openssl/crypto/dsa/dsa_gen.c

/* crypto/dsa/dsa_gen.c */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 * 
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 * 
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from 
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 * 
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#undef GENUINE_DSA

#ifdef GENUINE_DSA
/* Parameter generation follows the original release of FIPS PUB 186,
 * Appendix 2.2 (i.e. use SHA as defined in FIPS PUB 180) */
#define HASH    EVP_sha()
#else
/* Parameter generation follows the updated Appendix 2.2 for FIPS PUB 186,
 * also Appendix 2.2 of FIPS PUB 186-1 (i.e. use SHA as defined in
 * FIPS PUB 180-1) */
#define HASH    EVP_sha1()
#endif 

#include <openssl/opensslconf.h> /* To see if OPENSSL_NO_SHA is defined */

#ifndef OPENSSL_NO_SHA

#define OPENSSL_FIPSAPI

#include <stdio.h>
#include "cryptlib.h"
#include <openssl/evp.h>
#include <openssl/bn.h>
#include <openssl/rand.h>
#include <openssl/sha.h>
#ifdef OPENSSL_FIPS
#include <openssl/fips.h>
#include <openssl/fips_rand.h>
#endif

#include "dsa_locl.h"

int DSA_generate_parameters_ex(DSA *ret, int bits,
		const unsigned char *seed_in, int seed_len,
		int *counter_ret, unsigned long *h_ret, BN_GENCB *cb)
	{
	if(ret->meth->dsa_paramgen)
		return ret->meth->dsa_paramgen(ret, bits, seed_in, seed_len,
				counter_ret, h_ret, cb);
	else
		{
		const EVP_MD *evpmd;
		size_t qbits = bits >= 2048 ? 256 : 160;

		if (bits >= 2048)
			{
			qbits = 256;
			evpmd = EVP_sha256();
			}
		else
			{
			qbits = 160;
			evpmd = EVP_sha1();
			}

		return dsa_builtin_paramgen(ret, bits, qbits, evpmd,
			seed_in, seed_len, NULL, counter_ret, h_ret, cb);
		}
	}

int dsa_builtin_paramgen(DSA *ret, size_t bits, size_t qbits,
	const EVP_MD *evpmd, const unsigned char *seed_in, size_t seed_len,
	unsigned char *seed_out,
	int *counter_ret, unsigned long *h_ret, BN_GENCB *cb)
	{
	int ok=0;
	unsigned char seed[SHA256_DIGEST_LENGTH];
	unsigned char md[SHA256_DIGEST_LENGTH];
	unsigned char buf[SHA256_DIGEST_LENGTH],buf2[SHA256_DIGEST_LENGTH];
	BIGNUM *r0,*W,*X,*c,*test;
	BIGNUM *g=NULL,*q=NULL,*p=NULL;
	BN_MONT_CTX *mont=NULL;
	int i, k, n=0, m=0, qsize = qbits >> 3;
	int counter=0;
	int r=0;
	BN_CTX *ctx=NULL;
	unsigned int h=2;

#ifdef OPENSSL_FIPS
	if(FIPS_selftest_failed())
	    {
	    FIPSerr(FIPS_F_DSA_BUILTIN_PARAMGEN, FIPS_R_FIPS_SELFTEST_FAILED);
	    goto err;
	    }

	if (FIPS_module_mode() && !(ret->flags & DSA_FLAG_NON_FIPS_ALLOW) 
			&& (bits < OPENSSL_DSA_FIPS_MIN_MODULUS_BITS))
		{
		DSAerr(DSA_F_DSA_BUILTIN_PARAMGEN, DSA_R_KEY_SIZE_TOO_SMALL);
		goto err;
		}
#endif

	if (qsize != SHA_DIGEST_LENGTH && qsize != SHA224_DIGEST_LENGTH &&
	    qsize != SHA256_DIGEST_LENGTH)
		/* invalid q size */
		return 0;

	if (evpmd == NULL)
		/* use SHA1 as default */
		evpmd = EVP_sha1();

	if (bits < 512)
		bits = 512;

	bits = (bits+63)/64*64;

