Coincurve

Python CFFI bindings for libsecp256k1 (an experimental and optimized C library for EC operations on curve secp256k1).

This is a fork of https://github.com/ludbb/secp256k1-py.

New features include:

• Support for Windows (Python 3 only though, unlike Linux/macOS)
• Linux, macOS, and Windows all have binary packages for both 64 and 32-bit architectures
• A fix to remove CFFI warnings
• A global context is used by default, drastically increasing performance
• Each release uses newest version of libsecp256k1
• Implements a fix for https://bugs.python.org/issue28150 to support Python 3.6+ on macOS
• Linux & macOS wheels now use GMP
• Endomorphism optimization is now enabled

To retain backward compatibility with secp256k1-py, use coincurve version 2.1.1 specifically! Anything after that will have a modified (cleaner :) API and only support Python 3.

Installation

pip install coincurve==2.1.1

Precompiled binary packages (wheels)

Precompiled binary wheels is available for Python 2.7, 3.3, 3.4, and 3.5 on Linux. To take advantage of those you need to use pip >= 8.1.0.

API

class coincurve.PrivateKey(privkey, raw, flags)

The PrivateKey class loads or creates a private key by obtaining 32 bytes from urandom and operates over it.

Instantiation parameters

• privkey=None - generate a new private key if None, otherwise load a private key.
• raw=True - if True, it is assumed that privkey is just a sequence of bytes, otherwise it is assumed that it is in the DER format. This is not used when privkey is not specified.
• flags=coincurve.ALL_FLAGS - see Constants.

Methods and instance attributes

• pubkey: an instance of coincurve.PublicKey.

• private_key: raw bytes for the private key.

• set_raw_privkey(privkey)
  update the private_key for this instance with the bytes specified by privkey. If privkey is invalid, an Exception is raised. The pubkey is also updated based on the new private key.

• serialize() -> bytes
  convert the raw bytes present in private key to a hexadecimal string.

• deserialize(privkey_ser) -> bytes
  convert from a hexadecimal string to raw bytes and update the pubkey and private_key for this instance.

• tweak_add(scalar) -> bytes
  tweak the current private key by adding a 32 byte scalar to it and return a new raw private key composed of 32 bytes.

• tweak_mul(scalar) -> bytes
  tweak the current private key by multiplying it by a 32 byte scalar and return a new raw private key composed of 32 bytes.

• ecdsa_sign(msg, raw=False, digest=hashlib.sha256) -> internal object
  by default, create an ECDSA-SHA256 signature from the bytes in msg. If raw is True, then the digest function is not applied over msg, otherwise the digest must produce 256 bits or an Exception will be raised.
  
  The returned object is a structure from the C lib. If you want to store it (on a disk or similar), use ecdsa_serialize and later on use ecdsa_deserialize when loading.

• ecdsa_sign_recoverable(msg, raw=False, digest=hashlib.sha256) -> internal object
  create a recoverable ECDSA signature. See ecdsa_sign for parameters description.

NOTE: ecdsa_sign_recoverable can only be used if the secp256k1 C library is compiled with support for it. If there is no support, an Exception will be raised when calling it.

• schnorr_sign(msg, raw=False, digest=hashlib.sha256) -> bytes
  create a signature using a custom EC-Schnorr-SHA256 construction. It produces non-malleable 64-byte signatures which support public key recovery batch validation, and multiparty signing. msg, raw, and digest are used as described in ecdsa_sign.

• schnorr_generate_nonce_pair(msg, raw=False, digest=hashlib.sha256) -> (internal object, internal object)
  generate a nonce pair deterministically for use with schnorr_partial_sign. msg, raw, and digest are used as described in ecdsa_sign.

• schnorr_partial_sign(msg, privnonce, pubnonce_others, raw=False, digest=hashlib.sha256) -> bytes
  produce a partial Schnorr signature, which can be combined using schnorr_partial_combine to end up with a full signature that is verifiable using PublicKey.schnorr_verify. privnonce is the second item in the tuple returned by schnorr_generate_nonce_pair, pubnonce_others represent the combined public nonces excluding the one associated to this privnonce. msg, raw, and digest are used as described in ecdsa_sign.
  
