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Update comments in ECHDE-PSK part of ssl_write_client_key_exchange()

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Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
This commit is contained in:
Neil Armstrong 2022-03-23 17:44:07 +01:00
parent bc5e8f9dd0
commit 2540045542
1 changed files with 10 additions and 2 deletions
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12
library/ssl_tls12_client.c
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@ -3091,12 +3091,17 @@ ecdh_calc_secret:
ssl->out_msg[header_len] = (unsigned char) own_pubkey_len; ssl->out_msg[header_len] = (unsigned char) own_pubkey_len;
content_len = own_pubkey_len + 1; content_len = own_pubkey_len + 1;
/* The ECDH secret is the premaster secret used for key derivation. */ /* As RFC 5489 section 2, the premaster secret is formed as follows:
* - a uint16 containing the length (in octets) of the ECDH computation
* - the octet string produced by the ECDH computation
* - a uint16 containing the length (in octets) of the PSK
* - the PSK itself
*/
unsigned char *p = ssl->handshake->premaster; unsigned char *p = ssl->handshake->premaster;
unsigned char *p_end = p + sizeof( ssl->handshake->premaster ); unsigned char *p_end = p + sizeof( ssl->handshake->premaster );
size_t zlen = 0; size_t zlen = 0;
/* Compute ECDH shared secret. */ /* Perform ECDH computation after the uint16 reserved for the length */
status = psa_raw_key_agreement( PSA_ALG_ECDH, status = psa_raw_key_agreement( PSA_ALG_ECDH,
handshake->ecdh_psa_privkey, handshake->ecdh_psa_privkey,
handshake->ecdh_psa_peerkey, handshake->ecdh_psa_peerkey,
@ -3111,6 +3116,7 @@ ecdh_calc_secret:
if( status != PSA_SUCCESS || destruction_status != PSA_SUCCESS ) if( status != PSA_SUCCESS || destruction_status != PSA_SUCCESS )
return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED ); return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
/* Write the ECDH computation length before the ECDH computation */
MBEDTLS_PUT_UINT16_BE( zlen, p, 0 ); MBEDTLS_PUT_UINT16_BE( zlen, p, 0 );
p += 2 + zlen; p += 2 + zlen;
@ -3131,12 +3137,14 @@ ecdh_calc_secret:
return( MBEDTLS_ERR_SSL_INTERNAL_ERROR ); return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
} }
/* Write the PSK length as uint16 */
MBEDTLS_PUT_UINT16_BE( psk_len, p, 0 ); MBEDTLS_PUT_UINT16_BE( psk_len, p, 0 );
p += 2; p += 2;
if( p_end < p || (size_t)( p_end - p ) < psk_len ) if( p_end < p || (size_t)( p_end - p ) < psk_len )
return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA ); return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
/* Write the PSK itself */
memcpy( p, psk, psk_len ); memcpy( p, psk, psk_len );
p += psk_len; p += psk_len;