aes: Remove AES-XEX

AES-XEX is a building block for other cryptographic standards and not yet a
standard in and of itself. We'll just provide the standardized AES-XTS
algorithm, and not AES-XEX. The AES-XTS algorithm and interface provided
can be used to perform the AES-XEX algorithm when the length of the input
is a multiple of the AES block size.

include/mbedtls/aes.h

@@ -213,30 +213,6 @@ int mbedtls_aes_crypt_cbc( mbedtls_aes_context *ctx,
                     unsigned char *output );
 #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_XTS)
 /**
  * \brief           AES-XTS buffer encryption/decryption

include/mbedtls/config.h

@@ -501,13 +501,6 @@
  */
 #define MBEDTLS_CIPHER_MODE_CBC
 
-/**
- * \def MBEDTLS_CIPHER_MODE_XEX
- *
- * Enable Xor-encrypt-xor mode (XEX) for symmetric ciphers.
- */
-#define MBEDTLS_CIPHER_MODE_XEX
-
 /**
  * \def MBEDTLS_CIPHER_MODE_XTS
  *

library/aes.c

@@ -983,64 +983,6 @@ int mbedtls_aes_crypt_cbc( mbedtls_aes_context *ctx,
 }
 #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 )
-{
-    union xex_buf128 {
-        uint8_t  u8[16];
-        uint64_t u64[2];
-    };
-
-    union xex_buf128 scratch;
-    union xex_buf128 t_buf;
-    union xex_buf128 *inbuf;
-    union xex_buf128 *outbuf;
-
-    inbuf = (union xex_buf128*)input;
-    outbuf = (union xex_buf128*)output;
-
-    if( length % 16 )
-        return( MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH );
-
-
-    mbedtls_aes_crypt_ecb( tweak_ctx, MBEDTLS_AES_ENCRYPT, iv, t_buf.u8 );
-
-    goto first;
-
-    do
-    {
-        mbedtls_gf128mul_x_ble( t_buf.u8, t_buf.u8 );
-
-first:
-        /* PP <- T xor P */
-        scratch.u64[0] = (uint64_t)( inbuf->u64[0] ^ t_buf.u64[0] );
-        scratch.u64[1] = (uint64_t)( inbuf->u64[1] ^ t_buf.u64[1] );
-
-        /* CC <- E(Key2,PP) */
-        mbedtls_aes_crypt_ecb( crypt_ctx, mode, scratch.u8, outbuf->u8 );
-
-        /* C <- T xor CC */
-        outbuf->u64[0] = (uint64_t)( outbuf->u64[0] ^ t_buf.u64[0] );
-        outbuf->u64[1] = (uint64_t)( outbuf->u64[1] ^ t_buf.u64[1] );
-
-        inbuf  += 1;
-        outbuf += 1;
-        length -= 16;
-    } while( length > 0 );
-
-    return( 0 );
-}
-#endif /* MBEDTLS_CIPHER_MODE_XEX */
-
 #if defined(MBEDTLS_CIPHER_MODE_XTS)
 
 /* Endianess with 64 bits values */

library/version_features.c

@@ -249,9 +249,6 @@ static const char *features[] = {
 #if defined(MBEDTLS_CIPHER_MODE_CBC)
     "MBEDTLS_CIPHER_MODE_CBC",
 #endif /* MBEDTLS_CIPHER_MODE_CBC */
-#if defined(MBEDTLS_CIPHER_MODE_XEX)
-    "MBEDTLS_CIPHER_MODE_XEX",
-#endif /* MBEDTLS_CIPHER_MODE_XEX */
 #if defined(MBEDTLS_CIPHER_MODE_XTS)
     "MBEDTLS_CIPHER_MODE_XTS",
 #endif /* MBEDTLS_CIPHER_MODE_XTS */

programs/test/benchmark.c

@@ -99,7 +99,7 @@ int main( void )
 #define OPTIONS                                                         \
     "md4, md5, ripemd160, sha1, sha256, sha512,\n"                      \
     "arc4, des3, des, camellia, blowfish,\n"                            \
-    "aes_cbc, aes_gcm, aes_ccm, aes_cmac, aes_xex, aes_xts,\n"          \
+    "aes_cbc, aes_gcm, aes_ccm, aes_cmac, aes_xts,\n"                   \
     "des3_cmac, havege, ctr_drbg, hmac_drbg\n"                          \
     "rsa, dhm, ecdsa, ecdh.\n"
 
