src/third_party/openssl/openssl/engines/ccgost/gost_sign.c - cobalt - Git at Google

 /**********************************************************************
  *                          gost_sign.c                               *
  *             Copyright (c) 2005-2006 Cryptocom LTD                  *
  *         This file is distributed under the same license as OpenSSL *
  *                                                                    *
  *       Implementation of GOST R 34.10-94 signature algorithm        *
  *       for OpenSSL                                                  *
  *          Requires OpenSSL 0.9.9 for compilation                    *
  **********************************************************************/
 #include <string.h>
 #include <openssl/rand.h>
 #include <openssl/bn.h>
 #include <openssl/dsa.h>
 #include <openssl/evp.h>
 #include <openssl/err.h>

 #include "gost_params.h"
 #include "gost_lcl.h"
 #include "e_gost_err.h"

 #ifdef DEBUG_SIGN
 void dump_signature(const char *message, const unsigned char *buffer,
                     size_t len)
 {
     size_t i;
     fprintf(stderr, "signature %s Length=%d", message, len);
     for (i = 0; i < len; i++) {
         if (i % 16 == 0)
             fputc('\n', stderr);
         fprintf(stderr, " %02x", buffer[i]);
     }
     fprintf(stderr, "\nEnd of signature\n");
 }

 void dump_dsa_sig(const char *message, DSA_SIG *sig)
 {
     fprintf(stderr, "%s\nR=", message);
     BN_print_fp(stderr, sig->r);
     fprintf(stderr, "\nS=");
     BN_print_fp(stderr, sig->s);
     fprintf(stderr, "\n");
 }

 #else

 # define dump_signature(a,b,c)
 # define dump_dsa_sig(a,b)
 #endif

 /*
  * Computes signature and returns it as DSA_SIG structure
  */
 DSA_SIG *gost_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
 {
     BIGNUM *k = NULL, *tmp = NULL, *tmp2 = NULL;
     DSA_SIG *newsig = NULL, *ret = NULL;
     BIGNUM *md = hashsum2bn(dgst);
     /* check if H(M) mod q is zero */
     BN_CTX *ctx = BN_CTX_new();
     if(!ctx) {
         GOSTerr(GOST_F_GOST_DO_SIGN, ERR_R_MALLOC_FAILURE);
         goto err;
     }
     BN_CTX_start(ctx);
     newsig = DSA_SIG_new();
     if (!newsig) {
         GOSTerr(GOST_F_GOST_DO_SIGN, GOST_R_NO_MEMORY);
         goto err;
     }
     tmp = BN_CTX_get(ctx);
     k = BN_CTX_get(ctx);
     tmp2 = BN_CTX_get(ctx);
     if(!tmp || !k || !tmp2) {
         GOSTerr(GOST_F_GOST_DO_SIGN, ERR_R_MALLOC_FAILURE);
         goto err;
     }
     BN_mod(tmp, md, dsa->q, ctx);
     if (BN_is_zero(tmp)) {
         BN_one(md);
     }
     do {
         do {
             /*
              * Generate random number k less than q
              */
             BN_rand_range(k, dsa->q);
             /* generate r = (a^x mod p) mod q */
             BN_mod_exp(tmp, dsa->g, k, dsa->p, ctx);
             if (!(newsig->r)) {
                 newsig->r = BN_new();
                 if(!newsig->r) {
                     GOSTerr(GOST_F_GOST_DO_SIGN, ERR_R_MALLOC_FAILURE);
                     goto err;
                 }
             }
             BN_mod(newsig->r, tmp, dsa->q, ctx);
         }
         while (BN_is_zero(newsig->r));
         /* generate s = (xr + k(Hm)) mod q */
         BN_mod_mul(tmp, dsa->priv_key, newsig->r, dsa->q, ctx);
         BN_mod_mul(tmp2, k, md, dsa->q, ctx);
         if (!newsig->s) {
             newsig->s = BN_new();
             if(!newsig->s) {
                 GOSTerr(GOST_F_GOST_DO_SIGN, ERR_R_MALLOC_FAILURE);
                 goto err;
             }
         }
         BN_mod_add(newsig->s, tmp, tmp2, dsa->q, ctx);
     }
     while (BN_is_zero(newsig->s));

     ret = newsig;
  err:
     BN_free(md);
     if(ctx) {
         BN_CTX_end(ctx);
         BN_CTX_free(ctx);
     }
     if(!ret && newsig) {
         DSA_SIG_free(newsig);
     }
     return ret;
 }

