git.distorted.org.uk Git - u/mdw/putty/blob - sshrsa.c

   1 /*
   2  * RSA implementation just sufficient for ssh client-side
   3  * initialisation step
   4  *
   5  * Rewritten for more speed by Joris van Rantwijk, Jun 1999.
   6  */
   7
   8 #include <stdio.h>
   9 #include <stdlib.h>
  10 #include <string.h>
  11
  12 #include "ssh.h"
  13
  14
  15 int makekey(unsigned char *data, struct RSAKey *result,
  16             unsigned char **keystr, int order) {
  17     unsigned char *p = data;
  18     int i;
  19
  20     if (result) {
  21         result->bits = 0;
  22         for (i=0; i<4; i++)
  23             result->bits = (result->bits << 8) + *p++;
  24     } else
  25         p += 4;
  26
  27     /*
  28      * order=0 means exponent then modulus (the keys sent by the
  29      * server). order=1 means modulus then exponent (the keys
  30      * stored in a keyfile).
  31      */
  32
  33     if (order == 0)
  34         p += ssh1_read_bignum(p, result ? &result->exponent : NULL);
  35     if (result)
  36         result->bytes = (((p[0] << 8) + p[1]) + 7) / 8;
  37     if (keystr) *keystr = p+2;
  38     p += ssh1_read_bignum(p, result ? &result->modulus : NULL);
  39     if (order == 1)
  40         p += ssh1_read_bignum(p, result ? &result->exponent : NULL);
  41
  42     return p - data;
  43 }
  44
  45 int makeprivate(unsigned char *data, struct RSAKey *result) {
  46     return ssh1_read_bignum(data, &result->private_exponent);
  47 }
  48
  49 void rsaencrypt(unsigned char *data, int length, struct RSAKey *key) {
  50     Bignum b1, b2;
  51     int i;
  52     unsigned char *p;
  53
  54     memmove(data+key->bytes-length, data, length);
  55     data[0] = 0;
  56     data[1] = 2;
  57
  58     for (i = 2; i < key->bytes-length-1; i++) {
  59         do {
  60             data[i] = random_byte();
  61         } while (data[i] == 0);
  62     }
  63     data[key->bytes-length-1] = 0;
  64
  65     b1 = bignum_from_bytes(data, key->bytes);
  66
  67     b2 = modpow(b1, key->exponent, key->modulus);
  68
  69     p = data;
  70     for (i=key->bytes; i-- ;) {
  71         *p++ = bignum_byte(b2, i);
  72     }
  73
  74     freebn(b1);
  75     freebn(b2);
  76 }
  77
  78 Bignum rsadecrypt(Bignum input, struct RSAKey *key) {
  79     Bignum ret;
  80     ret = modpow(input, key->private_exponent, key->modulus);
  81     return ret;
  82 }
  83
  84 int rsastr_len(struct RSAKey *key) {
  85     Bignum md, ex;
  86     int mdlen, exlen;
  87
  88     md = key->modulus;
  89     ex = key->exponent;
  90     mdlen = (ssh1_bignum_bitcount(md)+15) / 16;
  91     exlen = (ssh1_bignum_bitcount(ex)+15) / 16;
  92     return 4 * (mdlen+exlen) + 20;
  93 }
  94
  95 void rsastr_fmt(char *str, struct RSAKey *key) {
  96     Bignum md, ex;
  97     int len = 0, i, nibbles;
  98     static const char hex[] = "0123456789abcdef";
  99
 100     md = key->modulus;
 101     ex = key->exponent;
 102
 103     len += sprintf(str+len, "0x");
 104
 105     nibbles = (3 + ssh1_bignum_bitcount(ex))/4; if (nibbles<1) nibbles=1;
 106     for (i=nibbles; i-- ;)
 107         str[len++] = hex[(bignum_byte(ex, i/2) >> (4*(i%2))) & 0xF];
 108
 109     len += sprintf(str+len, ",0x");
 110
 111     nibbles = (3 + ssh1_bignum_bitcount(md))/4; if (nibbles<1) nibbles=1;
 112     for (i=nibbles; i-- ;)
 113         str[len++] = hex[(bignum_byte(md, i/2) >> (4*(i%2))) & 0xF];
 114
 115     str[len] = '\0';
 116 }
 117
 118 /*
 119  * Generate a fingerprint string for the key. Compatible with the
 120  * OpenSSH fingerprint code.
 121  */
 122 void rsa_fingerprint(char *str, int len, struct RSAKey *key) {
 123     struct MD5Context md5c;
 124     unsigned char digest[16];
 125     char buffer[16*3+40];
 126     int numlen, slen, i;
 127
 128     MD5Init(&md5c);
 129     numlen = ssh1_bignum_length(key->modulus) - 2;
 130     for (i = numlen; i-- ;) {
 131         unsigned char c = bignum_byte(key->modulus, i);
 132         MD5Update(&md5c, &c, 1);
 133     }
 134     numlen = ssh1_bignum_length(key->exponent) - 2;
 135     for (i = numlen; i-- ;) {
 136         unsigned char c = bignum_byte(key->exponent, i);
 137         MD5Update(&md5c, &c, 1);
 138     }
 139     MD5Final(digest, &md5c);
 140
 141     sprintf(buffer, "%d ", ssh1_bignum_bitcount(key->modulus));
 142     for (i = 0; i < 16; i++)
 143         sprintf(buffer+strlen(buffer), "%s%02x", i?":":"", digest[i]);
 144     strncpy(str, buffer, len); str[len-1] = '\0';
 145     slen = strlen(str);
 146     if (key->comment && slen < len-1) {
 147         str[slen] = ' ';
 148         strncpy(str+slen+1, key->comment, len-slen-1);
 149         str[len-1] = '\0';
 150     }
 151 }
 152
 153 void freersakey(struct RSAKey *key) {
 154     if (key->modulus) freebn(key->modulus);
 155     if (key->exponent) freebn(key->exponent);
 156     if (key->private_exponent) freebn(key->private_exponent);
 157     if (key->comment) sfree(key->comment);
 158 }