ReleaseNotes.txt

========================================================================
Release Notes for Intel(R) Multi-Buffer Crypto for IPsec Library

v1.0 April 2021
========================================================================

General
- Top level `lib` directory tidy up
  - build scripts and header file left at the top level
  - `lib/x86_64` directory created
  - files requiring compilation moved from `lib/include`
- Symbols not stripped from static library at installation
- API name changes and unification
  - mapping provided for backwards compatibility
- NASM version check in the build script
- CET enabling in the build scripts

Library
- CET enabling (endbranch opcodes added)
- ZUC-EIA3-256 support for SSE, AVX, AVX2 and AVX512 (VAES)
  - 4 byte tag length only
- Chacha20 optimizations for SSE, AVX and AVX2
- ZUC-EEA3-256 support for SSE, AVX, AVX2 and AVX512 (VAES)
- SNOW-V and SNOW-V-AEAD support for SSE
- Poly1305 AVX512 and AVX512-IFMA implementations added
- Chacha20-Poly1305 AEAD implementations extended to AVX512 and AVX512-IFMA
- CBCS AVX512 optimizations
- Extended CBCS to return last cipher block to maintain context between calls
- AVX/SSE transition fixes
- Added SGL support for AEAD Chacha20-Poly1305
- Poly1305 minor optimization in the scalar code
- GHASH API change
- IFMA CPU feature detection
- SGL support added for AES-GCM through job API
- Added CRC functions through job API

Test Applications
- ZUC-EEA3-256 tests added to test and xvalidation applications
- SNOW-V and SNOW-V-AEAD tests added to test and xvalidation applications
- IMIX support added to the xvalidation application
- AEAD Chacha20-Poly1305 tests added
- SGL tests added for AES-GCM through job API
- CRC function tests added through job API

Performance Application
- ZUC-EEA3-256 support added
- SNOW-V and SNOW-V-AEAD support added
- AEAD Chacha20-Poly1305 support added
- Created `ipsec_perf_tool.py` to run multiple `ipsec_perf`
  instances at the same time
- DOCSIS cipher combined with CRC32 treated as AEAD algorithm
- CRC functions added

v0.55 October 2020
========================================================================

General
- Restructured project to move all library code into new 'lib' directory
- Renamed LibPerfApp directory to perf
- Renamed LibTestApp directory to test

Library
- AES-CCM-256 implementation for SSE, AVX and AVX512 (VAES)
- AES-CMAC-256 implementation for SSE, AVX and AVX512 (VAES)
- 32bit and 64bit HEC compute API added
- AES-GMAC direct API added to support Scatter-Gather list (SGL)
- CALC_AAD_HASH macro improved for AVX512 (VAES), boosting performance
  for AES-GMAC, GHASH and hash calculation for AAD in AES-GCM
- ZUC-EEA3 and ZUC-EIA3 Multi-buffer implemented for SSE using
  GFNI instructions.
- AES-XCBC-128 implementation for AVX512 (VAES)
- AES-CBCS-128 implementation for SSE and AVX (1:9 crypt:skip pattern)
- Chacha20 SSE, AVX and AVX512 implementations
- Automatic multi-buffer manager initialization API added
- Error handling API added
- Build with SAFE_DATA and SAFE_PARAM options by default
- Poly1305 scalar implementation
- AEAD Chacha20-Poly1305 implementation
- CRC implementation for RNC, LTE, WiMAX, SCTP, Ethernet and CRC16 CCIT 

Test Applications
- CCM tests extended to test AES-CCM-256
- CMAC tests extended to test AES-CMAC-256
- HEC tests added to test app
- AES-GMAC SGL tests added to test app
- AES-XCBC-128 tests added to test app
- AES-CBCS-128 tests added to test app
- AES-CBCS-128 support added to xvalidation app
- Chacha20 tests added to test and xvalidation app
- Poly1305 tests added to test and xvalidation app
- AEAD Chacha20-Poly1305 tests added to test and xvalidation app
- CRC tests added
- Automatic architecture detection done by default