	/* NB: seed_len == 0 is special case: copy generated seed to
 	 * seed_in if it is not NULL.
 	 */
	if (seed_len && (seed_len < (size_t)qsize))
		seed_in = NULL;		/* seed buffer too small -- ignore */
	if (seed_len > (size_t)qsize) 
		seed_len = qsize;	/* App. 2.2 of FIPS PUB 186 allows larger SEED,
					 * but our internal buffers are restricted to 160 bits*/
	if (seed_in != NULL)
		memcpy(seed, seed_in, seed_len);

	if ((ctx=BN_CTX_new()) == NULL)
		goto err;

	if ((mont=BN_MONT_CTX_new()) == NULL)
		goto err;

	BN_CTX_start(ctx);
	r0 = BN_CTX_get(ctx);
	g = BN_CTX_get(ctx);
	W = BN_CTX_get(ctx);
	q = BN_CTX_get(ctx);
	X = BN_CTX_get(ctx);
	c = BN_CTX_get(ctx);
	p = BN_CTX_get(ctx);
	test = BN_CTX_get(ctx);

	if (!BN_lshift(test,BN_value_one(),bits-1))
		goto err;

	for (;;)
		{
		for (;;) /* find q */
			{
			int seed_is_random;

			/* step 1 */
			if(!BN_GENCB_call(cb, 0, m++))
				goto err;

			if (!seed_len)
				{
				if (RAND_pseudo_bytes(seed, qsize) < 0)
					goto err;
				seed_is_random = 1;
				}
			else
				{
				seed_is_random = 0;
				seed_len=0; /* use random seed if 'seed_in' turns out to be bad*/
				}
			memcpy(buf , seed, qsize);
			memcpy(buf2, seed, qsize);
			/* precompute "SEED + 1" for step 7: */
			for (i = qsize-1; i >= 0; i--)
				{
				buf[i]++;
				if (buf[i] != 0)
					break;
				}

			/* step 2 */
			if (!EVP_Digest(seed, qsize, md,   NULL, evpmd, NULL))
				goto err;
			if (!EVP_Digest(buf,  qsize, buf2, NULL, evpmd, NULL))
				goto err;
			for (i = 0; i < qsize; i++)
				md[i]^=buf2[i];

			/* step 3 */
			md[0] |= 0x80;
			md[qsize-1] |= 0x01;
			if (!BN_bin2bn(md, qsize, q))
				goto err;

			/* step 4 */
			r = BN_is_prime_fasttest_ex(q, DSS_prime_checks, ctx,
					seed_is_random, cb);
			if (r > 0)
				break;
			if (r != 0)
				goto err;

			/* do a callback call */
			/* step 5 */
			}

		if(!BN_GENCB_call(cb, 2, 0)) goto err;
		if(!BN_GENCB_call(cb, 3, 0)) goto err;

		/* step 6 */
		counter=0;
		/* "offset = 2" */

		n=(bits-1)/160;

		for (;;)
			{
			if ((counter != 0) && !BN_GENCB_call(cb, 0, counter))
				goto err;

			/* step 7 */
			BN_zero(W);
			/* now 'buf' contains "SEED + offset - 1" */
			for (k=0; k<=n; k++)
				{
				/* obtain "SEED + offset + k" by incrementing: */
				for (i = qsize-1; i >= 0; i--)
					{
					buf[i]++;
					if (buf[i] != 0)
						break;
					}

				if (!EVP_Digest(buf, qsize, md ,NULL, evpmd,
									NULL))
					goto err;

				/* step 8 */
				if (!BN_bin2bn(md, qsize, r0))
					goto err;
				if (!BN_lshift(r0,r0,(qsize << 3)*k)) goto err;
				if (!BN_add(W,W,r0)) goto err;
				}

