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-rw-r--r--crypto/ecc.c29
1 files changed, 17 insertions, 12 deletions
diff --git a/crypto/ecc.c b/crypto/ecc.c
index f53fb4d6af99..3581027e9f92 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -1416,6 +1416,12 @@ void ecc_point_mult_shamir(const struct ecc_point *result,
}
EXPORT_SYMBOL(ecc_point_mult_shamir);
+/*
+ * This function performs checks equivalent to Appendix A.4.2 of FIPS 186-5.
+ * Whereas A.4.2 results in an integer in the interval [1, n-1], this function
+ * ensures that the integer is in the range of [2, n-3]. We are slightly
+ * stricter because of the currently used scalar multiplication algorithm.
+ */
static int __ecc_is_key_valid(const struct ecc_curve *curve,
const u64 *private_key, unsigned int ndigits)
{
@@ -1455,16 +1461,11 @@ int ecc_is_key_valid(unsigned int curve_id, unsigned int ndigits,
EXPORT_SYMBOL(ecc_is_key_valid);
/*
- * ECC private keys are generated using the method of extra random bits,
- * equivalent to that described in FIPS 186-4, Appendix B.4.1.
- *
- * d = (c mod(n–1)) + 1 where c is a string of random bits, 64 bits longer
- * than requested
- * 0 <= c mod(n-1) <= n-2 and implies that
- * 1 <= d <= n-1
+ * ECC private keys are generated using the method of rejection sampling,
+ * equivalent to that described in FIPS 186-5, Appendix A.2.2.
*
* This method generates a private key uniformly distributed in the range
- * [1, n-1].
+ * [2, n-3].
*/
int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
{
@@ -1474,12 +1475,15 @@ int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
unsigned int nbits = vli_num_bits(curve->n, ndigits);
int err;
- /* Check that N is included in Table 1 of FIPS 186-4, section 6.1.1 */
- if (nbits < 160 || ndigits > ARRAY_SIZE(priv))
+ /*
+ * Step 1 & 2: check that N is included in Table 1 of FIPS 186-5,
+ * section 6.1.1.
+ */
+ if (nbits < 224 || ndigits > ARRAY_SIZE(priv))
return -EINVAL;
/*
- * FIPS 186-4 recommends that the private key should be obtained from a
+ * FIPS 186-5 recommends that the private key should be obtained from a
* RBG with a security strength equal to or greater than the security
* strength associated with N.
*
@@ -1492,12 +1496,13 @@ int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
if (crypto_get_default_rng())
return -EFAULT;
+ /* Step 3: obtain N returned_bits from the DRBG. */
err = crypto_rng_get_bytes(crypto_default_rng, (u8 *)priv, nbytes);
crypto_put_default_rng();
if (err)
return err;
- /* Make sure the private key is in the valid range. */
+ /* Step 4: make sure the private key is in the valid range. */
if (__ecc_is_key_valid(curve, priv, ndigits))
return -EINVAL;