Performance Application
- AES-CCM-256 support added
- AES-CMAC-256 support added
- AES-CBCS-128 support added
- Chacha20 support added
- Poly1305 support added
- AEAD Chacha20-Poly1305 support added


v0.54 April 2020
========================================================================

Library
- ZUC-EEA3 and ZUC-EIA3 algorithms added in job API (using cipher mode
  IMB_CIPHER_ZUC_EEA3 and hash_alg IMB_AUTH_ZUC_EIA3_BITLEN)
- SNOW3G-UEA2 and SNOW3G-UIA2 algorithms added in job API (using cipher type
  IMB_CIPHER_SNOW3G_UEA2_BITLEN and hash type IMB_AUTH_SNOW3G_UIA2_BITLEN)
- AVX512 implementation of stitched DOCSIS cipher with CRC32 calculations
- KASUMI-UEA1 and KASUMI-UIA1 algorithms added in job API (using cipher type
  IMB_CIPHER_KASUMI_UEA1_BITLEN and hash type IMB_AUTH_KASUMI_UIA1)
- New GHASH API added
- ZUC-EIA3 Multi-buffer API added and implemented for SSE and AVX.
- Added support for any IV size in AES-GCM, through the job API and new
  direct API
- Check for new flag NO_COMPAT_IMB_API_053, which exposes only new API,
  removing backwards compatibility with version v0.53.
- AES-CMAC implementation for VAES added
- SSE AES128-CTR, AES192-CTR, AES256-CTR and AES128-CCM by8 cipher
  implementations added
- Added by8/x8 implementations of SSE AES128-CBC, AES192-CBC, AES256-CBC,
  DOCSIS SEC BPI, AES-CCM and AES-CMAC.
- AES256-DOCSIS algorithm added.
- ZUC-EEA3 and ZUC-EIA3 Multi-buffer implemented for AVX2 and AVX512.
- ZUC-EEA3 and ZUC-EIA3 Multi-buffer implemented for AVX2 and AVX512,
  using this latter GFNI and VAES instructions where these are present
  in the CPU.
- Minimum required version for NASM is now 2.14.
- ZUC-EEA3 and ZUC-EIA3 Multi-buffer implemented with AESNI emulation instructions.
- SNOW3G-UIA2 and SNOW3G-UEA2 reimplemented for increased security and performance.
- AES-CBC improvement for VAES
- AES-CCM implementation for VAES added

LibTestApp
- Extended ZUC tests to validate ZUC-EEA3 and ZUC-EIA3 algorithms through
  job API
- Extended SNOW3G tests to validate SNOW3G-UEA2 and SNOW3G-UIA2 algorithms
  through job API
- Extended DOCSIS tests with combined CRC32 calculation cases
- Extended KASUMI tests to validate KASUMI-UEA1 and KASUMI-UIA1 algorithms
  through job API
- Extended ZUC tests to validate ZUC-EIA3 multi-buffer implementation
  through direct and job API
- Extended AES-DOCSIS tests with 256-bit keys

LibPerfApp
- Added support for ZUC-EEA3 and ZUC-EIA3 algorithms
- Added support for SNOW3G-UEA2 and SNOW3G-UIA2 algorithms
- Added support for DOCSIS combined with CRC32
- Added support for KASUMI-UEA1 and KASUMI-UIA1 algorithms

v0.53 October 2019
========================================================================

