X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=secnet.git;a=blobdiff_plain;f=rsa.c;h=f7dd69db6f69115e03c94779a2529468b642619f;hp=0bd106ff3526935734641b239cdb3ec91649de2b;hb=c6a3b1f54ccc754be82f0a2ea5b4d60746053a2b;hpb=39a6b1e27fba043e9f988fa10f76ea68b796cbfd;ds=sidebyside

diff --git a/rsa.c b/rsa.c
index 0bd106f..f7dd69d 100644
--- a/rsa.c
+++ b/rsa.c
@@ -34,18 +34,19 @@ struct rsapub {
 };
 /* Sign data. NB data must be smaller than modulus */
 
+#define RSA_MAX_MODBYTES 2048
+/* The largest modulus I've seen is 15360 bits, which works out at 1920
+ * bytes.  Using keys this big is quite implausible, but it doesn't cost us
+ * much to support them.
+ */
+
 static const char *hexchars="0123456789abcdef";
 
-static string_t rsa_sign(void *sst, uint8_t *data, int32_t datalen)
+static void emsa_pkcs1(MP_INT *n, MP_INT *m,
+		       const uint8_t *data, int32_t datalen)
 {
-    struct rsapriv *st=sst;
-    MP_INT a, b, u, v, tmp, tmp2;
-    char buff[2048];
+    char buff[2*RSA_MAX_MODBYTES + 1];
     int msize, i;
-    string_t signature;
-
-    mpz_init(&a);
-    mpz_init(&b);
 
     /* RSA PKCS#1 v1.5 signature padding:
      *
@@ -65,7 +66,7 @@ static string_t rsa_sign(void *sst, uint8_t *data, int32_t datalen)
      * -iwj 17.9.2002
      */
 
-    msize=mpz_sizeinbase(&st->n, 16);
+    msize=mpz_sizeinbase(n, 16);
 
     if (datalen*2+6>=msize) {
 	fatal("rsa_sign: message too big");
@@ -86,7 +87,20 @@ static string_t rsa_sign(void *sst, uint8_t *data, int32_t datalen)
 
     buff[msize]=0;
 
-    mpz_set_str(&a, buff, 16);
+    mpz_set_str(m, buff, 16);
+}
+
+static string_t rsa_sign(void *sst, uint8_t *data, int32_t datalen)
+{
+    struct rsapriv *st=sst;
+    MP_INT a, b, u, v, tmp, tmp2;
+    string_t signature;
+
+    mpz_init(&a);
+    mpz_init(&b);
+
+    /* Construct the message representative. */
+    emsa_pkcs1(&st->n, &a, data, datalen);
 
     /*
      * Produce an RSA signature (a^d mod n) using the Chinese
@@ -135,32 +149,13 @@ static bool_t rsa_sig_check(void *sst, uint8_t *data, int32_t datalen,
 {
     struct rsapub *st=sst;
     MP_INT a, b, c;
-    char buff[2048];
-    int msize, i;
     bool_t ok;
 
     mpz_init(&a);
     mpz_init(&b);
     mpz_init(&c);
 
-    msize=mpz_sizeinbase(&st->n, 16);
-
-    strcpy(buff,"0001");
-
-    for (i=0; i<datalen; i++) {
-	buff[msize+(-datalen+i)*2]=hexchars[(data[i]&0xf0)>>4];
-	buff[msize+(-datalen+i)*2+1]=hexchars[data[i]&0xf];
-    }
-
-    buff[msize-datalen*2-2]= '0';
-    buff[msize-datalen*2-1]= '0';
-
-    for (i=4; i<msize-datalen*2-2; i++)
-	buff[i]='f';
-
-    buff[msize]=0;
-
-    mpz_set_str(&a, buff, 16);
+    emsa_pkcs1(&st->n, &a, data, datalen);
 
     mpz_set_str(&b, signature, 16);
 
@@ -204,6 +199,9 @@ static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
     } else {
 	cfgfatal(loc,"rsa-public","you must provide an encryption key\n");
     }
+    if (mpz_sizeinbase(&st->e, 256) > RSA_MAX_MODBYTES) {
+	cfgfatal(loc, "rsa-public", "implausibly large public exponent\n");
+    }
     
     i=list_elem(args,1);
     if (i) {
@@ -218,6 +216,9 @@ static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
     } else {
 	cfgfatal(loc,"rsa-public","you must provide a modulus\n");
     }
+    if (mpz_sizeinbase(&st->n, 256) > RSA_MAX_MODBYTES) {
+	cfgfatal(loc, "rsa-public", "implausibly large modulus\n");
+    }
     return new_closure(&st->cl);
 }
 
@@ -307,7 +308,7 @@ static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
     /* Read the public key */
     keyfile_get_int(loc,f); /* Not sure what this is */
     length=(keyfile_get_short(loc,f)+7)/8;
-    if (length>1024) {
+    if (length>RSA_MAX_MODBYTES) {
 	cfgfatal(loc,"rsa-private","implausible length %ld for modulus\n",
 		 length);
     }
@@ -319,7 +320,7 @@ static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
     read_mpbin(&st->n,b,length);
     free(b);
     length=(keyfile_get_short(loc,f)+7)/8;
-    if (length>1024) {
+    if (length>RSA_MAX_MODBYTES) {
 	cfgfatal(loc,"rsa-private","implausible length %ld for e\n",length);
     }
     b=safe_malloc(length,"rsapriv_apply");
@@ -350,7 +351,7 @@ static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
 
     /* Read d */
     length=(keyfile_get_short(loc,f)+7)/8;
-    if (length>1024) {
+    if (length>RSA_MAX_MODBYTES) {
 	cfgfatal(loc,"rsa-private","implausibly long (%ld) decryption key\n",
 		 length);
     }
@@ -364,7 +365,7 @@ static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
     free(b);
     /* Read iqmp (inverse of q mod p) */
     length=(keyfile_get_short(loc,f)+7)/8;
-    if (length>1024) {
+    if (length>RSA_MAX_MODBYTES) {
 	cfgfatal(loc,"rsa-private","implausibly long (%ld)"
 		 " iqmp auxiliary value\n", length);
     }
@@ -378,7 +379,7 @@ static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
     free(b);
     /* Read q (the smaller of the two primes) */
     length=(keyfile_get_short(loc,f)+7)/8;
-    if (length>1024) {
+    if (length>RSA_MAX_MODBYTES) {
 	cfgfatal(loc,"rsa-private","implausibly long (%ld) q value\n",
 		 length);
     }
@@ -392,7 +393,7 @@ static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
     free(b);
     /* Read p (the larger of the two primes) */
     length=(keyfile_get_short(loc,f)+7)/8;
-    if (length>1024) {
+    if (length>RSA_MAX_MODBYTES) {
 	cfgfatal(loc,"rsa-private","implausibly long (%ld) p value\n",
 		 length);
     }
@@ -430,8 +431,9 @@ static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
 	/*
 	 * Verify that d*e is congruent to 1 mod (p-1), and mod
 	 * (q-1). This is equivalent to it being congruent to 1 mod
-	 * lcm(p-1,q-1), i.e. congruent to 1 mod phi(n). Note that
-	 * phi(n) is _not_ simply (p-1)*(q-1).
+	 * lambda(n) = lcm(p-1,q-1).  The usual `textbook' condition,
+	 * that d e == 1 (mod (p-1)(q-1)) is sufficient, but not
+	 * actually necessary.
 	 */
 	mpz_mul(&tmp, &d, &e);
 	mpz_sub_ui(&tmp2, &st->p, 1);