X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/blobdiff_plain/374330e25a6b51c40436fa869a381dd510790f6e..d8770b1245ff0acd81f581c5667563e0d127104a:/sshrsa.c

diff --git a/sshrsa.c b/sshrsa.c
index 70cf9bbe..36069ad7 100644
--- a/sshrsa.c
+++ b/sshrsa.c
@@ -1,412 +1,494 @@
 /*
  * RSA implementation just sufficient for ssh client-side
  * initialisation step
+ *
+ * Rewritten for more speed by Joris van Rantwijk, Jun 1999.
  */
 
-/*#include <windows.h>
-#define RSADEBUG
-#define DLVL 2
-#include "stel.h"*/
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <assert.h>
 
 #include "ssh.h"
 
-typedef unsigned short *Bignum;
-
-static unsigned short Zero[1] = { 0 };
-
-#if defined TESTMODE || defined RSADEBUG
-#ifndef DLVL
-#define DLVL 10000
-#endif
-#define debug(x) bndebug(#x,x)
-static int level = 0;
-static void bndebug(char *name, Bignum b) {
-    int i;
-    int w = 50-level-strlen(name)-5*b[0];
-    if (level >= DLVL)
-	return;
-    if (w < 0) w = 0;
-    dprintf("%*s%s%*s", level, "", name, w, "");
-    for (i=b[0]; i>0; i--)
-	dprintf(" %04x", b[i]);
-    dprintf("\n");
-}
-#define dmsg(x) do {if(level<DLVL){dprintf("%*s",level,"");printf x;}} while(0)
-#define enter(x) do { dmsg(x); level += 4; } while(0)
-#define leave(x) do { level -= 4; dmsg(x); } while(0)
-#else
-#define debug(x)
-#define dmsg(x)
-#define enter(x)
-#define leave(x)
-#endif
-
-static Bignum newbn(int length) {
-    Bignum b = malloc((length+1)*sizeof(unsigned short));
-    if (!b)
-	abort();		       /* FIXME */
-    b[0] = length;
-    return b;
-}
 
-static void freebn(Bignum b) {
-    free(b);
-}
-
-static int msb(Bignum r) {
+int makekey(unsigned char *data, struct RSAKey *result,
+	    unsigned char **keystr, int order) {
+    unsigned char *p = data;
     int i;
-    int j;
-    unsigned short n;
 
-    for (i=r[0]; i>0; i--)
-	if (r[i])
-	    break;
+    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);
 
-    j = (i-1)*16;
-    n = r[i];
-    if (n & 0xFF00) j += 8, n >>= 8;
-    if (n & 0x00F0) j += 4, n >>= 4;
-    if (n & 0x000C) j += 2, n >>= 2;
-    if (n & 0x0002) j += 1, n >>= 1;
+    return p - data;
+}
 
-    return j;
+int makeprivate(unsigned char *data, struct RSAKey *result) {
+    return ssh1_read_bignum(data, &result->private_exponent);
 }
 
-static void add(Bignum r1, Bignum r2, Bignum result) {
+void rsaencrypt(unsigned char *data, int length, struct RSAKey *key) {
+    Bignum b1, b2;
     int i;
-    long stuff = 0;
-
-    enter((">add\n"));
-    debug(r1);
-    debug(r2);
-
-    for (i = 1 ;; i++) {
-	if (i <= r1[0])
-	    stuff += r1[i];
-	if (i <= r2[0])
-	    stuff += r2[i];
-	if (i <= result[0])
-	    result[i] = stuff & 0xFFFFU;
-	if (i > r1[0] && i > r2[0] && i >= result[0])
-	    break;
-	stuff >>= 16;
-    }
+    unsigned char *p;
 
-    debug(result);
-    leave(("<add\n"));
-}
+    memmove(data+key->bytes-length, data, length);
+    data[0] = 0;
+    data[1] = 2;
 