Library
- AES-CCM performance optimizations done
  - full assembly implementation
  - authentication decoupled from cipher
  - CCM chain order expected to be HASH_CIPHER for encryption and
    CIPHER_HASH for decryption
- AES-CTR implementation for VAES added
- AES-CBC implementation for VAES added
- Single buffer AES-GCM performance improvements added for VPCLMULQDQ + VAES
- Multi-buffer AES-GCM implementation added for VPCLMULQDQ + VAES
- Data transposition optimizations and unification across the library
  implemented
- Generation of make dependency files for Linux added
- AES-ECB implementation added
- PON specific stitched algorithm implementation added
  - stitched AES-CTR-128 (optional) with CRC32 and BIP (running 32-bit XOR)
- AES-CMAC-128 implementation for bit length messages added
- ZUC-EEA3 and ZUC-EIA3 implementation added
- FreeBSD experimental support added
- KASUMI-F8 and KASUMI-F9 implementation added
- SNOW3G-UEA2 and SNOW3G-UIA2 implementation added
- AES-CTR implementation for bit length (128-NEA2/192-NEA2/256-NEA2) messages added
- SAFE_PARAM, SAFE_DATA and SAFE_LOOKUP compile time options added.
  Find more about these options in the README file or on-line at
  https://github.com/intel/intel-ipsec-mb/blob/master/README.

LibTestApp
- New API tests added
- CMAC test vectors extended
- New chained operation tests added
- Out-of-place chained operation tests added
- AES-ECB tests added
- PON algorithm tests added
- Extra AES-CTR test vectors added
- Extra AES-CBC test vectors added
- AES-CMAC-128 bit length message tests added
- CPU capability detection used to disable tests if instruction not present
- ZUC-EEA3 and ZUC-EIA3 tests added
- New cross architecture test application (ipsec_xvalid) added,
  which mixes different implementations (based on different architectures),
  to double check their correctness
- SNOW3G-UEA2 and SNOW3G-UIA2 tests added
- AES-CTR-128 bit length message tests added
- Negative tests extended to cover all API's

LibPerfApp
- Job size and number of iterations options added
- Single architecture test option added
- AAD size option added
- Allow zero length source buffer option added
- Custom performance test combination added:
  cipher-algo, hash-algo and aead-algo arguments.
- Cipher direction option added
- The maximum buffer size extended from 2K to 16K
- Support for user defined range of job sizes added

Fixes
- Uninitialized memory reported by Valgrind fixed
- Flush decryption job fixed (issue #33)
- NULL_CIPHER order check removed (issue #30)
- Save XMM registers when emulating AES fixed (issue #28)
- SSE & AVX AES-CMAC fixed (issue #27)
- Missing GCM pointers fixed for AES-NI emulation (issue #29)

v0.52 December 2018
========================================================================

03 Dec, 2018

General
- Added AESNI emulation implementation
- Added AES-GCM multi-buffer implementation for AVX512
- Added flexible job chain order support
- GCM submit and flush functions moved into architecture MB manager modules
- AVX512/AVX2/AVX/SSE AAD GHASH computation performance improvement
- GCM API's added to MB_MGR structure
- Added plain SHA support in JOB API
- Added architectural compiler optimizations for GCC/CC

LibTestApp
- Added option not to run GCM tests
- Added AESNI emulation tests
- Added plain SHA tests
- Updated to take advantage of new GCM macros

LibPerfApp
- Buffer alignment update
- Updated to take advantage of new GCM macros

v0.51 September 2018
========================================================================

13 Sep, 2018

General
- AES-CMAC performance optimizations
- Implemented store to load optimizations in
  - AES-CMAC submit and flush jobs for SSE and AVX
  - HMAC-MD5, HMAC-SHA submit jobs for AVX
  - HMAC-MD5 submit job for AVX2
- Added zero-sized message support in GCM
- Stack execution flag disabled in new asm modules

LibTestApp
- Added AES vectors
- Added DOCSIS AES vectors
- Added CFB validation

LibPerfApp
- Smoke test option added

v0.50 June 2018
========================================================================

13 Jun, 2018

General
- Added support for compile time and runtime library version checking
- Added support for full MD5 digest size
- Replaced defines for API with symbols for binary compatibility
- Added HMAC-SHA & HMAC-MD5 vectors to LibTestApp
- Added support for zero cipher length in AES-CCM
- Added new API's to compute SHA1, SHA224, SHA256, SHA384 and SHA512 hashes
  to support key reduction cases where key is longer than a block size
- Extended support for HMAC full digest sizes for HMAC-SHA1, HMAC-SHA224,
  HMAC-SHA256, HMAC-SHA384 and HMAC-SHA512. Previously only truncated sizes
  were supported.
- Added AES-CMAC support for output digest size between 4 and 16 bytes
- Added GHASH support for output digest size up to 16 bytes
- Optimized submit job API's with store to load optimization in SSE, AVX,
  AVX2 (excluding MD5)
- Improved performance application accuracy by increase number of
  test iterations
- Extended multi-thread features of LibPerfApp Windows version to match
  Linux version of the application

v0.49 March 2018
========================================================================

