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Introduce helper function to retrieve explicit IV len for transform

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The structure `mbedtls_ssl_transform` representing record protection
transformations should ideally be used through a function-based
interface only, as this will ease change of implementation as well
as the addition of new record protection routines in the future.

This commit makes a step in that direction by introducing the
helper function `ssl_transform_get_explicit_iv_len()` which
returns the size of the pre-expansion during record encryption
due to the potential addition of an explicit IV.

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
This commit is contained in:
Hanno Becker 2020-05-28 07:17:36 +01:00
parent 17263803aa
commit c0eefa8b92
1 changed files with 12 additions and 7 deletions
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19
library/ssl_msg.c
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@ -4985,6 +4985,15 @@ int mbedtls_ssl_parse_change_cipher_spec( mbedtls_ssl_context *ssl )
* and the caller has to make sure there's space for this.
*/
static size_t ssl_transform_get_explicit_iv_len(
mbedtls_ssl_transform const *transform )
{
if( transform->minor_ver < MBEDTLS_SSL_MINOR_VERSION_2 )
return( 0 );
return( transform->ivlen - transform->fixed_ivlen );
}
void mbedtls_ssl_update_out_pointers( mbedtls_ssl_context *ssl,
mbedtls_ssl_transform *transform )
{
@ -5013,14 +5022,10 @@ void mbedtls_ssl_update_out_pointers( mbedtls_ssl_context *ssl,
ssl->out_iv = ssl->out_hdr + 5;
}
ssl->out_msg = ssl->out_iv;
/* Adjust out_msg to make space for explicit IV, if used. */
if( transform != NULL &&
ssl->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_2 )
{
ssl->out_msg = ssl->out_iv + transform->ivlen - transform->fixed_ivlen;
}
else
ssl->out_msg = ssl->out_iv;
if( transform != NULL )
ssl->out_msg += ssl_transform_get_explicit_iv_len( transform );
}
/* Once ssl->in_hdr as the address of the beginning of the