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Compute record expansion in steps to ease readability

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Hanno Becker 2018-08-17 15:28:19 +01:00
parent 448146407f
commit 3136ede0e8
1 changed files with 13 additions and 15 deletions
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28
library/ssl_tls.c
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@ -6839,7 +6839,7 @@ const char *mbedtls_ssl_get_version( const mbedtls_ssl_context *ssl )
int mbedtls_ssl_get_record_expansion( const mbedtls_ssl_context *ssl ) int mbedtls_ssl_get_record_expansion( const mbedtls_ssl_context *ssl )
{ {
size_t transform_expansion; size_t transform_expansion = 0;
const mbedtls_ssl_transform *transform = ssl->transform_out; const mbedtls_ssl_transform *transform = ssl->transform_out;
unsigned block_size; unsigned block_size;
@ -6865,23 +6865,21 @@ int mbedtls_ssl_get_record_expansion( const mbedtls_ssl_context *ssl )
block_size = mbedtls_cipher_get_block_size( block_size = mbedtls_cipher_get_block_size(
&transform->cipher_ctx_enc ); &transform->cipher_ctx_enc );
/* Expansion due to the addition of the MAC. */
transform_expansion += transform->maclen;
/* Expansion due to the addition of CBC padding;
* Theoretically up to 256 bytes, but we never use
* more than the block size of the underlying cipher. */
transform_expansion += block_size;
/* For TLS 1.1 or higher, an explicit IV is added
* after the record header. */
#if defined(MBEDTLS_SSL_PROTO_TLS1_1) || defined(MBEDTLS_SSL_PROTO_TLS1_2) #if defined(MBEDTLS_SSL_PROTO_TLS1_1) || defined(MBEDTLS_SSL_PROTO_TLS1_2)
if( ssl->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_2 ) if( ssl->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_2 )
{ transform_expansion += block_size;
/* Expansion due to addition of
* - MAC
* - CBC padding (theoretically up to 256 bytes, but
* we never use more than block_size)
* - explicit IV
*/
transform_expansion = transform->maclen + 2 * block_size;
}
else
#endif /* MBEDTLS_SSL_PROTO_TLS1_1 || MBEDTLS_SSL_PROTO_TLS1_2 */ #endif /* MBEDTLS_SSL_PROTO_TLS1_1 || MBEDTLS_SSL_PROTO_TLS1_2 */
{
/* No explicit IV prior to TLS 1.1. */
transform_expansion = transform->maclen + block_size;
}
break; break;
default: default: