checking in all the old panacean stuff
This commit is contained in:
643
sFTPlugins/psftp/SSHDSS.C
Normal file
643
sFTPlugins/psftp/SSHDSS.C
Normal file
@@ -0,0 +1,643 @@
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/*
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* Digital Signature Standard implementation for PuTTY.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <assert.h>
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#include "ssh.h"
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#include "misc.h"
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static void sha_mpint(SHA_State * s, Bignum b)
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{
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unsigned char lenbuf[4];
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int len;
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len = (bignum_bitcount(b) + 8) / 8;
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PUT_32BIT(lenbuf, len);
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SHA_Bytes(s, lenbuf, 4);
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while (len-- > 0) {
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lenbuf[0] = bignum_byte(b, len);
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SHA_Bytes(s, lenbuf, 1);
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}
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memset(lenbuf, 0, sizeof(lenbuf));
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}
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static void sha512_mpint(SHA512_State * s, Bignum b)
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{
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unsigned char lenbuf[4];
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int len;
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len = (bignum_bitcount(b) + 8) / 8;
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PUT_32BIT(lenbuf, len);
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SHA512_Bytes(s, lenbuf, 4);
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while (len-- > 0) {
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lenbuf[0] = bignum_byte(b, len);
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SHA512_Bytes(s, lenbuf, 1);
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}
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memset(lenbuf, 0, sizeof(lenbuf));
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}
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static void getstring(char **data, int *datalen, char **p, int *length)
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{
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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;
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*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;
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*datalen -= *length;
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}
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static Bignum getmp(char **data, int *datalen)
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{
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char *p;
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int 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 = bignum_from_bytes((unsigned char *)p, length);
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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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{
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Bignum b;
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b = bignum_from_bytes((unsigned char *)*data, 20);
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*data += 20;
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*datalen -= 20;
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return b;
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}
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static void *dss_newkey(char *data, int len)
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{
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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 = snew(struct dss_key);
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if (!dss)
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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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{
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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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{
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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 * (bignum_bitcount(dss->p) + 15) / 16;
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len += 4 * (bignum_bitcount(dss->q) + 15) / 16;
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len += 4 * (bignum_bitcount(dss->g) + 15) / 16;
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len += 4 * (bignum_bitcount(dss->y) + 15) / 16;
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p = snewn(len, char);
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if (!p)
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return NULL;
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pos = 0;
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pos += sprintf(p + pos, "0x");
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nibbles = (3 + bignum_bitcount(dss->p)) / 4;
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if (nibbles < 1)
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nibbles = 1;
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for (i = nibbles; i--;)
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p[pos++] =
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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 + bignum_bitcount(dss->q)) / 4;
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if (nibbles < 1)
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nibbles = 1;
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for (i = nibbles; i--;)
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p[pos++] =
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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 + bignum_bitcount(dss->g)) / 4;
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if (nibbles < 1)
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nibbles = 1;
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for (i = nibbles; i--;)
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p[pos++] =
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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 + bignum_bitcount(dss->y)) / 4;
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if (nibbles < 1)
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nibbles = 1;
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for (i = nibbles; i--;)
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p[pos++] =
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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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{
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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, (unsigned char *)"\0\0\0\7ssh-dss", 11);
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#define ADD_BIGNUM(bignum) \
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numlen = (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, "ssh-dss %d ", 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 ? ":" : "",
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digest[i]);
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ret = snewn(strlen(buffer) + 1, char);
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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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{
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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(" %02x", (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 || slen != 7 || 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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r = get160(&sig, &siglen);
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s = get160(&sig, &siglen);
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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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/*
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* Step 2. u1 <- SHA(message) * w mod q.
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*/
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SHA_Simple(data, datalen, (unsigned char *)hash);
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p = hash;
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slen = 20;
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sha = get160(&p, &slen);
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u1 = modmul(sha, w, dss->q);
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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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/*
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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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yu2p = modpow(dss->y, u2, dss->p);
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gu1yu2p = modmul(gu1p, yu2p, dss->p);
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v = modmul(gu1yu2p, One, dss->q);
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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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static unsigned char *dss_public_blob(void *key, int *len)
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{
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struct dss_key *dss = (struct dss_key *) key;
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int plen, qlen, glen, ylen, bloblen;
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int i;
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unsigned char *blob, *p;
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plen = (bignum_bitcount(dss->p) + 8) / 8;
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qlen = (bignum_bitcount(dss->q) + 8) / 8;
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glen = (bignum_bitcount(dss->g) + 8) / 8;
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ylen = (bignum_bitcount(dss->y) + 8) / 8;
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/*
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* string "ssh-dss", mpint p, mpint q, mpint g, mpint y. Total
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* 27 + sum of lengths. (five length fields, 20+7=27).
