path: root/HISTORY.txt

October 10, 2020:
    A paper by Konstantinos Chalkias, François Garillot, and Valeria
    Nikolaenko, to be found at:

    https://eprint.iacr.org/2020/1244.pdf
    
    discusses malleability in EdDSA implementations.  Their test
    vectors reveal unintentional malleability in libdecaf's version
    of EdDSA verify, in violation of RFC 8032.  With this malleability,
    an attacker could modify an existing valid signature to create a
    new signature that is still valid, but only for the same message.
    
    Releave v1.0.1, correcting this flaw.

July 12, 2018:
    Release 1.0 with Johan Pascal's build scripts.

October 13, 2017:
    OK, back to preparations for 1.0, today with major changes.
    
    Another group (Isis Lovecruft and Henry de Valence) implemented
    Decaf for Ed25519, whereas this code was implemented for IsoEd25519.
    
    These curves are isogenous, but not exactly the same, so the
    encodings all came out differently.
     
    To harmonize these two so that there is only one implementation
    for Ed25519, we've hammered out a compromise implementation called
    Ristretto.  This is different from the old Decaf encoding in two
    major ways:
        * It checks the sign of x on Ed25519 instead of IsoEd25519.
        * It considers a number "negative" if its low bit is set,
          instead of its high bit.
    
    To avoid extra branches in the code, Ed448Goldilocks is also
    getting these changes to match Ristretto.
    
    The C++ class is also renamed to Ristretto, but IsoEd25519 is a
    synonym for that class.
    
    We might need to check the high bit again instead of low bit if
    E-521 is ever implemented, but I'll special case it then.

April 22, 2017:
    Remove STROBE in preparation for 1.0 release.  STROBE has its own
    repo now at https://strobe.sourceforge.io.  I might re-integrate
    it into Decaf once I have produced a version that matches the
    STROBE v1 spec, but it's just confusing to keep v0.2 in here.
    
    Change x{25519,448}_generate_key to _derive_public_key.

January 15, 2016:
    Lots of changes since the last entry in HISTORY.TXT.
    
    Pushing eventually toward a 1.0 release, at least for the curves
    themselves (i.e. not for STROBE), still a fair amount of stuff to
    do.
    
    I have pretty much all the functions I want implemented, except
    that maybe there should be a compatibility mode for whatever CFRG
    decides the real life format should be.
    
    The library now supports multiple curves at once.  A decaffeinated
    curve isogenous to Curve25519 is now supported, but not especially
    fast.  This is all still a little rough around the edges.  To make
    it work in a sane way, most of the headers are generated using
    Python templates.  Probably those should be turned back into .h
    files for syntax hilighting purposes; the code generation system
    in general needs quite a tuneup.
    
    The plus side is that this reduces the source code size, especially
    for supporting many curves over many fields.
    
    Currently the code only kind of halfway works on ARM, and not as
    fast as it used to (on NEON anyway), by maybe 15-20%.  I'm
    investigating why.  It's about as fast as it used to be on x86,
    maybe a hair slower.
    
    Montgomery ladder is currently out.  Putting it back in might help
    pin down the ARM NEON performance regression.

    The BAT is currently broken.
    
    Tracking at 55 TODO items, about half of which are important-ish.
    Source code size is currently 12.8k wc-lines, including tests and
    old fields (p480 and p521).  I'm still trying to get that down, but
    with things like 600 lines of NEON f_impl.c, that's not an easy task.

April 23, 2015:
    Removed the original Goldilocks code; Decaf now stands on its own.
    This cuts the source code approximately in half, to a still-large
    13.7k wc-lines.  (Most of these lines are in the arch-specific
    field implementations.)
    
    Note that the decaf_crypto routines are not intended to set
    standards.  They should be secure, but they're intended more as
    examples of how the core ECC library could be used.
    
