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An AES (Rijndael) Implementation in C/C++ (as specified in FIPS-197)

Change (26/09/2018)

  1. Changes to test programs to allow them to be built on Linux/GCC (with thanks to Michael Mohr).

  2. Rationalisation of the defines DLL_IMPORT, DYNAMIC_DLL and USE_DLL in the test code - now DLL_IMPORT and DLL_DYNAMIC_LOAD

  3. Update the test_avs test to allow the testing of static, DLL and dynamically loaded DLL libraries.

Change (21/05/2018)

  1. Properly dectect presence of AESNI when using GCC (my thanks to Peter Gutmann for this fix)

Changes (6/12/2016)

  1. Changed function definition of has_aes_ni() to has_aes_ni(void), suggested by Peter Gutmann

  2. Changed the default location for the vsyasm assembler to: C:\Program Files\yasm

Changes (27/09/2015)

  1. Added automatic dynamic table initialisation (my thanks to Henrik S. Gaßmann who proposed this addition).

Changes (09/09/2014)

  1. Added the ability to use Intel's hardware support for AES with GCC on Windows and Linux

Changes (01/09/2014)

  1. Clarify some user choices in the file aes_amd64.asm

  2. Change the detection of the x86 and x86_64 processors in aesopt.h to allow assembler code use with GCC

Changes (14/11/2013)

  1. Added the ability to use Intel's hardware support for AES on Windows using Microsoft Visual Studio.

  2. Added the include 'stdint.h' and used the uintt instead of the old uintt (e.g. uint_32t is now uint32_t).

  3. Added a missing .text directive in aes_x86_v2.asm that caused runtime errors in one build configuration.

Changes (16/04/2007)

These changes remove errors in the VC++ build files and add some improvements in file naming consitency and portability. There are no changes to overcome reported bugs in the code.

  1. gen_tabs() has been renamed to aes_init() to better decribe its function to those not familiar with AES internals.

  2. via_ace.h has been renamed to aes_via_ace.h.

  3. Minor changes have been made to aestab.h and aestab.c to enable all the code to be compiled in either C or C++.

  4. The code for detecting memory alignment in aesmdoes.c has been simplified and a new routine has been added:

    aes_test_alignment_detection()
    

    to check that the aligment test is likely to be correct.

  5. The addition of support for Structured Exception Handling (SEH) to YASM (well done Peter and Michael!) has allowed the AMD64 x64 assembler code to be changed to comply with SEH requriements.

  6. Corrections to build files (for win32 debug build).

Overview

This code implements AES for both 32 and 64 bit systems with optional assembler support for x86 and AMD64/EM64T (but optimised for AMD64).

The basic AES source code files are as follows:

aes.h the header file needed to use AES in C aescpp.h the header file required with to use AES in C++ aesopt.h the header file for setting options (and some common code) aestab.h the header file for the AES table declaration aescrypt.c the main C source code file for encryption and decryption aeskey.c the main C source code file for the key schedule aestab.c the main file for the AES tables brg_types.h a header defining some standard types and DLL defines brg_endian.h a header containing code to detect or define endianness aes_x86_v1.asm x86 assembler (YASM) alternative to aescrypt.c using large tables aes_x86_v2.asm x86 assembler (YASM) alternative to aescrypt.c using compressed tables aes_amd64.asm AMD64 assembler (YASM) alternative to aescrypt.c using compressed tables

In addition AES modes are implemented in the files:

aes_modes.c AES modes with optional support for VIA ACE detection and use aes_via_ace.h the header file for VIA ACE support

and Intel hardware support for AES (AES_NI) is implemented in the files

aes_ni.h defines for AES_NI implementation aes_ni.c the AES_NI implementation

Other associated files for testing and support are:

aesaux.h header for auxilliary routines for testsing aesaux.c auxilliary routines for testsingt aestst.h header file for setting the testing environment rdtsc.h a header file that provides access to the Time Stamp Counter aestst.c a simple test program for quick tests of the AES code aesgav.c a program to generate and verify the test vector files aesrav.c a program to verify output against the test vector files aestmr.c a program to time the code on x86 systems modetest.c a program to test the AES modes support vbxam.doc a demonstration of AES DLL use from Visual Basic in Microsoft Word vb.txt Visual Basic code from the above example (win32 only) aesxam.c an example of AES use tablegen.c a program to generate a simplified 'aestab.c' file for use with compilers that find aestab.c too complex yasm.rules the YASM build rules file for Microsoft Visual Studio 2005 via_ace.txt describes support for the VIA ACE cryptography engine aes.txt this file

Building The AES Libraries

A. Versions

The code can be used to build static and dynamic libraries, each in five versions:

Key scheduling code in C, encrypt/decrypt in:

C           C source code                        (win32 and x64)
ASM_X86_V1C large table x86 assembler code       (win32)
ASM_X86_V2C compressed table x86 assembler code  (win32)
ASM_AMD64   compressed table x64 assembler code  (x64)

Key scheduling and encrypt/decrypt code in assembler:

ASM_X86_V2  compressed table x86 assembler       (win32)

The C version can be compiled for Win32 or x64 whereas the x86 and x64 assembler versions are for Win32 and x64 respectively.