			/* more of step 8 */
			if (!BN_mask_bits(W,bits-1)) goto err;
			if (!BN_copy(X,W)) goto err;
			if (!BN_add(X,X,test)) goto err;

			/* step 9 */
			if (!BN_lshift1(r0,q)) goto err;
			if (!BN_mod(c,X,r0,ctx)) goto err;
			if (!BN_sub(r0,c,BN_value_one())) goto err;
			if (!BN_sub(p,X,r0)) goto err;

			/* step 10 */
			if (BN_cmp(p,test) >= 0)
				{
				/* step 11 */
				r = BN_is_prime_fasttest_ex(p, DSS_prime_checks,
						ctx, 1, cb);
				if (r > 0)
						goto end; /* found it */
				if (r != 0)
					goto err;
				}

			/* step 13 */
			counter++;
			/* "offset = offset + n + 1" */

			/* step 14 */
			if (counter >= 4096) break;
			}
		}
end:
	if(!BN_GENCB_call(cb, 2, 1))
		goto err;

	/* We now need to generate g */
	/* Set r0=(p-1)/q */
	if (!BN_sub(test,p,BN_value_one())) goto err;
	if (!BN_div(r0,NULL,test,q,ctx)) goto err;

	if (!BN_set_word(test,h)) goto err;
	if (!BN_MONT_CTX_set(mont,p,ctx)) goto err;

	for (;;)
		{
		/* g=test^r0%p */
		if (!BN_mod_exp_mont(g,test,r0,p,ctx,mont)) goto err;
		if (!BN_is_one(g)) break;
		if (!BN_add(test,test,BN_value_one())) goto err;
		h++;
		}

	if(!BN_GENCB_call(cb, 3, 1))
		goto err;

	ok=1;
err:
	if (ok)
		{
		if(ret->p) BN_free(ret->p);
		if(ret->q) BN_free(ret->q);
		if(ret->g) BN_free(ret->g);
		ret->p=BN_dup(p);
		ret->q=BN_dup(q);
		ret->g=BN_dup(g);
		if (ret->p == NULL || ret->q == NULL || ret->g == NULL)
			{
			ok=0;
			goto err;
			}
		if (counter_ret != NULL) *counter_ret=counter;
		if (h_ret != NULL) *h_ret=h;
		if (seed_out)
			memcpy(seed_out, seed, qsize);
		}
	if(ctx)
		{
		BN_CTX_end(ctx);
		BN_CTX_free(ctx);
		}
	if (mont != NULL) BN_MONT_CTX_free(mont);
	return ok;
	}

#ifdef OPENSSL_FIPS

/* Security strength of parameter values for (L,N): see FIPS186-3 4.2
 * and SP800-131A
 */


static int fips_ffc_strength(size_t L, size_t N)
	{
	if (L >= 15360 && N >= 512)
		return 256;
	if (L >= 7680 && N >= 384)
		return 192;
	if (L >= 3072 && N >= 256)
		return 128;
	if (L >= 2048 && N >= 224)
		return 112;
	if (L >= 1024 && N >= 160)
		return  80;
	return 0;
	}

/* Valid DSA2 parameters from FIPS 186-3 */

static int dsa2_valid_parameters(size_t L, size_t N)
	{
	if (L == 1024 && N == 160)
		return 80;
	if (L == 2048 && N == 224)
		return 112;
	if (L == 2048 && N == 256)
		return 112;
	if (L == 3072 && N == 256)
		return 128;
	return 0;
	}

int fips_check_dsa_prng(DSA *dsa, size_t L, size_t N)
	{
	int strength;
	if (!FIPS_module_mode())
		return 1;

	if (dsa->flags & (DSA_FLAG_NON_FIPS_ALLOW|DSA_FLAG_FIPS_CHECKED))
		return 1;

