Re: [PATCH v2 2/2] crypto: ecdh & ecc - Initialize ctx->private_key in proper byte order

From: Jarkko Sakkinen
Date: Wed Apr 17 2024 - 18:43:47 EST

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In reply to: Stefan Berger: "[PATCH v2 2/2] crypto: ecdh & ecc - Initialize ctx->private_key in proper byte order"
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On Wed Apr 17, 2024 at 7:21 PM EEST, Stefan Berger wrote:
> The private key in ctx->private_key is currently initialized in reverse
> byte order in ecdh_set_secret and whenever the key is needed in proper
> byte order the variable priv is introduced and the bytes from
> ctx->private_key are copied into priv while being byte-swapped
> (ecc_swap_digits). To get rid of the unnecessary byte swapping initialize
> ctx->private_key in proper byte order and clean up all functions that were
> previously using priv or were called with ctx->private_key:
>
> - ecc_gen_privkey: Directly initialize the passed ctx->private_key with
> random bytes and get rid of the priv variable. This function only has
> ecdh_set_secret as a caller.
>
> - crypto_ecdh_shared_secret: Called only from ecdh_compute_value with
> ctx->private_key. Get rid of the priv variable and work with the passed
> private_key directly.
>
> - ecc_make_pub_key: Called only from ecdh_compute_value with
> ctx->private_key. Get rid of the priv variable and work with the passed
> private_key directly.
>
> Cc: Salvatore Benedetto <salvatore.benedetto@xxxxxxxxx>
> Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> ---
> crypto/ecc.c | 29 ++++++++++-------------------
> crypto/ecdh.c | 8 +++-----
> include/crypto/internal/ecc.h | 3 ++-
> 3 files changed, 15 insertions(+), 25 deletions(-)
>
> diff --git a/crypto/ecc.c b/crypto/ecc.c
> index 2e05387b9499..c1d2e884be1e 100644
> --- a/crypto/ecc.c
> +++ b/crypto/ecc.c
> @@ -1497,10 +1497,10 @@ EXPORT_SYMBOL(ecc_is_key_valid);
> * This method generates a private key uniformly distributed in the range
> * [2, n-3].
> */
> -int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
> +int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits,
> + u64 *private_key)
> {
> const struct ecc_curve *curve = ecc_get_curve(curve_id);
> - u64 priv[ECC_MAX_DIGITS];
> unsigned int nbytes = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
> unsigned int nbits = vli_num_bits(curve->n, ndigits);
> int err;
> @@ -1509,7 +1509,7 @@ int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
> * 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))
> + if (nbits < 224)
> return -EINVAL;
>
> /*
> @@ -1527,17 +1527,16 @@ int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey)
> return -EFAULT;
>
> /* Step 3: obtain N returned_bits from the DRBG. */
> - err = crypto_rng_get_bytes(crypto_default_rng, (u8 *)priv, nbytes);
> + err = crypto_rng_get_bytes(crypto_default_rng,
> + (u8 *)private_key, nbytes);
> crypto_put_default_rng();
> if (err)
> return err;
>
> /* Step 4: make sure the private key is in the valid range. */
> - if (__ecc_is_key_valid(curve, priv, ndigits))
> + if (__ecc_is_key_valid(curve, private_key, ndigits))
> return -EINVAL;
>
> - ecc_swap_digits(priv, privkey, ndigits);
> -
> return 0;
> }
> EXPORT_SYMBOL(ecc_gen_privkey);
> @@ -1547,23 +1546,20 @@ int ecc_make_pub_key(unsigned int curve_id, unsigned int ndigits,
> {
> int ret = 0;
> struct ecc_point *pk;
> - u64 priv[ECC_MAX_DIGITS];
> const struct ecc_curve *curve = ecc_get_curve(curve_id);
>
> - if (!private_key || ndigits > ARRAY_SIZE(priv)) {
> + if (!private_key) {
> ret = -EINVAL;
> goto out;
> }
>
> - ecc_swap_digits(private_key, priv, ndigits);
> -
> pk = ecc_alloc_point(ndigits);
