[PATCH 4.19 058/243] crypto: ecc - check for invalid values in the key verification test

Greg Kroah-Hartman
2019-12-11T15:18:17Z

From: Vitaly Chikunov <vt@altlinux.org>

[ Upstream commit 2eb4942b6609d35a4e835644a33203b0aef7443d ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
crypto/ecc.c | 42 ++++++++++++++++++++++++++----------------
1 file changed, 26 insertions(+), 16 deletions(-)

diff --git a/crypto/ecc.c b/crypto/ecc.c
index adcce310f6462..ed1237115066b 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -912,30 +912,43 @@ 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.
@@ -979,11 +992,8 @@ 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);
--
2.20.1