-static void sub(Bignum r1, Bignum r2, Bignum result) {
-    int i;
-    long stuff = 0;
-
-    enter((">sub\n"));
-    debug(r1);
-    debug(r2);
-
-    for (i = 1 ;; i++) {
-	if (i <= r1[0])
-	    stuff += r1[i];
-	if (i <= r2[0])
-	    stuff -= r2[i];
-	if (i <= result[0])
-	    result[i] = stuff & 0xFFFFU;
-	if (i > r1[0] && i > r2[0] && i >= result[0])
-	    break;
-	stuff = stuff<0 ? -1 : 0;
+    for (i = 2; i < key->bytes-length-1; i++) {
+	do {
+	    data[i] = random_byte();
+	} while (data[i] == 0);
     }
+    data[key->bytes-length-1] = 0;
 
-    debug(result);
-    leave(("<sub\n"));
-}
+    b1 = bignum_from_bytes(data, key->bytes);
 
-static int ge(Bignum r1, Bignum r2) {
-    int i;
+    b2 = modpow(b1, key->exponent, key->modulus);
 
-    enter((">ge\n"));
-    debug(r1);
-    debug(r2);
-
-    if (r1[0] < r2[0])
-	i = r2[0];
-    else
-	i = r1[0];
-
-    while (i > 0) {
-	unsigned short n1 = (i > r1[0] ? 0 : r1[i]);
-	unsigned short n2 = (i > r2[0] ? 0 : r2[i]);
-
-	if (n1 > n2) {
-	    dmsg(("greater\n"));
-	    leave(("<ge\n"));
-	    return 1;		       /* r1 > r2 */
-	} else if (n1 < n2) {
-	    dmsg(("less\n"));
-	    leave(("<ge\n"));
-	    return 0;		       /* r1 < r2 */
-	}
-
-	i--;
+    p = data;
+    for (i=key->bytes; i-- ;) {
+        *p++ = bignum_byte(b2, i);
     }
 
-    dmsg(("equal\n"));
-    leave(("<ge\n"));
-    return 1;			       /* r1 = r2 */
+    freebn(b1);
+    freebn(b2);
 }
 
-static void modmult(Bignum r1, Bignum r2, Bignum modulus, Bignum result) {
-    Bignum temp = newbn(modulus[0]+1);
-    Bignum tmp2 = newbn(modulus[0]+1);
-    int i;
-    int bit, bits, digit, smallbit;
-
-    enter((">modmult\n"));
-    debug(r1);
-    debug(r2);
-    debug(modulus);
-
-    for (i=1; i<=result[0]; i++)
-	result[i] = 0;		       /* result := 0 */
-    for (i=1; i<=temp[0]; i++)
-	temp[i] = (i > r2[0] ? 0 : r2[i]);   /* temp := r2 */
-
-    bits = 1+msb(r1);
-
-    for (bit = 0; bit < bits; bit++) {
-	digit = 1 + bit / 16;
-	smallbit = bit % 16;
-
-	debug(temp);
-	if (digit <= r1[0] && (r1[digit] & (1<<smallbit))) {
-	    dmsg(("bit %d\n", bit));
-	    add(temp, result, tmp2);
-	    if (ge(tmp2, modulus))
-		sub(tmp2, modulus, result);
-	    else
-		add(tmp2, Zero, result);
-	    debug(result);
-	}
-
-	add(temp, temp, tmp2);
-	if (ge(tmp2, modulus))
-	    sub(tmp2, modulus, temp);
-	else
-	    add(tmp2, Zero, temp);
-    }
+Bignum rsadecrypt(Bignum input, struct RSAKey *key) {
+    Bignum ret;
+    ret = modpow(input, key->private_exponent, key->modulus);
+    return ret;
+}
 
-    freebn(temp);
-    freebn(tmp2);
+int rsastr_len(struct RSAKey *key) {
+    Bignum md, ex;
+    int mdlen, exlen;
 
-    debug(result);
-    leave(("<modmult\n"));
+    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;
 }
 
