/**********************************************************************
 *                          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 algoritgthm      *
 *       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 "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 = DSA_SIG_new();
	BIGNUM *md = hashsum2bn(dgst);
	/* check if H(M) mod q is zero */
	BN_CTX *ctx=BN_CTX_new();
	BN_CTX_start(ctx);
	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);
	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();
			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();
		BN_mod_add(newsig->s,tmp,tmp2,dsa->q,ctx);
		}
	while (BN_is_zero(newsig->s));		
	err:
	BN_free(md);
	BN_CTX_end(ctx);
	BN_CTX_free(ctx);
	return newsig;
	}	


/*
 * 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, *tmp=NULL;
	BIGNUM *q2=NULL;
	BIGNUM *u=NULL,*v=NULL,*z1=NULL,*z2=NULL;
	BIGNUM *tmp2=NULL,*tmp3=NULL;
	int ok;
	BN_CTX *ctx = BN_CTX_new();

	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);
		return 0;
		}
	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);
	
	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);
	
	BN_free(md);
	BN_CTX_end(ctx);
	BN_CTX_free(ctx);
	if (ok!=0)
		{
		GOSTerr(GOST_F_GOST_DO_VERIFY,GOST_R_SIGNATURE_MISMATCH);
		}	
	return (ok==0);
	}

/*
 * 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 = BN_CTX_new();
	if (!dsa->g)
		{
		GOSTerr(GOST_F_GOST_COMPUTE_PUBLIC,GOST_R_KEY_IS_NOT_INITALIZED);
		return 0;
		}	
	/* Compute public key  y = a^x mod p */
	dsa->pub_key=BN_new();
	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();
	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;
	}