If Intel's hardware support for AES (AES_NI) is available, it can be used with either the C or the ASM_AMD64 version. If ASM_AMD64 is to be used, it is important that the define USE_INTEL_AES_IF_PRESENT in asm_amd64.asm is set to the same value as it has in aesopt.h

B. YASM

If you wish to use the x86 assembler files you will also need the YASM open source x86 assembler (r1331 or later) for Windows which can be obtained from:

http://www.tortall.net/projects/yasm/

This assembler (vsyasm.exe) should be placed in the directory:

C:\Program Files\yasm

C. Configuration

The following configurations are available as projects for Visual Studio but the following descriptions should allow them to be built in other x86 environments

lib_generic_c       Win32 and x64
    headers:        aes.h, aesopt.h, aestab.h, brg_endian.h, tdefs.h
	                (+ aes_ni.h for AES_NI)
    C source:       aescrypt.c, aeskey.c, aestab.c, aes_modes.c
	                (+ aes_ni.c for AES_NI)
    defines

dll_generic_c       Win32 and x64
    headers:        aes.h, aesopt.h, aestab.h, brg_endian.h, tdefs.h
	                (+ aes_ni.h for AES_NI)
    C source:       aescrypt.c, aeskey.c, aestab.c, aes_modes.c
	                (+ aes_ni.c for AES_NI)
    defines         DLL_EXPORT

lib_asm_x86_v1c     Win32
    headers:        aes.h, aesopt.h, aestab.h, brg_endian.h, tdefs.h
    C source:       aeskey.c, aestab.c, aes_modes.c
    x86 assembler:  aes_x86_v1.asm
    defines         ASM_X86_V1C (set for C and assembler files)

dll_asm_x86_v1c     Win32
    headers:        aes.h, aesopt.h, aestab.h, brg_endian.h, tdefs.h
    C source:       aeskey.c, aestab.c, aes_modes.c
    x86 assembler:  aes_x86_v1.asm
    defines         DLL_EXPORT, ASM_X86_V1C (set for C and assembler files)

lib_asm_x86_v2c     Win32
    headers:        aes.h, aesopt.h, aestab.h, brg_endian.h, tdefs.h
    C source:       aeskey.c, aestab.c, aes_modes.c
    x86 assembler:  aes_x86_v2.asm
    defines         ASM_X86_V2C (set for C and assembler files)

dll_asm_x86_v2c     Win32
    headers:        aes.h, aesopt.h, aestab.h, brg_endian.h, tdefs.h
    C source:       aeskey.c, aestab.c, aes_modes.c
    x86 assembler:  aes_x86_v1.asm
    defines         DLL_EXPORT, ASM_X86_V2C (set for C and assembler files)

lib_asm_x86_v2      Win32
    headers:        aes.h, aesopt.h, aestab.h, brg_endian.h, tdefs.h
    C source:       aes_modes.c
    x86 assembler:  aes_x86_v1.asm
    defines         ASM_X86_V2 (set for C and assembler files)

dll_asm_x86_v2      Win32
    headers:        aes.h, aesopt.h, aestab.h, brg_endian.h, tdefs.h
    C source:       aes_modes.c
    x86 assembler:  aes_x86_v1.asm
    defines         DLL_EXPORT, ASM_AMD64_C (set for C and assembler files)

lib_asm_amd64_c     x64
    headers:        aes.h, aesopt.h, aestab.h, brg_endian.h, tdefs.h
	                (+ aes_ni.h for AES_NI)
    C source:       aes_modes.c (+ aes_ni.c for AES_NI)
    x86 assembler:  aes_amd64.asm
    defines         ASM_AMD64_C (set for C and assembler files)

dll_asm_amd64_c     x64
    headers:        aes.h, aesopt.h, aestab.h, brg_endian.h, tdefs.h
	                (+ aes_ni.h for AES_NI)
    C source:       aes_modes.c (+ aes_ni.c for AES_NI)
    x86 assembler:  aes_amd64.asm
    defines         DLL_EXPORT, ASM_AMD64_C (set for C and assembler files)

