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crypto: atmel-ecc - clean up and improve ECDH comments

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Improve the kerneldoc for struct atmel_ecdh_ctx by removing the stale
"unsupported curves" wording, since the device only supports a single
curve (P-256), and move the set_secret() constraint to the description.

In atmel_ecdh_set_secret(), clarify that the device generates the
private key, and drop the redundant "only supports NIST P256" comment.

In atmel_ecdh_done() and atmel_ecdh_generate_public_key(), clarify the
truncation comments. Also note that a P-256 public key consists of two
32-byte coordinates in atmel_ecdh_compute_shared_secret(), and remove
the unnecessary fall-through comment and other redundant comments.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Thorsten Blum
2026-06-09 12:05:54 +02:00
committed by Herbert Xu
parent 4c7a4a3404
commit 3e84fb698a
1 changed files with 14 additions and 24 deletions
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38
drivers/crypto/atmel-ecc.c
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@@ -27,15 +27,14 @@ static struct atmel_ecc_driver_data driver_data;
/**
* struct atmel_ecdh_ctx - transformation context
* @client : pointer to i2c client device
* @fallback : used for unsupported curves or when user wants to use its own
* private key.
* @public_key : generated when calling set_secret(). It's the responsibility
* of the user to not call set_secret() while
* generate_public_key() or compute_shared_secret() are in flight.
* @curve_id : elliptic curve id
* @do_fallback: true when the device doesn't support the curve or when the user
* wants to use its own private key.
* @client: I2C client device
* @fallback: ECDH fallback used for caller-provided private keys
* @public_key: cached public key for the device-generated private key
* @curve_id: elliptic curve id
* @do_fallback: true when ECDH operations should use @fallback
*
* The caller must not invoke set_secret() while generate_public_key()
* or compute_shared_secret() are in flight.
*/
struct atmel_ecdh_ctx {
struct i2c_client *client;
@@ -55,7 +54,7 @@ static void atmel_ecdh_done(struct atmel_i2c_work_data *work_data, void *areq,
if (status)
goto free_work_data;
/* might want less than we've got */
/* copy only as much as requested, capped at 32 bytes */
n_sz = min(ATMEL_ECC_NIST_P256_N_SIZE, req->dst_len);
/* copy the shared secret */
@@ -64,15 +63,15 @@ static void atmel_ecdh_done(struct atmel_i2c_work_data *work_data, void *areq,
if (copied != n_sz)
status = -EINVAL;
/* fall through */
free_work_data:
kfree_sensitive(work_data);
kpp_request_complete(req, status);
}
/*
* A random private key is generated and stored in the device. The device
* returns the pair public key.
* If no private key is provided, generate one in the device and cache
* the corresponding public key. The generated private key never leaves
* the device.
*/
static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
unsigned int len)
@@ -83,9 +82,7 @@ static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
struct ecdh params;
int ret = -ENOMEM;
/* free the old public key, if any */
kfree(ctx->public_key);
/* make sure you don't free the old public key twice */
ctx->public_key = NULL;
if (crypto_ecdh_decode_key(buf, len, &params) < 0) {
@@ -94,7 +91,6 @@ static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
}
if (params.key_size) {
/* fallback to ecdh software implementation */
ctx->do_fallback = true;
return crypto_kpp_set_secret(ctx->fallback, buf, len);
}
@@ -103,11 +99,6 @@ static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
if (!cmd)
return -ENOMEM;
/*
* The device only supports NIST P256 ECC keys. The public key size will
* always be the same. Use a macro for the key size to avoid unnecessary
* computations.
*/
public_key = kmalloc(ATMEL_ECC_PUBKEY_SIZE, GFP_KERNEL);
if (!public_key)
goto free_cmd;
@@ -120,7 +111,6 @@ static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
if (ret)
goto free_public_key;
/* save the public key */
memcpy(public_key, &cmd->data[RSP_DATA_IDX], ATMEL_ECC_PUBKEY_SIZE);
ctx->public_key = public_key;
@@ -149,7 +139,7 @@ static int atmel_ecdh_generate_public_key(struct kpp_request *req)
if (!ctx->public_key)
return -EINVAL;
/* might want less than we've got */
/* copy only as much as requested, capped at 64 bytes */
nbytes = min(ATMEL_ECC_PUBKEY_SIZE, req->dst_len);
/* public key was saved at private key generation */
@@ -175,7 +165,7 @@ static int atmel_ecdh_compute_shared_secret(struct kpp_request *req)
return crypto_kpp_compute_shared_secret(req);
}
/* must have exactly two points to be on the curve */
/* A P-256 public key must contain two 32-byte coordinates */
if (req->src_len != ATMEL_ECC_PUBKEY_SIZE)
return -EINVAL;