	if (!L || !N)
		{
		L = BN_num_bits(dsa->p);
		N = BN_num_bits(dsa->q);
		}
	if (!dsa2_valid_parameters(L, N))
		{
		FIPSerr(FIPS_F_FIPS_CHECK_DSA_PRNG, FIPS_R_INVALID_PARAMETERS);
		return 0;
		}

	strength = fips_ffc_strength(L, N);

	if (!strength)
		{
	    	FIPSerr(FIPS_F_FIPS_CHECK_DSA_PRNG,FIPS_R_KEY_TOO_SHORT);
		return 0;
		}

	if (FIPS_rand_strength() >= strength)
		return 1;

	FIPSerr(FIPS_F_FIPS_CHECK_DSA_PRNG,FIPS_R_PRNG_STRENGTH_TOO_LOW);
	return 0;

	}
#endif /* OPENSSL_FIPS */

/* This is a parameter generation algorithm for the DSA2 algorithm as
 * described in FIPS 186-3.
 */

int dsa_builtin_paramgen2(DSA *ret, size_t L, size_t N,
	const EVP_MD *evpmd, const unsigned char *seed_in, size_t seed_len,
	int idx, unsigned char *seed_out,
	int *counter_ret, unsigned long *h_ret, BN_GENCB *cb)
	{
	int ok=-1;
	unsigned char *seed = NULL, *seed_tmp = NULL;
	unsigned char md[EVP_MAX_MD_SIZE];
	int mdsize;
	BIGNUM *r0,*W,*X,*c,*test;
	BIGNUM *g=NULL,*q=NULL,*p=NULL;
	BN_MONT_CTX *mont=NULL;
	int i, k, n=0, m=0, qsize = N >> 3;
	int counter=0;
	int r=0;
	BN_CTX *ctx=NULL;
	EVP_MD_CTX mctx;
	unsigned int h=2;

	EVP_MD_CTX_init(&mctx);

#ifdef OPENSSL_FIPS
	if(FIPS_selftest_failed())
	    {
	    FIPSerr(FIPS_F_DSA_BUILTIN_PARAMGEN2,
		    FIPS_R_FIPS_SELFTEST_FAILED);
	    goto err;
	    }

	if (!fips_check_dsa_prng(ret, L, N))
		goto err;
#endif

	if (evpmd == NULL)
		{
		if (N == 160)
			evpmd = EVP_sha1();
		else if (N == 224)
			evpmd = EVP_sha224();
		else
			evpmd = EVP_sha256();
		}

	mdsize = M_EVP_MD_size(evpmd);
	/* If unverificable g generation only don't need seed */
	if (!ret->p || !ret->q || idx >= 0)
		{
		if (seed_len == 0)
			seed_len = mdsize;

		seed = OPENSSL_malloc(seed_len);

		if (seed_out)
			seed_tmp = seed_out;
		else
			seed_tmp = OPENSSL_malloc(seed_len);

		if (!seed || !seed_tmp)
			goto err;

		if (seed_in)
			memcpy(seed, seed_in, seed_len);

		}

	if ((ctx=BN_CTX_new()) == NULL)
		goto err;

	if ((mont=BN_MONT_CTX_new()) == NULL)
		goto err;

	BN_CTX_start(ctx);
	r0 = BN_CTX_get(ctx);
	g = BN_CTX_get(ctx);
	W = BN_CTX_get(ctx);
	X = BN_CTX_get(ctx);
	c = BN_CTX_get(ctx);
	test = BN_CTX_get(ctx);

