X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=secnet.git;a=blobdiff_plain;f=rsa.c;h=f7dd69db6f69115e03c94779a2529468b642619f;hp=0ca5d19fc08475a22a6c62d2f3d82a0acc2c06df;hb=c6a3b1f54ccc754be82f0a2ea5b4d60746053a2b;hpb=2cd2cf055c0c424f60751f7ac4007771e377f262

diff --git a/rsa.c b/rsa.c
index 0ca5d19..f7dd69d 100644
--- a/rsa.c
+++ b/rsa.c
@@ -34,12 +34,18 @@ 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 void emsa_pkcs1(MP_INT *n, MP_INT *m,
 		       const uint8_t *data, int32_t datalen)
 {
-    char buff[2048];
+    char buff[2*RSA_MAX_MODBYTES + 1];
     int msize, i;
 
     /* RSA PKCS#1 v1.5 signature padding:
@@ -193,6 +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) {
@@ -207,6 +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);
 }
 
@@ -296,7 +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);
     }
@@ -308,7 +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");
@@ -339,7 +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);
     }
@@ -353,7 +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);
     }
@@ -367,7 +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);
     }
@@ -381,7 +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);
     }