mdw@git.distorted.org.uk Git - secnet/blob - rsa.c

   1 #include <stdio.h>
   2 #include <gmp.h>
   3 #include "secnet.h"
   4 #include "util.h"
   5
   6 #define AUTHFILE_ID_STRING "SSH PRIVATE KEY FILE FORMAT 1.1\n"
   7
   8 struct rsapriv {
   9     closure_t cl;
  10     struct rsaprivkey_if ops;
  11     struct cloc loc;
  12     MP_INT d;
  13     MP_INT n;
  14 };
  15 struct rsapub {
  16     closure_t cl;
  17     struct rsapubkey_if ops;
  18     struct cloc loc;
  19     MP_INT e;
  20     MP_INT n;
  21 };
  22 /* Sign data. NB data must be smaller than modulus */
  23
  24 static char *hexchars="0123456789abcdef";
  25
  26 static string_t rsa_sign(void *sst, uint8_t *data, uint32_t datalen)
  27 {
  28     struct rsapriv *st=sst;
  29     MP_INT a, b;
  30     char buff[2048];
  31     int msize, i;
  32     string_t signature;
  33
  34     mpz_init(&a);
  35     mpz_init(&b);
  36
  37     msize=mpz_sizeinbase(&st->n, 16);
  38
  39     if (datalen*2+4>=msize) {
  40         fatal("rsa_sign: message too big\n");
  41     }
  42
  43     strcpy(buff,"0001");
  44
  45     for (i=0; i<datalen; i++) {
  46         buff[4+i*2]=hexchars[(data[i]&0xf0)>>4];
  47         buff[5+i*2]=hexchars[data[i]&0xf];
  48     }
  49     buff[4+datalen*2]=0;
  50
  51     for (i=datalen*2+4; i<msize; i++)
  52         buff[i]='f';
  53
  54     buff[msize]=0;
  55
  56     mpz_set_str(&a, buff, 16);
  57
  58     mpz_powm(&b, &a, &st->d, &st->n);
  59
  60     signature=write_mpstring(&b);
  61
  62     mpz_clear(&b);
  63     mpz_clear(&a);
  64     return signature;
  65 }
  66
  67 static bool_t rsa_sig_check(void *sst, uint8_t *data, uint32_t datalen,
  68                             string_t signature)
  69 {
  70     struct rsapub *st=sst;
  71     MP_INT a, b, c;
  72     char buff[2048];
  73     int msize, i;
  74     bool_t ok;
  75
  76     mpz_init(&a);
  77     mpz_init(&b);
  78     mpz_init(&c);
  79
  80     msize=mpz_sizeinbase(&st->n, 16);
  81
  82     strcpy(buff,"0001");
  83
  84     for (i=0; i<datalen; i++) {
  85         buff[4+i*2]=hexchars[(data[i]&0xf0)>>4];
  86         buff[5+i*2]=hexchars[data[i]&0xf];
  87     }
  88     buff[4+datalen*2]=0;
  89
  90     for (i=datalen*2+4; i<msize; i++)
  91         buff[i]='f';
  92
  93     buff[msize]=0;
  94
  95     mpz_set_str(&a, buff, 16);
  96
  97     mpz_set_str(&b, signature, 16);
  98
  99     mpz_powm(&c, &b, &st->e, &st->n);
 100
 101     ok=(mpz_cmp(&a, &c)==0);
 102
 103     mpz_clear(&c);
 104     mpz_clear(&b);
 105     mpz_clear(&a);
 106
 107     return ok;
 108 }
 109
 110 static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
 111                             list_t *args)
 112 {
 113     struct rsapub *st;
 114     item_t *i;
 115     string_t e,n;
 116
 117     st=safe_malloc(sizeof(*st),"rsapub_apply");
 118     st->cl.description="rsapub";
 119     st->cl.type=CL_RSAPUBKEY;
 120     st->cl.apply=NULL;
 121     st->cl.interface=&st->ops;
 122     st->ops.st=st;
 123     st->ops.check=rsa_sig_check;
 124     st->loc=loc;
 125
 126     i=list_elem(args,0);
 127     if (i) {
 128         if (i->type!=t_string) {
 129             cfgfatal(i->loc,"rsa-public","first argument must be a string");
 130         }
 131         e=i->data.string;
 132         if (mpz_init_set_str(&st->e,e,10)!=0) {
