[u/mdw/putty] / sshdss.c

#include <stdio.h>
#include <stdlib.h>

#include "ssh.h"

#define GET_32BIT(cp) \
    (((unsigned long)(unsigned char)(cp)[0] << 24) | \
    ((unsigned long)(unsigned char)(cp)[1] << 16) | \
    ((unsigned long)(unsigned char)(cp)[2] << 8) | \
    ((unsigned long)(unsigned char)(cp)[3]))

#define PUT_32BIT(cp, value) { \
    (cp)[0] = (unsigned char)((value) >> 24); \
    (cp)[1] = (unsigned char)((value) >> 16); \
    (cp)[2] = (unsigned char)((value) >> 8); \
    (cp)[3] = (unsigned char)(value); }

#if 0
#define DEBUG_DSS
#else
#define diagbn(x,y)
#endif

static void getstring(char **data, int *datalen, char **p, int *length) {
    *p = NULL;
    if (*datalen < 4)
        return;
    *length = GET_32BIT(*data);
    *datalen -= 4; *data += 4;
    if (*datalen < *length)
        return;
    *p = *data;
    *data += *length; *datalen -= *length;
}
static Bignum getmp(char **data, int *datalen) {
    char *p;
    int length;
    Bignum b;

    getstring(data, datalen, &p, &length);
    if (!p)
        return NULL;
    if (p[0] & 0x80)
        return NULL;                   /* negative mp */
    b = bignum_from_bytes(p, length);
    return b;
}

static Bignum get160(char **data, int *datalen) {
    Bignum b;

    b = bignum_from_bytes(*data, 20);
    *data += 20; *datalen -= 20;

    return b;
}

struct dss_key {
    Bignum p, q, g, y;
};

static void *dss_newkey(char *data, int len) {
    char *p;
    int slen;
    struct dss_key *dss;

    dss = smalloc(sizeof(struct dss_key));
    if (!dss) return NULL;
    getstring(&data, &len, &p, &slen);

#ifdef DEBUG_DSS
    {
        int i;
        printf("key:");
        for (i=0;i<len;i++)
            printf("  %02x", (unsigned char)(data[i]));
        printf("\n");
    }
#endif

    if (!p || memcmp(p, "ssh-dss", 7)) {
	sfree(dss);
	return NULL;
    }
    dss->p = getmp(&data, &len);
    dss->q = getmp(&data, &len);
    dss->g = getmp(&data, &len);
    dss->y = getmp(&data, &len);

    return dss;
}

static void dss_freekey(void *key) {
    struct dss_key *dss = (struct dss_key *)key;
    freebn(dss->p);
    freebn(dss->q);
    freebn(dss->g);
    freebn(dss->y);
    sfree(dss);
}

static char *dss_fmtkey(void *key) {
    struct dss_key *dss = (struct dss_key *)key;
    char *p;
    int len, i, pos, nibbles;
    static const char hex[] = "0123456789abcdef";
    if (!dss->p)
        return NULL;
    len = 8 + 4 + 1;                   /* 4 x "0x", punctuation, \0 */
    len += 4 * (ssh1_bignum_bitcount(dss->p)+15)/16;
    len += 4 * (ssh1_bignum_bitcount(dss->q)+15)/16;
    len += 4 * (ssh1_bignum_bitcount(dss->g)+15)/16;
    len += 4 * (ssh1_bignum_bitcount(dss->y)+15)/16;
    p = smalloc(len);
    if (!p) return NULL;

    pos = 0;
    pos += sprintf(p+pos, "0x");
    nibbles = (3 + ssh1_bignum_bitcount(dss->p))/4; if (nibbles<1) nibbles=1;
    for (i=nibbles; i-- ;)
        p[pos++] = hex[(bignum_byte(dss->p, i/2) >> (4*(i%2))) & 0xF];
    pos += sprintf(p+pos, ",0x");
    nibbles = (3 + ssh1_bignum_bitcount(dss->q))/4; if (nibbles<1) nibbles=1;
    for (i=nibbles; i-- ;)
        p[pos++] = hex[(bignum_byte(dss->q, i/2) >> (4*(i%2))) & 0xF];
    pos += sprintf(p+pos, ",0x");
    nibbles = (3 + ssh1_bignum_bitcount(dss->g))/4; if (nibbles<1) nibbles=1;
    for (i=nibbles; i-- ;)
        p[pos++] = hex[(bignum_byte(dss->g, i/2) >> (4*(i%2))) & 0xF];
    pos += sprintf(p+pos, ",0x");
    nibbles = (3 + ssh1_bignum_bitcount(dss->y))/4; if (nibbles<1) nibbles=1;
    for (i=nibbles; i-- ;)
        p[pos++] = hex[(bignum_byte(dss->y, i/2) >> (4*(i%2))) & 0xF];
    p[pos] = '\0';
    return p;
}

static char *dss_fingerprint(void *key) {
    struct dss_key *dss = (struct dss_key *)key;
    struct MD5Context md5c;
    unsigned char digest[16], lenbuf[4];
    char buffer[16*3+40];
    char *ret;
    int numlen, i;

