python cffi bindings for libsecp256k1
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secpy256k1
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README.md

secpy256k1

NOTE: THIS LIBRARY HAS ONLY BEEN TESTED ON MACOSX. AND IT HAS BEEN BARELY TESTED REALLY AT ALL.

This library is designed to directly mimic the functionality of bitcoin-cores's libsecp256k1 library. It is designed to be a lower level wrapper around libsecp256k1 so it can be be easily integrated into other projects.

The CFFI library is used to create the Python bindings.

Quick Install (MacOSX ONLY)

From libsecp256k1, make sure libsecp256k1.dylib is installed in /usr/local/lib/ via:

$ ./autogen.sh
$ ./configure --enable-module-ecdh --enable-module-recovery --enable-experimental
$ make
$ sudo make install

Install from PyPi:

$ pip install secpy256k1

Import the secpy256k1 package at the top of your python script:

import secpy256k1

Development

$ git clone git@github.com:rrybarczyk/secpy256k1.git
$ cd ./secpy256k1

Build submodule bitcoin-core libsecp256k1 repo library repo:

$ cd ./secp256k1
$ git submodule init
$ git submodule update
$ ./autogen.sh
$ ./configure --enable-module-ecdh --enable-module-recovery --enable-experimental
$ make
$ sudo make install

Install dependencies and build _secpy256k1 bindings:

$ pipenv install

Test

The tests are currently lacking. Intend to use test vectors from the libsecp256k1 library.

$ pipenv run pytest

Example File

$ pipenv run python ./secpy256k1/examples/ex_script.py

API

Functions and Context Initialzation

Barring context_create, the first argument to each function is a secp256k1_context object. The context object is initialized as SECP256K1_CONTEXT_NONE, SECP256K1_CONTEXT_VERIFY, or SECP256K1_CONTEXT_SIGN.

For functions that are context agnostic, it is customary to use SECP256K1_NONE. These functions are:

  • context_destroy Destroy a secp256k1 context object.
  • context_clone Copies a secp256k1 context object.
  • context_set_illegal_callback (TODO) Set a callback function to be called when an illegal argument is passed to an API call. It will only trigger for violations that are mentioned explicitly in the header.
  • context_set_error_callback (TODO) Set a callback function to be called when an internal consistency check fails. The default is crashing.
  • scratch_space_create (TODO) Create a secp256k1 scratch space object.
  • ec_pubkey_parse Parse a variable-length public key into the pubkey object.
  • ec_pubkey_serialize Serialize a pubkey object into a serialized byte sequence.
  • ecdsa_signature_parse_compact Parse an ECDSA signature in compact (64 bytes) format.
  • ecdsa_signature_parse_der Parse a DER ECDSA signature.
  • ecdsa_signature_serialize_der Serialize an ECDSA signature in DER format.
  • ecdsa_signature_serialize_compact Serialize an ECDSA signature in compact (64 byte) format.
  • ecdsa_signature_normalize Convert a signature to a normalized lower-S form.
  • ec_seckey_verify Verify an ECDSA secret key.
  • ec_privkey_negate Negates a private key in place.
  • ec_pubkey_negate Negates a public key in place.
  • ec_privkey_tweak_add Tweak a private key by adding tweak to it.
  • ec_privkey_tweak_mul Tweak a private key by multiplying it by a tweak.
  • ec_pubkey_combine Add a number of public keys together.

The functions that require the context to be initialized to SECP256K1_CONTEXT_VERIFY are:

  • ecdsa_verify Verify an ECDSA signature.
  • ec_pubkey_tweak_add Tweak a public key by adding tweak times the generator to it.
  • ec_pubkey_tweak_mul Tweak a public key by multiplying it by a tweak value.

The functions that require the context to be initialized as SECP256K1_CONTEXT_SIGN are:

  • ecdsa_sign Create an ECDSA signature.
  • ec_pubkey_create Compute the public key for a secret key.
  • context_randomize Updates the context randomization to protect against side-channel leakage.

