fltrECC

Swift wrapper for Bitcoin Core secp256k1 or libsecp256k1

fltrWallet

This package is used for elliptic curve encryption in fltrWallet for Apple devices.

Using

Swift Package Manager (SPM) is supported. Add a reference to your Package.swift file under

dependencies: [
    ...
    .package(url: "https://github.com/fltrWallet/fltrECC", .branch("main")),
    ...
],

Scalar and Point

The most primitive constructs for doing ECC (elliptic curve cryptography). Scalars can be used to instantiate secret keys while Points create public key.

The major difference here between secret keys and scalars (and public keys and points) are that many unsafe operations can be performed directly on Scalars and Points.

For example

let first = Scalar.random()
let second = Scalar.random()
let third = first * second + first

This requires significant understanding of elliptic curve arithmatic but is none the less essential in creating libraries for generating private keys, such as BIP32.

Optional results

Addition resulting in infinity is statistically next to impossible in its frequency. Some libraries (rightly) treat such occurence as less likely than hardware error. Meaning they wont even check for their occurence. Since Swift is such a handy language at treating optionals, we have gone for the most conservative interpretation of such operations. Consider the following example:

let a = Scalar.random()
let b = Scalar.random()
guard let x = a + b else { throw Infinity() }

There is this theoretical chance that the addition results in x = 0, which is not within the domain of elliptic curve operations.

SecretKey and PublicKey

There are two sets of secret and public keys. One set starting with DSA for the old way of encoding, decoding and encrypting. Schnorr signatures and their updated encoding are implemented under the X prefix. Operations for recoverable signatures and diffie hellman secret sharing are only available in the DSA types.

fltrECCTesting

There is a testing library to simplify writing unit tests or integration tests where ECC types are needed. It provides for numerical types instead of its formal counterparts. Let us have a look at an example explaining its use:

import fltrECC
import fltrECCTesting

let scalar: Scalar = 12
let publicKey = X.PublicKey(15)

This would be highly dangerous in proper code but very useful in unit tests where the added expressivity makes for easier to read tests.

fltrECCAdapter

This is the lowest level module that can be imported if you only want assistance in wrapping the libsecp256k1 library. It lives under the C namespaces such as C.negate(into: scalar).

Attribution

This project fltrBtc includes libsecp256k1 of Bitcoin Core, under the following license:

Copyright (c) 2013 Pieter Wuille

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

fltrWallet / fltrECC