/*
* RSA implementation just sufficient for ssh client-side
* initialisation step
*
* Rewritten for more speed by Joris van Rantwijk, Jun 1999.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include "ssh.h"
int makekey(unsigned char *data, struct RSAKey *result,
unsigned char **keystr, int order) {
unsigned char *p = data;
int i;
if (result) {
result->bits = 0;
for (i=0; i<4; i++)
result->bits = (result->bits << 8) + *p++;
} else
p += 4;
/*
* order=0 means exponent then modulus (the keys sent by the
* server). order=1 means modulus then exponent (the keys
* stored in a keyfile).
*/
if (order == 0)
p += ssh1_read_bignum(p, result ? &result->exponent : NULL);
if (result)
result->bytes = (((p[0] << 8) + p[1]) + 7) / 8;
if (keystr) *keystr = p+2;
p += ssh1_read_bignum(p, result ? &result->modulus : NULL);
if (order == 1)
p += ssh1_read_bignum(p, result ? &result->exponent : NULL);
return p - data;
}
int makeprivate(unsigned char *data, struct RSAKey *result) {
return ssh1_read_bignum(data, &result->private_exponent);
}
void rsaencrypt(unsigned char *data, int length, struct RSAKey *key) {
Bignum b1, b2;
int i;
unsigned char *p;
memmove(data+key->bytes-length, data, length);
data[0] = 0;
data[1] = 2;
for (i = 2; i < key->bytes-length-1; i++) {
do {
data[i] = random_byte();
} while (data[i] == 0);
}
data[key->bytes-length-1] = 0;
b1 = bignum_from_bytes(data, key->bytes);
b2 = modpow(b1, key->exponent, key->modulus);
p = data;
for (i=key->bytes; i-- ;) {
*p++ = bignum_byte(b2, i);
}
freebn(b1);
freebn(b2);
}
Bignum rsadecrypt(Bignum input, struct RSAKey *key) {
Bignum ret;
ret = modpow(input, key->private_exponent, key->modulus);
return ret;
}
int rsastr_len(struct RSAKey *key) {
Bignum md, ex;
int mdlen, exlen;
md = key->modulus;
ex = key->exponent;
mdlen = (ssh1_bignum_bitcount(md)+15) / 16;
exlen = (ssh1_bignum_bitcount(ex)+15) / 16;
return 4 * (mdlen+exlen) + 20;
}
void rsastr_fmt(char *str, struct RSAKey *key) {
Bignum md, ex;
int len = 0, i, nibbles;
static const char hex[] = "0123456789abcdef";
md = key->modulus;
ex = key->exponent;
len += sprintf(str+len, "0x");
nibbles = (3 + ssh1_bignum_bitcount(ex))/4; if (nibbles<1) nibbles=1;
for (i=nibbles; i-- ;)
str[len++] = hex[(bignum_byte(ex, i/2) >> (4*(i%2))) & 0xF];
len += sprintf(str+len, ",0x");
nibbles = (3 + ssh1_bignum_bitcount(md))/4; if (nibbles<1) nibbles=1;
for (i=nibbles; i-- ;)
str[len++] = hex[(bignum_byte(md, i/2) >> (4*(i%2))) & 0xF];
str[len] = '\0';
}
/*
* Generate a fingerprint string for the key. Compatible with the
* OpenSSH fingerprint code.
*/
void rsa_fingerprint(char *str, int len, struct RSAKey *key) {
struct MD5Context md5c;
unsigned char digest[16];
char buffer[16*3+40];
int numlen, slen, i;
MD5Init(&md5c);
numlen = ssh1_bignum_length(key->modulus) - 2;
for (i = numlen; i-- ;) {
unsigned char c = bignum_byte(key->modulus, i);
MD5Update(&md5c, &c, 1);
}
numlen = ssh1_bignum_length(key->exponent) - 2;
for (i = numlen; i-- ;) {
unsigned char c = bignum_byte(key->exponent, i);
MD5Update(&md5c, &c, 1);
}
MD5Final(digest, &md5c);
sprintf(buffer, "%d ", ssh1_bignum_bitcount(key->modulus));
for (i = 0; i < 16; i++)
sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
strncpy(str, buffer, len); str[len-1] = '\0';
slen = strlen(str);
if (key->comment && slen < len-1) {
str[slen] = ' ';
strncpy(str+slen+1, key->comment, len-slen-1);
str[len-1] = '\0';
}
}
/*
* Verify that the public data in an RSA key matches the private
* data. We also check the private data itself: we ensure that p >
* q and that iqmp really is the inverse of q mod p.