Set the context flag

# Set verify flag
flags = secpy256k1.lib.SECP256K1_CONTEXT_VERIFY

# Set sign flag
flags = secpy256k1.lib.SECP256K1_CONTEXT_SIGN

# Set none flag
flags = secpy256k1.lib.SECP256K1_CONTEXT_NONE

Initialize the context object

secp256k1_ctx = secpy256k1.context_create(flags)

Clone the context object

secp256k1_ctx_clone = secpy256k1.context_clone(secp256k1_ctx)

Destroy the context object

secp256k1_ctx_destroy = secpy256k1.context_destroy(secp256k1_ctx)

Update context randomization to protect against side-channel leakage

Call this function after secpy256k1.context_create or secpy256k1.context_clone and may call this repeatedly afterwards.

import os
seed32 = os.urandom(32)
func_res = secpy256k1.context_randomize(ctx=secp256k1_ctx, seed32)

Pubkey

Public key flags:

  1. SECP256K1_COMPRESSED - flags a 33-byte compressed pubkey
  2. SECP256K1_UNCOMPRESSED - flags a 65-byte uncompressed pubkey

Set pubkey compression flag:

# Set compressed pubkey flag
pubkey = bytes.fromhex('0250863ad64a87ae8a2fe83c1af1a8403cb53f53e486d8511dad8a04887e5b2352')
compression_flag = secpy256k1.lib.SECP256K1_COMPRESSED

# Set uncompressed pubkey flag
pubkey = bytes.fromhex('0479be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8')
compression_flag = secpy256k1.lib.SECP256K1_UNCOMPRESSED

Create a pointer to a secp256k1_pubkey object from a compressed or uncompressed serialized pubkey byte string:

pk_valid, secp256k1_pk = secpy256k1.ec_pubkey_parse(secp256k1_ctx, pubkey)

Serialize secp256k1_pubkey object into a serialized pubkey byte string:

# Set compression flag
compression_flag = secpy256k1.lib.SECP256k1_EC_COMPRESSED

pubkey_valid, pubkey, pubkey_len = secpy256k1.ec_pubkey_serialize(secp256k1_ctx, secp256k1_pk, compression_flag

Create a pointer to a secp26k1_pubkey object containing the corresponding public key to a given private key:

import os
priv_key = os.urandom(32)
func_ret, secp256k1_pubkey = secpy256k1.ec_pubkey_create(ctx=secp256k1_ctx, seckey=priv_key)

Negate public key:

TODO -> ec_pubkey_negate(ctx=secp256k1_ctx, pubkey=secp256k1_pubkey)

Negate private key:

TODO -> ec_privkey_negate(ctx=secp256k1_ctx, seckey=priv_key)

Add a number of public keys together:

pubkeys = [pubkey1, pubkey2, pubkey3]
func_ret, secp256k1_pubkey = secpy256k1.ec_pubkey_combine(ctx=secp256k1_ctx, pubkeys=pubkeys)

Signing (TODO)

  1. ecdsa_signature_parse_compact
  2. ecdsa_signature_parse_der
  3. ecdsa_signature_serialize_der
  4. ecdsa_signature_serialize_compact
  5. ecdsa_verify
  6. ecdsa_signature_normalize
  7. ecdsa_sign
  8. ec_seckey_verify

Tweaking

Define a tweak:

import os
tweak = os.urandom(32)

Tweak a secp256k1_pubkey object by adding tweak times the generator to it:

func_ret, secp256k1_pubkey_tweaked = secpy256k1.ec_pubkey_tweak_add(ctx=secp256k1_ctx, pubkey=secp256k1_pubkey, tweak=tweak)

Tweak a private key by adding tweak times the generator to it:

func_ret, priv_key_tweaked = secpy256k1.ec_privkey_tweak_add(ctx=secp256k1_ctx, seckey=priv_key, tweak=tweak)

Tweak a secp256k1_pubkey object by multiplying tweak by a tweak value:

func_ret, secp256k1_pubkey_tweaked = secpy256k1.ec_pubkey_tweak_mul(ctx=secp256k1_ctx, pubkey=secp256k1_pubkey, tweak=tweak)

Tweak a private key by multiplying tweak it by a tweak value:

func_ret, priv_key_tweaked = secpy256k1.ec_privkey_tweak_mul(ctx=secp256k1_ctx, seckey=priv_key, tweak=tweak)

EC Diffie-Hellman

Compute an ECDH secret in constant time:

func_ret, ecdh_secret = secpy256k1.ecdh(ctx=secp256k1_ctx, pubkey=secp256k1_pubkey, privkey=priv_key)