21 Mar, 2018

General
- AES-CMAC support added (AES-CMAC-128 and AES-CMAC-96)
- 3DES support added
- Library compiles to SO/DLL by default
- Install/uninstall targets added to makefiles
- Multiple API header files consolidated into one (intel-ipsec-mb.h)
- Unhalted cycles support added to LibPerfApp (Linux at the moment)
- ELF stack execute protection added for assembly files
- VZEROUPPER instruction issued after AVX2/AVX512 code to avoid
  expensive SSE<->AVX transitions
- MAN page added
- README documentation extensions and updates
- AVX512 DES performance smoothed out
- Multi-buffer manager instance allocate and free API's added
- Core affinity support added in LibPerfApp

v0.48 December 2017
========================================================================

12 Dec, 2017

General
- Linux SO compilation option added
- Windows DLL compilation option added
- AES CCM 128 support added
- Multithread command line option added to LibPerfApp
- Coding style fixes
- Coding style target added to Makefile

v0.47 October 2017
========================================================================

Oct 5, 2017

Intel(R) AVX-512 Instructions
- DES CBC AVX512 implementation
- DOCSIS DES AVX512 implementation
General
- DES CBC cipher added (generic x86 implementation)
- DOCSIS DES cipher added (generic x86 implementation)
- DES and DOCSIS DES tests added
- RPM SPEC file created

v0.46 June 2017
========================================================================

Jun 27, 2017

General
- AES GCM optimizations for AVX2
- Change of AES GCM API: renamed and expanded keys separated from the context
- New AES GCM API via job structure and API's
  -  use of the interface may simplify application design at the expense of
     slightly lower performance vs direct AES GCM API's
- AES GCM IV automatically padded with block counter (no need for application to do it)
- IV in AES CTR mode can be 12 bytes (no block counter); 16 byte format still allowed
- Macros added to ease access to job API for specific architecture
  - use of these macros can simplify application design but it may produce worse
    performance than calling architecture job API's directly
- Submit_job_nocheck() API added to gain some cycles by not validating job structure
- Result stability improvements in LibPerfApp

v0.45 March 2017
========================================================================

Mar 29, 2017

Intel(R) AVX-512 Instructions
- Added optimized HMAC-SHA224 and HMAC-SHA256
- Added optimized HMAC-SHA384 and HMAC-SHA512
General
- Windows x64 compilation target
- New DOCSIS SEC BPI V3.1 cipher
- GCM128 and GCM256 updates (with new API that is scatter gather list friendly)
- GCM192 added
- Added library API benchmark tool 'ipsec_perf' and
  script to compare results 'ipsec_diff_tool.py'
Bug Fixes (vs v0.44)
- AES CTR mode fix to allow message size not to be multiple of AES block size
- RSI and RDI registers clobbered when running HMAC-SHA224 or HMAC-SHA256
  on Windows using SHA extensions

v0.44 November 2016
========================================================================

Nov 21, 2016

Intel(R) AVX-512 Instructions
- AVX512 multi buffer manager added (uses AVX2 implementations by default)
- Optimized SHA1 implementation added
Intel(R) SHA Extensions
- SHA1, SHA224 and SHA256 implementations added for Intel(R) SSE
General
- NULL cipher added
- NULL hash added
- NASM tool chain compilation added (default)

=======================================
Feb 11, 2015

Fixed, so that the job auth_tag_output_len_in_bytes takes a different 
value for different MAC types. In particular, the valid values are(in bytes):
SHA1 - 12
sha224 - 14 
SHA256 - 16 
sha384 - 24
SHA512 - 32
XCBC - 12
MD5 - 12

=======================================
Oct 24, 2011

SHA_256 added to multibuffer
------------------------
12 Aug 2011

API

  The GCM API is distinct from the Multi-buffer API. This is because
  the GCM code is an optimized single-buffer implementation. By
  packaging them separately, the application has the option of where,
  when, and how to call the GCM code, independent of how it is calling
  the multi-buffer code.

