зеркало из https://github.com/github/putty.git
325 строки
8.2 KiB
C
325 строки
8.2 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include "ssh.h"
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#define GET_32BIT(cp) \
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(((unsigned long)(unsigned char)(cp)[0] << 24) | \
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((unsigned long)(unsigned char)(cp)[1] << 16) | \
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((unsigned long)(unsigned char)(cp)[2] << 8) | \
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((unsigned long)(unsigned char)(cp)[3]))
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#define PUT_32BIT(cp, value) { \
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(cp)[0] = (unsigned char)((value) >> 24); \
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(cp)[1] = (unsigned char)((value) >> 16); \
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(cp)[2] = (unsigned char)((value) >> 8); \
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(cp)[3] = (unsigned char)(value); }
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#if 0
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/*
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* Condition this section in for debugging of DSS.
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*/
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static void diagbn(char *prefix, Bignum md) {
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int i, nibbles, morenibbles;
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static const char hex[] = "0123456789ABCDEF";
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printf("%s0x", prefix ? prefix : "");
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nibbles = (3 + ssh1_bignum_bitcount(md))/4; if (nibbles<1) nibbles=1;
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morenibbles = 4*md[0] - nibbles;
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for (i=0; i<morenibbles; i++) putchar('-');
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for (i=nibbles; i-- ;)
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putchar(hex[(bignum_byte(md, i/2) >> (4*(i%2))) & 0xF]);
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if (prefix) putchar('\n');
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}
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#define DEBUG_DSS
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#else
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#define diagbn(x,y)
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#endif
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static void getstring(char **data, int *datalen, char **p, int *length) {
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*p = NULL;
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if (*datalen < 4)
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return;
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*length = GET_32BIT(*data);
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*datalen -= 4; *data += 4;
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if (*datalen < *length)
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return;
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*p = *data;
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*data += *length; *datalen -= *length;
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}
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static Bignum getmp(char **data, int *datalen) {
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char *p;
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int i, j, length;
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Bignum b;
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getstring(data, datalen, &p, &length);
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if (!p)
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return NULL;
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if (p[0] & 0x80)
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return NULL; /* negative mp */
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b = newbn((length+1)/2);
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for (i = 0; i < length; i++) {
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j = length - 1 - i;
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if (j & 1)
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b[j/2+1] |= ((unsigned char)p[i]) << 8;
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else
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b[j/2+1] |= ((unsigned char)p[i]);
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}
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while (b[0] > 1 && b[b[0]] == 0) b[0]--;
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return b;
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}
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static Bignum get160(char **data, int *datalen) {
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char *p;
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int i, j, length;
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Bignum b;
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p = *data;
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*data += 20; *datalen -= 20;
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length = 20;
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while (length > 0 && !p[0])
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p++, length--;
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b = newbn((length+1)/2);
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for (i = 0; i < length; i++) {
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j = length - 1 - i;
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if (j & 1)
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b[j/2+1] |= ((unsigned char)p[i]) << 8;
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else
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b[j/2+1] |= ((unsigned char)p[i]);
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}
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return b;
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}
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struct dss_key {
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Bignum p, q, g, y;
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};
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static void *dss_newkey(char *data, int len) {
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char *p;
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int slen;
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struct dss_key *dss;
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dss = smalloc(sizeof(struct dss_key));
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if (!dss) return NULL;
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getstring(&data, &len, &p, &slen);
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#ifdef DEBUG_DSS
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{
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int i;
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printf("key:");
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for (i=0;i<len;i++)
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printf(" %02x", (unsigned char)(data[i]));
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printf("\n");
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}
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#endif
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if (!p || memcmp(p, "ssh-dss", 7)) {
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sfree(dss);
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return NULL;
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}
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dss->p = getmp(&data, &len);
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dss->q = getmp(&data, &len);
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dss->g = getmp(&data, &len);
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dss->y = getmp(&data, &len);
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return dss;
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}
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static void dss_freekey(void *key) {
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struct dss_key *dss = (struct dss_key *)key;
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freebn(dss->p);
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freebn(dss->q);
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freebn(dss->g);
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freebn(dss->y);
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sfree(dss);
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}
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static char *dss_fmtkey(void *key) {
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struct dss_key *dss = (struct dss_key *)key;
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char *p;
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int len, i, pos, nibbles;
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static const char hex[] = "0123456789abcdef";
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if (!dss->p)
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return NULL;
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len = 8 + 4 + 1; /* 4 x "0x", punctuation, \0 */
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len += 4 * (dss->p[0] + dss->q[0] + dss->g[0] + dss->y[0]); /* digits */
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p = smalloc(len);
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if (!p) return NULL;
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pos = 0;
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pos += sprintf(p+pos, "0x");
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nibbles = (3 + ssh1_bignum_bitcount(dss->p))/4; if (nibbles<1) nibbles=1;
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for (i=nibbles; i-- ;)
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p[pos++] = hex[(bignum_byte(dss->p, i/2) >> (4*(i%2))) & 0xF];
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pos += sprintf(p+pos, ",0x");
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nibbles = (3 + ssh1_bignum_bitcount(dss->q))/4; if (nibbles<1) nibbles=1;
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for (i=nibbles; i-- ;)
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p[pos++] = hex[(bignum_byte(dss->q, i/2) >> (4*(i%2))) & 0xF];
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pos += sprintf(p+pos, ",0x");
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nibbles = (3 + ssh1_bignum_bitcount(dss->g))/4; if (nibbles<1) nibbles=1;
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for (i=nibbles; i-- ;)