-static void modpow(Bignum r1, Bignum r2, Bignum modulus, Bignum result) {
-    Bignum temp = newbn(modulus[0]+1);
-    Bignum tmp2 = newbn(modulus[0]+1);
-    int i;
-    int bit, bits, digit, smallbit;
-
-    enter((">modpow\n"));
-    debug(r1);
-    debug(r2);
-    debug(modulus);
-
-    for (i=1; i<=result[0]; i++)
-	result[i] = (i==1);	       /* result := 1 */
-    for (i=1; i<=temp[0]; i++)
-	temp[i] = (i > r1[0] ? 0 : r1[i]);   /* temp := r1 */
-
-    bits = 1+msb(r2);
-
-    for (bit = 0; bit < bits; bit++) {
-	digit = 1 + bit / 16;
-	smallbit = bit % 16;
-
-	debug(temp);
-	if (digit <= r2[0] && (r2[digit] & (1<<smallbit))) {
-	    dmsg(("bit %d\n", bit));
-	    modmult(temp, result, modulus, tmp2);
-	    add(tmp2, Zero, result);
-	    debug(result);
-	}
-
-	modmult(temp, temp, modulus, tmp2);
-	add(tmp2, Zero, temp);
-    }
+void rsastr_fmt(char *str, struct RSAKey *key) {
+    Bignum md, ex;
+    int len = 0, i, nibbles;
+    static const char hex[] = "0123456789abcdef";
 
-    freebn(temp);
-    freebn(tmp2);
+    md = key->modulus;
+    ex = key->exponent;
 
-    debug(result);
-    leave(("<modpow\n"));
-}
+    len += sprintf(str+len, "0x");
 
-int makekey(unsigned char *data, struct RSAKey *result,
-	    unsigned char **keystr) {
-    unsigned char *p = data;
-    Bignum bn[2];
-    int i, j;
-    int w, b;
+    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");
 
-    result->bits = 0;
-    for (i=0; i<4; i++)
-	result->bits = (result->bits << 8) + *p++;
+    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];
 
-    for (j=0; j<2; j++) {
+    str[len] = '\0';
+}
 
-	w = 0;
-	for (i=0; i<2; i++)
-	    w = (w << 8) + *p++;
+/*
+ * 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';
+    }
+}
 
-	result->bytes = b = (w+7)/8;   /* bits -> bytes */
-	w = (w+15)/16;		       /* bits -> words */
+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);
+}
 
-	bn[j] = newbn(w);
+/* ----------------------------------------------------------------------
+ * Implementation of the ssh-rsa signing key type. 
+ */
 
-	if (keystr) *keystr = p;       /* point at key string, second time */
+#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;
+}
 
-	for (i=1; i<=w; i++)
-	    bn[j][i] = 0;
-	for (i=0; i<b; i++) {
-	    unsigned char byte = *p++;
-	    if ((b-i) & 1)
-		bn[j][w-i/2] |= byte;
-	    else
-		bn[j][w-i/2] |= byte<<8;
-	}
+static void *rsa2_newkey(char *data, int len) {
+    char *p;
+    int slen;
+    struct RSAKey *rsa;
 
-	debug(bn[j]);
+    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;
 
-    result->exponent = bn[0];
-    result->modulus = bn[1];
-
-    return p - data;
+    return rsa;
 }
 
-void rsaencrypt(unsigned char *data, int length, struct RSAKey *key) {
-    Bignum b1, b2;
-    int w, i;
-    unsigned char *p;
-
-    debug(key->exponent);
+static void rsa2_freekey(void *key) {
+    struct RSAKey *rsa = (struct RSAKey *)key;
+    freersakey(rsa);
+    sfree(rsa);
+}
 
-    memmove(data+key->bytes-length, data, length);
-    data[0] = 0;
-    data[1] = 2;
+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;
+}
 
