Swiftpack.co - leif-ibsen/SwiftEdDSA as Swift Package

SwiftEdDSA

Contents:

• Usage
• Creating New Keys
• Loading Existing Keys
• Sign and Verify
• CryptoKit Compatibility
• Performance
• Dependencies
• References

SwiftEdDSA implements the EdDSA digital signature algorithm as defined in RFC 8032. It is based on the Edwards 25519 and Edwards 448 elliptic curves. SwiftEdDSA has functionality to create public and private keys, to sign messages, and to verify signatures.

Usage

In your project Package.swift file add a dependency like

  dependencies: [
  .package(url: "https://github.com/leif-ibsen/SwiftEdDSA", from: "2.2.0"),
  ]

Creating New Keys

To create a new private key instance

// Curve Ed25519 let privKey = PrivateKey(kind: .ed25519)

// Curve Ed448
let privKey = PrivateKey(kind: .ed448)

To create a new key pair

// Curve Ed25519 key pair let (pubKey, privKey) = Ed.makeKeyPair(kind: .ed25519)

// Curve Ed448 key pair
let (pubKey, privKey) = Ed.makeKeyPair(kind: .ed448)

Loading Existing Keys

To load keys from their PEM encoding

let pubPEM = """ -----BEGIN PUBLIC KEY----- MCowBQYDK2VwAyEA59XU+uLDn3fVTDfLZXJnITqbYoPwxSjfUehk8/E9stI= -----END PUBLIC KEY----- """ let privPEM = """ -----BEGIN PRIVATE KEY----- MC4CAQAwBQYDK2VwBCIEIHZN8jGTAPTSZoZO9PWDhTgRDrO5Q6cW1IWCxcsmoZ7X -----END PRIVATE KEY----- """

let pub = try PublicKey(pem: pubPEM)
let priv = try PrivateKey(pem: privPEM)

print(pub)
print(priv)

giving:

Sequence (2):
  Sequence (1):
    Object Identifier: 1.3.101.112
  Bit String (256): 11100111 11010101 11010100 11111010 11100010 11000011 10011111 01110111 11010101 01001100 00110111 11001011 01100101 01110010 01100111 00100001 00111010 10011011 01100010 10000011 11110000 11000101 00101000 11011111 01010001 11101000 01100100 11110011 11110001 00111101 10110010 11010010

Sequence (3):
  Integer: 0
  Sequence (1):
    Object Identifier: 1.3.101.112
  Octet String (34): 04 20 76 4d f2 31 93 00 f4 d2 66 86 4e f4 f5 83 85 38 11 0e b3 b9 43 a7 16 d4 85 82 c5 cb 26 a1 9e d7

To create a public key corresponding to a private key

let pubKey = PublicKey(privateKey: privKey)

Sign and Verify

To sign and verify a message

let pubPEM =
"""
-----BEGIN PUBLIC KEY-----
MCowBQYDK2VwAyEA59XU+uLDn3fVTDfLZXJnITqbYoPwxSjfUehk8/E9stI=
-----END PUBLIC KEY-----
"""
let privPEM =
"""
-----BEGIN PRIVATE KEY-----
MC4CAQAwBQYDK2VwBCIEIHZN8jGTAPTSZoZO9PWDhTgRDrO5Q6cW1IWCxcsmoZ7X
-----END PRIVATE KEY-----
"""

let pubKey = try PublicKey(pem: pubPEM)
let privKey = try PrivateKey(pem: privPEM)

let msg = Bytes("Hi, there".utf8)
let sig = try privKey.sign(message: msg)
print("Verified:", pubKey.verify(signature: sig, message: msg))

giving:

Verified: true

Compatibility with Apple's CryptoKit Framework

SwiftEdDSA keys of kind *.ed25519* corresponds to CryptoKit's *Curve25519* keys. Keys of kind *.ed448* is not supported in CryptoKit.

To convert SwiftEdDSA keys - say edPriv and edPub to corresponding CryptoKit keys:

let ckPriv = try CryptoKit.Curve25519.Signing.PrivateKey(rawRepresentation: edPriv.s)
let ckPub = try CryptoKit.Curve25519.Signing.PublicKey(rawRepresentation: edPub.r)

To convert CryptoKit keys - say ckPriv and ckPub to corresponding SwiftEdDSA keys:

let edPriv = try PrivateKey(s: Bytes(ckPriv.rawRepresentation))
let edPub = try PublicKey(r: Bytes(ckPub.rawRepresentation))

Performance

The signature generation and verification time for a short message and the time it takes to generate a new private key and to generate a public key from its private key was measured on an iMac 2021, Apple M1 chip. The results are shown below:

Operation	Ed25519	Ed448
Sign	0.8 mSec	2.1 mSec
Verify	1.1 mSec	3.0 mSec
Public Key Generation	2.8 mSec	6.6 mSec
Private Key Generation	0.67 uSec	0.61 uSec

The public key constructor computes and caches information that subsequently speed-up signature verification. If the same public key is to be used for many signature verifications, it is more efficient to use the same key instance for all verifications, rather than generate a new instance for each verification.

Dependencies

SwiftEdDSA requires Swift 5.0.

The SwiftEdDSA package depends on the ASN1 and BigInt packages

dependencies: [
    .package(url: "https://github.com/leif-ibsen/ASN1", from: "2.1.0"),
    .package(url: "https://github.com/leif-ibsen/BigInt", from: "1.13.0"),
],

References

Algorithms from the following books and papers have been used in the implementation. There are references in the source code where appropriate.

• [GUIDE] - Hankerson, Menezes, Vanstone: Guide to Elliptic Curve Cryptography. Springer 2004
• [RFC-8032] - Edwards-Curve Digital Signature Algorithm (EdDSA), January 2017