The blockchain that provides the digital content namespace for the LBRY protocol
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Wladimir J. van der Laan b2135359b3 Squashed 'src/secp256k1/' changes from 6c527ec..7a49cac
7a49cac Merge #410: Add string.h include to ecmult_impl
0bbd5d4 Add string.h include to ecmult_impl
c5b32e1 Merge #405: Make secp256k1_fe_sqrt constant time
926836a Make secp256k1_fe_sqrt constant time
e2a8e92 Merge #404: Replace 3M + 4S doubling formula with 2M + 5S one
8ec49d8 Add note about 2M + 5S doubling formula
5a91bd7 Merge #400: A couple minor cleanups
ac01378 build: add -DSECP256K1_BUILD to benchmark_internal build flags
a6c6f99 Remove a bunch of unused stdlib #includes
65285a6 Merge #403: configure: add flag to disable OpenSSL tests
a9b2a5d configure: add flag to disable OpenSSL tests
b340123 Merge #402: Add support for testing quadratic residues
e6e9805 Add function for testing quadratic residue field/group elements.
efd953a Add Jacobi symbol test via GMP
fa36a0d Merge #401: ecmult_const: unify endomorphism and non-endomorphism skew cases
c6191fd ecmult_const: unify endomorphism and non-endomorphism skew cases
0b3e618 Merge #378: .gitignore build-aux cleanup
6042217 Merge #384: JNI: align shared files copyright/comments to bitcoinj's
24ad20f Merge #399: build: verify that the native compiler works for static precomp
b3be852 Merge #398: Test whether ECDH and Schnorr are enabled for JNI
aa0b1fd build: verify that the native compiler works for static precomp
eee808d Test whether ECDH and Schnorr are enabled for JNI
7b0fb18 Merge #366: ARM assembly implementation of field_10x26 inner (rebase of #173)
001f176 ARM assembly implementation of field_10x26 inner
0172be9 Merge #397: Small fixes for sha256
3f8b78e Fix undefs in hash_impl.h
2ab4695 Fix state size in sha256 struct
6875b01 Merge #386: Add some missing `VERIFY_CHECK(ctx != NULL)`
2c52b5d Merge #389: Cast pointers through uintptr_t under JNI
43097a4 Merge #390: Update bitcoin-core GitHub links
31c9c12 Merge #391: JNI: Only call ecdsa_verify if its inputs parsed correctly
1cb2302 Merge #392: Add testcase which hits additional branch in secp256k1_scalar_sqr
d2ee340 Merge #388: bench_ecdh: fix call to secp256k1_context_create
093a497 Add testcase which hits additional branch in secp256k1_scalar_sqr
a40c701 JNI: Only call ecdsa_verify if its inputs parsed correctly
faa2a11 Update bitcoin-core GitHub links
47b9e78 Cast pointers through uintptr_t under JNI
f36f9c6 bench_ecdh: fix call to secp256k1_context_create
bcc4881 Add some missing `VERIFY_CHECK(ctx != NULL)` for functions that use `ARG_CHECK`
6ceea2c align shared files copyright/comments to bitcoinj's
70141a8 Update .gitignore
7b549b1 Merge #373: build: fix x86_64 asm detection for some compilers
bc7c93c Merge #374: Add note about y=0 being possible on one of the sextic twists
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86e2d07 JNI library: cleanup, removed unimplemented code
3093576a JNI library
bd2895f Merge pull request #371
e72e93a Add note about y=0 being possible on one of the sextic twists
3f8fdfb build: fix x86_64 asm detection for some compilers
e5a9047 [Trivial] Remove double semicolons
c18b869 Merge pull request #360
3026daa Merge pull request #302
03d4611 Add sage verification script for the group laws
a965937 Merge pull request #361
83221ec Add experimental features to configure
5d4c5a3 Prevent damage_array in the signature test from going out of bounds.
419bf7f Merge pull request #356
03d84a4 Benchmark against OpenSSL verification

git-subtree-dir: src/secp256k1
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2016-08-16 11:34:11 +02:00
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libsecp256k1

Build Status

Optimized C library for EC operations on curve secp256k1.

This library is a work in progress and is being used to research best practices. Use at your own risk.

Features:

  • secp256k1 ECDSA signing/verification and key generation.
  • Adding/multiplying private/public keys.
  • Serialization/parsing of private keys, public keys, signatures.
  • Constant time, constant memory access signing and pubkey generation.
  • Derandomized DSA (via RFC6979 or with a caller provided function.)
  • Very efficient implementation.

Implementation details

  • General
    • No runtime heap allocation.
    • Extensive testing infrastructure.
    • Structured to facilitate review and analysis.
    • Intended to be portable to any system with a C89 compiler and uint64_t support.
    • Expose only higher level interfaces to minimize the API surface and improve application security. ("Be difficult to use insecurely.")
  • Field operations
    • Optimized implementation of arithmetic modulo the curve's field size (2^256 - 0x1000003D1).
      • Using 5 52-bit limbs (including hand-optimized assembly for x86_64, by Diederik Huys).
      • Using 10 26-bit limbs.
    • Field inverses and square roots using a sliding window over blocks of 1s (by Peter Dettman).
  • Scalar operations
    • Optimized implementation without data-dependent branches of arithmetic modulo the curve's order.
      • Using 4 64-bit limbs (relying on __int128 support in the compiler).
      • Using 8 32-bit limbs.
  • Group operations
    • Point addition formula specifically simplified for the curve equation (y^2 = x^3 + 7).
    • Use addition between points in Jacobian and affine coordinates where possible.
    • Use a unified addition/doubling formula where necessary to avoid data-dependent branches.
    • Point/x comparison without a field inversion by comparison in the Jacobian coordinate space.
  • Point multiplication for verification (aP + bG).
    • Use wNAF notation for point multiplicands.
    • Use a much larger window for multiples of G, using precomputed multiples.
    • Use Shamir's trick to do the multiplication with the public key and the generator simultaneously.
    • Optionally (off by default) use secp256k1's efficiently-computable endomorphism to split the P multiplicand into 2 half-sized ones.
  • Point multiplication for signing
    • Use a precomputed table of multiples of powers of 16 multiplied with the generator, so general multiplication becomes a series of additions.
    • Access the table with branch-free conditional moves so memory access is uniform.
    • No data-dependent branches
    • The precomputed tables add and eventually subtract points for which no known scalar (private key) is known, preventing even an attacker with control over the private key used to control the data internally.

Build steps

libsecp256k1 is built using autotools:

$ ./autogen.sh
$ ./configure
$ make
$ ./tests
$ sudo make install  # optional