    MD5Init(&md5c);
    MD5Update(&md5c, "\0\0\0\7ssh-dss", 11);

#define ADD_BIGNUM(bignum) \
    numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \
    PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \
    for (i = numlen; i-- ;) { \
        unsigned char c = bignum_byte(bignum, i); \
        MD5Update(&md5c, &c, 1); \
    }
    ADD_BIGNUM(dss->p);
    ADD_BIGNUM(dss->q);
    ADD_BIGNUM(dss->g);
    ADD_BIGNUM(dss->y);
#undef ADD_BIGNUM

    MD5Final(digest, &md5c);

    sprintf(buffer, "ssh-dss %d ", ssh1_bignum_bitcount(dss->p));
    for (i = 0; i < 16; i++)
        sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
    ret = smalloc(strlen(buffer)+1);
    if (ret)
        strcpy(ret, buffer);
    return ret;
}

static int dss_verifysig(void *key, char *sig, int siglen,
			 char *data, int datalen) {
    struct dss_key *dss = (struct dss_key *)key;
    char *p;
    int slen;
    char hash[20];
    Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v;
    int ret;

    if (!dss->p)
        return 0;

#ifdef DEBUG_DSS
    {
        int i;
        printf("sig:");
        for (i=0;i<siglen;i++)
            printf("  %02x", (unsigned char)(sig[i]));
        printf("\n");
    }
#endif
    /*
     * Commercial SSH (2.0.13) and OpenSSH disagree over the format
     * of a DSA signature. OpenSSH is in line with the IETF drafts:
     * it uses a string "ssh-dss", followed by a 40-byte string
     * containing two 160-bit integers end-to-end. Commercial SSH
     * can't be bothered with the header bit, and considers a DSA
     * signature blob to be _just_ the 40-byte string containing
     * the two 160-bit integers. We tell them apart by measuring
     * the length: length 40 means the commercial-SSH bug, anything
     * else is assumed to be IETF-compliant.
     */
    if (siglen != 40) {                /* bug not present; read admin fields */
        getstring(&sig, &siglen, &p, &slen);
        if (!p || slen != 7 || memcmp(p, "ssh-dss", 7)) {
            return 0;
        }
        sig += 4, siglen -= 4;             /* skip yet another length field */
    }
    diagbn("p=", dss->p);
    diagbn("q=", dss->q);
    diagbn("g=", dss->g);
    diagbn("y=", dss->y);
    r = get160(&sig, &siglen);
    diagbn("r=", r);
    s = get160(&sig, &siglen);
    diagbn("s=", s);
    if (!r || !s)
        return 0;

    /*
     * Step 1. w <- s^-1 mod q.
     */
    w = modinv(s, dss->q);
    diagbn("w=", w);

    /*
     * Step 2. u1 <- SHA(message) * w mod q.
     */
    SHA_Simple(data, datalen, hash);
    p = hash; slen = 20; sha = get160(&p, &slen);
    diagbn("sha=", sha);
    u1 = modmul(sha, w, dss->q);
    diagbn("u1=", u1);

    /*
     * Step 3. u2 <- r * w mod q.
     */
    u2 = modmul(r, w, dss->q);
    diagbn("u2=", u2);

    /*
     * Step 4. v <- (g^u1 * y^u2 mod p) mod q.
     */
    gu1p = modpow(dss->g, u1, dss->p);
    diagbn("gu1p=", gu1p);
    yu2p = modpow(dss->y, u2, dss->p);
    diagbn("yu2p=", yu2p);
    gu1yu2p = modmul(gu1p, yu2p, dss->p);
    diagbn("gu1yu2p=", gu1yu2p);
    v = modmul(gu1yu2p, One, dss->q);
    diagbn("gu1yu2q=v=", v);
    diagbn("r=", r);

