crypto: ecc - check for invalid values in the key verification test

Currently used scalar multiplication algorithm (Matthieu Rivain, 2011)
have invalid values for scalar == 1, n-1, and for regularized version
n-2, which was previously not checked. Verify that they are not used as
private keys.

Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 26 insertions, 16 deletions

diff --git a/crypto/ecc.c b/crypto/ecc.c
index 8facafd67802..9d24e6522730 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -904,30 +904,43 @@ static inline void ecc_swap_digits(const u64 *in, u64 *out,
                 out[i] = __swab64(in[ndigits - 1 - i]);
 }
 
-int ecc_is_key_valid(unsigned int curve_id, unsigned int ndigits,
-                     const u64 *private_key, unsigned int private_key_len)
+static int __ecc_is_key_valid(const struct ecc_curve *curve,
+                              const u64 *private_key, unsigned int ndigits)
 {
-        int nbytes;
-        const struct ecc_curve *curve = ecc_get_curve(curve_id);
+        u64 one[ECC_MAX_DIGITS] = { 1, };
+        u64 res[ECC_MAX_DIGITS];
 
         if (!private_key)
                 return -EINVAL;
 
-        nbytes = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
-
-        if (private_key_len != nbytes)
+        if (curve->g.ndigits != ndigits)
                 return -EINVAL;
 
-        if (vli_is_zero(private_key, ndigits))
+        /* Make sure the private key is in the range [2, n-3]. */
+        if (vli_cmp(one, private_key, ndigits) != -1)
                 return -EINVAL;
-
-        /* Make sure the private key is in the range [1, n-1]. */
-        if (vli_cmp(curve->n, private_key, ndigits) != 1)
+        vli_sub(res, curve->n, one, ndigits);
+        vli_sub(res, res, one, ndigits);
+        if (vli_cmp(res, private_key, ndigits) != 1)
                 return -EINVAL;
 
         return 0;
 }
 
+int ecc_is_key_valid(unsigned int curve_id, unsigned int ndigits,
+                     const u64 *private_key, unsigned int private_key_len)
+{
+        int nbytes;
+        const struct ecc_curve *curve = ecc_get_curve(curve_id);
+
+        nbytes = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
+
+        if (private_key_len != nbytes)
+                return -EINVAL;
+
+        return __ecc_is_key_valid(curve, private_key, ndigits);
+}
+
 /*
  * ECC private keys are generated using the method of extra random bits,
  * equivalent to that described in FIPS 186-4, Appendix B.4.1.
@@ -971,11 +984,8 @@ int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
         if (err)
                 return err;
 
-        if (vli_is_zero(priv, ndigits))
-                return -EINVAL;
-
-        /* Make sure the private key is in the range [1, n-1]. */
-        if (vli_cmp(curve->n, priv, ndigits) != 1)
+        /* Make sure the private key is in the valid range. */
+        if (__ecc_is_key_valid(curve, priv, ndigits))
                 return -EINVAL;
 
         ecc_swap_digits(priv, privkey, ndigits);