 /*
  * Packs signature according to Cryptocom rules
  * and frees up DSA_SIG structure
  */
 /*-
 int pack_sign_cc(DSA_SIG *s,int order,unsigned char *sig, size_t *siglen)
         {
         *siglen = 2*order;
         memset(sig,0,*siglen);
         store_bignum(s->r, sig,order);
         store_bignum(s->s, sig + order,order);
         dump_signature("serialized",sig,*siglen);
         DSA_SIG_free(s);
         return 1;
         }
 */
 /*
  * Packs signature according to Cryptopro rules
  * and frees up DSA_SIG structure
  */
 int pack_sign_cp(DSA_SIG *s, int order, unsigned char *sig, size_t *siglen)
 {
     *siglen = 2 * order;
     memset(sig, 0, *siglen);
     store_bignum(s->s, sig, order);
     store_bignum(s->r, sig + order, order);
     dump_signature("serialized", sig, *siglen);
     DSA_SIG_free(s);
     return 1;
 }

 /*
  * Verifies signature passed as DSA_SIG structure
  *
  */

 int gost_do_verify(const unsigned char *dgst, int dgst_len,
                    DSA_SIG *sig, DSA *dsa)
 {
     BIGNUM *md = NULL, *tmp = NULL;
     BIGNUM *q2 = NULL;
     BIGNUM *u = NULL, *v = NULL, *z1 = NULL, *z2 = NULL;
     BIGNUM *tmp2 = NULL, *tmp3 = NULL;
     int ok = 0;
     BN_CTX *ctx = BN_CTX_new();
     if(!ctx) {
         GOSTerr(GOST_F_GOST_DO_VERIFY, ERR_R_MALLOC_FAILURE);
         goto err;
     }

     BN_CTX_start(ctx);
     if (BN_cmp(sig->s, dsa->q) >= 1 || BN_cmp(sig->r, dsa->q) >= 1) {
         GOSTerr(GOST_F_GOST_DO_VERIFY, GOST_R_SIGNATURE_PARTS_GREATER_THAN_Q);
         goto err;
     }
     md = hashsum2bn(dgst);

     tmp = BN_CTX_get(ctx);
     v = BN_CTX_get(ctx);
     q2 = BN_CTX_get(ctx);
     z1 = BN_CTX_get(ctx);
     z2 = BN_CTX_get(ctx);
     tmp2 = BN_CTX_get(ctx);
     tmp3 = BN_CTX_get(ctx);
     u = BN_CTX_get(ctx);
     if(!tmp || !v || !q2 || !z1 || !z2 || !tmp2 || !tmp3 || !u) {
         GOSTerr(GOST_F_GOST_DO_VERIFY, ERR_R_MALLOC_FAILURE);
         goto err;
     }

     BN_mod(tmp, md, dsa->q, ctx);
     if (BN_is_zero(tmp)) {
         BN_one(md);
     }
     BN_copy(q2, dsa->q);
     BN_sub_word(q2, 2);
     BN_mod_exp(v, md, q2, dsa->q, ctx);
     BN_mod_mul(z1, sig->s, v, dsa->q, ctx);
     BN_sub(tmp, dsa->q, sig->r);
     BN_mod_mul(z2, tmp, v, dsa->p, ctx);
     BN_mod_exp(tmp, dsa->g, z1, dsa->p, ctx);
     BN_mod_exp(tmp2, dsa->pub_key, z2, dsa->p, ctx);
     BN_mod_mul(tmp3, tmp, tmp2, dsa->p, ctx);
     BN_mod(u, tmp3, dsa->q, ctx);
     ok = (BN_cmp(u, sig->r) == 0);

     if (!ok) {
         GOSTerr(GOST_F_GOST_DO_VERIFY, GOST_R_SIGNATURE_MISMATCH);
     }
 err:
     if(md) BN_free(md);
     if(ctx) {
         BN_CTX_end(ctx);
         BN_CTX_free(ctx);
     }
     return ok;
 }