*/
int rsa_verify(struct RSAKey *key) {
Bignum n, ed, pm1, qm1;
int cmp;
/* n must equal pq. */
n = bigmul(key->p, key->q);
cmp = bignum_cmp(n, key->modulus);
freebn(n);
if (cmp != 0)
return 0;
/* e * d must be congruent to 1, modulo (p-1) and modulo (q-1). */
pm1 = copybn(key->p);
decbn(pm1);
ed = modmul(key->exponent, key->private_exponent, pm1);
cmp = bignum_cmp(ed, One);
sfree(ed);
if (cmp != 0)
return 0;
qm1 = copybn(key->q);
decbn(qm1);
ed = modmul(key->exponent, key->private_exponent, qm1);
cmp = bignum_cmp(ed, One);
sfree(ed);
if (cmp != 0)
return 0;
/*
* Ensure p > q.
*/
if (bignum_cmp(key->p, key->q) <= 0)
return 0;
/*
* Ensure iqmp * q is congruent to 1, modulo p.
*/
n = modmul(key->iqmp, key->q, key->p);
cmp = bignum_cmp(n, One);
sfree(n);
if (cmp != 0)
return 0;
return 1;
}
void freersakey(struct RSAKey *key) {
if (key->modulus) freebn(key->modulus);
if (key->exponent) freebn(key->exponent);
if (key->private_exponent) freebn(key->private_exponent);
if (key->comment) sfree(key->comment);
}
/* ----------------------------------------------------------------------
* Implementation of the ssh-rsa signing key type.
*/
#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 length;
Bignum b;
getstring(data, datalen, &p, &length);
if (!p)
return NULL;
b = bignum_from_bytes(p, length);
return b;
}
static void *rsa2_newkey(char *data, int len) {
char *p;
int slen;
struct RSAKey *rsa;
rsa = smalloc(sizeof(struct RSAKey));
if (!rsa) return NULL;
getstring(&data, &len, &p, &slen);
if (!p || slen != 7 || memcmp(p, "ssh-rsa", 7)) {
sfree(rsa);
return NULL;
}
rsa->exponent = getmp(&data, &len);
rsa->modulus = getmp(&data, &len);
rsa->private_exponent = NULL;
rsa->comment = NULL;
return rsa;
}
static void rsa2_freekey(void *key) {
struct RSAKey *rsa = (struct RSAKey *)key;
freersakey(rsa);
sfree(rsa);
}
static char *rsa2_fmtkey(void *key) {
struct RSAKey *rsa = (struct RSAKey *)key;
char *p;
int len;
len = rsastr_len(rsa);
p = smalloc(len);
rsastr_fmt(p, rsa);
return p;
}
static unsigned char *rsa2_public_blob(void *key, int *len) {
struct RSAKey *rsa = (struct RSAKey *)key;
int elen, mlen, bloblen;
int i;
unsigned char *blob, *p;
elen = (ssh1_bignum_bitcount(rsa->exponent)+8)/8;
mlen = (ssh1_bignum_bitcount(rsa->modulus)+8)/8;
/*
* string "ssh-rsa", mpint exp, mpint mod. Total 19+elen+mlen.
* (three length fields, 12+7=19).