  To combine pubnonces, use PublicKey.combine.
  
  Do not pass the pubnonce produced for the respective privnonce; combine the pubnonces from other signers and pass that instead.

class coincurve.PublicKey(pubkey, raw, flags)

The PublicKey class loads an existing public key and operates over it.

Instantiation parameters

• pubkey=None - do not load a public key if None, otherwise do.
• raw=False - if False, it is assumed that pubkey has gone through PublicKey.deserialize already, otherwise it must be specified as bytes.
• flags=coincurve.FLAG_VERIFY - see Constants.

Methods and instance attributes

• public_key: an internal object representing the public key.

• serialize(compressed=True) -> bytes
  convert the public_key to bytes. If compressed is True, 33 bytes will be produced, otherwise 65 will be.

• deserialize(pubkey_ser) -> internal object
  convert the bytes resulting from a previous serialize call back to an internal object and update the public_key for this instance. The length of pubkey_ser determines if it was serialized with compressed=True or not. This will raise an Exception if the size is invalid or if the key is invalid.

• combine(pubkeys) -> internal object
  combine multiple public keys (those returned from PublicKey.deserialize) and return a public key (which can be serialized as any other regular public key). The public_key for this instance is updated to use the resulting combined key. If it is not possible the combine the keys, an Exception is raised.

• tweak_add(scalar) -> internal object
  tweak the current public key by adding a 32 byte scalar times the generator to it and return a new PublicKey instance.

• tweak_mul(scalar) -> internal object
  tweak the current public key by multiplying it by a 32 byte scalar and return a new PublicKey instance.

• ecdsa_verify(msg, raw_sig, raw=False, digest=hashlib.sha256) -> bool
  verify an ECDSA signature and return True if the signature is correct, False otherwise. raw_sig is expected to be an object returned from ecdsa_sign (or if it was serialized using ecdsa_serialize, then first run it through ecdsa_deserialize). msg, raw, and digest are used as described in ecdsa_sign.

• schnorr_verify(msg, schnorr_sig, raw=False, digest=hashlib.sha256) -> bool
  verify a Schnorr signature and return True if the signature is correct, False otherwise. schnorr_sig is expected to be the result from either schnorr_partial_combine or schnorr_sign. msg, raw, and digest are used as described in ecdsa_sign.

• ecdh(scalar) -> bytes
  compute an EC Diffie-Hellman secret in constant time. The instance public_key is used as the public point, and the scalar specified must be composed of 32 bytes. It outputs 32 bytes representing the ECDH secret computed. If the scalar is invalid, an Exception is raised.

NOTE: ecdh can only be used if the secp256k1 C library is compiled with support for it. If there is no support, an Exception will be raised when calling it.

class coincurve.ECDSA

The ECDSA class is intended to be used as a mix in. Its methods can be accessed from any coincurve.PrivateKey or coincurve.PublicKey instances.

Methods

• ecdsa_serialize(raw_sig) -> bytes
  convert the result from ecdsa_sign to DER.

• ecdsa_deserialie(ser_sig) -> internal object
  convert DER bytes to an internal object.

• ecdsa_serialize_compact(raw_sig) -> bytes
  convert the result from ecdsa_sign to a compact serialization of 64 bytes.

• ecdsa_deserialize_compact(ser_sig) -> internal object
  convert a compact serialization of 64 bytes to an internal object.

• ecdsa_signature_normalize(raw_sig, check_only=False) -> (bool, internal object | None)
  check and optionally convert a signature to a normalized lower-S form. If check_only is True then the normalized signature is not returned.
  
  This function always return a tuple containing a boolean (True if not previously normalized or False if signature was already normalized), and the normalized signature. When check_only is True, the normalized signature returned is always None.

• ecdsa_recover(msg, recover_sig, raw=False, digest=hashlib.sha256) -> internal object
  recover an ECDSA public key from a signature generated by ecdsa_sign_recoverable. recover_sig is expected to be an object returned from ecdsa_sign_recoverable (or if it was serialized using ecdsa_recoverable_serialize, then first run it through ecdsa_recoverable_deserialize). msg, raw, and digest are used as described in ecdsa_sign.
  