 /*
  * Computes public keys for GOST R 34.10-94 algorithm
  *
  */
 int gost94_compute_public(DSA *dsa)
 {
     /* Now fill algorithm parameters with correct values */
     BN_CTX *ctx;
     if (!dsa->g) {
         GOSTerr(GOST_F_GOST94_COMPUTE_PUBLIC, GOST_R_KEY_IS_NOT_INITALIZED);
         return 0;
     }
     ctx = BN_CTX_new();
     if(!ctx) {
         GOSTerr(GOST_F_GOST94_COMPUTE_PUBLIC, ERR_R_MALLOC_FAILURE);
         return 0;
     }

     dsa->pub_key = BN_new();
     if(!dsa->pub_key) {
         GOSTerr(GOST_F_GOST94_COMPUTE_PUBLIC, ERR_R_MALLOC_FAILURE);
         BN_CTX_free(ctx);
         return 0;
     }
     /* Compute public key  y = a^x mod p */
     BN_mod_exp(dsa->pub_key, dsa->g, dsa->priv_key, dsa->p, ctx);
     BN_CTX_free(ctx);
     return 1;
 }

 /*
  * Fill GOST 94 params, searching them in R3410_paramset array
  * by nid of paramset
  *
  */
 int fill_GOST94_params(DSA *dsa, int nid)
 {
     R3410_params *params = R3410_paramset;
     while (params->nid != NID_undef && params->nid != nid)
         params++;
     if (params->nid == NID_undef) {
         GOSTerr(GOST_F_FILL_GOST94_PARAMS, GOST_R_UNSUPPORTED_PARAMETER_SET);
         return 0;
     }
 #define dump_signature(a,b,c)
     if (dsa->p) {
         BN_free(dsa->p);
     }
     dsa->p = NULL;
     BN_dec2bn(&(dsa->p), params->p);
     if (dsa->q) {
         BN_free(dsa->q);
     }
     dsa->q = NULL;
     BN_dec2bn(&(dsa->q), params->q);
     if (dsa->g) {
         BN_free(dsa->g);
     }
     dsa->g = NULL;
     BN_dec2bn(&(dsa->g), params->a);
     return 1;
 }

 /*
  *  Generate GOST R 34.10-94 keypair
  *
  *
  */
 int gost_sign_keygen(DSA *dsa)
 {
     dsa->priv_key = BN_new();
     if(!dsa->priv_key) {
         GOSTerr(GOST_F_GOST_SIGN_KEYGEN, ERR_R_MALLOC_FAILURE);
         return 0;
     }
     BN_rand_range(dsa->priv_key, dsa->q);
     return gost94_compute_public(dsa);
 }

 /* Unpack signature according to cryptocom rules  */
 /*-
 DSA_SIG *unpack_cc_signature(const unsigned char *sig,size_t siglen)
         {
         DSA_SIG *s;
         s = DSA_SIG_new();
         if (s == NULL)
                 {
                 GOSTerr(GOST_F_UNPACK_CC_SIGNATURE,GOST_R_NO_MEMORY);
                 return(NULL);
                 }
         s->r = getbnfrombuf(sig, siglen/2);
         s->s = getbnfrombuf(sig + siglen/2, siglen/2);
         return s;
         }
 */
 /* Unpack signature according to cryptopro rules  */
 DSA_SIG *unpack_cp_signature(const unsigned char *sig, size_t siglen)
 {
     DSA_SIG *s;

     s = DSA_SIG_new();
     if (s == NULL) {
         GOSTerr(GOST_F_UNPACK_CP_SIGNATURE, GOST_R_NO_MEMORY);
         return NULL;
     }
     s->s = getbnfrombuf(sig, siglen / 2);
     s->r = getbnfrombuf(sig + siglen / 2, siglen / 2);
     return s;
 }

 /* Convert little-endian byte array into bignum */
 BIGNUM *hashsum2bn(const unsigned char *dgst)
 {
     unsigned char buf[32];
     int i;
     for (i = 0; i < 32; i++) {
         buf[31 - i] = dgst[i];
     }
     return getbnfrombuf(buf, 32);
 }

 /* Convert byte buffer to bignum, skipping leading zeros*/
 BIGNUM *getbnfrombuf(const unsigned char *buf, size_t len)
 {
     while (*buf == 0 && len > 0) {
         buf++;
         len--;
     }
     if (len) {
         return BN_bin2bn(buf, len, NULL);
     } else {
         BIGNUM *b = BN_new();
         BN_zero(b);
         return b;
     }
 }