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*/
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bloblen = 27 + plen + qlen + glen + ylen;
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blob = snewn(bloblen, unsigned char);
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p = blob;
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PUT_32BIT(p, 7);
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p += 4;
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memcpy(p, "ssh-dss", 7);
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p += 7;
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PUT_32BIT(p, plen);
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p += 4;
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for (i = plen; i--;)
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*p++ = bignum_byte(dss->p, i);
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PUT_32BIT(p, qlen);
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p += 4;
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for (i = qlen; i--;)
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*p++ = bignum_byte(dss->q, i);
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PUT_32BIT(p, glen);
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p += 4;
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for (i = glen; i--;)
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*p++ = bignum_byte(dss->g, i);
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PUT_32BIT(p, ylen);
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p += 4;
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for (i = ylen; i--;)
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*p++ = bignum_byte(dss->y, i);
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assert(p == blob + bloblen);
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*len = bloblen;
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return blob;
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}
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static unsigned char *dss_private_blob(void *key, int *len)
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{
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struct dss_key *dss = (struct dss_key *) key;
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int xlen, bloblen;
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int i;
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unsigned char *blob, *p;
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xlen = (bignum_bitcount(dss->x) + 8) / 8;
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/*
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* mpint x, string[20] the SHA of p||q||g. Total 4 + xlen.
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*/
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bloblen = 4 + xlen;
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blob = snewn(bloblen, unsigned char);
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p = blob;
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PUT_32BIT(p, xlen);
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p += 4;
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for (i = xlen; i--;)
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*p++ = bignum_byte(dss->x, i);
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assert(p == blob + bloblen);
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*len = bloblen;
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return blob;
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}
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static void *dss_createkey(unsigned char *pub_blob, int pub_len,
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unsigned char *priv_blob, int priv_len)
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{
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struct dss_key *dss;
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char *pb = (char *) priv_blob;
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char *hash;
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int hashlen;
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SHA_State s;
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unsigned char digest[20];
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Bignum ytest;
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dss = dss_newkey((char *) pub_blob, pub_len);
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dss->x = getmp(&pb, &priv_len);
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/*
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* Check the obsolete hash in the old DSS key format.
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*/
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hashlen = -1;
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getstring(&pb, &priv_len, &hash, &hashlen);
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if (hashlen == 20) {
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SHA_Init(&s);
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sha_mpint(&s, dss->p);
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sha_mpint(&s, dss->q);
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sha_mpint(&s, dss->g);
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SHA_Final(&s, digest);
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if (0 != memcmp(hash, digest, 20)) {
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dss_freekey(dss);
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return NULL;
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}
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}
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/*
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* Now ensure g^x mod p really is y.
