
167 mp_div(0, &rp
->dp
, rp
->d
, phi
);
169 rp
->dq
= MP_NEW
; phi
= mp_sub(phi
, rp
->q
, MP_ONE
);
170 mp_div(0, &rp
->dq
, rp
->d
, phi
);
178 /* --- Tidy up when something goes wrong --- */
195 /*----- That's all, folks -------------------------------------------------*/