[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); }

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 i, j, length;
    Bignum b;

    getstring(data, datalen, &p, &length);
    if (!p)
        return NULL;
    if (p[0] & 0x80)
        return NULL;                   /* negative mp */
    b = newbn((length+1)/2);
    for (i = 0; i < length; i++) {
        j = length - 1 - i;
        if (j & 1)
            b[j/2+1] |= ((unsigned char)p[i]) << 8;
        else
            b[j/2+1] |= ((unsigned char)p[i]);
    }
    return b;
}

static Bignum get160(char **data, int *datalen) {
    char *p;
    int i, j, length;
    Bignum b;

    p = *data;
    *data += 20; *datalen -= 20;

    length = 20;
    while (length > 0 && !p[0])
        p++, length--;
    b = newbn((length+1)/2);
    for (i = 0; i < length; i++) {
        j = length - 1 - i;
        if (j & 1)
            b[j/2+1] |= ((unsigned char)p[i]) << 8;
        else
            b[j/2+1] |= ((unsigned char)p[i]);
    }
    return b;
}

static Bignum dss_p, dss_q, dss_g, dss_y;

static void dss_setkey(char *data, int len) {
    char *p;
    int slen;
    getstring(&data, &len, &p, &slen);
    if (!p || memcmp(p, "ssh-dss", 7)) {
        dss_p = NULL;
        return;
    }
    dss_p = getmp(&data, &len);
    dss_q = getmp(&data, &len);
    dss_g = getmp(&data, &len);
    dss_y = getmp(&data, &len);
}

static char *dss_fmtkey(void) {
    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 * (dss_p[0] + dss_q[0] + dss_g[0] + dss_y[0]);   /* digits */
    p = malloc(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) {
    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, "%d ", ssh1_bignum_bitcount(dss_p));
    for (i = 0; i < 16; i++)
        sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
    ret = malloc(strlen(buffer)+1);
    if (ret)
        strcpy(ret, buffer);
    return ret;
}

static int dss_verifysig(char *sig, int siglen, char *data, int datalen) {
    char *p;
    int i, slen;
    char hash[20];
    Bignum qm2, r, s, w, i1, i2, i3, u1, u2, sha, v;
    int ret;

    if (!dss_p)
        return 0;

    /*
     * 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 || memcmp(p, "ssh-dss", 7)) {
            return 0;
        }
        sig += 4, siglen -= 4;             /* skip yet another length field */
    }
    r = get160(&sig, &siglen);
    s = get160(&sig, &siglen);
    if (!r || !s)
        return 0;

    /*
     * Step 1. w <- s^-1 mod q.
     */
    w = newbn(dss_q[0]);
    qm2 = copybn(dss_q);
    decbn(qm2); decbn(qm2);
    /* Now qm2 is q-2, and by Fermat's Little Theorem, s^qm2 == s^-1 (mod q).
     * This is a silly way to do it; may fix it later. */
    modpow(s, qm2, dss_q, w);

    /*
     * Step 2. u1 <- SHA(message) * w mod q.
     */
    u1 = newbn(dss_q[0]);
    SHA_Simple(data, datalen, hash);
    p = hash; slen = 20; sha = get160(&p, &slen);
    modmul(sha, w, dss_q, u1);

    /*
     * Step 3. u2 <- r * w mod q.
     */
    u2 = newbn(dss_q[0]);
    modmul(r, w, dss_q, u2);

    /*
     * Step 4. v <- (g^u1 * y^u2 mod p) mod q.
     */
    i1 = newbn(dss_p[0]);
    i2 = newbn(dss_p[0]);
    i3 = newbn(dss_p[0]);
    v = newbn(dss_q[0]);
    modpow(dss_g, u1, dss_p, i1);
    modpow(dss_y, u2, dss_p, i2);
    modmul(i1, i2, dss_p, i3);
    modmul(i3, One, dss_q, v);

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

    ret = 1;
    for (i = 1; i <= v[0] || i <= r[0]; i++) {
        if ((i > v[0] && r[i] != 0) ||
            (i > r[0] && v[i] != 0) ||
            (i <= v[0] && i <= r[0] && r[i] != v[i]))
            ret = 0;
    }

    freebn(w);
    freebn(qm2);
    freebn(sha);
    freebn(i1);
    freebn(i2);
    freebn(i3);
    freebn(v);
    freebn(r);
    freebn(s);