 133             cfgfatal(i->loc,"rsa-public","encryption key \"%s\" is not a "
 134                      "decimal number string\n",e);
 135         }
 136     } else {
 137         cfgfatal(loc,"rsa-public","you must provide an encryption key\n");
 138     }
 139
 140     i=list_elem(args,1);
 141     if (i) {
 142         if (i->type!=t_string) {
 143             cfgfatal(i->loc,"rsa-public","second argument must be a string");
 144         }
 145         n=i->data.string;
 146         if (mpz_init_set_str(&st->n,n,10)!=0) {
 147             cfgfatal(i->loc,"rsa-public","modulus \"%s\" is not a decimal "
 148                      "number string\n",n);
 149         }
 150     } else {
 151         cfgfatal(loc,"rsa-public","you must provide a modulus\n");
 152     }
 153     return new_closure(&st->cl);
 154 }
 155
 156 static uint32_t keyfile_get_int(FILE *f)
 157 {
 158     uint32_t r;
 159     r=fgetc(f)<<24;
 160     r|=fgetc(f)<<16;
 161     r|=fgetc(f)<<8;
 162     r|=fgetc(f);
 163     return r;
 164 }
 165
 166 static uint16_t keyfile_get_short(FILE *f)
 167 {
 168     uint16_t r;
 169     r=fgetc(f)<<8;
 170     r|=fgetc(f);
 171     return r;
 172 }
 173
 174 static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
 175                              list_t *args)
 176 {
 177     struct rsapriv *st;
 178     FILE *f;
 179     string_t filename;
 180     item_t *i;
 181     long length;
 182     uint8_t *b, *c;
 183     int cipher_type;
 184     MP_INT e,sig,plain,check;
 185
 186     st=safe_malloc(sizeof(*st),"rsapriv_apply");
 187     st->cl.description="rsapriv";
 188     st->cl.type=CL_RSAPRIVKEY;
 189     st->cl.apply=NULL;
 190     st->cl.interface=&st->ops;
 191     st->ops.st=st;
 192     st->ops.sign=rsa_sign;
 193     st->loc=loc;
 194
 195     /* Argument is filename pointing to SSH1 private key file */
 196     i=list_elem(args,0);
 197     if (i) {
 198         if (i->type!=t_string) {
 199             cfgfatal(i->loc,"rsa-public","first argument must be a string");
 200         }
 201         filename=i->data.string;
 202     } else {
 203         filename=""; /* Make compiler happy */
 204         cfgfatal(loc,"rsa-private","you must provide a filename\n");
 205     }
 206
 207     f=fopen(filename,"rb");
 208     if (!f) {
 209         if (just_check_config) {
 210             Message(M_WARNING,"rsa-private (%s:%d): cannot open keyfile "
 211                     "\"%s\"; assuming it's valid while we check the "
 212                     "rest of the configuration\n",loc.file,loc.line,filename);
 213             goto assume_valid;
 214         } else {
 215             fatal_perror("rsa-private (%s:%d): cannot open file \"%s\"",
 216                          loc.file,loc.line,filename);
 217         }
 218     }
 219
 220     /* Check that the ID string is correct */
 221     length=strlen(AUTHFILE_ID_STRING)+1;
 222     b=safe_malloc(length,"rsapriv_apply");
 223     if (fread(b,length,1,f)!=1 || memcmp(b,AUTHFILE_ID_STRING,length)!=0) {
 224         cfgfatal(loc,"rsa-private","file \"%s\" is not a "
 225                  "SSH1 private keyfile\n",filename);
 226     }
 227     free(b);
 228
 229     cipher_type=fgetc(f);
 230     keyfile_get_int(f); /* "Reserved data" */
 231     if (cipher_type != 0) {
 232         cfgfatal(loc,"rsa-private","we don't support encrypted keyfiles\n");
 233     }
 234
 235     /* Read the public key */
