[PATCH v3 01/10] crypto: ecdsa - Convert byte arrays with key coordinates to digits

Stefan Berger
2024-02-23T20:42:12Z

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
first have to be copied into a temporary byte array with leading zeros
and can then be copied into the final digit array using ecc_swap_digits.

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.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
crypto/ecdsa.c | 14 +++++++++-----
include/crypto/internal/ecc.h | 19 +++++++++++++++++++
2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c
index fbd76498aba8..ba8fb76fd165 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 = 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..bee3329af7de 100644
--- a/include/crypto/internal/ecc.h
+++ b/include/crypto/internal/ecc.h
@@ -56,6 +56,25 @@ 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 sz = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
+ u8 tmp[ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT];
+ unsigned int o = sz - nbytes;
+
+ memset(tmp, 0, o);
+ memcpy(&tmp[o], in, nbytes);
+ ecc_swap_digits(tmp, out, ndigits);
+}
+
/**
* ecc_is_key_valid() - Validate a given ECDH private key
*
--
2.43.0