  In order to call ecdsa_recover from a PublicKey instance, it's necessary to create the instance by settings flags to ALL_FLAGS: coincurve.PublicKey(..., flags=coincurve.ALL_FLAGS).

• ecdsa_recoverable_serialize(recover_sig) -> (bytes, int)
  convert the result from ecdsa_sign_recoverable to a tuple composed of 65 bytesand an integer denominated as recovery id.

• ecdsa_recoverable_deserialize(ser_sig, rec_id)-> internal object
  convert the result from ecdsa_recoverable_serialize back to an internal object that can be used by ecdsa_recover.

• ecdsa_recoverable_convert(recover_sig) -> internal object
  convert a recoverable signature to a normal signature, i.e. one that can be used by ecdsa_serialize and related methods.

NOTE: ecdsa_recover* can only be used if the secp256k1 C library is compiled with support for it. If there is no support, an Exception will be raised when calling any of them.

Constants

coincurve.FLAG_SIGN

coincurve.FLAG_VERIFY

coincurve.ALL_FLAGS

ALL_FLAGS combines FLAG_SIGN and FLAG_VERIFY using bitwise OR.

These flags are used during context creation (undocumented here) and affect which parts of the context are initialized in the C library. In these bindings, some calls are disabled depending on the active flags but this should not be noticeable unless you are manually specifying flags.

Example

from coincurve import PrivateKey, PublicKey

privkey = PrivateKey()
privkey_der = privkey.serialize()
assert privkey.deserialize(privkey_der) == privkey.private_key

sig = privkey.ecdsa_sign(b'hello')
verified = privkey.pubkey.ecdsa_verify(b'hello', sig)
assert verified

sig_der = privkey.ecdsa_serialize(sig)
sig2 = privkey.ecdsa_deserialize(sig_der)
vrf2 = privkey.pubkey.ecdsa_verify(b'hello', sig2)
assert vrf2

pubkey = privkey.pubkey
pub = pubkey.serialize()

pubkey2 = PublicKey(pub, raw=True)
assert pubkey2.serialize() == pub
assert pubkey2.ecdsa_verify(b'hello', sig)

from coincurve import PrivateKey

key = '31a84594060e103f5a63eb742bd46cf5f5900d8406e2726dedfc61c7cf43ebad'
msg = '9e5755ec2f328cc8635a55415d0e9a09c2b6f2c9b0343c945fbbfe08247a4cbe'
sig = '30440220132382ca59240c2e14ee7ff61d90fc63276325f4cbe8169fc53ade4a407c2fc802204d86fbe3bde6975dd5a91fdc95ad6544dcdf0dab206f02224ce7e2b151bd82ab'

privkey = PrivateKey(bytes(bytearray.fromhex(key)), raw=True)
sig_check = privkey.ecdsa_sign(bytes(bytearray.fromhex(msg)), raw=True)
sig_ser = privkey.ecdsa_serialize(sig_check)

assert sig_ser == bytes(bytearray.fromhex(sig))

from coincurve import PrivateKey

key = '7ccca75d019dbae79ac4266501578684ee64eeb3c9212105f7a3bdc0ddb0f27e'
pub_compressed = '03e9a06e539d6bf5cf1ca5c41b59121fa3df07a338322405a312c67b6349a707e9'
pub_uncompressed = '04e9a06e539d6bf5cf1ca5c41b59121fa3df07a338322405a312c67b6349a707e94c181c5fe89306493dd5677143a329065606740ee58b873e01642228a09ecf9d'

privkey = PrivateKey(bytes(bytearray.fromhex(key)))
pubkey_ser = privkey.pubkey.serialize()
pubkey_ser_uncompressed = privkey.pubkey.serialize(compressed=False)

assert pubkey_ser == bytes(bytearray.fromhex(pub_compressed))
assert pubkey_ser_uncompressed == bytes(bytearray.fromhex(pub_uncompressed))