@@ -233,7 +233,7 @@ unsigned char buf[BUFSIZE];
 typedef struct {
     char md4, md5, ripemd160, sha1, sha256, sha512,
          arc4, des3, des,
-         aes_cbc, aes_gcm, aes_ccm, aes_cmac, aes_xex, aes_xts,
+         aes_cbc, aes_gcm, aes_ccm, aes_cmac, aes_xts,
          des3_cmac, aria, camellia, blowfish,
          havege, ctr_drbg, hmac_drbg,
          rsa, dhm, ecdsa, ecdh;
@@ -279,8 +279,6 @@ int main( int argc, char *argv[] )
                 todo.des = 1;
             else if( strcmp( argv[i], "aes_cbc" ) == 0 )
                 todo.aes_cbc = 1;
-            else if( strcmp( argv[i], "aes_xex" ) == 0 )
-                todo.aes_xex = 1;
             else if( strcmp( argv[i], "aes_xts" ) == 0 )
                 todo.aes_xts = 1;
             else if( strcmp( argv[i], "aes_gcm" ) == 0 )
@@ -430,29 +428,6 @@ int main( int argc, char *argv[] )
         mbedtls_aes_free( &aes );
     }
 #endif
-#if defined(MBEDTLS_CIPHER_MODE_XEX)
-    if( todo.aes_xex )
-    {
-        int keysize;
-        mbedtls_aes_context crypt_ctx, tweak_ctx;
-        mbedtls_aes_init( &crypt_ctx );
-        mbedtls_aes_init( &tweak_ctx );
-        for( keysize = 128; keysize <= 256; keysize += 64 )
-        {
-            mbedtls_snprintf( title, sizeof( title ), "AES-XEX-%d", keysize );
-
-            memset( buf, 0, sizeof( buf ) );
-            memset( tmp, 0, sizeof( tmp ) );
-            mbedtls_aes_setkey_enc( &crypt_ctx, tmp, keysize );
-            mbedtls_aes_setkey_enc( &tweak_ctx, tmp, keysize );
-
-            TIME_AND_TSC( title,
-                mbedtls_aes_crypt_xex( &crypt_ctx, &tweak_ctx, MBEDTLS_AES_ENCRYPT, BUFSIZE, tmp, buf, buf ) );
-        }
-        mbedtls_aes_free( &crypt_ctx );
-        mbedtls_aes_free( &tweak_ctx );
-    }
-#endif
 #if defined(MBEDTLS_CIPHER_MODE_XTS)
     if( todo.aes_xts )
     {

tests/CMakeLists.txt

@@ -48,7 +48,6 @@ add_test_suite(aes aes.ecb)
 add_test_suite(aes aes.cbc)
 add_test_suite(aes aes.cfb)
 add_test_suite(aes aes.rest)
-add_test_suite(aes aes.xex)
 add_test_suite(aes aes.xts)
 add_test_suite(arc4)
 add_test_suite(aria)

tests/suites/test_suite_aes.function

@@ -151,80 +151,6 @@ exit:
 }
 /* END_CASE */
 
-/* BEGIN_CASE depends_on:MBEDTLS_CIPHER_MODE_XEX */
-void aes_encrypt_xex( char *hex_key_string, char *hex_iv_string,
-                      char *hex_src_string, char *hex_dst_string,
-                      int xex_result )
-{
-    unsigned char key_str[100] = { 0, };
-    unsigned char iv_str[100]  = { 0, };
-    unsigned char src_str[100] = { 0, };
-    unsigned char dst_str[100] = { 0, };
-    unsigned char output[100]  = { 0, };
-    mbedtls_aes_context crypt_ctx, tweak_ctx;
-    int key_len, data_len;
-
-    mbedtls_aes_init( &crypt_ctx );
-    mbedtls_aes_init( &tweak_ctx );
-
-    key_len = unhexify( key_str, hex_key_string );
-    unhexify( iv_str, hex_iv_string );
-    data_len = unhexify( src_str, hex_src_string );
-
-    mbedtls_aes_setkey_enc( &crypt_ctx, key_str,               ( key_len * 8 ) / 2 );
-    mbedtls_aes_setkey_enc( &tweak_ctx, key_str + key_len / 2, ( key_len * 8 ) / 2 );
-
-    TEST_ASSERT( mbedtls_aes_crypt_xex( &crypt_ctx, &tweak_ctx, MBEDTLS_AES_ENCRYPT, data_len, iv_str, src_str, output ) == xex_result );
-    if( xex_result == 0 )
-    {
-        hexify( dst_str, output, data_len );
-
-        TEST_ASSERT( strcmp( (char *) dst_str, hex_dst_string ) == 0 );
-    }
-
-exit:
-    mbedtls_aes_free( &crypt_ctx );
-    mbedtls_aes_free( &tweak_ctx );
-}
-/* END_CASE */
-
-/* BEGIN_CASE depends_on:MBEDTLS_CIPHER_MODE_XEX */
-void aes_decrypt_xex( char *hex_key_string, char *hex_iv_string,
-                      char *hex_src_string, char *hex_dst_string,
-                      int xex_result )
-{
-    unsigned char key_str[100] = { 0, };
-    unsigned char iv_str[100]  = { 0, };
-    unsigned char src_str[100] = { 0, };
-    unsigned char dst_str[100] = { 0, };
-    unsigned char output[100]  = { 0, };
-    mbedtls_aes_context crypt_ctx, tweak_ctx;
-    int key_len, data_len;
-
-    mbedtls_aes_init( &crypt_ctx );
-    mbedtls_aes_init( &tweak_ctx );
-
-    key_len = unhexify( key_str, hex_key_string );
-    unhexify( iv_str, hex_iv_string );
-    data_len = unhexify( src_str, hex_src_string );
-
-    mbedtls_aes_setkey_dec( &crypt_ctx, key_str,               ( key_len * 8 ) / 2 );
-    mbedtls_aes_setkey_enc( &tweak_ctx, key_str + key_len / 2, ( key_len * 8 ) / 2 );
-
-    TEST_ASSERT( mbedtls_aes_crypt_xex( &crypt_ctx, &tweak_ctx, MBEDTLS_AES_DECRYPT, data_len, iv_str, src_str, output ) == xex_result );
-    if( xex_result == 0 )
-    {
-        hexify( dst_str, output, data_len );
-
-        TEST_ASSERT( strcmp( (char *) dst_str, hex_dst_string ) == 0 );
-    }
-
-exit:
-    mbedtls_aes_free( &crypt_ctx );
-    mbedtls_aes_free( &tweak_ctx );
-}
-/* END_CASE */
-
 /* BEGIN_CASE depends_on:MBEDTLS_CIPHER_MODE_XTS */
 void aes_encrypt_xts( char *hex_key_string, char *hex_iv_string,
                       char *hex_src_string, char *hex_dst_string,