Notes:

ASM_X86_V1C is defined if using the version 1 assembler code (aescrypt1.asm). The defines in the assember file must match those in aes.h and aesopt.h). Also remember to include/exclude the right assembler and C files in the build to avoid undefined or multiply defined symbols - include aes_x86_v1.asm and exclude aescrypt.c

ASM_X86_V2 is defined if using the version 2 assembler code (aes_x86_v2.asm). This version provides a full, self contained assembler version and does not use any C source code files except for the mutiple block encryption modes that are provided by aes_modes.c. The define ASM_X86_V2 must be set on the YASM command line (or in aes_x86_v2.asm) to use this version and all C files except aec_modes.c and, for the DLL build, aestab.c must be excluded from the build.

ASM_X86_V2C is defined when using the version 2 assembler code (aes_x86_v2.asm) with faster key scheduling provided by the in C code (the options in the assember file must match those in aes.h and aesopt.h). In this case aeskey.c and aestab.c are needed with aes_x86_v2.asm and the define ASM_X86_V2C must be set for both the C files and for aes_x86_v2.asm in the build commands(or in aesopt.h and aes_x86_v2.asm). Include aes_x86_v2.asm, aeskey.c and aestab.c, exclude aescrypt.c for this option.

ASM_AMD64_C is defined when using the AMD64 assembly code because the C key scheduling is used in this case.

DLL_EXPORT must be defined to generate the DLL version of the code and to run tests on it

DLL_IMPORT must be defined to use the DLL version of the code in an application program

Directories the paths for the various directories for test vector input and output have to be set in aestst.h

VIA ACE see the via_ace.txt for this item

Static The static libraries are named: Libraries aes_lib_generic_c.lib aes_lib_asm_x86_v1c.lib aes_lib_asm_x86_v2.lib aes_lib_asm_x86_v2c.lib aes_lib_asm_amd64_c.lib

        and placed in one of the the directories:

            lib\win32\release\
            lib\win32\debug\
            lib\x64\release\
            lib\x64\debug\

        in the aes root directory depending on the platform(win32 or
        x64) and the build (release or debug). After any of these is
        built it is then copied into the aes\lib directory, which is
		the library location that is subsequently used for testing. 
		Hence testing is always for the last static library built.

Dynamic These libraries are named: Libraries aes_lib_generic_c.dll aes_lib_asm_x86_v1c.dll aes_lib_asm_x86_v2.dll aes_lib_asm_x86_v2c.dll aes_lib_asm_amd64_c.dll

        and placed in one of the the directories:

            dll\win32\release\
            dll\win32\debug\
            dll\x64\release\
            dll\x64\debug\

        in the aes root directory depending on the platform(win32 or
        x64) and the build (release or debug).  Each DLL library:

            aes_<ext>.dll

        has three associated files:

            aes_dll_<ext>.lib   the library file for implicit linking
            aes_dll_<ext>.exp   the exports file
            aes_dll_<ext>.pdb   the symbol file

        After any DLL is built it and its three related files are then
        copied to the aes\dll directory, which is the library location
		used in subsequent testing.  Hence testing is always for the 
		last DLL built.

D. Testing

These tests require that the test vector files are placed in the 'testvals' subdirectory. If the AES Algorithm Validation Suite tests are used then the *.fax files need to be put in the 'testvals\fax' subdirectory. This is covered in more detail below.

The projects test_lib and time_lib are used to test and time the last static library built. They use the files:

test_lib:       Win32 (x64 for the C and AMD64 versions)
    headers:    aes.h, aescpp.h, brg_types.h, aesaux.h and aestst.h
    C source:   aesaux.c, aesrav.c
    defines:

time_lib:       Win32 (x64 for the C and AMD64 versions)
    headers:    aes.h, aescpp.h, brg_types.h, aesaux.h, aestst.h and rdtsc.h
    C source:   aesaux.c, aestmr.c
    defines:

The projects test_dll and time_dll are used to test and time the last DLL built. These use the files:

test_dll:       Win32 (x64 for the C and AMD64 versions)
    headers:    aes.h, aescpp.h, brg_types.h, aesaux.h and aestst.h
    C source:   aesaux.c, aesrav.c
    defines:    DLL_IMPORT

time_dll:       Win32 (x64 for the C and AMD64 versions)
    headers:    aes.h, aescpp.h, brg_types.h, aesaux.h aestst.h and rdtsc.h
    C source:   aesaux.c, aestmr.c
    defines:    DLL_IMPORT

and default to linkingto with the AES DLL using dynamic (run-time) linking. Implicit linking can be used by adding the lib file associated with the AES DLL (in the aes\dll sub-directory) to the build (under project Properties|Linker in Visual Studio) and removing the DLL_DYNAMIC_LOAD define (under project Properties|C/C++|Preprocessor).

