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Implement AES-XEX mode

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XEX mode, known as "xor-encrypt-xor", is the simple case of the XTS
mode, known as "XEX with ciphertext stealing". When the buffers to be
encrypted/decrypted have a length divisible by the length of a standard
AES block (16), XTS is exactly like XEX.
This commit is contained in:
Aorimn 2016-01-31 12:15:51 +01:00 committed by Jaeden Amero
parent b053658f95
commit 0089d36ae5
2 changed files with 77 additions and 0 deletions
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24
include/mbedtls/aes.h
View File

@ -213,6 +213,30 @@ int mbedtls_aes_crypt_cbc( mbedtls_aes_context *ctx,
unsigned char *output ); unsigned char *output );
#endif /* MBEDTLS_CIPHER_MODE_CBC */ #endif /* MBEDTLS_CIPHER_MODE_CBC */
#if defined(MBEDTLS_CIPHER_MODE_XEX)
/**
* \brief AES-XEX buffer encryption/decryption
* Length should be a multiple of the block size (16 bytes)
*
* \param crypt_ctx AES context for encrypting data
* \param tweak_ctx AES context for xor-ing with data
* \param mode MBEDTLS_AES_ENCRYPT or MBEDTLS_AES_DECRYPT
* \param length length of the input data
* \param iv initialization vector
* \param input buffer holding the input data
* \param output buffer holding the output data
*
* \return 0 if successful, or MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH
*/
int mbedtls_aes_crypt_xex( mbedtls_aes_context *crypt_ctx,
mbedtls_aes_context *tweak_ctx,
int mode,
size_t length,
unsigned char iv[16],
const unsigned char *input,
unsigned char *output );
#endif /* MBEDTLS_CIPHER_MODE_XEX */
#if defined(MBEDTLS_CIPHER_MODE_CFB) #if defined(MBEDTLS_CIPHER_MODE_CFB)
/** /**
* \brief This function performs an AES-CFB128 encryption or decryption * \brief This function performs an AES-CFB128 encryption or decryption

53
library/aes.c
View File

@ -44,6 +44,10 @@
#include "mbedtls/aesni.h" #include "mbedtls/aesni.h"
#endif #endif
#if defined(MBEDTLS_CIPHER_MODE_XEX)
#include "mbedtls/gf128mul.h"
#endif
#if defined(MBEDTLS_SELF_TEST) #if defined(MBEDTLS_SELF_TEST)
#if defined(MBEDTLS_PLATFORM_C) #if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h" #include "mbedtls/platform.h"
@ -983,6 +987,55 @@ int mbedtls_aes_crypt_cbc( mbedtls_aes_context *ctx,
} }
#endif /* MBEDTLS_CIPHER_MODE_CBC */ #endif /* MBEDTLS_CIPHER_MODE_CBC */
#if defined(MBEDTLS_CIPHER_MODE_XEX)
/*
* AES-XEX buffer encryption/decryption
*/
int mbedtls_aes_crypt_xex( mbedtls_aes_context *crypt_ctx,
mbedtls_aes_context *tweak_ctx,
int mode,
size_t length,
unsigned char iv[16],
const unsigned char *input,
unsigned char *output )
{
int i;
unsigned char t_buf[16];
unsigned char scratch[16];
if( length % 16 )
return( MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH );
mbedtls_aes_crypt_ecb( tweak_ctx, MBEDTLS_AES_ENCRYPT, iv, t_buf );
goto first;
do
{
gf128mul_x_ble( t_buf, t_buf );
first:
/* PP <- T xor P */
for( i = 0; i < 16; i++ )
scratch[i] = (unsigned char)( input[i] ^ t_buf[i] );
/* CC <- E(Key2,PP) */
mbedtls_aes_crypt_ecb( crypt_ctx, mode, scratch, output );
/* C <- T xor CC */
for( i = 0; i < 16; i++ )
output[i] = (unsigned char)( output[i] ^ t_buf[i] );
input += 16;
output += 16;
length -= 16;
} while( length > 0 );
return( 0 );
}
#endif /* MBEDTLS_CIPHER_MODE_XEX */
#if defined(MBEDTLS_CIPHER_MODE_CFB) #if defined(MBEDTLS_CIPHER_MODE_CFB)
/* /*
* AES-CFB128 buffer encryption/decryption * AES-CFB128 buffer encryption/decryption