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Cross-platform Python CFFI bindings for libsecp256k1
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README.rst

Coincurve

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This library provides well-tested Python CFFI bindings for libsecp256k1, the heavily optimized C library used by Bitcoin Core for operations on elliptic curve secp256k1.

Table of Contents

Features

  • Fastest available implementation (more than 10x faster than OpenSSL)
  • Clean, easy to use API
  • Frequent updates from libsecp256k1 master
  • Linux, macOS, and Windows all have binary packages for both 64 and 32-bit architectures
  • Linux & macOS use GMP for faster computation
  • Deterministic signatures via RFC 6979
  • Non-malleable signatures (lower-S form) by default
  • Secure, non-malleable ECDH implementation
  • Implements a fix for https://bugs.python.org/issue28150 to support Python 3.6+ on macOS

Users

Installation

Coincurve is distributed on PyPI and is available on Linux/macOS and Windows and supports Python 2.7/3.5+ and PyPy3.5-v5.8.1+.

$ pip install coincurve

If you are on a system that doesn't have a precompiled binary wheel (e.g. FreeBSD) then pip will fetch source to build yourself. You must have the necessary packages.

On Debian/Ubuntu for example the necessary packages are:

  • build-essential
  • automake
  • pkg-config
  • libtool
  • libffi-dev
  • libgmp-dev

API

Coincurve provides a simple API.

coincurve.verify_signature

verify_signature(signature, message, public_key, hasher=sha256, context=GLOBAL_CONTEXT)

Verifies some message was signed by the owner of a public key.

  • Parameters:

    • signature (bytes) - The signature to verify.
    • message (bytes) - The message that was supposedly signed.
    • public_key (bytes) - A public key in compressed or uncompressed form.
    • hasher - The hash function to use, can be None. hasher(message) must return 32 bytes.
    • context (coincurve.Context)
  • Returns: bool

coincurve.PrivateKey

All instances have a public_key of type coincurve.PublicKey

PrivateKey(secret=None, context=GLOBAL_CONTEXT)

  • Parameters:

    • secret (bytes) - The secret to use.
    • context (coincurve.Context)

Methods:

classmethod from_hex(hexed, context=GLOBAL_CONTEXT)

classmethod from_int(num, context=GLOBAL_CONTEXT)

classmethod from_pem(pem, context=GLOBAL_CONTEXT)

classmethod from_der(der, context=GLOBAL_CONTEXT)

sign(message, hasher=sha256, custom_nonce=None)

  • Parameters:

    • message (bytes) - The message to sign.
    • hasher - The hash function to use, can be None. hasher(message) must return 32 bytes.
    • custom_nonce - A tuple of arity 2 in the form of (nonce_fn, nonce_data). Refer to: secp256k1.h
  • Returns: bytes. 68 <= len(signature) <= 71

sign_recoverable(message, hasher=sha256)

  • Parameters:

    • message (bytes) - The message to sign.
    • hasher - The hash function to use, can be None. hasher(message) must return 32 bytes.
  • Returns: bytes

ecdh(public_key)

Computes a Diffie-Hellman secret in constant time. Note: This prevents malleability by returning sha256(x) instead of the x coordinate directly. See https://github.com/ofek/coincurve/issues/9.

  • Parameters:

    • public_key (bytes) - Another party's public key in compressed or uncompressed form.
  • Returns: bytes

add(scalar, update=False)

  • Parameters:

    • scalar (bytes) - The scalar to add.
    • update (bool) - If True, will update and return self.
  • Returns: coincurve.PrivateKey

multiply(scalar, update=False)

  • Parameters:

    • scalar (bytes) - The scalar to multiply.
    • update (bool) - If True, will update and return self.
  • Returns: coincurve.PrivateKey

to_hex()

to_int()

to_pem()

to_der()

coincurve.PublicKey

PublicKey(data, context=GLOBAL_CONTEXT)

  • Parameters:

    • data (bytes) - The public key in compressed or uncompressed form.
    • context (coincurve.Context)

Methods:

classmethod from_secret(secret, context=GLOBAL_CONTEXT)

classmethod from_valid_secret(secret, context=GLOBAL_CONTEXT)

classmethod from_point(x, y, context=GLOBAL_CONTEXT)

classmethod from_signature_and_message(serialized_sig, message, hasher=sha256, context=GLOBAL_CONTEXT)

classmethod combine_keys(public_keys, context=GLOBAL_CONTEXT)

  • Parameters:

    • public_keys (list) - A list of coincurve.PublicKey to add.
    • context (coincurve.Context)
  • Returns: coincurve.PublicKey

format(compressed=True)

  • Parameters:

    • compressed (bool)
  • Returns: The public key serialized to bytes.

point()

  • Returns: (x, y)

verify(signature, message, hasher=sha256)

Verifies some message was signed by the owner of this public key.

  • Parameters:

    • signature (bytes) - The signature to verify.
    • message (bytes) - The message that was supposedly signed.
    • hasher - The hash function to use, can be None. hasher(message) must return 32 bytes.
  • Returns: bool

add(scalar, update=False)

  • Parameters:

    • scalar (bytes) - The scalar to add.
    • update (bool) - If True, will update and return self.
  • Returns: coincurve.PublicKey

multiply(scalar, update=False)

  • Parameters:

    • scalar (bytes) - The scalar to multiply.
    • update (bool) - If True, will update and return self.
  • Returns: coincurve.PublicKey

combine(public_keys, update=False)

  • Parameters:

    • public_keys (list) - A list of coincurve.PublicKey to add.
    • update (bool) - If True, will update and return self.
  • Returns: coincurve.PublicKey

License

Coincurve is distributed under the terms of both

at your option.

Credits

  • Contributors of libsecp256k1.
  • Contributors of secp256k1-py. While Coincurve is nearly a complete rewrite, much of the build system provided by ulope remains.

History

Important changes are emphasized.

9.0.0

  • Fixed wheels for macOS
  • Breaking: Drop support for 32-bit macOS

8.0.2

  • No longer package tests

8.0.0

  • New: Binary wheels for Python 3.7!
  • Changed: Binary wheels on macOS for Python 3.5 now use Homebrew Python for compilation due to new security requirements
  • Make build system support new GitHub & PyPI security requirements
  • Improvements from libsecp256k1 master

7.1.0

  • Pin version of libsecp256k1
  • Improve docs

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