    The SHAKE stuff is also mostly an experiment, particularly the
    STROBE protocol/mode stuff.  This is all fine, because the ECC
    library itself is the core, and doesn't require the SHAKE stuff.
    (Except for the C++ header, which should probably also be factored
    so that it doesn't need the SHAKE stuff.)
    
    I've started work on making a Decaf BAT, but not done yet.
    
    I haven't ripped out all old multi-field code, because I intend
    to add support for other fields eventually.  Maybe properly this
    time, instead of with a million compile flags like the original.

March 23, 2015:
    I've been fleshing out Decaf, and hopefully the API is somewhere
    near final.  I will probably move a few things around and add a
    scalar inversion command (for AugPAKE and such).
    
    I've built a "decaf_fast" implementation which is about as fast as
    Goldilocks, except that verification still isn't as fast, because
    it needs a precomputed wNAF table which I haven't implemented yet.
    Precomputation is noticeably faster than in Goldilocks; while
    neither is especially optimized, the extended point format works
    slightly better for that purpose.
    
    While optimizing decaf_fast I also found a minor perf problem in
    the constant time lookup code, so that's fixed (I hope?) and
    everything is faster at least on my test machine.
    
    At some point soon-ish, I'd like to start removing the base
    Goldilocks code from this branch.  That will require porting more
    of the tests.  I might make a C++ header for Decaf, which would
    definitely simplify testing.

March 1, 2015:
    While by no means complete or stable, I've done most of the ground
    work to implement the "Decaf" point encoding.  This point encoding
    essentially divides the cofactor by 4, turning Goldilocks (or
    Ridinghood or E-521) into a prime-order group.  Furthermore, like
    the Goldilocks encoding, this encoding avoids incompleteness in
    the twisted Edwards formulas with a=-1 by sticking to the order-2q
    subgroup.

    Because the group is prime order, and because the "isogeny strategy"
    is not needed, the decaf API can be very simple.  I'm still working
    on exactly what it should be though.  The goal is to have a single-
    file (or a few files) for a "ref" version, which is designed for
    auditability.  The ref version won't be quite so simple as TweetNaCl,
    but nearly so simple and much better commented.  Then there can also
    be an optimized version, perhaps per-platform, which is as fast as
    the original Goldilocks code but hopefully still simpler.

    I'm experimenting with SHAKE as the hash function here.  Possibly I
    will also add Keyak as an encryption primitive, so that everything
    can be based on Keccak-f, but I'm open to suggestions.  For example,
    if there's a way to make BLAKE2 as simple and useful as SHAKE
    (including in oversized curves like E-521), then the extra speed
    would certainly be welcome.

October 27, 2014:
    Added more support for >512-bit primes.  Changed shared secret
    to not overflow the buffer in this case.  Changed hashing to
    SHA512-PRNG; this doesn't change the behavior in the case that
    only one block is required.

    E-521 appears to be working.  Needs more testing, and maybe some
    careful analysis since the carry-handling bounds are awfully tight
    under the current analysis (the "< 5<<57" that it #if0 asserts is
    not actually tight enough under the current analysis; need
    it to be < (1+epsilon) << 59).
    
    So you actually do need to reduce often, at least in the x86_64_r12
    version.
    
    p521/arch_ref64: simple and relatively slow impl.  Like
    p448/arch_ref64, this arch reduces after every add or sub.
    
    p521/arch_x86_64_r12: aggressive, fast implementation.  This impl
    stores 521 bits not in 9 limbs, but 12!  Limbs 3,7,11 are 0, and
    are there only for vector alignment.  (TODO: remove those limbs
    from precomputed tables, so that we don't have to look them up!).
    The carry handling on this build is very tight, and probably could
    stand more analysis.  This is why I have the careful balancing of
    "hexad" and "nonad" multiplies in its Chung-Hasan mul routine.
    
    (TODO: reconsider whether this is even worthwhile on machines
    without AVX2.)
    
    The 'r12 build is a work in progress, and currently only works on
    clang (because it rearranges vectors in the timesW function).
    