  For example, the application might be enqueuing multi-buffer requests
  for a separate thread to process. In this scenario, if a particular
  packet used GCM, then the application could choose whether to call
  the GCM routines directly, or whether to enqueue those requests and
  have the compute thread call the GCM routines.

GCM API

  The GCM functions are defined as described the the header
  files. They are simple computational routines, with no state
  associated with them.

Multi-Buffer API: Two Sets of Functions

  There are two parallel interfaces, one suffixed with "_sse" and one
  suffixed with "_avx". These are functionally equivalent. The "_sse"
  functions work on WSM and later processors. The "_avx" functions
  offer better performance, but they only run on processors after WSM.

  The same interface object structures are used for both sets of
  interfaces, although one cannot mix the two interfaces on the same
  initialized object (e.g. it would be wrong to initialize with
  init_mb_mgr_sse() and then to pass that to submit_job_avx() ). After
  the MB_MGR structure has been initialized with one of the two
  initialization functions (init_mb_mgr_sse() or init_mb_mgr_avx()),
  only the corresponding functions should be used on it.

  There are several ways in which an application could use these
  interfaces.

  1) Direct
     If an application is only going to be run on a post-WSM machine,
     it can just call the "_avx" functions directly. Conversely, if it
     is just going to be run on WSM machines, it can call the "_sse"
     functions directly.

  2) Via Branches
     If an application can run on both WSM and SNB and wants the
     improved performance on SNB, then it can use some method to
     determine if it is on SNB, and then use a conditional branch to
     determine which function to call. E.g. this could be wrapped in a
     macro along the lines of:
     #define submit_job(mb_mgr) \
        if (_use_avx) submit_job_avx(mb_mgr); \
        else          submit_job_sse(mb_mgr)

  3) Via a Function Table
     One can embed the function addresses into a structure, call them
     through this structure, and change the structure based on which
     set of functions one wishes to use, e.g.

        struct funcs_t {
            init_mb_mgr_t       init_mb_mgr;
            get_next_job_t      get_next_job;
            submit_job_t        submit_job;
            get_completed_job_t get_completed_job;
            flush_job_t         flush_job;
        };
        
        funcs_t funcs_sse = {
            init_mb_mgr_sse,
            get_next_job_sse,
            submit_job_sse,
            get_completed_job_sse,
            flush_job_sse
        };
        funcs_t funcs_avx = {
            init_mb_mgr_avx,
            get_next_job_avx,
            submit_job_avx,
            get_completed_job_avx,
            flush_job_avx
        };
        funcs_t *funcs = &funcs_sse;
        ...
        if (do_avx)
            funcs = &funcs_avx;
        ...
        funcs->init_mb_mgr(&mb_mgr);

  For simplicity in the rest of this document, the functions will be
  referred to no suffix.

API: Overview

  The basic unit of work is a "job". It is represented by a
  JOB_AES_HMAC structure. It contains all of the information needed to
  perform encryption/decryption and SHA1/HMAC authentication on one
  buffer for IPSec processing.

  The basic paradigm is that the application needs to be able to
  provide new jobs before old jobs have completed processing. One
  might call this an "asynchronous" interface. 

  The basic interface is that the application "submits" a job to the
  multi-buffer manager (MB_MGR), and it may receive a completed job
  back, or it may receive NULL. The returned job, if there is one,
  will not be the same as the submitted job, but the jobs will be
  returned in the same order in which they are submitted.