    return ret;
}

struct ssh_hostkey ssh_dss = {
    dss_setkey,
    dss_fmtkey,
    dss_fingerprint,
    dss_verifysig,
    "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
7cca0d81	18	static void getstring(char *data, int datalen, char *p, int length) {
	19	*p = NULL;
	20	if (*datalen < 4)
	21	return;
	22	length = GET_32BIT(data);
	23	datalen -= 4; data += 4;
	24	if (datalen < length)
	25	return;
	26	p = data;
	27	data += length; datalen -= length;
	28	}
	29	static Bignum getmp(char *data, int datalen) {
	30	char *p;
	31	int i, j, length;
	32	Bignum b;
	33
	34	getstring(data, datalen, &p, &length);
	35	if (!p)
	36	return NULL;
	37	if (p[0] & 0x80)
	38	return NULL; /* negative mp */
	39	b = newbn((length+1)/2);
	40	for (i = 0; i < length; i++) {
	41	j = length - 1 - i;
	42	if (j & 1)
	43	b[j/2+1] \|= ((unsigned char)p[i]) << 8;
	44	else
	45	b[j/2+1] \|= ((unsigned char)p[i]);
	46	}
	47	return b;
	48	}
	49
	50	static Bignum get160(char *data, int datalen) {
	51	char *p;
	52	int i, j, length;
	53	Bignum b;
	54
	55	p = *data;
	56	data += 20; datalen -= 20;
	57
	58	length = 20;
	59	while (length > 0 && !p[0])
	60	p++, length--;
	61	b = newbn((length+1)/2);
	62	for (i = 0; i < length; i++) {
	63	j = length - 1 - i;
	64	if (j & 1)
	65	b[j/2+1] \|= ((unsigned char)p[i]) << 8;
	66	else
	67	b[j/2+1] \|= ((unsigned char)p[i]);
	68	}
	69	return b;
	70	}
	71
	72	static Bignum dss_p, dss_q, dss_g, dss_y;
	73
	74	static void dss_setkey(char *data, int len) {
	75	char *p;
	76	int slen;
	77	getstring(&data, &len, &p, &slen);
	78	if (!p \|\| memcmp(p, "ssh-dss", 7)) {
	79	dss_p = NULL;
	80	return;
	81	}
82	dss_p = getmp(&data, &len);
83	dss_q = getmp(&data, &len);
84	dss_g = getmp(&data, &len);
85	dss_y = getmp(&data, &len);
86	}
87
88	static char *dss_fmtkey(void) {
89	char *p;
d5859615	90	int len, i, pos, nibbles;
d5859615	91	static const char hex[] = "0123456789abcdef";
7cca0d81	92	if (!dss_p)
7cca0d81	93	return NULL;
d5859615	94	len = 8 + 4 + 1; /* 4 x "0x", punctuation, \0 */
7cca0d81	95	len += 4 * (dss_p[0] + dss_q[0] + dss_g[0] + dss_y[0]); /* digits */
	96	p = malloc(len);
	97	if (!p) return NULL;
d5859615	98
	99	pos = 0;
	100	pos += sprintf(p+pos, "0x");
	101	nibbles = (3 + ssh1_bignum_bitcount(dss_p))/4; if (nibbles<1) nibbles=1;
	102	for (i=nibbles; i-- ;)
	103	p[pos++] = hex[(bignum_byte(dss_p, i/2) >> (4*(i%2))) & 0xF];
3aa0b691	104	pos += sprintf(p+pos, ",0x");
d5859615	105	nibbles = (3 + ssh1_bignum_bitcount(dss_q))/4; if (nibbles<1) nibbles=1;
	106	for (i=nibbles; i-- ;)
	107	p[pos++] = hex[(bignum_byte(dss_q, i/2) >> (4*(i%2))) & 0xF];
3aa0b691	108	pos += sprintf(p+pos, ",0x");
d5859615	109	nibbles = (3 + ssh1_bignum_bitcount(dss_g))/4; if (nibbles<1) nibbles=1;
	110	for (i=nibbles; i-- ;)
	111	p[pos++] = hex[(bignum_byte(dss_g, i/2) >> (4*(i%2))) & 0xF];
3aa0b691	112	pos += sprintf(p+pos, ",0x");
d5859615	113	nibbles = (3 + ssh1_bignum_bitcount(dss_y))/4; if (nibbles<1) nibbles=1;
	114	for (i=nibbles; i-- ;)
	115	p[pos++] = hex[(bignum_byte(dss_y, i/2) >> (4*(i%2))) & 0xF];
	116	p[pos] = '\0';
7cca0d81	117	return p;
	118	}
	119
d5859615	120	static char *dss_fingerprint(void) {
	121	struct MD5Context md5c;
	122	unsigned char digest[16], lenbuf[4];
	123	char buffer[16*3+40];
	124	char *ret;
	125	int numlen, i;
	126
	127	MD5Init(&md5c);
	128	MD5Update(&md5c, "\0\0\0\7ssh-dss", 11);
	129
	130	#define ADD_BIGNUM(bignum) \
	131	numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \
