From: Mark Wooding <mdw@distorted.org.uk>
Date: Thu, 25 Jul 2013 17:30:46 +0000 (+0100)
Subject: rsa.c: Factor out constructing the EMSA-PKCS1 message representative.
X-Git-Tag: debian/0.3.0_beta2~41
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=secnet.git;a=commitdiff_plain;h=2cd2cf055c0c424f60751f7ac4007771e377f262

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

This was done in two different places for no reason I could understand.
Replace them both with a single implementation.

Signed-off-by: Mark Wooding <mdw@distorted.org.uk>
---

diff --git a/rsa.c b/rsa.c
index fed468d..0ca5d19 100644
--- 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);