  Since there can be a semi-arbitrary number of outstanding jobs,
  management of the job object is handled by the MB_MGR. The
  application gets a pointer to a new job object by calling
  get_next_job(). It then fills in the data fields and submits it by
  calling submit_job(). If a job is returned, then that job has been
  completed, and the application should do whatever it needs to do in
  order to further process that buffer. 

  The job object is not explicitly returned to the MB_MGR. Rather it
  is implicitly returned by the next call to get_next_job(). Another
  way to put this is that the data within the job object is
  guaranteed to be valid until the next call to get_next_job().

  In order to reduce latency, there is an optional function that may
  be called, get_completed_job(). This returns the next job if that
  job has previously been completed. But if that job has not been
  completed, no processing is done, and the function returns
  NULL. This may be used to reduce the number of outstanding jobs
  within the MB_MGR.

  At times, it may be necessary to process the jobs currently within
  the MB_MGR without providing new jobs as input. This process is
  called "flushing", and it is invoked by calling flush_job(). If
  there are any jobs within the MB_MGR, this will complete processing
  on the earliest job and return it. It will only return NULL if there
  are no jobs within the MB_MGR.

  Flushing will be described in more detail below.

  The presumption is that the same AES key will apply to a number of
  buffers. For increased efficiency, it requires that the AES key
  expansion happens as a distinct step apart from buffer
  encryption/decryption. The expanded keys are stored in a data
  structure (array), and this expanded key structure is used by the
  job object.

  There are two variants provided, MB_MGR and MB_MGR2. They are
  functionally equivalent. The reason that two are provided is that
  they differ slightly in their implementation, and so they may have
  slightly different characteristics in terms of latency and overhead.

API: Usage Skeleton
  The basic usage is illustrated in the following pseudo_code:

    init_mb_mgr(&mb_mgr);
    ...
    aes_keyexp_128(key, enc_exp_keys, dec_exp_keys);
    ...
    while (work_to_be_done) {
        job = get_next_job(&mb_mgr);
        // TODO: Fill in job fields
        job = submit_job(&mb_mgr);
        while (job) {
            // TODO: Complete processing on job
    	job = get_completed_job(&mb_mgr);
        }
    }

API: Job Fields
  The mode is determined by the fields "cipher_direction" and
  "chain_order". The first specifies encrypt or decrypt, and the
  second specifies whether whether the hash should be done before or
  after the cipher operation.
  In the current implementation, only two combinations of these are
  supported. For encryption, these should be set to "ENCRYPT" and
  "CIPHER_HASH", and for decryption, these should be set to "DECRYPT"
  and "HASH_CIPHER".

  The expanded keys are pointed to by "aes_enc_key_expanded" and
  "aes_dec_key_expanded". These arrays must be aligned on a 16-byte
  boundary. Only one of these is necessary (as determined by
  "cipher_direction"). 

  One selects AES128 vs AES256 by using the "aes_key_len_in_bytes"
  field. The only valid values are 16 (AES128) and 32 (AES256).

  One selects the AES mode (CBC versus counter-mode) using
  "cipher_mode".

  One selects the hash algorithm (SHA1-HMAC, AES-XCBC, or MD5-HMAC)
  using "hash_alg".

  The data to be encrypted/decrypted is defined by
  "src + cipher_start_src_offset_in_bytes". The length of data is
  given by "msg_len_to_cipher_in_bytes". It must be a multiple of
  16 bytes.

  The destination for the cipher operation is given by "dst" (NOT by
  "dst + cipher_start_src_offset_in_bytes". In many/most applications,
  the destination pointer may overlap the source pointer. That is,
  "dst" may be equal to "src + cipher_start_src_offset_in_bytes".

  The IV for the cipher operation is given by "iv". The
  "iv_len_in_bytes" should be 16. This pointer does not need to be
  aligned. 

  The data to be hashed is defined by
  "src + hash_start_src_offset_in_bytes". The length of data is
  given by "msg_len_to_hash_in_bytes".

  The output of the hash operation is defined by
  "auth_tag_output". The number of bytes written is given by
  "auth_tag_output_len_in_bytes". Currently the only valid value for
  this parameter is 12.