> if (!pk) {
> ret = -ENOMEM;
> goto out;
> }
>
> - ecc_point_mult(pk, &curve->g, priv, NULL, curve, ndigits);
> + ecc_point_mult(pk, &curve->g, private_key, NULL, curve, ndigits);
>
> /* SP800-56A rev 3 5.6.2.1.3 key check */
> if (ecc_is_pubkey_valid_full(curve, pk)) {
> @@ -1647,13 +1643,11 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
> {
> int ret = 0;
> struct ecc_point *product, *pk;
> - u64 priv[ECC_MAX_DIGITS];
> u64 rand_z[ECC_MAX_DIGITS];
> unsigned int nbytes;
> const struct ecc_curve *curve = ecc_get_curve(curve_id);
>
> - if (!private_key || !public_key ||
> - ndigits > ARRAY_SIZE(priv) || ndigits > ARRAY_SIZE(rand_z)) {
> + if (!private_key || !public_key || ndigits > ARRAY_SIZE(rand_z)) {
> ret = -EINVAL;
> goto out;
> }
> @@ -1674,15 +1668,13 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
> if (ret)
> goto err_alloc_product;
>
> - ecc_swap_digits(private_key, priv, ndigits);
> -
> product = ecc_alloc_point(ndigits);
> if (!product) {
> ret = -ENOMEM;
> goto err_alloc_product;
> }
>
> - ecc_point_mult(product, pk, priv, rand_z, curve, ndigits);
> + ecc_point_mult(product, pk, private_key, rand_z, curve, ndigits);
>
> if (ecc_point_is_zero(product)) {
> ret = -EFAULT;
> @@ -1692,7 +1684,6 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
> ecc_swap_digits(product->x, secret, ndigits);
>
> err_validity:
> - memzero_explicit(priv, sizeof(priv));
> memzero_explicit(rand_z, sizeof(rand_z));
> ecc_free_point(product);
> err_alloc_product:
> diff --git a/crypto/ecdh.c b/crypto/ecdh.c
> index c02c9a2b9682..72cfd1590156 100644
> --- a/crypto/ecdh.c
> +++ b/crypto/ecdh.c
> @@ -27,7 +27,6 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
> unsigned int len)
> {
> struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
> - u64 priv[ECC_MAX_DIGITS];
> struct ecdh params;
> int ret = 0;
>
> @@ -41,15 +40,14 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
> return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
> ctx->private_key);
>
> - memcpy(ctx->private_key, params.key, params.key_size);
> - ecc_swap_digits(ctx->private_key, priv, ctx->ndigits);
> + ecc_digits_from_bytes(params.key, params.key_size,
> + ctx->private_key, ctx->ndigits);
>
> if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
> - priv, params.key_size) < 0) {
> + ctx->private_key, params.key_size) < 0) {
> memzero_explicit(ctx->private_key, params.key_size);
> ret = -EINVAL;
> }
> - memzero_explicit(priv, sizeof(priv));
>
> return ret;
> }
> diff --git a/include/crypto/internal/ecc.h b/include/crypto/internal/ecc.h
> index 4e2f5f938e91..7ca1f463d1ec 100644
> --- a/include/crypto/internal/ecc.h
> +++ b/include/crypto/internal/ecc.h
> @@ -103,7 +103,8 @@ int ecc_is_key_valid(unsigned int curve_id, unsigned int ndigits,
> * Returns 0 if the private key was generated successfully, a negative value
> * if an error occurred.
> */
> -int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey);
> +int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits,
> + u64 *private_key);
>
> /**
> * ecc_make_pub_key() - Compute an ECC public key

Acked-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

BR, Jarkko

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Previous message: Jarkko Sakkinen: "Re: [PATCH v2 1/2] crypto: ecdh - Pass private key in proper byte order to check valid key"
In reply to: Stefan Berger: "[PATCH v2 2/2] crypto: ecdh & ecc - Initialize ctx->private_key in proper byte order"
Next in thread: Stefan Berger: "[PATCH v2 1/2] crypto: ecdh - Pass private key in proper byte order to check valid key"
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