    Timings for the fast, aggressive arch on Haswell:
        mul:    146cy
        sqr:    111cy
        invert: 62kcy
        
        keygen: 270kcy
        ecdh:   803kcy
        sign:   283kcy
        verif:  907kcy
        
    Same rules as other Goldi benchmarks.  Turbo off, HT off,
    timing-channel protected (no dataflow from secrets to branches,
    memory lookups or known vt instructions), compressed points.
    

October 23, 2014:
    Pushing through changes for curve flexibility.  First up is
    Ed480-Ridinghood, because it has the same number of words.  Next
    is E-521.
    
    Experimental support for Ed480-Ridinghood.  To use, compile with
        make ... FIELD=p480 -XCFLAGS=-DGOLDI_FIELD_BITS=480
    
    I still need to figure out what to do about the fact that the library
    is called "goldilocks", but in will soon support curves that are not
    ed448-goldilocks, at least experimentally.
        
    Currently the whole system's header "goldilocks.h" doesn't have
    a simpler way to override field size, but it does work (as a hack)
    with -DGOLDI_FIELD_BITS=...
    
    There is no support yet for coexistence of multiple fields in one
    library.  The field routines will have unique names, but scalarmul*
    won't, and the top-level goldilocks routines have fixed names.
    
    Current timings on Haswell:
        Goldilocks: 178kcy keygen, 536kcy ecdh
        Ridinghood: 193kcy keygen, 617kcy ecdh
    
    Note that Ridinghood ECDH does worse than 480/448.  This is at least
    in part because I haven't calculated the overflow handling limits yet
    in ec_point.h (this is a disadvantage of dropping the automated
    tool for generating that file).  So I'm reducing much more often
    than I need to.  (There's a really loud TODO in ec_point.h for that.)
    
    Also, I haven't tested the limits on these reductions in a while, so
    it could be that there are actual (security-critical) bugs in this
    area, at least for p448.  Now that there's field flexibility, it's
    probably a good idea to make a field impl with extra words to check
    this.
    
    Furthermore, field_mulw_scc will perform differently on these two
    curves based on whether the curve constant is positive or negative.
    I should probably go optimize the "hot" routines like montgomery_step
    to have separate cases for positive and negative.

September 29, 2014:
    Yesterday I put in some more architecture detection, but it should
    really be based on the arch directory, because what's in there really
    was a terrible hack.  So I've changed it to use $arch/arch_config.h
    to get WORD_BITS.
    
    I've tweaked the eBAT construction code to rename the architectures
    using test/batarch.map.  Maybe I should also rename them internally,
    but not yet.
    
    I added some new TODO.txt items.  Some folks have been asking for a
    more factored library, instead of this combined arithmetic, curve code,
    encodings and protocol all-in-one jumble.  Likewise the hash and RNG
    should be flexible.
    
    I've also been meaning to put more work in on SPAKE2EE, which would
    also mean finalizing the Elligator code.

September 18, 2014:
    Begin work on a "ref" implementation.  Currently this is just the
    arch_ref64 architecture.  The ref implementation always weak_reduces
    after arithmetic, and doesn't use vectors or other hackery.  Currently
    it still must declare field elements as vector aligned, though,
    other code outside the arch directory can be vectorized.

    Change goldilocks.c to use field_eq instead of calling deep into field
    apis.

September 6, 2014:
    Pull in minor changes from David Leon Gil and Nicholas Wilson, with
    some adjustments.  I hope the adjustments don't break their compiles.

    `make bat` now makes a bat which passes supercop-fastbuild, though
    the benchmarks are rather different from `make bench`.  I need to track
    down why.

August 4, 2014:
    Experiments and bug fixes.

    Add really_memset = memset_s (except not because I'm setting -std=c99),
    thanks David Leon Gil.  I think I put it in the right places.