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*/
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ytest = modpow(dss->g, dss->x, dss->p);
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if (0 != bignum_cmp(ytest, dss->y)) {
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dss_freekey(dss);
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return NULL;
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}
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freebn(ytest);
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return dss;
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}
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static void *dss_openssh_createkey(unsigned char **blob, int *len)
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{
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char **b = (char **) blob;
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struct dss_key *dss;
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dss = snew(struct dss_key);
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if (!dss)
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return NULL;
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dss->p = getmp(b, len);
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dss->q = getmp(b, len);
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dss->g = getmp(b, len);
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dss->y = getmp(b, len);
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dss->x = getmp(b, len);
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if (!dss->p || !dss->q || !dss->g || !dss->y || !dss->x) {
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sfree(dss->p);
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sfree(dss->q);
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sfree(dss->g);
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sfree(dss->y);
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sfree(dss->x);
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sfree(dss);
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return NULL;
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}
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return dss;
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}
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static int dss_openssh_fmtkey(void *key, unsigned char *blob, int len)
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{
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struct dss_key *dss = (struct dss_key *) key;
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int bloblen, i;
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bloblen =
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ssh2_bignum_length(dss->p) +
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ssh2_bignum_length(dss->q) +
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ssh2_bignum_length(dss->g) +
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ssh2_bignum_length(dss->y) +
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ssh2_bignum_length(dss->x);
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if (bloblen > len)
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return bloblen;
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bloblen = 0;
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#define ENC(x) \
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PUT_32BIT(blob+bloblen, ssh2_bignum_length((x))-4); bloblen += 4; \
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for (i = ssh2_bignum_length((x))-4; i-- ;) blob[bloblen++]=bignum_byte((x),i);
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ENC(dss->p);
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ENC(dss->q);
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ENC(dss->g);
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ENC(dss->y);
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ENC(dss->x);
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return bloblen;
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}
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static int dss_pubkey_bits(void *blob, int len)
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{
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struct dss_key *dss;
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int ret;
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dss = dss_newkey((char *) blob, len);
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ret = bignum_bitcount(dss->p);
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dss_freekey(dss);
|
||||
|
||||
return ret;
|
||||
}
|
||||
|
||||
static unsigned char *dss_sign(void *key, char *data, int datalen, int *siglen)
|
||||
{
|
||||
/*
|
||||
* The basic DSS signing algorithm is:
|
||||
*
|
||||
* - invent a random k between 1 and q-1 (exclusive).
|
||||
* - Compute r = (g^k mod p) mod q.
|
||||
* - Compute s = k^-1 * (hash + x*r) mod q.
|
||||
*
|
||||
* This has the dangerous properties that:
|
||||
*
|
||||
* - if an attacker in possession of the public key _and_ the
|
||||
* signature (for example, the host you just authenticated
|
||||
* to) can guess your k, he can reverse the computation of s
|
||||
* and work out x = r^-1 * (s*k - hash) mod q. That is, he
|
||||
* can deduce the private half of your key, and masquerade
|
||||
* as you for as long as the key is still valid.
|
||||
*
|
||||
* - since r is a function purely of k and the public key, if
|
||||
* the attacker only has a _range of possibilities_ for k
|
||||
* it's easy for him to work through them all and check each
|
||||
* one against r; he'll never be unsure of whether he's got
|
||||
* the right one.
|
||||
*
|
||||
* - if you ever sign two different hashes with the same k, it
|
||||
* will be immediately obvious because the two signatures
|
||||
* will have the same r, and moreover an attacker in
|
||||
* possession of both signatures (and the public key of
|
||||
* course) can compute k = (hash1-hash2) * (s1-s2)^-1 mod q,
|
||||
* and from there deduce x as before.
|
||||
*
|
||||
* - the Bleichenbacher attack on DSA makes use of methods of
|
||||
* generating k which are significantly non-uniformly
|
||||
* distributed; in particular, generating a 160-bit random
|
||||
* number and reducing it mod q is right out.
|
||||
*
|
||||
* For this reason we must be pretty careful about how we
|
||||
* generate our k. Since this code runs on Windows, with no
|
||||
* particularly good system entropy sources, we can't trust our
|
||||
* RNG itself to produce properly unpredictable data. Hence, we
|
||||
* use a totally different scheme instead.
|
||||
*
|
||||
* What we do is to take a SHA-512 (_big_) hash of the private
|
||||
* key x, and then feed this into another SHA-512 hash that
|
||||
* also includes the message hash being signed. That is:
|
||||
*
|
||||
* proto_k = SHA512 ( SHA512(x) || SHA160(message) )
|
||||
*
|
||||
* This number is 512 bits long, so reducing it mod q won't be
|
||||
* noticeably non-uniform. So
|
||||
*
|
||||
* k = proto_k mod q
|
||||
*
|
||||
* This has the interesting property that it's _deterministic_:
|
||||
* signing the same hash twice with the same key yields the
|
||||
* same signature.
|
||||
*
|
||||
* Despite this determinism, it's still not predictable to an
|
||||
* attacker, because in order to repeat the SHA-512
|
||||
* construction that created it, the attacker would have to
|
||||
* know the private key value x - and by assumption he doesn't,
|
||||
* because if he knew that he wouldn't be attacking k!
|
||||
*
|
||||
* (This trick doesn't, _per se_, protect against reuse of k.
|
||||
* Reuse of k is left to chance; all it does is prevent
|
||||
* _excessively high_ chances of reuse of k due to entropy
|
||||
* problems.)