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p[pos++] = hex[(bignum_byte(dss->g, i/2) >> (4*(i%2))) & 0xF];
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pos += sprintf(p+pos, ",0x");
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nibbles = (3 + ssh1_bignum_bitcount(dss->y))/4; if (nibbles<1) nibbles=1;
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for (i=nibbles; i-- ;)
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p[pos++] = hex[(bignum_byte(dss->y, i/2) >> (4*(i%2))) & 0xF];
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p[pos] = '\0';
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return p;
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}
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static char *dss_fingerprint(void *key) {
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struct dss_key *dss = (struct dss_key *)key;
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struct MD5Context md5c;
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unsigned char digest[16], lenbuf[4];
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char buffer[16*3+40];
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char *ret;
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int numlen, i;
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MD5Init(&md5c);
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MD5Update(&md5c, "\0\0\0\7ssh-dss", 11);
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#define ADD_BIGNUM(bignum) \
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numlen = (ssh1_bignum_bitcount(bignum)+8)/8; \
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PUT_32BIT(lenbuf, numlen); MD5Update(&md5c, lenbuf, 4); \
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for (i = numlen; i-- ;) { \
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unsigned char c = bignum_byte(bignum, i); \
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MD5Update(&md5c, &c, 1); \
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}
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ADD_BIGNUM(dss->p);
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ADD_BIGNUM(dss->q);
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ADD_BIGNUM(dss->g);
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ADD_BIGNUM(dss->y);
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#undef ADD_BIGNUM
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MD5Final(digest, &md5c);
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sprintf(buffer, "%d ", ssh1_bignum_bitcount(dss->p));
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for (i = 0; i < 16; i++)
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sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
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ret = smalloc(strlen(buffer)+1);
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if (ret)
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strcpy(ret, buffer);
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return ret;
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}
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static int dss_verifysig(void *key, char *sig, int siglen,
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char *data, int datalen) {
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struct dss_key *dss = (struct dss_key *)key;
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char *p;
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int slen;
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char hash[20];
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Bignum r, s, w, gu1p, yu2p, gu1yu2p, u1, u2, sha, v;
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int ret;
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if (!dss->p)
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return 0;
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#ifdef DEBUG_DSS
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{
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int i;
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printf("sig:");
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for (i=0;i<siglen;i++)
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printf(" %02xf", (unsigned char)(sig[i]));
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printf("\n");
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}
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#endif
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/*
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* Commercial SSH (2.0.13) and OpenSSH disagree over the format
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* of a DSA signature. OpenSSH is in line with the IETF drafts:
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* it uses a string "ssh-dss", followed by a 40-byte string
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* containing two 160-bit integers end-to-end. Commercial SSH
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* can't be bothered with the header bit, and considers a DSA
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* signature blob to be _just_ the 40-byte string containing
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* the two 160-bit integers. We tell them apart by measuring
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* the length: length 40 means the commercial-SSH bug, anything
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* else is assumed to be IETF-compliant.
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*/
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if (siglen != 40) { /* bug not present; read admin fields */
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getstring(&sig, &siglen, &p, &slen);
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if (!p || memcmp(p, "ssh-dss", 7)) {
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return 0;
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}
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sig += 4, siglen -= 4; /* skip yet another length field */
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}
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diagbn("p=", dss->p);
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diagbn("q=", dss->q);
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diagbn("g=", dss->g);
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diagbn("y=", dss->y);
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r = get160(&sig, &siglen);
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diagbn("r=", r);
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s = get160(&sig, &siglen);
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diagbn("s=", s);
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if (!r || !s)
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return 0;
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/*
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* Step 1. w <- s^-1 mod q.
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*/
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w = modinv(s, dss->q);
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diagbn("w=", w);
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/*
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* Step 2. u1 <- SHA(message) * w mod q.
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*/
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SHA_Simple(data, datalen, hash);
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p = hash; slen = 20; sha = get160(&p, &slen);
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diagbn("sha=", sha);
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u1 = modmul(sha, w, dss->q);
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diagbn("u1=", u1);
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/*
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* Step 3. u2 <- r * w mod q.
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*/
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u2 = modmul(r, w, dss->q);
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diagbn("u2=", u2);
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/*
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* Step 4. v <- (g^u1 * y^u2 mod p) mod q.
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*/
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gu1p = modpow(dss->g, u1, dss->p);
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diagbn("gu1p=", gu1p);
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yu2p = modpow(dss->y, u2, dss->p);
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diagbn("yu2p=", yu2p);
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gu1yu2p = modmul(gu1p, yu2p, dss->p);
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diagbn("gu1yu2p=", gu1yu2p);
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v = modmul(gu1yu2p, One, dss->q);
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diagbn("gu1yu2q=v=", v);
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diagbn("r=", r);
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/*
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* Step 5. v should now be equal to r.
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*/
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ret = !bignum_cmp(v, r);
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freebn(w);
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freebn(sha);
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freebn(gu1p);
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freebn(yu2p);
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freebn(gu1yu2p);
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freebn(v);
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freebn(r);
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freebn(s);
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return ret;
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}
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int dss_sign(void *key, char *sig, int siglen,
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char *data, int datalen) {
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return 0; /* do nothing */
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}
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struct ssh_signkey ssh_dss = {
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dss_newkey,
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dss_freekey,
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dss_fmtkey,
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dss_fingerprint,
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dss_verifysig,
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dss_sign,
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"ssh-dss",
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"dss"
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};
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