  The ipad and opad are given as the result of hashing the HMAC key
  xor'ed with the appropriate value. That is, rather than passing in
  the HMAC key and rehashing the initial block for every buffer, the
  hashing of the initial block is done separately, and the results of
  this hash are used as input in the job structure.

  Similar to the expanded AES keys, the premise here is that one HMAC
  key will apply to many buffers, so we want to do that hashing once
  and not for each buffer.

  The "status" reflects the status of the returned job. It should be
  "STS_COMPLETED". 

  The "user_data" field is ignored. It can be used to attach
  application data to the job object.

Flushing Concerns
  As long as jobs are coming in at a reasonable rate, jobs should be
  returned at a reasonable rate. However, if there is a lull in the
  arrival of new jobs, the last few jobs that were submitted tend to
  stay in the MB_MGR until new jobs arrive. This might result in there
  being an unreasonable latency for these jobs.

  In this case, flush_job() should be used to complete processing on
  these outstanding jobs and prevent them from having excessive
  latency.

  Exactly when and how to use flush_job() is up to the application,
  and is a balancing act. The processing of flush_job() is less
  efficient than that of submit_job(), so calling flush_job() too
  often will lower the system efficiency. Conversely, calling
  flush_job() too rarely may result in some jobs seeing excessive
  latency. 

  There are several strategies that the application may employ for
  flushing. One usage model is that there is a (thread-safe) queue
  containing work items. One or more threads puts work onto this
  queue, and one or more processing threads removes items from this
  queue and processes them through the MB_MGR. In this usage, a simple
  flushing strategy is that when the processing thread wants to do
  more work, but the queue is empty, it then proceeds to flush jobs
  until either the queue contains more work, or the MB_MGR no longer
  contains jobs (i.e. that flush_job() returns NULL). A variation on
  this is that when the work queue is empty, the processing thread
  might pause for a short time to see if any new work appears, before
  it starts flushing.

  In other usage models, there may be no such queue. An alternate
  flushing strategy is that have a separate "flush thread" hanging
  around. It wakes up periodically and checks to see if any work has
  been requested since the last time it woke up. If some period of
  time has gone by with no new work appearing, it would proceed to
  flush the MB_MGR.

AES Key Usage
  If the AES mode is CBC, then the fields aes_enc_key_expanded or
  aes_dec_key_expanded are using depending on whether the data is
  being encrypted or decrypted. However, if the AES mode is CNTR
  (counter mode), then only aes_enc_key_expanded is used, even for a
  decrypt operation. 

  The application can handle this dichotomy, or it might choose to
  simply set both fields in all cases.

Thread Safety
  The MB_MGR and the associated functions ARE NOT thread safe. If
  there are multiple threads that may be calling these functions
  (e.g. a processing thread and a flushing thread), it is the
  responsibility of the application to put in place sufficient locking
  so that no two threads will make calls to the same MB_MGR object at
  the same time.

XMM Register Usage
  The current implementation is designed for integration in the Linux
  Kernel. All of the functions satisfy the Linux ABI with respect to
  general purpose registers. However, the submit_job() and flush_job()
  functions use XMM registers without saving/restoring any of them. It
  is up to the application to manage the saving/restoring of XMM
  registers itself.

Auxiliary Functions
  There are several auxiliary functions packed with MB_MGR. These may
  be used, or the application may choose to use their own version. Two
  of these, aes_keyexp_128() and aes_keyexp_256() expand AES keys into
  a form that is acceptable for reference in the job structure. 

  In the case of AES128, the expanded key structure should be an array
  of 11 128-bit words, aligned on a 16-byte boundary. In the case of
  AES256, it should be an array of 15 128-bit words, aligned on a
  16-byte boundary. 

  There is also a function, sha1(), which will compute the SHA1 digest
  of a single 64-byte block. It can be used to compute the ipad and
  opad digests. There is a similar function, md5(), which can be used
  when using MD5-HMAC.

  For further details on the usage of these functions, see the sample
  test application.