}
}
+/*
+ * Verify that the public data in an RSA key matches the private
+ * data. We also check the private data itself: we ensure that p >
+ * q and that iqmp really is the inverse of q mod p.
+ */
+int rsa_verify(struct RSAKey *key) {
+ Bignum n, ed, pm1, qm1;
+ int cmp;
+
+ /* n must equal pq. */
+ n = bigmul(key->p, key->q);
+ cmp = bignum_cmp(n, key->modulus);
+ freebn(n);
+ if (cmp != 0)
+ return 0;
+
+ /* e * d must be congruent to 1, modulo (p-1) and modulo (q-1). */
+ pm1 = copybn(key->p);
+ decbn(pm1);
+ ed = modmul(key->exponent, key->private_exponent, pm1);
+ cmp = bignum_cmp(ed, One);
+ sfree(ed);
+ if (cmp != 0)
+ return 0;
+
+ qm1 = copybn(key->q);
+ decbn(qm1);
+ ed = modmul(key->exponent, key->private_exponent, qm1);
+ cmp = bignum_cmp(ed, One);
+ sfree(ed);
+ if (cmp != 0)
+ return 0;
+
+ /*
+ * Ensure p > q.
+ */
+ if (bignum_cmp(key->p, key->q) <= 0)
+ return 0;
+
+ /*
+ * Ensure iqmp * q is congruent to 1, modulo p.
+ */
+ n = modmul(key->iqmp, key->q, key->p);
+ cmp = bignum_cmp(n, One);
+ sfree(n);
+ if (cmp != 0)
+ return 0;
+
+ return 1;
+}
+
void freersakey(struct RSAKey *key) {
if (key->modulus) freebn(key->modulus);
if (key->exponent) freebn(key->exponent);
len = rsastr_len(rsa);
p = smalloc(len);
- rsastr_fmt(p, rsa);
+ rsastr_fmt(p, rsa);
return p;
}
rsa->q = getmp(&pb, &priv_len);
rsa->iqmp = getmp(&pb, &priv_len);
+ if (!rsa_verify(rsa)) {
+ rsa2_freekey(rsa);
+ return NULL;
+ }
+
return rsa;
}
static void *rsa2_openssh_createkey(unsigned char **blob, int *len) {
char **b = (char **)blob;
struct RSAKey *rsa;
- char *p;
- int slen;
rsa = smalloc(sizeof(struct RSAKey));
if (!rsa) return NULL;
/*
* This is the magic ASN.1/DER prefix that goes in the decoded
* signature, between the string of FFs and the actual SHA hash
- * value. As closely as I can tell, the meaning of it is:
+ * value. The meaning of it is:
*
* 00 -- this marks the end of the FFs; not part of the ASN.1 bit itself
*
* 30 21 -- a constructed SEQUENCE of length 0x21
* 30 09 -- a constructed sub-SEQUENCE of length 9
* 06 05 -- an object identifier, length 5
- * 2B 0E 03 02 1A --
+ * 2B 0E 03 02 1A -- object id { 1 3 14 3 2 26 }
+ * (the 1,3 comes from 0x2B = 43 = 40*1+3)
* 05 00 -- NULL
* 04 14 -- a primitive OCTET STRING of length 0x14
* [0x14 bytes of hash data follows]
+ *
+ * The object id in the middle there is listed as `id-sha1' in
+ * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1d2.asn (the
+ * ASN module for PKCS #1) and its expanded form is as follows:
+ *
+ * id-sha1 OBJECT IDENTIFIER ::= {
+ * iso(1) identified-organization(3) oiw(14) secsig(3)
+ * algorithms(2) 26 }
*/
static unsigned char asn1_weird_stuff[] = {
0x00,0x30,0x21,0x30,0x09,0x06,0x05,0x2B,
0x0E,0x03,0x02,0x1A,0x05,0x00,0x04,0x14,
};
+#define ASN1_LEN ( (int) sizeof(asn1_weird_stuff) )
+
static int rsa2_verifysig(void *key, char *sig, int siglen,
char *data, int datalen) {
struct RSAKey *rsa = (struct RSAKey *)key;
if (bignum_byte(out, bytes-2) != 1)
ret = 0;
/* Most of the rest should be FF. */
- for (i = bytes-3; i >= 20 + sizeof(asn1_weird_stuff); i--) {
+ for (i = bytes-3; i >= 20 + ASN1_LEN; i--) {
if (bignum_byte(out, i) != 0xFF)
ret = 0;
}
/* Then we expect to see the asn1_weird_stuff. */
- for (i = 20 + sizeof(asn1_weird_stuff) - 1, j=0; i >= 20; i--,j++) {
+ for (i = 20 + ASN1_LEN - 1, j=0; i >= 20; i--,j++) {
if (bignum_byte(out, i) != asn1_weird_stuff[j])
ret = 0;
}
bytes = smalloc(nbytes);
bytes[0] = 1;
- for (i = 1; i < nbytes-20-sizeof(asn1_weird_stuff); i++)
+ for (i = 1; i < nbytes-20-ASN1_LEN; i++)
bytes[i] = 0xFF;
- for (i = nbytes-20-sizeof(asn1_weird_stuff), j=0; i < nbytes-20; i++,j++)
+ for (i = nbytes-20-ASN1_LEN, j=0; i < nbytes-20; i++,j++)
bytes[i] = asn1_weird_stuff[j];
for (i = nbytes-20, j=0; i < nbytes; i++,j++)
bytes[i] = hash[j];