*/
bloblen = 19+elen+mlen;
blob = smalloc(bloblen);
p = blob;
PUT_32BIT(p, 7); p += 4;
memcpy(p, "ssh-rsa", 7); p += 7;
PUT_32BIT(p, elen); p += 4;
for (i = elen; i-- ;) *p++ = bignum_byte(rsa->exponent, i);
PUT_32BIT(p, mlen); p += 4;
for (i = mlen; i-- ;) *p++ = bignum_byte(rsa->modulus, i);
assert(p == blob + bloblen);
*len = bloblen;
return blob;
}
static unsigned char *rsa2_private_blob(void *key, int *len) {
struct RSAKey *rsa = (struct RSAKey *)key;
int dlen, plen, qlen, ulen, bloblen;
int i;
unsigned char *blob, *p;
dlen = (ssh1_bignum_bitcount(rsa->private_exponent)+8)/8;
plen = (ssh1_bignum_bitcount(rsa->p)+8)/8;
qlen = (ssh1_bignum_bitcount(rsa->q)+8)/8;
ulen = (ssh1_bignum_bitcount(rsa->iqmp)+8)/8;
/*
* mpint private_exp, mpint p, mpint q, mpint iqmp. Total 16 +
* sum of lengths.
*/
bloblen = 16+dlen+plen+qlen+ulen;
blob = smalloc(bloblen);
p = blob;
PUT_32BIT(p, dlen); p += 4;
for (i = dlen; i-- ;) *p++ = bignum_byte(rsa->private_exponent, i);
PUT_32BIT(p, plen); p += 4;
for (i = plen; i-- ;) *p++ = bignum_byte(rsa->p, i);
PUT_32BIT(p, qlen); p += 4;
for (i = qlen; i-- ;) *p++ = bignum_byte(rsa->q, i);
PUT_32BIT(p, ulen); p += 4;
for (i = ulen; i-- ;) *p++ = bignum_byte(rsa->iqmp, i);
assert(p == blob + bloblen);
*len = bloblen;
return blob;
}
static void *rsa2_createkey(unsigned char *pub_blob, int pub_len,
unsigned char *priv_blob, int priv_len) {
struct RSAKey *rsa;
char *pb = (char *)priv_blob;
rsa = rsa2_newkey((char *)pub_blob, pub_len);
rsa->private_exponent = getmp(&pb, &priv_len);
rsa->p = getmp(&pb, &priv_len);
rsa->q = getmp(&pb, &priv_len);
rsa->iqmp = getmp(&pb, &priv_len);
if (!rsa_verify(rsa)) {
rsa2_freekey(rsa);
return NULL;
}
return rsa;
}
static void *rsa2_openssh_createkey(unsigned char **blob, int *len) {
char **b = (char **)blob;
struct RSAKey *rsa;
rsa = smalloc(sizeof(struct RSAKey));
if (!rsa) return NULL;
rsa->comment = NULL;
rsa->modulus = getmp(b, len);
rsa->exponent = getmp(b, len);
rsa->private_exponent = getmp(b, len);
rsa->iqmp = getmp(b, len);
rsa->p = getmp(b, len);
rsa->q = getmp(b, len);
if (!rsa->modulus || !rsa->exponent || !rsa->private_exponent ||
!rsa->iqmp || !rsa->p || !rsa->q) {
sfree(rsa->modulus);
sfree(rsa->exponent);
sfree(rsa->private_exponent);
sfree(rsa->iqmp);
sfree(rsa->p);
sfree(rsa->q);
sfree(rsa);
return NULL;
}
return rsa;
}
static char *rsa2_fingerprint(void *key) {
struct RSAKey *rsa = (struct RSAKey *)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-rsa", 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(rsa->exponent);
ADD_BIGNUM(rsa->modulus);
#undef ADD_BIGNUM
MD5Final(digest, &md5c);
sprintf(buffer, "ssh-rsa %d ", ssh1_bignum_bitcount(rsa->modulus));
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;
}
/*
* This is the magic ASN.1/DER prefix that goes in the decoded
* signature, between the string of FFs and the actual SHA hash
* value. The meaning of it is:
*
* 00 -- this marks the end of the FFs; not part of the ASN.1 bit itself
*
* 30 21 -- a constructed SEQUENCE of length 0x21
