yuzu-emu/mbedtls
2
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity

Clarify sequence length calculation comment

Browse source 
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
This commit is contained in:
Neil Armstrong 2022-09-13 14:49:24 +02:00
parent cb679f23bc
commit 1d0294f6ed
1 changed files with 27 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

31
library/psa_crypto_pake.c
View file

@ -513,19 +513,42 @@ psa_status_t psa_pake_output( psa_pake_operation_t *operation,
operation->buffer_offset = 0;
}
/* Load output sequence length */
/*
* Steps sequences are stored as:
* struct {
* opaque point <1..2^8-1>;
* } ECPoint;
*
* Where byte 0 stores the ECPoint curve point length.
*
* The sequence length is equal to:
* - data length extracted from byte 0
* - byte 0 size (1)
*/
if( operation->state == PSA_PAKE_OUTPUT_X2S &&
operation->sequence == PSA_PAKE_X1_STEP_KEY_SHARE )
{
if( operation->role == PSA_PAKE_ROLE_SERVER )
/* Length is stored after 3bytes curve */
/*
* The X2S KEY SHARE Server steps sequence is stored as:
* struct {
* ECPoint X;
* opaque r <1..2^8-1>;
* } ECSchnorrZKP;
*
* And MbedTLS uses a 3 bytes Ephemeral public key ECPoint,
* so byte 3 stores the r Schnorr signature length.
*
* The sequence length is equal to:
* - curve storage size (3)
* - data length extracted from byte 3
* - byte 3 size (1)
*/
length = 3 + operation->buffer[3] + 1;
else
/* Length is stored at the first byte */
length = operation->buffer[0] + 1;
}
else
/* Length is stored at the first byte of the next chunk */
length = operation->buffer[operation->buffer_offset] + 1;
if( length > operation->buffer_length )