	/* if p, q already supplied generate g only */
	if (ret->p && ret->q)
		{
		p = ret->p;
		q = ret->q;
		if (idx >= 0)
			memcpy(seed_tmp, seed, seed_len);
		goto g_only;
		}
	else
		{
		p = BN_CTX_get(ctx);
		q = BN_CTX_get(ctx);
		}

	if (!BN_lshift(test,BN_value_one(),L-1))
		goto err;
	for (;;)
		{
		for (;;) /* find q */
			{
			unsigned char *pmd;
			/* step 1 */
			if(!BN_GENCB_call(cb, 0, m++))
				goto err;

			if (!seed_in)
				{
				if (RAND_pseudo_bytes(seed, seed_len) < 0)
					goto err;
				}
			/* step 2 */
			if (!EVP_Digest(seed, seed_len, md, NULL, evpmd, NULL))
				goto err;
			/* Take least significant bits of md */
			if (mdsize > qsize)
				pmd = md + mdsize - qsize;
			else
				pmd = md;

			if (mdsize < qsize)
				memset(md + mdsize, 0, qsize - mdsize);

			/* step 3 */
			pmd[0] |= 0x80;
			pmd[qsize-1] |= 0x01;
			if (!BN_bin2bn(pmd, qsize, q))
				goto err;

			/* step 4 */
			r = BN_is_prime_fasttest_ex(q, DSS_prime_checks, ctx,
					seed_in ? 1 : 0, cb);
			if (r > 0)
				break;
			if (r != 0)
				goto err;
			/* Provided seed didn't produce a prime: error */
			if (seed_in)
				{
				ok = 0;
				DSAerr(DSA_F_DSA_BUILTIN_PARAMGEN2, DSA_R_Q_NOT_PRIME);
				goto err;
				}

			/* do a callback call */
			/* step 5 */
			}
		/* Copy seed to seed_out before we mess with it */
		if (seed_out)
			memcpy(seed_out, seed, seed_len);

		if(!BN_GENCB_call(cb, 2, 0)) goto err;
		if(!BN_GENCB_call(cb, 3, 0)) goto err;

		/* step 6 */
		counter=0;
		/* "offset = 1" */

		n=(L-1)/(mdsize << 3);

		for (;;)
			{
			if ((counter != 0) && !BN_GENCB_call(cb, 0, counter))
				goto err;

			/* step 7 */
			BN_zero(W);
			/* now 'buf' contains "SEED + offset - 1" */
			for (k=0; k<=n; k++)
				{
				/* obtain "SEED + offset + k" by incrementing: */
				for (i = seed_len-1; i >= 0; i--)
					{
					seed[i]++;
					if (seed[i] != 0)
						break;
					}

				if (!EVP_Digest(seed, seed_len, md ,NULL, evpmd,
									NULL))
					goto err;

				/* step 8 */
				if (!BN_bin2bn(md, mdsize, r0))
					goto err;
				if (!BN_lshift(r0,r0,(mdsize << 3)*k)) goto err;
				if (!BN_add(W,W,r0)) goto err;
				}

			/* more of step 8 */
			if (!BN_mask_bits(W,L-1)) goto err;
			if (!BN_copy(X,W)) goto err;
			if (!BN_add(X,X,test)) goto err;

			/* step 9 */
			if (!BN_lshift1(r0,q)) goto err;
			if (!BN_mod(c,X,r0,ctx)) goto err;
			if (!BN_sub(r0,c,BN_value_one())) goto err;
			if (!BN_sub(p,X,r0)) goto err;

			/* step 10 */
			if (BN_cmp(p,test) >= 0)
				{
				/* step 11 */
				r = BN_is_prime_fasttest_ex(p, DSS_prime_checks,
						ctx, 1, cb);
				if (r > 0)
						goto end; /* found it */
				if (r != 0)
					goto err;
				}

			/* step 13 */
			counter++;
			/* "offset = offset + n + 1" */

			/* step 14 */
			if (counter >= (int)(4 * L)) break;
			}
		if (seed_in)
			{
			ok = 0;
			DSAerr(DSA_F_DSA_BUILTIN_PARAMGEN2, DSA_R_INVALID_PARAMETERS);
			goto err;
			}
		}
end:
	if(!BN_GENCB_call(cb, 2, 1))
		goto err;

	g_only:

