rsa.c: Factor out constructing the EMSA-PKCS1 message representative.

[secnet.git] / rsa.c

diff --git a/rsa.c b/rsa.c
index caa030bd0223656c065a7013775df69523b714f7..0ca5d19fc08475a22a6c62d2f3d82a0acc2c06df 100644 (file)
--- a/rsa.c
+++ b/rsa.c
@@ -36,16 +36,11 @@ struct rsapub {
 
 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];
     int msize, i;
-    string_t signature;
-
-    mpz_init(&a);
-    mpz_init(&b);
 
     /* RSA PKCS#1 v1.5 signature padding:
      *
@@ -65,7 +60,7 @@ 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 +81,20 @@ 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 +143,13 @@ 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);
 
@@ -194,7 +183,7 @@ static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
     i=list_elem(args,0);
     if (i) {
        if (i->type!=t_string) {
-           cfgfatal(i->loc,"rsa-public","first argument must be a string");
+           cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
        }
        e=i->data.string;
        if (mpz_init_set_str(&st->e,e,10)!=0) {
@@ -208,7 +197,7 @@ static list_t *rsapub_apply(closure_t *self, struct cloc loc, dict_t *context,
     i=list_elem(args,1);
     if (i) {
        if (i->type!=t_string) {
-           cfgfatal(i->loc,"rsa-public","second argument must be a string");
+           cfgfatal(i->loc,"rsa-public","second argument must be a string\n");
        }
        n=i->data.string;
        if (mpz_init_set_str(&st->n,n,10)!=0) {
@@ -267,7 +256,7 @@ static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
     i=list_elem(args,0);
     if (i) {
        if (i->type!=t_string) {
-           cfgfatal(i->loc,"rsa-public","first argument must be a string");
+           cfgfatal(i->loc,"rsa-public","first argument must be a string\n");
        }
        filename=i->data.string;
     } else {
@@ -313,7 +302,7 @@ static list_t *rsapriv_apply(closure_t *self, struct cloc loc, dict_t *context,
     }
     b=safe_malloc(length,"rsapriv_apply");
     if (fread(b,length,1,f) != 1) {
-       cfgfatal_maybefile(f,loc,"rsa-private","error reading modulus");
+       cfgfatal_maybefile(f,loc,"rsa-private","error reading modulus\n");
     }
     mpz_init(&st->n);
     read_mpbin(&st->n,b,length);
@@ -430,8 +419,9 @@ 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);