 /*
  * Pack bignum into byte buffer of given size, filling all leading bytes by
  * zeros
  */
 int store_bignum(BIGNUM *bn, unsigned char *buf, int len)
 {
     int bytes = BN_num_bytes(bn);
     if (bytes > len)
         return 0;
     memset(buf, 0, len);
     BN_bn2bin(bn, buf + len - bytes);
     return 1;
 }
	/**********************************************************************
	* gost_sign.c *
	* Copyright (c) 2005-2006 Cryptocom LTD *
	* This file is distributed under the same license as OpenSSL *
	* *
	* Implementation of GOST R 34.10-94 signature algorithm *
	* for OpenSSL *
	* Requires OpenSSL 0.9.9 for compilation *
	**********************************************************************/
	#include <string.h>
	#include <openssl/rand.h>
	#include <openssl/bn.h>
	#include <openssl/dsa.h>
	#include <openssl/evp.h>
	#include <openssl/err.h>

	#include "gost_params.h"
	#include "gost_lcl.h"
	#include "e_gost_err.h"

	#ifdef DEBUG_SIGN
	void dump_signature(const char message, const unsigned char buffer,
	size_t len)
	{
	size_t i;
	fprintf(stderr, "signature %s Length=%d", message, len);
	for (i = 0; i < len; i++) {
	if (i % 16 == 0)
	fputc('\n', stderr);
	fprintf(stderr, " %02x", buffer[i]);
	}
	fprintf(stderr, "\nEnd of signature\n");
	}

	void dump_dsa_sig(const char message, DSA_SIG sig)
	{
	fprintf(stderr, "%s\nR=", message);
	BN_print_fp(stderr, sig->r);
	fprintf(stderr, "\nS=");
	BN_print_fp(stderr, sig->s);
	fprintf(stderr, "\n");
	}

	#else

	# define dump_signature(a,b,c)
	# define dump_dsa_sig(a,b)
	#endif

	/*
	* Computes signature and returns it as DSA_SIG structure
	*/
	DSA_SIG gost_do_sign(const unsigned char dgst, int dlen, DSA *dsa)
	{
	BIGNUM k = NULL, tmp = NULL, *tmp2 = NULL;
	DSA_SIG newsig = NULL, ret = NULL;
	BIGNUM *md = hashsum2bn(dgst);
	/* check if H(M) mod q is zero */
	BN_CTX *ctx = BN_CTX_new();
	if(!ctx) {
	GOSTerr(GOST_F_GOST_DO_SIGN, ERR_R_MALLOC_FAILURE);
	goto err;
	}
	BN_CTX_start(ctx);
	newsig = DSA_SIG_new();
	if (!newsig) {
	GOSTerr(GOST_F_GOST_DO_SIGN, GOST_R_NO_MEMORY);
	goto err;
	}
	tmp = BN_CTX_get(ctx);
	k = BN_CTX_get(ctx);
	tmp2 = BN_CTX_get(ctx);
	if(!tmp \|\| !k \|\| !tmp2) {
	GOSTerr(GOST_F_GOST_DO_SIGN, ERR_R_MALLOC_FAILURE);
	goto err;
	}
	BN_mod(tmp, md, dsa->q, ctx);
	if (BN_is_zero(tmp)) {
	BN_one(md);
	}
	do {
	do {
	/*
	* Generate random number k less than q
	*/
	BN_rand_range(k, dsa->q);
	/* generate r = (a^x mod p) mod q */
	BN_mod_exp(tmp, dsa->g, k, dsa->p, ctx);
	if (!(newsig->r)) {
	newsig->r = BN_new();
	if(!newsig->r) {
	GOSTerr(GOST_F_GOST_DO_SIGN, ERR_R_MALLOC_FAILURE);
	goto err;
	}
	}
	BN_mod(newsig->r, tmp, dsa->q, ctx);
	}
	while (BN_is_zero(newsig->r));
	/* generate s = (xr + k(Hm)) mod q */
	BN_mod_mul(tmp, dsa->priv_key, newsig->r, dsa->q, ctx);
	BN_mod_mul(tmp2, k, md, dsa->q, ctx);
	if (!newsig->s) {
	newsig->s = BN_new();
	if(!newsig->s) {
	GOSTerr(GOST_F_GOST_DO_SIGN, ERR_R_MALLOC_FAILURE);
	goto err;
	}
	}
	BN_mod_add(newsig->s, tmp, tmp2, dsa->q, ctx);
	}
	while (BN_is_zero(newsig->s));

	ret = newsig;
	err:
	BN_free(md);
	if(ctx) {
	BN_CTX_end(ctx);
	BN_CTX_free(ctx);
	}
	if(!ret && newsig) {
	DSA_SIG_free(newsig);
	}
	return ret;
	}