    /*
     * Step 5. v should now be equal to r.
     */

    ret = !bignum_cmp(v, r);

    freebn(w);
    freebn(sha);
    freebn(gu1p);
    freebn(yu2p);
    freebn(gu1yu2p);
    freebn(v);
    freebn(r);
    freebn(s);

    return ret;
}

int dss_sign(void *key, char *sig, int siglen,
	     char *data, int datalen) {
    return 0;			       /* do nothing */
}

struct ssh_signkey ssh_dss = {
    dss_newkey,
    dss_freekey,
    dss_fmtkey,
    dss_fingerprint,
    dss_verifysig,
    dss_sign,
    "ssh-dss",
    "dss"
};
Commit	Line	Data
7cca0d81	1	#include <stdio.h>
	2	#include <stdlib.h>
	3
e5574168	4	#include "ssh.h"
e5574168	5
7cca0d81	6	#define GET_32BIT(cp) \
	7	(((unsigned long)(unsigned char)(cp)[0] << 24) \| \
	8	((unsigned long)(unsigned char)(cp)[1] << 16) \| \
	9	((unsigned long)(unsigned char)(cp)[2] << 8) \| \
	10	((unsigned long)(unsigned char)(cp)[3]))
	11
d5859615	12	#define PUT_32BIT(cp, value) { \
	13	(cp)[0] = (unsigned char)((value) >> 24); \
	14	(cp)[1] = (unsigned char)((value) >> 16); \
	15	(cp)[2] = (unsigned char)((value) >> 8); \
	16	(cp)[3] = (unsigned char)(value); }
	17
9c621433	18	#if 0
c5fbd713	19	#define DEBUG_DSS
9c621433	20	#else
	21	#define diagbn(x,y)
	22	#endif
	23
7cca0d81	24	static void getstring(char *data, int datalen, char *p, int length) {
	25	*p = NULL;
	26	if (*datalen < 4)
	27	return;
	28	length = GET_32BIT(data);
	29	datalen -= 4; data += 4;
	30	if (datalen < length)
	31	return;
	32	p = data;
	33	data += length; datalen -= length;
	34	}
	35	static Bignum getmp(char *data, int datalen) {
	36	char *p;
3709bfe9	37	int length;
7cca0d81	38	Bignum b;
	39
	40	getstring(data, datalen, &p, &length);
	41	if (!p)
	42	return NULL;
	43	if (p[0] & 0x80)
	44	return NULL; /* negative mp */
3709bfe9	45	b = bignum_from_bytes(p, length);
7cca0d81	46	return b;
	47	}
	48
	49	static Bignum get160(char *data, int datalen) {
7cca0d81	50	Bignum b;
7cca0d81	51
3709bfe9	52	b = bignum_from_bytes(*data, 20);
7cca0d81	53	data += 20; datalen -= 20;
7cca0d81	54
7cca0d81	55	return b;
	56	}
	57
e055a386	58	struct dss_key {
	59	Bignum p, q, g, y;
	60	};
7cca0d81	61
e055a386	62	static void dss_newkey(char data, int len) {
7cca0d81	63	char *p;
7cca0d81	64	int slen;
e055a386	65	struct dss_key *dss;
e055a386	66
dcbde236	67	dss = smalloc(sizeof(struct dss_key));
e055a386	68	if (!dss) return NULL;
7cca0d81	69	getstring(&data, &len, &p, &slen);
9c621433	70
	71	#ifdef DEBUG_DSS
	72	{
	73	int i;
	74	printf("key:");
	75	for (i=0;i<len;i++)
	76	printf(" %02x", (unsigned char)(data[i]));
	77	printf("\n");
	78	}
	79	#endif
	80
7cca0d81	81	if (!p \|\| memcmp(p, "ssh-dss", 7)) {
dcbde236	82	sfree(dss);
e055a386	83	return NULL;
7cca0d81	84	}
e055a386	85	dss->p = getmp(&data, &len);
	86	dss->q = getmp(&data, &len);
	87	dss->g = getmp(&data, &len);
	88	dss->y = getmp(&data, &len);
	89
	90	return dss;
7cca0d81	91	}
7cca0d81	92
e055a386	93	static void dss_freekey(void *key) {
	94	struct dss_key dss = (struct dss_key )key;
	95	freebn(dss->p);
	96	freebn(dss->q);
	97	freebn(dss->g);
	98	freebn(dss->y);
dcbde236	99	sfree(dss);
e055a386	100	}
	101
