Re: [PATCH v6 06/13] crypto: ecc - Implement vli_mmod_fast_521 for NIST p521
From: Stefan Berger
Date: Mon Mar 18 2024 - 14:39:01 EST
On 3/18/24 01:47, Bharat Bhushan wrote:
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From: Stefan Berger <stefanb@xxxxxxxxxxxxxxxxxx>
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Subject: [EXTERNAL] [PATCH v6 06/13] crypto: ecc - Implement
vli_mmod_fast_521 for NIST p521
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From: Stefan Berger <stefanb@xxxxxxxxxxxxx>
Implement vli_mmod_fast_521 following the description for how to calculate
the modulus for NIST P521 in the NIST publication "Recommendations for
Discrete Logarithm-Based Cryptography: Elliptic Curve Domain Parameters"
section G.1.4.
NIST p521 requires 9 64bit digits, so increase the ECC_MAX_DIGITS so that
arrays fit the larger numbers.
Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
---
crypto/ecc.c | 25 +++++++++++++++++++++++++
include/crypto/internal/ecc.h | 3 ++-
2 files changed, 27 insertions(+), 1 deletion(-)
diff --git a/crypto/ecc.c b/crypto/ecc.c index 415a2f4e7291..99d41887c005
100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -902,6 +902,28 @@ static void vli_mmod_fast_384(u64 *result, const
u64 *product, #undef AND64H #undef AND64L
+/*
+ * Computes result = product % curve_prime
+ * from "Recommendations for Discrete Logarithm-Based Cryptography:
+ * Elliptic Curve Domain Parameters" section G.1.4
+ */
+static void vli_mmod_fast_521(u64 *result, const u64 *product,
+ const u64 *curve_prime, u64 *tmp) {
+ const unsigned int ndigits = ECC_CURVE_NIST_P521_DIGITS;
+ size_t i;
+
+ /* Initialize result with lowest 521 bits from product */
+ vli_set(result, product, ndigits);
+ result[8] &= 0x1ff;
+
+ for (i = 0; i < ndigits; i++)
+ tmp[i] = (product[8 + i] >> 9) | (product[9 + i] << 55);
+ tmp[8] &= 0x1ff;
Can we get away from this hardcoding, like 9, 55, 0x1ff etc.
Or at least add comment about these.
+
+ vli_mod_add(result, result, tmp, curve_prime, ndigits); }
+
/* Computes result = product % curve_prime for different curve_primes.
*
* Note that curve_primes are distinguished just by heuristic check and @@ -
941,6 +963,9 @@ static bool vli_mmod_fast(u64 *result, u64 *product,
case ECC_CURVE_NIST_P384_DIGITS:
vli_mmod_fast_384(result, product, curve_prime, tmp);
break;
+ case ECC_CURVE_NIST_P521_DIGITS:
+ vli_mmod_fast_521(result, product, curve_prime, tmp);
+ break;
default:
pr_err_ratelimited("ecc: unsupported digits size!\n");
return false;
diff --git a/include/crypto/internal/ecc.h b/include/crypto/internal/ecc.h index
ab722a8986b7..4e2f5f938e91 100644
--- a/include/crypto/internal/ecc.h
+++ b/include/crypto/internal/ecc.h
@@ -33,7 +33,8 @@
#define ECC_CURVE_NIST_P192_DIGITS 3
#define ECC_CURVE_NIST_P256_DIGITS 4
#define ECC_CURVE_NIST_P384_DIGITS 6
-#define ECC_MAX_DIGITS (512 / 64) /* due to ecrdsa */
+#define ECC_CURVE_NIST_P521_DIGITS 9
Maybe these can be defined as:
#define ECC_CURVE_NIST_P521_DIGITS (DIV_ROUND_UP(521, 64) /* NIST P521 */)
I think for NIST P521 9 can be pre-calculated. It will not change
anymore in the future.
+#define ECC_MAX_DIGITS DIV_ROUND_UP(521, 64) /* NIST P521 */
/* NIST_P521 is max digits */
#define ECC_MAX_DIGITS ECC_CURVE_ _DIGITS
In this case I think the DIV_ROUND_UP() along with the comment shows
that it needs to be updated if ever a larger curve comes along.
Thanks
-Bharat
#define ECC_DIGITS_TO_BYTES_SHIFT 3
--
2.43.0