0 Link is linked into this project and the symbol DLL_DYNAMIC_LOAD is left undefined, then implicit linking will be used

The above tests take command line arguments that determine which test are run as follows:

test_lib /t:[knec] /k:[468]
test_dll /t:[knec] /k:[468]

where the symbols in square brackets can be used in any combination (without the brackets) and have the following meanings:

    /t:[knec]   selects which tests are used
    /k:[468]    selects the key lengths used
    /c          compares output with reference (see later)

    k: generate ECB Known Answer Test files
    n: generate ECB Known Answer Test files (new)
    e: generate ECB Monte Carlo Test files
    c: generate CBC Monte Carlo Test files

and the characters giving the lengths are digits representing the key lengths in 32-bit units (4, 6, 8 for lengths of 128, 192 or 256 bits respectively).

The project test_modes tests the AES modes. It uses the files:

test_modes:     Win32 or x64
    headers:    aes.h, aescpp.h, brg_types.h, aesaux,h and aestst.h
    C source:   aesaux.c, modetest.c
    defines:    none for static library test, DLL_IMPORT for DLL test

which again links to the last library built.

E. Other Applications

These are:

gen_tests       builds the test_vector files. The commad line is
                    gen_tests /t:knec /k:468 /c
                as described earlier
                
test_aes_avs    run the AES Algorithm Validation Suite tests for
                ECB, CBC, CFB and OFB modes

gen_tables      builds a simple version of aes_tab.c (in aestab2.c)
                for compilers that cannot handle the normal version
aes_example     provides an example of AES use

These applications are linked to the last static library built or, if DLL_IMPORT is defined during compilation, to the last DLL built.

F. Use of the VIA ACE Cryptography Engine (x86 only)

The use of the code with the VIA ACE cryptography engine in described in the file via_ace.txt. In outline aes_modes.c is used and USE_VIA_ACE_IF_PRESENT is defined either in section 2 of aesopt.h or as a compilation option in Visual Studio. If in addition ASSUME_VIA_ACE_PRESENT is also defined then all normal AES code will be removed if not needed to support VIA ACE use. If VIA ACE support is needed and AES assembler is being used only the ASM_X86_V1C and ASM_X86_V2C versions should be used since ASM_X86_V2 and ASM_AMD64 do not support the VIA ACE engine.

G. The AES Test Vector Files

These files fall in the following groups (where is a two digit number):

  1. ecbvk.txt ECB vectors with variable key
  2. ecbvt.txt ECB vectors with variable text
  3. ecbnk.txt new ECB vectors with variable key
  4. ecbnt.txt new ECB vectors with variable text
  5. ecbme.txt ECB monte carlo encryption test vectors
  6. ecbmd.txt ECB monte carlo decryption test vectors
  7. cbcme.txt CBC monte carlo encryption test vectors
  8. cbcmd.txt CBC monte carlo decryption test vectors

The first digit of the numeric suffix on the filename gives the block size in 32 bit units and the second numeric digit gives the key size. For example, the file ecbvk44.txt provides the test vectors for ECB encryption with a 128 bit block size and a 128 bit key size. The test routines expect to find these files in the 'testvals' subdirectory within the aes root directory. The 'outvals' subdirectory is used for outputs that are compared with the files in 'testvals'. Note that the monte carlo test vectors are the result of applying AES iteratively 10000 times, not just once.

The AES Algorithm Validation Suite tests can be run for ECB, CBC, CFB and OFB modes (CFB1 and CFB8 are not implemented). The test routine uses the *.fax test files, which should be placed in the 'testvals\fax' subdirectory.

H. The Basic AES Calling Interface

The basic AES code keeps its state in a context, there being different contexts for encryption and decryption:

aes_encrypt_ctx
aes_decrypt_ctx

The AES code is initialised with the call

aes_init(void)

although this is only essential if the option to generate the AES tables at run-time has been set in the options (i.e.fixed tables are not being used).

The AES encryption key is set by one of the calls:

aes_encrypt_key128(const unsigned char *key, aes_encrypt_ctx cx[1])
aes_encrypt_key192(const unsigned char *key, aes_encrypt_ctx cx[1])
aes_encrypt_key256(const unsigned char *key, aes_encrypt_ctx cx[1])

or by:

aes_encrypt_key(const unsigned char *key, int key_len, 
                                            aes_encrypt_ctx cx[1])

where the key length is set by 'key_len', which can be the length in bits or bytes.