 236     keyfile_get_int(f); /* Not sure what this is */
 237     length=(keyfile_get_short(f)+7)/8;
 238     if (length>1024) {
 239         cfgfatal(loc,"rsa-private","implausible length %ld for modulus\n",
 240                  length);
 241     }
 242     b=safe_malloc(length,"rsapriv_apply");
 243     if (fread(b,length,1,f) != 1) {
 244         cfgfatal(loc,"rsa-private","error reading modulus\n");
 245     }
 246     mpz_init(&st->n);
 247     read_mpbin(&st->n,b,length);
 248     free(b);
 249     length=(keyfile_get_short(f)+7)/8;
 250     if (length>1024) {
 251         cfgfatal(loc,"rsa-private","implausible length %ld for e\n",length);
 252     }
 253     b=safe_malloc(length,"rsapriv_apply");
 254     if (fread(b,length,1,f)!=1) {
 255         cfgfatal(loc,"rsa-private","error reading e\n");
 256     }
 257     mpz_init(&e);
 258     read_mpbin(&e,b,length);
 259     free(b);
 260
 261     length=keyfile_get_int(f);
 262     if (length>1024) {
 263         cfgfatal(loc,"rsa-private","implausibly long (%ld) key comment\n",
 264                  length);
 265     }
 266     c=safe_malloc(length+1,"rsapriv_apply");
 267     if (fread(c,length,1,f)!=1) {
 268         cfgfatal(loc,"rsa-private","error reading key comment\n");
 269     }
 270     c[length]=0;
 271
 272     /* Check that the next two pairs of characters are identical - the
 273        keyfile is not encrypted, so they should be */
 274     if (keyfile_get_short(f) != keyfile_get_short(f)) {
 275         cfgfatal(loc,"rsa-private","corrupt keyfile\n");
 276     }
 277
 278     /* Read d */
 279     length=(keyfile_get_short(f)+7)/8;
 280     if (length>1024) {
 281         cfgfatal(loc,"rsa-private","implausibly long (%ld) decryption key\n",
 282                  length);
 283     }
 284     b=safe_malloc(length,"rsapriv_apply");
 285     if (fread(b,length,1,f)!=1) {
 286         cfgfatal(loc,"rsa-private","error reading decryption key\n");
 287     }
 288     mpz_init(&st->d);
 289     read_mpbin(&st->d,b,length);
 290     free(b);
 291
 292     if (fclose(f)!=0) {
 293         fatal_perror("rsa-private (%s:%d): fclose",loc.file,loc.line);
 294     }
 295
 296     /* Now do trial signature/check to make sure it's a real keypair:
 297        sign the comment string! */
 298     i=list_elem(args,1);
 299     if (i && i->type==t_bool && i->data.bool==False) {
 300         Message(M_INFO,"rsa-private (%s:%d): skipping RSA key validity "
 301                 "check\n",loc.file,loc.line);
 302     } else {
 303         mpz_init(&sig);
 304         mpz_init(&plain);
 305         mpz_init(&check);
 306         read_mpbin(&plain,c,strlen(c));
 307         mpz_powm(&sig, &plain, &st->d, &st->n);
 308         mpz_powm(&check, &sig, &e, &st->n);
 309         if (mpz_cmp(&plain,&check)!=0) {
 310             cfgfatal(loc,"rsa-private","file \"%s\" does not contain a "
 311                      "valid RSA key!\n",filename);
 312         }
 313         mpz_clear(&sig);
 314         mpz_clear(&plain);
 315         mpz_clear(&check);
 316     }
 317
 318     free(c);
 319     mpz_clear(&e);
 320
 321 assume_valid:
 322     return new_closure(&st->cl);
 323 }
 324
 325 init_module rsa_module;
 326 void rsa_module(dict_t *dict)
 327 {
 328     add_closure(dict,"rsa-private",rsapriv_apply);
 329     add_closure(dict,"rsa-public",rsapub_apply);
 330 }