	102	static char dss_fmtkey(void key) {
	103	struct dss_key dss = (struct dss_key )key;
7cca0d81	104	char *p;
d5859615	105	int len, i, pos, nibbles;
d5859615	106	static const char hex[] = "0123456789abcdef";
e055a386	107	if (!dss->p)
7cca0d81	108	return NULL;
d5859615	109	len = 8 + 4 + 1; /* 4 x "0x", punctuation, \0 */
3709bfe9	110	len += 4 * (ssh1_bignum_bitcount(dss->p)+15)/16;
	111	len += 4 * (ssh1_bignum_bitcount(dss->q)+15)/16;
	112	len += 4 * (ssh1_bignum_bitcount(dss->g)+15)/16;
	113	len += 4 * (ssh1_bignum_bitcount(dss->y)+15)/16;
dcbde236	114	p = smalloc(len);
7cca0d81	115	if (!p) return NULL;
d5859615	116
	117	pos = 0;
	118	pos += sprintf(p+pos, "0x");
e055a386	119	nibbles = (3 + ssh1_bignum_bitcount(dss->p))/4; if (nibbles<1) nibbles=1;
d5859615	120	for (i=nibbles; i-- ;)
e055a386	121	p[pos++] = hex[(bignum_byte(dss->p, i/2) >> (4*(i%2))) & 0xF];
3aa0b691	122	pos += sprintf(p+pos, ",0x");
e055a386	123	nibbles = (3 + ssh1_bignum_bitcount(dss->q))/4; if (nibbles<1) nibbles=1;
d5859615	124	for (i=nibbles; i-- ;)
e055a386	125	p[pos++] = hex[(bignum_byte(dss->q, i/2) >> (4*(i%2))) & 0xF];
3aa0b691	126	pos += sprintf(p+pos, ",0x");
e055a386	127	nibbles = (3 + ssh1_bignum_bitcount(dss->g))/4; if (nibbles<1) nibbles=1;
d5859615	128	for (i=nibbles; i-- ;)
e055a386	129	p[pos++] = hex[(bignum_byte(dss->g, i/2) >> (4*(i%2))) & 0xF];
3aa0b691	130	pos += sprintf(p+pos, ",0x");
e055a386	131	nibbles = (3 + ssh1_bignum_bitcount(dss->y))/4; if (nibbles<1) nibbles=1;
d5859615	132	for (i=nibbles; i-- ;)
e055a386	133	p[pos++] = hex[(bignum_byte(dss->y, i/2) >> (4*(i%2))) & 0xF];
d5859615	134	p[pos] = '\0';
7cca0d81	135	return p;
	136	}
	137
e055a386	138	static char dss_fingerprint(void key) {
e055a386	139	struct dss_key dss = (struct dss_key )key;
d5859615	140	struct MD5Context md5c;
	141	unsigned char digest[16], lenbuf[4];
	142	char buffer[16*3+40];
	143	char *ret;
	144	int numlen, i;
	145
	146	MD5Init(&md5c);
	147	MD5Update(&md5c, "\0\0\0\7ssh-dss", 11);
	148
	149	#define ADD_BIGNUM(bignum) \
	150	numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \
	151	PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \
	152	for (i = numlen; i-- ;) { \
	153	unsigned char c = bignum_byte(bignum, i); \
	154	MD5Update(&md5c, &c, 1); \
	155	}
e055a386	156	ADD_BIGNUM(dss->p);
	157	ADD_BIGNUM(dss->q);
	158	ADD_BIGNUM(dss->g);
	159	ADD_BIGNUM(dss->y);
d5859615	160	#undef ADD_BIGNUM
	161
	162	MD5Final(digest, &md5c);
	163
5d03233b	164	sprintf(buffer, "ssh-dss %d ", ssh1_bignum_bitcount(dss->p));
d5859615	165	for (i = 0; i < 16; i++)
d5859615	166	sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
dcbde236	167	ret = smalloc(strlen(buffer)+1);
d5859615	168	if (ret)
	169	strcpy(ret, buffer);
	170	return ret;
	171	}
	172
e055a386	173	static int dss_verifysig(void key, char sig, int siglen,
	174	char *data, int datalen) {
	175	struct dss_key dss = (struct dss_key )key;
7cca0d81	176	char *p;
c5fbd713	177	int slen;
7cca0d81	178	char hash[20];
59600f67	179	Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v;
7cca0d81	180	int ret;
7cca0d81	181
e055a386	182	if (!dss->p)
7cca0d81	183	return 0;