    Try to work around what I think is a compiler bug in GCC -O3 on non-AVX
    platforms.  I can't seem to work around it as -Os, so I'm just flagging
    a warning (-Werror makes it an error) for now.  Will take more
    investigation.  Thanks Samuel Neves.

    Added an experimental (not ready yet!) ARM NEON implementation in
    arch_neon_experimental.  This implementation seems to work, but needs
    more testing.  It is currently asm-heavy and not GCC clean.  I am
    planning to have a flag for it to use intrinsics instead of asm;
    currently the intrinsics are commented out.  On clang this does ECDH
    in 1850kcy on my BeagleBone Black, comparable to Curve41417.  Once this
    is ready, I will probably move it to arch_neon proper, since arch_neon
    isn't particularly tuned.

July 11, 2014:
    This is mostly a cleanup release.

    Added CRANDOM_MIGHT_IS_MUST config flag (default: 1).  When set, this
    causes crandom to assume that all features in the target arch will
    be available, instead of detecting them.  This makes sense because
    the rest of the Goldilocks code is not (yet?) able to detect features.
    Also, I'd like to submit this to SUPERCOP eventually, and SUPERCOP won't
    pass -DMUST_HAVE_XXX on the command line the way the Makefile here did.
    
    Flag EXPERIMENT_CRANDOM_BUFFER_CUTOFF_BYTES to disable the crandom
    output buffer.  This buffer improves performance (very marginally at
    Goldilocks sizes), but can cause problems with forking and VM
    snapshotting.  By default, the buffer is now disabled.
    
    I've slightly tweaked the Elligator implementation (which is still
    unused) to make it easier to invert.  This makes anything using Elligator
    (i.e. nothing) incompatible with previous releases.
    
    I've been factoring "magic" constants such as curve orders, window sizes,
    etc into a few headers, to reduce the effort to port the code to other
    primes, curves, etc.  For example, I could test the Microsoft curves, and
    something like:
        x^2 + y^2 = 1 +- 5382[45] x^2 y^2 mod 2^480-2^240-1
    ("Goldeneye"? "Ridinghood"?) might be a reasonable thing to try for
    64-bit CPUs.
    
    In a similar vein, most of the internal code has been changed to say
    "field" instead of p448, so that a future version of magic.h can decide
    which field header to include.
    
    You can now `make bat` to create an eBAT in build/ed448-goldilocks.  This
    is only minimally tested, though, because SUPERCOP doesn't work on my
    machine and I'm too lazy to reverse engineer it.  It sets a new macro,
    SUPERCOP_WONT_LET_ME_OPEN_FILES, which causes goldilocks_init() to fall
    back to something horribly insecure if crandom_init_from_file raises
    EMFILE.
    
    Slightly improved documentation.
    
    Removed some old commented-out code; restored the /* C-style */ comment
    discipline.
    
    The AMD-64 version should now be GCC clean, at least for reasonably
    recent GCC (tested on OS X.9.3, Haswell, gcc-4.9).
    
    History no longer says "2104".

May 3, 2014:
    Minor changes to internal routines mean that this version is not
    compatible with the previous one.

    Added ARM NEON code.
    
    Added the ability to precompute multiples of a partner's public key.  This
    takes slightly longer than a signature verification, but reduces future
    verifications with the precomputed key by ~63% and ECDH by ~70%.
    
        goldilocks_precompute_public_key
        goldilocks_destroy_precomputed_public_key
        goldilocks_verify_precomputed
        goldilocks_shared_secret_precomputed
    
    The precomputation feature are is protected by a macro
        GOLDI_IMPLEMENT_PRECOMPUTED_KEYS
    which can be #defined to 0 to compile these functions out.  Unlike most
    of Goldilocks' functions, goldilocks_precompute_public_key uses malloc()
    (and goldilocks_destroy_precomputed_public_key uses free()).
    
