[PATCH v6 02/13] crypto: ecdsa - Convert byte arrays with key coordinates to digits

Stefan Berger
2024-03-12T18:37:40Z

From: Stefan Berger <stefanb@linux.ibm.com>

For NIST P192/256/384 the public key's x and y parameters could be copied
directly from a given array since both parameters filled 'ndigits' of
digits (a 'digit' is a u64). For support of NIST P521 the key parameters
need to have leading zeros prepended to the most significant digit since
only 2 bytes of the most significant digit are provided.

Therefore, implement ecc_digits_from_bytes to convert a byte array into an
array of digits and use this function in ecdsa_set_pub_key where an input
byte array needs to be converted into digits.

Suggested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Tested-by: Lukas Wunner <lukas@wunner.de>
---
crypto/ecdsa.c | 14 +++++++++-----
include/crypto/internal/ecc.h | 21 +++++++++++++++++++++
2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c
index fbd76498aba8..6653dec17327 100644
--- a/crypto/ecdsa.c
+++ b/crypto/ecdsa.c
@@ -222,9 +222,8 @@ static int ecdsa_ecc_ctx_reset(struct ecc_ctx *ctx)
static int ecdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key, unsigned int keylen)
{
struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+ unsigned int digitlen, ndigits;
const unsigned char *d = key;
- const u64 *digits = (const u64 *)&d[1];
- unsigned int ndigits;
int ret;

ret = ecdsa_ecc_ctx_reset(ctx);
@@ -238,12 +237,17 @@ static int ecdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key, unsig
return -EINVAL;

keylen--;
- ndigits = (keylen >> 1) / sizeof(u64);
+ digitlen = keylen >> 1;
+
+ ndigits = DIV_ROUND_UP(digitlen, sizeof(u64));
if (ndigits != ctx->curve->g.ndigits)
return -EINVAL;

- ecc_swap_digits(digits, ctx->pub_key.x, ndigits);
- ecc_swap_digits(&digits[ndigits], ctx->pub_key.y, ndigits);
+ d++;
+
+ ecc_digits_from_bytes(d, digitlen, ctx->pub_key.x, ndigits);
+ ecc_digits_from_bytes(&d[digitlen], digitlen, ctx->pub_key.y, ndigits);
+
ret = ecc_is_pubkey_valid_full(ctx->curve, &ctx->pub_key);

ctx->pub_key_set = ret == 0;
diff --git a/include/crypto/internal/ecc.h b/include/crypto/internal/ecc.h
index 4f6c1a68882f..ab722a8986b7 100644
--- a/include/crypto/internal/ecc.h
+++ b/include/crypto/internal/ecc.h
@@ -56,6 +56,27 @@ static inline void ecc_swap_digits(const void *in, u64 *out, unsigned int ndigit
out[i] = get_unaligned_be64(&src[ndigits - 1 - i]);
}

+/**
+ * ecc_digits_from_bytes() - Create ndigits-sized digits array from byte array
+ * @in: Input byte array
+ * @nbytes Size of input byte array
+ * @out Output digits array
+ * @ndigits: Number of digits to create from byte array
+ */
+static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
+ u64 *out, unsigned int ndigits)
+{
+ unsigned int o = nbytes & 7;
+ __be64 msd = 0;
+
+ if (o) {
+ memcpy((u8 *)&msd + sizeof(msd) - o, in, o);
+ out[--ndigits] = be64_to_cpu(msd);
+ in += o;
+ }
+ ecc_swap_digits(in, out, ndigits);
+}
+
/**
* ecc_is_key_valid() - Validate a given ECDH private key
*
--
2.43.0