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Minor changes to documentation and code comments for clarity

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Signed-off-by: Aditya Deshpande <aditya.deshpande@arm.com>
This commit is contained in:
Aditya Deshpande
2023-04-19 03:31:10 +01:00
parent 7b9934dcdd
commit 641cb8914d
4 changed files with 59 additions and 31 deletions
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31
3rdparty/p256-m/p256-m_driver_entrypoints.c vendored
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@ -27,7 +27,23 @@
#if defined(MBEDTLS_P256M_EXAMPLE_DRIVER_ENABLED)
psa_status_t p256_to_psa_error(int ret)
/* INFORMATION ON PSA KEY EXPORT FORMATS:
*
* PSA exports SECP256R1 keys in two formats:
* 1. Keypair format: 32 byte string which is just the private key (public key
* can be calculated from the private key)
* 2. Public Key format: A leading byte 0x04 (indicating uncompressed format),
* followed by the 64 byte public key. This results in a
* total of 65 bytes.
*
* p256-m's internal format for private keys matches PSA. Its format for public
* keys is only 64 bytes; the same as PSA but without the leading byte (0x04).
* Hence, when passing public keys from PSA to p256-m, the leading byte is
* removed.
*/
/* Convert between p256-m and PSA error codes */
static psa_status_t p256_to_psa_error(int ret)
{
switch (ret) {
case P256_SUCCESS:
@ -104,6 +120,9 @@ psa_status_t p256_transparent_key_agreement(
return status;
}
/* We add 1 to peer_key pointer to omit the leading byte of the public key
* representation (0x04). See information about PSA key formats at the top
* of the file. */
status = p256_to_psa_error(
p256_ecdh_shared_secret(shared_secret, key_buffer, peer_key+1));
if (status == PSA_SUCCESS) {
@ -159,6 +178,9 @@ static psa_status_t p256_verify_hash_with_public_key(
return status;
}
/* We add 1 to public_key_buffer pointer to omit the leading byte of the
* public key representation (0x04). See information about PSA key formats
* at the top of the file. */
const uint8_t *public_key_buffer = key_buffer + 1;
status = p256_to_psa_error(
p256_ecdsa_verify(signature, public_key_buffer, hash, hash_length));
@ -190,9 +212,10 @@ psa_status_t p256_transparent_verify_hash(
* requires size_t*, so we use a pointer to a stack variable. */
size_t *public_key_length_ptr = &public_key_length;
/* The contents of key_buffer may either be the 32 byte private key
* (keypair representation), or the 65 byte public key. To ensure the
* latter is obtained, the public key is exported. */
/* The contents of key_buffer may either be the 32 byte private key
* (keypair format), or 0x04 followed by the 64 byte public key (public
* key format). To ensure the key is in the latter format, the public key
* is exported. */
status = psa_driver_wrapper_export_public_key(
attributes,
key_buffer,