* 30 09 -- a constructed sub-SEQUENCE of length 9
* 06 05 -- an object identifier, length 5
* 2B 0E 03 02 1A -- object id { 1 3 14 3 2 26 }
* (the 1,3 comes from 0x2B = 43 = 40*1+3)
* 05 00 -- NULL
* 04 14 -- a primitive OCTET STRING of length 0x14
* [0x14 bytes of hash data follows]
*
* The object id in the middle there is listed as `id-sha1' in
* ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1d2.asn (the
* ASN module for PKCS #1) and its expanded form is as follows:
*
* id-sha1 OBJECT IDENTIFIER ::= {
* iso(1) identified-organization(3) oiw(14) secsig(3)
* algorithms(2) 26 }
*/
static unsigned char asn1_weird_stuff[] = {
0x00,0x30,0x21,0x30,0x09,0x06,0x05,0x2B,
0x0E,0x03,0x02,0x1A,0x05,0x00,0x04,0x14,
};
#define ASN1_LEN ( (int) sizeof(asn1_weird_stuff) )
static int rsa2_verifysig(void *key, char *sig, int siglen,
char *data, int datalen) {
struct RSAKey *rsa = (struct RSAKey *)key;
Bignum in, out;
char *p;
int slen;
int bytes, i, j, ret;
unsigned char hash[20];
getstring(&sig, &siglen, &p, &slen);
if (!p || slen != 7 || memcmp(p, "ssh-rsa", 7)) {
return 0;
}
in = getmp(&sig, &siglen);
out = modpow(in, rsa->exponent, rsa->modulus);
freebn(in);
ret = 1;
bytes = ssh1_bignum_bitcount(rsa->modulus) / 8;
/* Top (partial) byte should be zero. */
if (bignum_byte(out, bytes-1) != 0)
ret = 0;
/* First whole byte should be 1. */
if (bignum_byte(out, bytes-2) != 1)
ret = 0;
/* Most of the rest should be FF. */
for (i = bytes-3; i >= 20 + ASN1_LEN; i--) {
if (bignum_byte(out, i) != 0xFF)
ret = 0;
}
/* Then we expect to see the asn1_weird_stuff. */
for (i = 20 + ASN1_LEN - 1, j=0; i >= 20; i--,j++) {
if (bignum_byte(out, i) != asn1_weird_stuff[j])
ret = 0;
}
/* Finally, we expect to see the SHA-1 hash of the signed data. */
SHA_Simple(data, datalen, hash);
for (i = 19, j=0; i >= 0; i--,j++) {
if (bignum_byte(out, i) != hash[j])
ret = 0;
}
return ret;
}
unsigned char *rsa2_sign(void *key, char *data, int datalen, int *siglen) {
struct RSAKey *rsa = (struct RSAKey *)key;
unsigned char *bytes;
int nbytes;
unsigned char hash[20];
Bignum in, out;
int i, j;
SHA_Simple(data, datalen, hash);
nbytes = (ssh1_bignum_bitcount(rsa->modulus)-1) / 8;
bytes = smalloc(nbytes);
bytes[0] = 1;
for (i = 1; i < nbytes-20-ASN1_LEN; i++)
bytes[i] = 0xFF;
for (i = nbytes-20-ASN1_LEN, j=0; i < nbytes-20; i++,j++)
bytes[i] = asn1_weird_stuff[j];
for (i = nbytes-20, j=0; i < nbytes; i++,j++)
bytes[i] = hash[j];
in = bignum_from_bytes(bytes, nbytes);
sfree(bytes);
out = modpow(in, rsa->private_exponent, rsa->modulus);
freebn(in);
nbytes = (ssh1_bignum_bitcount(out)+7)/8;
bytes = smalloc(4+7+4+nbytes);
PUT_32BIT(bytes, 7);
memcpy(bytes+4, "ssh-rsa", 7);
PUT_32BIT(bytes+4+7, nbytes);
for (i = 0; i < nbytes; i++)
bytes[4+7+4+i] = bignum_byte(out, nbytes-1-i);
freebn(out);
*siglen = 4+7+4+nbytes;
return bytes;
}
const struct ssh_signkey ssh_rsa = {
rsa2_newkey,
rsa2_freekey,
rsa2_fmtkey,
rsa2_public_blob,
rsa2_private_blob,
rsa2_createkey,
rsa2_openssh_createkey,
rsa2_fingerprint,
rsa2_verifysig,
rsa2_sign,
"ssh-rsa",
"rsa2"
};