SwiftKyber
Contents:
SwiftKyber is a Swift implementation of the proposed PQC (Post Quantum Cryptography) key encapsulation mechanism: CRYSTALS-Kyber.SwiftKyber makes it possible to explore CRYSTALS-Kyber in a Swift context.
Usage
In your project Package.swift file add a dependency like dependencies: [
.package(url: "https://github.com/leif-ibsen/SwiftKyber", from: "1.3.0"),
]
How it Works
Suppose Alice and Bob wish to share a secret key they can use as a symmetric encryption key:- Alice generates a Kyber key pair, publicKey and secretKey. She sends publicKey to Bob
- Bob runs publicKey.Encapsulate() to generate a shared secret K and a cipher text cipher
- Bob sends cipher to Alice
- Alice runs secretKey.Decapsulate(ct: cipher) to generate the same shared secret K
Here is a Kyber.K512 example:
import SwiftKyber
// Alice:
let (publicKey, secretKey) = Kyber.K512.GenerateKeyPair()
// Bob:
let (cipher, K1) = publicKey.Encapsulate()
print("Bob's K: ", K1)
// Alice:
let K2 = try secretKey.Decapsulate(ct: cipher)
print("Alice's K:", K2)
giving (for example):
Bob's K: [106, 169, 16, 187, 123, 157, 206, 223, 236, 143, 173, 180, 243, 130, 157, 122, 150, 68, 167, 31, 33, 246, 28, 150, 215, 182, 71, 72, 128, 37, 202, 17]
Alice's K: [106, 169, 16, 187, 123, 157, 206, 223, 236, 143, 173, 180, 243, 130, 157, 122, 150, 68, 167, 31, 33, 246, 28, 150, 215, 182, 71, 72, 128, 37, 202, 17]
Key Representation
SwiftKyber public and secret keys can be stored in three formats:- DER encoded - a byte array
- PEM encoded - a string
- As raw bytes
- Generate new keys
- Store existing keys in DER or PEM format or as raw bytes
- Load keys from their DER or PEM encoding or from their raw bytes
import SwiftKyber
let (pk, sk) = Kyber.K768.GenerateKeyPair()
generates a new public key pk and a new secret key sk for the K768 instance.
Keys can be stored in DER format, in PEM format or as raw bytes.
import SwiftKyber
let (pk, _) = Kyber.K512.GenerateKeyPair()
let pkDer = pk.der // The DER encoding - a byte array
let pkPem = pk.pem // The PEM encoding - a String
let pkBytes = pk.bytes // The raw bytes
let newPkFromDER = try PublicKey(der: pkDer)
let newPkFromPEM = try PublicKey(pem: pkPem)
let newPkFromRaw = try PublicKey(bytes: pkBytes)
assert(pk == newPkFromDER)
assert(pk == newPkFromPEM)
assert(pk == newPkFromRaw)
and for secret keys:
import SwiftKyber
let (_, sk) = Kyber.K512.GenerateKeyPair()
let skDer = sk.der // The DER encoding - a byte array
let skPem = sk.pem // The PEM encoding - a String
let skBytes = sk.bytes // The raw bytes
let newSkFromDER = try SecretKey(der: skDer)
let newSkFromPEM = try SecretKey(pem: skPem)
let newSkFromRaw = try SecretKey(bytes: skBytes)
assert(sk == newSkFromDER)
assert(sk == newSkFromPEM)
assert(sk == newSkFromRaw)
ASN1 reservations
The DER and PEM formats are based on the ASN1 structure of the keys. These structures are defined in [KEYS], but it is my understanding that the ASN1 representation is not settled yet: It may change, there may be no ASN1 structure at all or I may have misread [KEYS].Performance
SwiftKyber's key generation, encapsulation and decapsulation performance was measured on an iMac 2021, Apple M1 chip. The table below shows the figures in milli seconds for the three Kyber instances.| Instance | GenerateKeyPair | Encapsulate | Decapsulate |
|---|---|---|---|
| Kyber.K512 | 0.14 mSec | 0.16 mSec | 0.18 mSec |
| Kyber.K768 | 0.22 mSec | 0.25 mSec | 0.28 mSec |
| Kyber.K1024 | 0.33 mSec | 0.36 mSec | 0.40 mSec |
Dependencies
The SwiftKyber package depends on the ASN1 and BigInt packagesdependencies: [
.package(url: "https://github.com/leif-ibsen/ASN1", from: "2.2.0"),
.package(url: "https://github.com/leif-ibsen/BigInt", from: "1.14.0"),
],
SwiftKyber does not do Big Integer arithmetic, but BigInt is a dependency because ASN1 depends on it.
References
Algorithms from the following papers have been used in the implementation. There are references in the source code where appropriate.
- [KYBER] - CRYSTALS-Kyber, Algorithm Specifications And Supporting Documentation, January 2021
- [DRAFT] - Kyber Post-Quantum KEM, draft-cfrg-schwabe-kyber-03, September 2023
- [KEYS] - Quantum Safe Cryptography Key Information for CRYSTALS-Kyber, October 2022