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gcm: Support software fallback for non-AES ciphers in a gcm operation.

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When MBEDTLS_HARDWARE_GCM is enabled, we ALT all the GCM functions that are
declared in mbedtls/gcm.h with our H/W port functions, due to which even
if non-AES ciphers such as ARIA, CAMELLIA, BLOWFISH, etc. are selected
for a GCM operation, we perform an AES-GCM operation, thus resulting into
an incorrect calculation.
Thus in such cases we need to fallback to the software definitions of
GCM.

Currently, it is not directly possible to pull in software definitions of GCM
related functions directly due to gcm_alt.h, but this commit renames the
functions by appending `_soft` to their names, thus making them look different
functions in all and thus they are made available to pull in during compilation.

The change is configrable using the config MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK.
As this config is enabled by default, building the mbedtls crypto library
(libmbedcrypto.a) with this change increases its size by ~2.5KB.
This commit is contained in:
harshal.patil 2023-12-19 13:28:05 +05:30 committed by nilesh.kale
parent 3f0cdd8b5e
commit 803d5e8c91
2 changed files with 45 additions and 9 deletions
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24
include/mbedtls/gcm.h
View File

@ -44,7 +44,17 @@
extern "C" {
#endif
#if !defined(MBEDTLS_GCM_ALT)
#if defined(MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK)
#define SOFT(name) name##_soft
#else
#define SOFT(name) name
#endif /* MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK */
#if defined(MBEDTLS_GCM_ALT)
#include "gcm_alt.h"
#endif /* !MBEDTLS_GCM_ALT */
#if !defined(MBEDTLS_GCM_ALT) || defined(MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK)
#if defined(MBEDTLS_GCM_LARGE_TABLE)
#define MBEDTLS_GCM_HTABLE_SIZE 256
@ -55,7 +65,8 @@ extern "C" {
/**
* \brief The GCM context structure.
*/
typedef struct mbedtls_gcm_context {
typedef struct SOFT(mbedtls_gcm_context) {
#if defined(MBEDTLS_BLOCK_CIPHER_C)
mbedtls_block_cipher_context_t MBEDTLS_PRIVATE(block_cipher_ctx); /*!< The cipher context used. */
#else
@ -72,11 +83,7 @@ typedef struct mbedtls_gcm_context {
#MBEDTLS_GCM_DECRYPT. */
unsigned char MBEDTLS_PRIVATE(acceleration); /*!< The acceleration to use. */
}
mbedtls_gcm_context;
#else /* !MBEDTLS_GCM_ALT */
#include "gcm_alt.h"
#endif /* !MBEDTLS_GCM_ALT */
SOFT(mbedtls_gcm_context);
/**
* \brief This function initializes the specified GCM context,
@ -364,6 +371,9 @@ int mbedtls_gcm_finish(mbedtls_gcm_context *ctx,
*/
void mbedtls_gcm_free(mbedtls_gcm_context *ctx);
#endif /* !defined(MBEDTLS_GCM_ALT) || defined(MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK) */
#if defined(MBEDTLS_SELF_TEST)
/**

30
library/gcm.c
View File

@ -39,7 +39,33 @@
#include "aesce.h"
#endif
#if !defined(MBEDTLS_GCM_ALT)
#if defined(MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK)
#undef mbedtls_gcm_context
#undef mbedtls_gcm_init
#undef mbedtls_gcm_setkey
#undef mbedtls_gcm_starts
#undef mbedtls_gcm_update_ad
#undef mbedtls_gcm_update
#undef mbedtls_gcm_finish
#undef mbedtls_gcm_crypt_and_tag
#undef mbedtls_gcm_auth_decrypt
#undef mbedtls_gcm_free
#define mbedtls_gcm_context mbedtls_gcm_context_soft
#define mbedtls_gcm_init mbedtls_gcm_init_soft
#define mbedtls_gcm_setkey mbedtls_gcm_setkey_soft
#define mbedtls_gcm_starts mbedtls_gcm_starts_soft
#define mbedtls_gcm_update_ad mbedtls_gcm_update_ad_soft
#define mbedtls_gcm_update mbedtls_gcm_update_soft
#define mbedtls_gcm_finish mbedtls_gcm_finish_soft
#define mbedtls_gcm_crypt_and_tag mbedtls_gcm_crypt_and_tag_soft
#define mbedtls_gcm_auth_decrypt mbedtls_gcm_auth_decrypt_soft
#define mbedtls_gcm_free mbedtls_gcm_free_soft
#endif
#if !defined(MBEDTLS_GCM_ALT) || defined(MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK)
/* Used to select the acceleration mechanism */
#define MBEDTLS_GCM_ACC_SMALLTABLE 0
@ -780,7 +806,7 @@ void mbedtls_gcm_free(mbedtls_gcm_context *ctx)
mbedtls_platform_zeroize(ctx, sizeof(mbedtls_gcm_context));
}
#endif /* !MBEDTLS_GCM_ALT */
#endif /* !defined(MBEDTLS_GCM_ALT) || defined(MBEDTLS_GCM_NON_AES_CIPHER_SOFT_FALLBACK) */
#if defined(MBEDTLS_SELF_TEST) && defined(MBEDTLS_CCM_GCM_CAN_AES)
/*