	/*
	* Packs signature according to Cryptocom rules
	* and frees up DSA_SIG structure
	*/
	/*-
	int pack_sign_cc(DSA_SIG s,int order,unsigned char sig, size_t *siglen)
	{
	siglen = 2order;
	memset(sig,0,*siglen);
	store_bignum(s->r, sig,order);
	store_bignum(s->s, sig + order,order);
	dump_signature("serialized",sig,*siglen);
	DSA_SIG_free(s);
	return 1;
	}
	*/
	/*
	* Packs signature according to Cryptopro rules
	* and frees up DSA_SIG structure
	*/
	int pack_sign_cp(DSA_SIG s, int order, unsigned char sig, size_t *siglen)
	{
	siglen = 2 order;
	memset(sig, 0, *siglen);
	store_bignum(s->s, sig, order);
	store_bignum(s->r, sig + order, order);
	dump_signature("serialized", sig, *siglen);
	DSA_SIG_free(s);
	return 1;
	}

	/*
	* Verifies signature passed as DSA_SIG structure
	*
	*/

	int gost_do_verify(const unsigned char *dgst, int dgst_len,
	DSA_SIG sig, DSA dsa)
	{
	BIGNUM md = NULL, tmp = NULL;
	BIGNUM *q2 = NULL;
	BIGNUM u = NULL, v = NULL, z1 = NULL, z2 = NULL;
	BIGNUM tmp2 = NULL, tmp3 = NULL;
	int ok = 0;
	BN_CTX *ctx = BN_CTX_new();
	if(!ctx) {
	GOSTerr(GOST_F_GOST_DO_VERIFY, ERR_R_MALLOC_FAILURE);
	goto err;
	}

	BN_CTX_start(ctx);
	if (BN_cmp(sig->s, dsa->q) >= 1 \|\| BN_cmp(sig->r, dsa->q) >= 1) {
	GOSTerr(GOST_F_GOST_DO_VERIFY, GOST_R_SIGNATURE_PARTS_GREATER_THAN_Q);
	goto err;
	}
	md = hashsum2bn(dgst);

	tmp = BN_CTX_get(ctx);
	v = BN_CTX_get(ctx);
	q2 = BN_CTX_get(ctx);
	z1 = BN_CTX_get(ctx);
	z2 = BN_CTX_get(ctx);
	tmp2 = BN_CTX_get(ctx);
	tmp3 = BN_CTX_get(ctx);
	u = BN_CTX_get(ctx);
	if(!tmp \|\| !v \|\| !q2 \|\| !z1 \|\| !z2 \|\| !tmp2 \|\| !tmp3 \|\| !u) {
	GOSTerr(GOST_F_GOST_DO_VERIFY, ERR_R_MALLOC_FAILURE);
	goto err;
	}

	BN_mod(tmp, md, dsa->q, ctx);
	if (BN_is_zero(tmp)) {
	BN_one(md);
	}
	BN_copy(q2, dsa->q);
	BN_sub_word(q2, 2);
	BN_mod_exp(v, md, q2, dsa->q, ctx);
	BN_mod_mul(z1, sig->s, v, dsa->q, ctx);
	BN_sub(tmp, dsa->q, sig->r);
	BN_mod_mul(z2, tmp, v, dsa->p, ctx);
	BN_mod_exp(tmp, dsa->g, z1, dsa->p, ctx);
	BN_mod_exp(tmp2, dsa->pub_key, z2, dsa->p, ctx);
	BN_mod_mul(tmp3, tmp, tmp2, dsa->p, ctx);
	BN_mod(u, tmp3, dsa->q, ctx);
	ok = (BN_cmp(u, sig->r) == 0);

	if (!ok) {
	GOSTerr(GOST_F_GOST_DO_VERIFY, GOST_R_SIGNATURE_MISMATCH);
	}
	err:
	if(md) BN_free(md);
	if(ctx) {
	BN_CTX_end(ctx);
	BN_CTX_free(ctx);
	}
	return ok;
	}