	/* We now need to generate g */
	/* Set r0=(p-1)/q */
	if (!BN_sub(test,p,BN_value_one())) goto err;
	if (!BN_div(r0,NULL,test,q,ctx)) goto err;

	if (idx < 0)
		{
		if (!BN_set_word(test,h))
			goto err;
		}
	else
		h = 1;
	if (!BN_MONT_CTX_set(mont,p,ctx)) goto err;

	for (;;)
		{
		__fips_constseg
		static const unsigned char ggen[4] = {0x67,0x67,0x65,0x6e};
		if (idx >= 0)
			{
			md[0] = idx & 0xff;
			md[1] = (h >> 8) & 0xff;
			md[2] = h & 0xff;
			if (!EVP_DigestInit_ex(&mctx, evpmd, NULL))
				goto err;
			if (!EVP_DigestUpdate(&mctx, seed_tmp, seed_len))
				goto err;
			if (!EVP_DigestUpdate(&mctx, ggen, sizeof(ggen)))
				goto err;
			if (!EVP_DigestUpdate(&mctx, md, 3))
				goto err;
			if (!EVP_DigestFinal_ex(&mctx, md, NULL))
				goto err;
			if (!BN_bin2bn(md, mdsize, test))
				goto err;
			}
		/* g=test^r0%p */
		if (!BN_mod_exp_mont(g,test,r0,p,ctx,mont)) goto err;
		if (!BN_is_one(g)) break;
		if (idx < 0 && !BN_add(test,test,BN_value_one())) goto err;
		h++;
		if ( idx >= 0 && h > 0xffff)
			goto err;
		}

	if(!BN_GENCB_call(cb, 3, 1))
		goto err;

	ok=1;
err:
	if (ok == 1)
		{
		if (p != ret->p)
			{
			if(ret->p) BN_free(ret->p);
			ret->p=BN_dup(p);
			}
		if (q != ret->q)
			{
			if(ret->q) BN_free(ret->q);
			ret->q=BN_dup(q);
			}
		if(ret->g) BN_free(ret->g);
		ret->g=BN_dup(g);
		if (ret->p == NULL || ret->q == NULL || ret->g == NULL)
			{
			ok=-1;
			goto err;
			}
		if (counter_ret != NULL) *counter_ret=counter;
		if (h_ret != NULL) *h_ret=h;
		}
	if (seed)
		OPENSSL_free(seed);
	if (seed_out != seed_tmp)
		OPENSSL_free(seed_tmp);
	if(ctx)
		{
		BN_CTX_end(ctx);
		BN_CTX_free(ctx);
		}
	if (mont != NULL) BN_MONT_CTX_free(mont);
	EVP_MD_CTX_cleanup(&mctx);
	return ok;
	}

int dsa_paramgen_check_g(DSA *dsa)
	{
	BN_CTX *ctx;
	BIGNUM *tmp;
	BN_MONT_CTX *mont = NULL;
	int rv = -1;
	ctx = BN_CTX_new();
	if (!ctx)
		return -1;
	BN_CTX_start(ctx);
	if (BN_cmp(dsa->g, BN_value_one()) <= 0)
		return 0;
	if (BN_cmp(dsa->g, dsa->p) >= 0)
		return 0;
	tmp = BN_CTX_get(ctx);
	if (!tmp)
		goto err;
	if ((mont=BN_MONT_CTX_new()) == NULL)
		goto err;
	if (!BN_MONT_CTX_set(mont,dsa->p,ctx))
		goto err;
	/* Work out g^q mod p */
	if (!BN_mod_exp_mont(tmp,dsa->g,dsa->q, dsa->p, ctx, mont))
		goto err;
	if (!BN_cmp(tmp, BN_value_one()))
		rv = 1;
	else
		rv = 0;
	err:
	BN_CTX_end(ctx);
	if (mont)
		BN_MONT_CTX_free(mont);
	BN_CTX_free(ctx);
	return rv;

	}

#endif