Similarly, the AES decryption key is set by one of:

aes_decrypt_key128(const unsigned char *key, aes_decrypt_ctx cx[1])
aes_decrypt_key192(const unsigned char *key, aes_decrypt_ctx cx[1])
aes_decrypt_key256(const unsigned char *key, aes_decrypt_ctx cx[1])

or by:

aes_decrypt_key(const unsigned char *key, int key_len, 
                                            aes_decrypt_ctx cx[1])

Encryption and decryption for a single 16 byte block is then achieved using:

aes_encrypt(const unsigned char *in, unsigned char *out, 
                                        const aes_encrypt_ctx cx[1])
aes_decrypt(const unsigned char *in, unsigned char *out, 
                                        const aes_decrypt_ctx cx[1])

The above subroutines return a value of EXIT_SUCCESS or EXIT_FAILURE depending on whether the operation succeeded or failed.

I. The Calling Interface for the AES Modes

The subroutines for the AES modes, ECB, CBC, CFB, OFB and CTR, each process blocks of variable length and can also be called several times to complete single mode operations incrementally on long messages (or those messages, not all of which are available at the same time). The calls:

aes_ecb_encrypt(const unsigned char *ibuf, unsigned char *obuf,
                int len, const aes_encrypt_ctx cx[1])

aes_ecb_decrypt(const unsigned char *ibuf, unsigned char *obuf,
                int len, const aes_decrypt_ctx cx[1])

for ECB operations and those for CBC:

aes_cbc_encrypt(const unsigned char *ibuf, unsigned char *obuf,
                int len, unsigned char *iv, const aes_encrypt_ctx cx[1])

aes_cbc_decrypt(const unsigned char *ibuf, unsigned char *obuf,
                int len, unsigned char *iv, const aes_decrypt_ctx cx[1])

can only process blocks whose lengths are multiples of 16 bytes but the calls for CFB, OFB and CTR mode operations:

aes_cfb_encrypt(const unsigned char *ibuf, unsigned char *obuf,
                int len, unsigned char *iv, aes_encrypt_ctx cx[1])

aes_cfb_decrypt(const unsigned char *ibuf, unsigned char *obuf,
                int len, unsigned char *iv, aes_encrypt_ctx cx[1])

aes_ofb_encrypt(const unsigned char *ibuf, unsigned char *obuf,
                int len, unsigned char *iv, aes_encrypt_ctx cx[1])

aes_ofb_decrypt(const unsigned char *ibuf, unsigned char *obuf,
                int len, unsigned char *iv, aes_encrypt_ctx cx[1])

aes_ctr_encrypt(const unsigned char *ibuf, unsigned char *obuf,
        int len, unsigned char *cbuf, cbuf_inc ctr_inc, aes_encrypt_ctx cx[1])

aes_ctr_decrypt(const unsigned char *ibuf, unsigned char *obuf,
        int len, unsigned char *cbuf, cbuf_inc ctr_inc, aes_encrypt_ctx cx[1])

can process blocks of any length. Note also that CFB, OFB and CTR mode calls only use AES encryption contexts even during decryption operations.

The calls CTR mode operations use a buffer (cbuf) which holds the counter value together with a function parameter:

void cbuf_inc(unsigned char *cbuf);

that is ued to update the counter value after each 16 byte AES operation. The counter buffer is updated appropriately to allow for incremental operations.

Please note the following IMPORTANT points about the AES mode subroutines:

1. All modes are reset when a new AES key is set.

2. Incremental calls to the different modes cannot 
   be mixed. If a change of mode is needed a new 
   key must be set or a reset must be issued (see 
   below).
   
3. For modes with IVs, the IV value is an input AND
   an output since it is updated after each call to 
   the value needed for any subsequent incremental
   call(s). If the mode is reset, the IV hence has
   to be set (or reset) as well.
   
4. ECB operations must be multiples of 16 bytes
   but do not need to be reset for new operations.
   
5. CBC operations must also be multiples of 16 
   bytes and are reset for a new operation by 
   setting the IV.
   
6. CFB, OFB and CTR mode must be reset by setting 
   a new IV value AND by calling:
   
       aes_mode_reset(aes_encrypt_ctx cx[1])
       
   For CTR mode the cbuf value also has to be reset.
   
7. CFB, OFB and CTR modes only use AES encryption 
   operations and contexts and do not need AES
   decryption operations.
   
8. AES keys remain valid across resets and changes
   of mode (but encryption and decryption keys must 
   both be set if they are needed).  

Brian Gladman 26/09/2018