	/*
	* Computes public keys for GOST R 34.10-94 algorithm
	*
	*/
	int gost94_compute_public(DSA *dsa)
	{
	/* Now fill algorithm parameters with correct values */
	BN_CTX *ctx;
	if (!dsa->g) {
	GOSTerr(GOST_F_GOST94_COMPUTE_PUBLIC, GOST_R_KEY_IS_NOT_INITALIZED);
	return 0;
	}
	ctx = BN_CTX_new();
	if(!ctx) {
	GOSTerr(GOST_F_GOST94_COMPUTE_PUBLIC, ERR_R_MALLOC_FAILURE);
	return 0;
	}

	dsa->pub_key = BN_new();
	if(!dsa->pub_key) {
	GOSTerr(GOST_F_GOST94_COMPUTE_PUBLIC, ERR_R_MALLOC_FAILURE);
	BN_CTX_free(ctx);
	return 0;
	}
	/* Compute public key y = a^x mod p */
	BN_mod_exp(dsa->pub_key, dsa->g, dsa->priv_key, dsa->p, ctx);
	BN_CTX_free(ctx);
	return 1;
	}

	/*
	* Fill GOST 94 params, searching them in R3410_paramset array
	* by nid of paramset
	*
	*/
	int fill_GOST94_params(DSA *dsa, int nid)
	{
	R3410_params *params = R3410_paramset;
	while (params->nid != NID_undef && params->nid != nid)
	params++;
	if (params->nid == NID_undef) {
	GOSTerr(GOST_F_FILL_GOST94_PARAMS, GOST_R_UNSUPPORTED_PARAMETER_SET);
	return 0;
	}
	#define dump_signature(a,b,c)
	if (dsa->p) {
	BN_free(dsa->p);
	}
	dsa->p = NULL;
	BN_dec2bn(&(dsa->p), params->p);
	if (dsa->q) {
	BN_free(dsa->q);
	}
	dsa->q = NULL;
	BN_dec2bn(&(dsa->q), params->q);
	if (dsa->g) {
	BN_free(dsa->g);
	}
	dsa->g = NULL;
	BN_dec2bn(&(dsa->g), params->a);
	return 1;
	}

	/*
	* Generate GOST R 34.10-94 keypair
	*
	*
	*/
	int gost_sign_keygen(DSA *dsa)
	{
	dsa->priv_key = BN_new();
	if(!dsa->priv_key) {
	GOSTerr(GOST_F_GOST_SIGN_KEYGEN, ERR_R_MALLOC_FAILURE);
	return 0;
	}
	BN_rand_range(dsa->priv_key, dsa->q);
	return gost94_compute_public(dsa);
	}

	/* Unpack signature according to cryptocom rules */
	/*-
	DSA_SIG unpack_cc_signature(const unsigned char sig,size_t siglen)
	{
	DSA_SIG *s;
	s = DSA_SIG_new();
	if (s == NULL)
	{
	GOSTerr(GOST_F_UNPACK_CC_SIGNATURE,GOST_R_NO_MEMORY);
	return(NULL);
	}
	s->r = getbnfrombuf(sig, siglen/2);
	s->s = getbnfrombuf(sig + siglen/2, siglen/2);
	return s;
	}
	*/
	/* Unpack signature according to cryptopro rules */
	DSA_SIG unpack_cp_signature(const unsigned char sig, size_t siglen)
	{
	DSA_SIG *s;

	s = DSA_SIG_new();
	if (s == NULL) {
	GOSTerr(GOST_F_UNPACK_CP_SIGNATURE, GOST_R_NO_MEMORY);
	return NULL;
	}
	s->s = getbnfrombuf(sig, siglen / 2);
	s->r = getbnfrombuf(sig + siglen / 2, siglen / 2);
	return s;
	}

	/* Convert little-endian byte array into bignum */
	BIGNUM hashsum2bn(const unsigned char dgst)
	{
	unsigned char buf[32];
	int i;
	for (i = 0; i < 32; i++) {
	buf[31 - i] = dgst[i];
	}
	return getbnfrombuf(buf, 32);
	}

	/* Convert byte buffer to bignum, skipping leading zeros*/
	BIGNUM getbnfrombuf(const unsigned char buf, size_t len)
	{
	while (*buf == 0 && len > 0) {
	buf++;
	len--;
	}
	if (len) {
	return BN_bin2bn(buf, len, NULL);
	} else {
	BIGNUM *b = BN_new();
	BN_zero(b);
	return b;
	}
	}

	/*
	* Pack bignum into byte buffer of given size, filling all leading bytes by
	* zeros
	*/
	int store_bignum(BIGNUM bn, unsigned char buf, int len)
	{
	int bytes = BN_num_bytes(bn);
	if (bytes > len)
	return 0;
	memset(buf, 0, len);
	BN_bn2bin(bn, buf + len - bytes);
	return 1;
	}