7cca0d81	184
9c621433	185	#ifdef DEBUG_DSS
	186	{
	187	int i;
	188	printf("sig:");
	189	for (i=0;i<siglen;i++)
3709bfe9	190	printf(" %02x", (unsigned char)(sig[i]));
9c621433	191	printf("\n");
	192	}
	193	#endif
7f7837c8	194	/*
	195	* Commercial SSH (2.0.13) and OpenSSH disagree over the format
	196	* of a DSA signature. OpenSSH is in line with the IETF drafts:
	197	* it uses a string "ssh-dss", followed by a 40-byte string
	198	* containing two 160-bit integers end-to-end. Commercial SSH
	199	* can't be bothered with the header bit, and considers a DSA
	200	* signature blob to be _just_ the 40-byte string containing
	201	* the two 160-bit integers. We tell them apart by measuring
	202	* the length: length 40 means the commercial-SSH bug, anything
	203	* else is assumed to be IETF-compliant.
	204	*/
	205	if (siglen != 40) { /* bug not present; read admin fields */
	206	getstring(&sig, &siglen, &p, &slen);
efa4a6f2	207	if (!p \|\| slen != 7 \|\| memcmp(p, "ssh-dss", 7)) {
7f7837c8	208	return 0;
	209	}
	210	sig += 4, siglen -= 4; /* skip yet another length field */
7cca0d81	211	}
e055a386	212	diagbn("p=", dss->p);
	213	diagbn("q=", dss->q);
	214	diagbn("g=", dss->g);
	215	diagbn("y=", dss->y);
7cca0d81	216	r = get160(&sig, &siglen);
9c621433	217	diagbn("r=", r);
7cca0d81	218	s = get160(&sig, &siglen);
9c621433	219	diagbn("s=", s);
7cca0d81	220	if (!r \|\| !s)
	221	return 0;
	222
	223	/*
	224	* Step 1. w <- s^-1 mod q.
	225	*/
e055a386	226	w = modinv(s, dss->q);
9c621433	227	diagbn("w=", w);
7cca0d81	228
	229	/*
	230	* Step 2. u1 <- SHA(message) * w mod q.
	231	*/
7cca0d81	232	SHA_Simple(data, datalen, hash);
7cca0d81	233	p = hash; slen = 20; sha = get160(&p, &slen);
9c621433	234	diagbn("sha=", sha);
e055a386	235	u1 = modmul(sha, w, dss->q);
9c621433	236	diagbn("u1=", u1);
7cca0d81	237
	238	/*
	239	* Step 3. u2 <- r * w mod q.
	240	*/
e055a386	241	u2 = modmul(r, w, dss->q);
9c621433	242	diagbn("u2=", u2);
7cca0d81	243
	244	/*
	245	* Step 4. v <- (g^u1 * y^u2 mod p) mod q.
	246	*/
e055a386	247	gu1p = modpow(dss->g, u1, dss->p);
59600f67	248	diagbn("gu1p=", gu1p);
e055a386	249	yu2p = modpow(dss->y, u2, dss->p);
59600f67	250	diagbn("yu2p=", yu2p);
e055a386	251	gu1yu2p = modmul(gu1p, yu2p, dss->p);
59600f67	252	diagbn("gu1yu2p=", gu1yu2p);
e055a386	253	v = modmul(gu1yu2p, One, dss->q);
9c621433	254	diagbn("gu1yu2q=v=", v);
9c621433	255	diagbn("r=", r);
7cca0d81	256
	257	/*
	258	* Step 5. v should now be equal to r.
	259	*/
	260
c5fbd713	261	ret = !bignum_cmp(v, r);
7cca0d81	262
7cca0d81	263	freebn(w);
7cca0d81	264	freebn(sha);
59600f67	265	freebn(gu1p);
	266	freebn(yu2p);
	267	freebn(gu1yu2p);
7cca0d81	268	freebn(v);
	269	freebn(r);
	270	freebn(s);
	271
	272	return ret;
	273	}
	274
e055a386	275	int dss_sign(void key, char sig, int siglen,
	276	char *data, int datalen) {
	277	return 0; /* do nothing */
	278	}
	279
	280	struct ssh_signkey ssh_dss = {
	281	dss_newkey,
	282	dss_freekey,
7cca0d81	283	dss_fmtkey,
d5859615	284	dss_fingerprint,
7cca0d81	285	dss_verifysig,
e055a386	286	dss_sign,
d5859615	287	"ssh-dss",
d5859615	288	"dss"
e5574168	289	};