	132	PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \
	133	for (i = numlen; i-- ;) { \
	134	unsigned char c = bignum_byte(bignum, i); \
	135	MD5Update(&md5c, &c, 1); \
	136	}
	137	ADD_BIGNUM(dss_p);
	138	ADD_BIGNUM(dss_q);
	139	ADD_BIGNUM(dss_g);
	140	ADD_BIGNUM(dss_y);
	141	#undef ADD_BIGNUM
	142
	143	MD5Final(digest, &md5c);
	144
	145	sprintf(buffer, "%d ", ssh1_bignum_bitcount(dss_p));
	146	for (i = 0; i < 16; i++)
	147	sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
	148	ret = malloc(strlen(buffer)+1);
	149	if (ret)
	150	strcpy(ret, buffer);
	151	return ret;
	152	}
	153
7cca0d81	154	static int dss_verifysig(char sig, int siglen, char data, int datalen) {
	155	char *p;
	156	int i, slen;
	157	char hash[20];
	158	Bignum qm2, r, s, w, i1, i2, i3, u1, u2, sha, v;
	159	int ret;
	160
	161	if (!dss_p)
	162	return 0;
	163
7f7837c8	164	/*
	165	* Commercial SSH (2.0.13) and OpenSSH disagree over the format
	166	* of a DSA signature. OpenSSH is in line with the IETF drafts:
	167	* it uses a string "ssh-dss", followed by a 40-byte string
	168	* containing two 160-bit integers end-to-end. Commercial SSH
	169	* can't be bothered with the header bit, and considers a DSA
	170	* signature blob to be _just_ the 40-byte string containing
	171	* the two 160-bit integers. We tell them apart by measuring
	172	* the length: length 40 means the commercial-SSH bug, anything
	173	* else is assumed to be IETF-compliant.
	174	*/
	175	if (siglen != 40) { /* bug not present; read admin fields */
	176	getstring(&sig, &siglen, &p, &slen);
	177	if (!p \|\| memcmp(p, "ssh-dss", 7)) {
	178	return 0;
	179	}
	180	sig += 4, siglen -= 4; /* skip yet another length field */
7cca0d81	181	}
7cca0d81	182	r = get160(&sig, &siglen);
	183	s = get160(&sig, &siglen);
	184	if (!r \|\| !s)
	185	return 0;
	186
	187	/*
	188	* Step 1. w <- s^-1 mod q.
	189	*/
	190	w = newbn(dss_q[0]);
	191	qm2 = copybn(dss_q);
	192	decbn(qm2); decbn(qm2);
	193	/* Now qm2 is q-2, and by Fermat's Little Theorem, s^qm2 == s^-1 (mod q).
	194	* This is a silly way to do it; may fix it later. */
	195	modpow(s, qm2, dss_q, w);
	196
	197	/*
	198	* Step 2. u1 <- SHA(message) * w mod q.
	199	*/
	200	u1 = newbn(dss_q[0]);
	201	SHA_Simple(data, datalen, hash);
	202	p = hash; slen = 20; sha = get160(&p, &slen);
	203	modmul(sha, w, dss_q, u1);
	204
	205	/*
	206	* Step 3. u2 <- r * w mod q.
	207	*/
	208	u2 = newbn(dss_q[0]);
	209	modmul(r, w, dss_q, u2);
	210
	211	/*
	212	* Step 4. v <- (g^u1 * y^u2 mod p) mod q.
	213	*/
	214	i1 = newbn(dss_p[0]);
	215	i2 = newbn(dss_p[0]);
	216	i3 = newbn(dss_p[0]);
	217	v = newbn(dss_q[0]);
	218	modpow(dss_g, u1, dss_p, i1);
	219	modpow(dss_y, u2, dss_p, i2);
	220	modmul(i1, i2, dss_p, i3);
	221	modmul(i3, One, dss_q, v);
	222
	223	/*
	224	* Step 5. v should now be equal to r.
	225	*/
	226
	227	ret = 1;
	228	for (i = 1; i <= v[0] \|\| i <= r[0]; i++) {
	229	if ((i > v[0] && r[i] != 0) \|\|
	230	(i > r[0] && v[i] != 0) \|\|
	231	(i <= v[0] && i <= r[0] && r[i] != v[i]))
	232	ret = 0;
	233	}
	234
	235	freebn(w);
	236	freebn(qm2);
	237	freebn(sha);
	238	freebn(i1);
	239	freebn(i2);
	240	freebn(i3);
	241	freebn(v);
	242	freebn(r);
	243	freebn(s);
	244
	245	return ret;
246	}
247
e5574168	248	struct ssh_hostkey ssh_dss = {
7cca0d81	249	dss_setkey,
7cca0d81	250	dss_fmtkey,
d5859615	251	dss_fingerprint,
7cca0d81	252	dss_verifysig,
d5859615	253	"ssh-dss",
d5859615	254	"dss"
e5574168	255	};