-    for (i = 2; i < key->bytes-length-1; i++) {
-	do {
-	    data[i] = random_byte();
-	} while (data[i] == 0);
-    }
-    data[key->bytes-length-1] = 0;
+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;
+}
 
-    w = (key->bytes+1)/2;
+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;
+}
 
-    b1 = newbn(w);
-    b2 = newbn(w);
+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);
+
+    return rsa;
+}
 
-    p = data;
-    for (i=1; i<=w; i++)
-	b1[i] = 0;
-    for (i=0; i<key->bytes; i++) {
-	unsigned char byte = *p++;
-	if ((key->bytes-i) & 1)
-	    b1[w-i/2] |= byte;
-	else
-	    b1[w-i/2] |= byte<<8;
+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;
     }
 
-    debug(b1);
-
-    modpow(b1, key->exponent, key->modulus, b2);
+    return rsa;
+}
 
-    debug(b2);
+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;
+}
 
-    p = data;
-    for (i=0; i<key->bytes; i++) {
-	unsigned char b;
-	if (i & 1)
-	    b = b2[w-i/2] & 0xFF;
-	else
-	    b = b2[w-i/2] >> 8;
-	*p++ = b;
+/*
+ * 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. As closely as I can tell, 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 -- 
+ *       05 00 -- NULL
+ *    04 14 -- a primitive OCTET STRING of length 0x14
+ *       [0x14 bytes of hash data follows]
+ */
+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;
     }
 
-    freebn(b1);
-    freebn(b2);
+    return ret;
 }
 
-int rsastr_len(struct RSAKey *key) {
-    Bignum md, ex;
+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;
 
-    md = key->modulus;
-    ex = key->exponent;
-    return 4 * (ex[0]+md[0]) + 10;
-}
+    SHA_Simple(data, datalen, hash);
 
-void rsastr_fmt(char *str, struct RSAKey *key) {
-    Bignum md, ex;
-    int len = 0, i;
+    nbytes = (ssh1_bignum_bitcount(rsa->modulus)-1) / 8;
+    bytes = smalloc(nbytes);
 
-    md = key->modulus;
-    ex = key->exponent;
+    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];
 
-    for (i=1; i<=ex[0]; i++) {
-	sprintf(str+len, "%04x", ex[i]);
-	len += strlen(str+len);
-    }
-    str[len++] = '/';
-    for (i=1; i<=md[0]; i++) {
-	sprintf(str+len, "%04x", md[i]);
-	len += strlen(str+len);
-    }
-    str[len] = '\0';
-}
+    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);
 
-#ifdef TESTMODE
-
-#ifndef NODDY
-#define p1 10007
-#define p2 10069
-#define p3 10177
-#else
-#define p1 3
-#define p2 7
-#define p3 13
-#endif
-
-unsigned short P1[2] = { 1, p1 };
-unsigned short P2[2] = { 1, p2 };
-unsigned short P3[2] = { 1, p3 };
-unsigned short bigmod[5] = { 4, 0, 0, 0, 32768U };
-unsigned short mod[5] = { 4, 0, 0, 0, 0 };
-unsigned short a[5] = { 4, 0, 0, 0, 0 };
-unsigned short b[5] = { 4, 0, 0, 0, 0 };
-unsigned short c[5] = { 4, 0, 0, 0, 0 };
-unsigned short One[2] = { 1, 1 };
-unsigned short Two[2] = { 1, 2 };
-
-int main(void) {
-    modmult(P1, P2, bigmod, a);   debug(a);
-    modmult(a, P3, bigmod, mod);  debug(mod);
-
-    sub(P1, One, a);              debug(a);
-    sub(P2, One, b);              debug(b);
-    modmult(a, b, bigmod, c);     debug(c);
-    sub(P3, One, a);              debug(a);
-    modmult(a, c, bigmod, b);     debug(b);
-
-    modpow(Two, b, mod, a);       debug(a);
-
-    return 0;
+    *siglen = 4+7+4+nbytes;
+    return bytes;
 }
 
-#endif
+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"
+};