    Changed private keys to be derived from just the symmetric part.  This
    means that you can compress them to 32 bytes for cold storage, or derive
    keypairs from crypto secrets from other systems.
        goldilocks_derive_private_key
        goldilocks_underive_private_key
        goldilocks_private_to_public
    
    Fixed a number of bugs related to vector alignment on Sandy Bridge, which
    has AVX but uses SSE2 alignment (because it doesn't have AVX2).  Maybe I
    should just switch it to use AVX2 alignment?
    
    Beginning to factor out curve-specific magic, so as to build other curves
    with the Goldilocks framework.  That would enable fair tests against eg
    E-521, Ed25519 etc.  Still would be a lot of work.
    
    More thorough testing of arithmetic.  Now uses GMP for testing framework,
    but not in the actual library.
    
    Added some high-level tests for the whole library, including some (bs)
    negative testing.  Obviously, effective negative testing is a very difficult
    proposition in a crypto library.

March 29, 2014:
    Added a test directory with various tests.  Currently testing SHA512 Monte
    Carlo, compatibility of the different scalarmul functions, and some
    identities on EC point ops.  Began moving these tests out of benchmarker.
    
    Added scan-build support.
    
    Improved some internal interfaces.  Made a structure for Barrett primes
    instead of passing parameters individually.  Moved some field operations
    to places that make more sense, eg Barrett serialize and deserialize.  The
    deserialize operation now checks that its argument is in [0,q).
    
    Added more documentation.
    
    Changed the names of a bunch of functions.  Still not entirely consistent,
    but getting more so.
    
    Some minor speed improvements.  For example, multiply is now a couple cycles
    faster.
    
    Added a hackish attempt at thread-safety and initialization sanity checking
    in the Goldilocks top-level routines.
    
    Fixed some vector alignment bugs.  Compiling with -O0 should now work.
    
    Slightly simplified recode_wnaf.

    Add a config.h file for future configuration.  EXPERIMENT flags moved here.
    
    I've decided against major changes to SHA512 for the moment.  They add speed
    but also significantly bloat the code, which is going to hurt L1 cache
    performance.  Perhaps we should link to OpenSSL if a faster SHA512 is desired.
    
    Reorganize the source tree into src, test; factor arch stuff into src/arch_*.
    
    Make most of the code 32-bit clean.  There's now a 32-bit generic and 32-bit
    vectorless ARM version.  No NEON version yet because I don't have a test
    machine (could use my phone in a pinch I guess?).  The 32-bit version still
    isn't heavily optimized, but on ARM it's using a nicely reworked signed/phi-adic
    multiplier.  The squaring is also based on this, but could really stand some
    improvement.
    
    When passed an even exponent (or extra doubles), the Montgomery ladder should
    now be accept points if and only if they lie on the curve.  This needs
    additional testing, but it passes the zero bit exponent test.
    
    On 32-bit, use 8x4x14 instead of 5x5x18 table organization.  Probably there's
    a better heuristic.

March 5, 2014:
    First revision.
    
    Private keys are now longer.  They now store a copy of the public key, and
    a secret symmetric key for signing purposes.
    
    Signatures are now supported, though like everything else in this library,
    their format is not stable.  They use a deterministic Schnorr mode,
    similar to EdDSA.  Precomputed low-latency signing is not supported (yet?).
    The hash function is SHA-512.
    
    The deterministic hashing mode needs to be changed to HMAC (TODO!).  It's
    currently envelope-MAC.
    
    Probably in the future there will be a distinction between ECDH key and
    signing keys (and possibly also MQV keys etc).
    
    Began renaming internal functions.  Removing p448_ prefixes from EC point
    operations.  Trying to put the verb first.  For example,
    "p448_isogeny_un_to_tw" is now called "twist_and_double".
    
    Began documenting with Doxygen.  Use "make doc" to make a very incomplete
    documentation directory.
    
    There have been many other internal changes.

Feb 21, 2014:
    Initial import and benchmarking scripts.
    
    Keygen and ECDH are implemented, but there's no hash function.