|
||||
*
|
||||
* Thanks to Colin Plumb for the general idea of using x to
|
||||
* ensure k is hard to guess, and to the Cambridge University
|
||||
* Computer Security Group for helping to argue out all the
|
||||
* fine details.
|
||||
*/
|
||||
struct dss_key *dss = (struct dss_key *) key;
|
||||
SHA512_State ss;
|
||||
unsigned char digest[20], digest512[64];
|
||||
Bignum proto_k, k, gkp, hash, kinv, hxr, r, s;
|
||||
unsigned char *bytes;
|
||||
int nbytes, i;
|
||||
|
||||
SHA_Simple(data, datalen, digest);
|
||||
|
||||
/*
|
||||
* Hash some identifying text plus x.
|
||||
*/
|
||||
SHA512_Init(&ss);
|
||||
SHA512_Bytes(&ss, "DSA deterministic k generator", 30);
|
||||
sha512_mpint(&ss, dss->x);
|
||||
SHA512_Final(&ss, digest512);
|
||||
|
||||
/*
|
||||
* Now hash that digest plus the message hash.
|
||||
*/
|
||||
SHA512_Init(&ss);
|
||||
SHA512_Bytes(&ss, digest512, sizeof(digest512));
|
||||
SHA512_Bytes(&ss, digest, sizeof(digest));
|
||||
SHA512_Final(&ss, digest512);
|
||||
|
||||
memset(&ss, 0, sizeof(ss));
|
||||
|
||||
/*
|
||||
* Now convert the result into a bignum, and reduce it mod q.
|
||||
*/
|
||||
proto_k = bignum_from_bytes(digest512, 64);
|
||||
k = bigmod(proto_k, dss->q);
|
||||
freebn(proto_k);
|
||||
|
||||
memset(digest512, 0, sizeof(digest512));
|
||||
|
||||
/*
|
||||
* Now we have k, so just go ahead and compute the signature.
|
||||
*/
|
||||
gkp = modpow(dss->g, k, dss->p); /* g^k mod p */
|
||||
r = bigmod(gkp, dss->q); /* r = (g^k mod p) mod q */
|
||||
freebn(gkp);
|
||||
|
||||
hash = bignum_from_bytes(digest, 20);
|
||||
kinv = modinv(k, dss->q); /* k^-1 mod q */
|
||||
hxr = bigmuladd(dss->x, r, hash); /* hash + x*r */
|
||||
s = modmul(kinv, hxr, dss->q); /* s = k^-1 * (hash + x*r) mod q */
|
||||
freebn(hxr);
|
||||
freebn(kinv);
|
||||
freebn(hash);
|
||||
|
||||
/*
|
||||
* Signature blob is
|
||||
*
|
||||
* string "ssh-dss"
|
||||
* string two 20-byte numbers r and s, end to end
|
||||
*
|
||||
* i.e. 4+7 + 4+40 bytes.
|
||||
*/
|
||||
nbytes = 4 + 7 + 4 + 40;
|
||||
bytes = snewn(nbytes, unsigned char);
|
||||
PUT_32BIT(bytes, 7);
|
||||
memcpy(bytes + 4, "ssh-dss", 7);
|
||||
PUT_32BIT(bytes + 4 + 7, 40);
|
||||
for (i = 0; i < 20; i++) {
|
||||
bytes[4 + 7 + 4 + i] = bignum_byte(r, 19 - i);
|
||||
bytes[4 + 7 + 4 + 20 + i] = bignum_byte(s, 19 - i);
|
||||
}
|
||||
freebn(r);
|
||||
freebn(s);
|
||||
|
||||
*siglen = nbytes;
|
||||
return bytes;
|
||||
}
|
||||
|
||||
const struct ssh_signkey ssh_dss = {
|
||||
dss_newkey,
|
||||
dss_freekey,
|
||||
dss_fmtkey,
|
||||
dss_public_blob,
|
||||
dss_private_blob,
|
||||
dss_createkey,
|
||||
dss_openssh_createkey,
|
||||
dss_openssh_fmtkey,
|
||||
dss_pubkey_bits,
|
||||
dss_fingerprint,
|
||||
dss_verifysig,
|
||||
dss_sign,
|
||||
"ssh-dss",
|
||||
"dss"
|
||||
};
|
||||
Reference in New Issue
Block a user