How to sign and verify with ML-DSA-65 in Swift

1// swift-tools-version:6.2
2import PackageDescription
3 
4let package = Package(
5    name: "howto",
6    platforms: [.macOS(.v15)],
7    dependencies: [
8        .package(url: "https://github.com/apple/swift-crypto.git", exact: "5.0.3"),
9        .package(url: "https://github.com/apple/swift-asn1.git", exact: "1.7.3"),
10    ],
11    targets: [
12        .executableTarget(
13            name: "mldsa",
14            dependencies: [
15                .product(name: "Crypto", package: "swift-crypto"),
16                .product(name: "SwiftASN1", package: "swift-asn1"),
17            ]
18        ),
19    ]
20)
21 

1import Crypto // CryptoKit's MLDSA65 API (iOS 26 / macOS 26), also on Linux via swift-crypto
2import Foundation
3 
4func signAndVerify() throws {
5    let privateKey = try MLDSA65.PrivateKey()
6    let publicKey = privateKey.publicKey
7    let message = Data("hello, post-quantum world".utf8)
8 
9    let signature = try privateKey.signature(for: message) // randomized (hedged) signing
10    print("public key \(publicKey.rawRepresentation.count) bytes, signature \(signature.count) bytes")
11    print("verified: \(publicKey.isValidSignature(signature, for: message))")
12    print("tampered message: \(publicKey.isValidSignature(signature, for: Data("hello, post-quantum world!".utf8)))")
13 
14    let context = Data("invoice-v1".utf8)
15    let invoiceSignature = try privateKey.signature(for: message, context: context)
16    print("with the context: \(publicKey.isValidSignature(invoiceSignature, for: message, context: context)), without: \(publicKey.isValidSignature(invoiceSignature, for: message))")
17}
18 

1import Crypto
2import SwiftASN1
3 
4/// An ML-DSA-65 public key from an SPKI ("BEGIN PUBLIC KEY") PEM, e.g. written by OpenSSL 3.5.
5/// CryptoKit takes the raw 1952-byte key, so unwrap the SubjectPublicKeyInfo first.
6func publicKey(fromSPKIPEM pem: String) throws -> MLDSA65.PublicKey {
7    let document = try PEMDocument(pemString: pem)
8    guard document.discriminator == "PUBLIC KEY" else { throw ASN1Error.invalidPEMDocument(reason: "not a PUBLIC KEY") }
9    let root = try DER.parse(document.derBytes)
10    guard case .constructed(let nodes) = root.content else { throw ASN1Error.invalidASN1Object(reason: "SPKI is not a SEQUENCE") }
11    var children = nodes.makeIterator()
12    guard let algorithm = children.next(), let key = children.next(),
13          case .constructed(let algorithmNodes) = algorithm.content,
14          let oidNode = algorithmNodes.first(where: { _ in true }) else {
15        throw ASN1Error.invalidASN1Object(reason: "malformed SubjectPublicKeyInfo")
16    }
17    let oid = try ASN1ObjectIdentifier(derEncoded: oidNode)
18    guard oid == [2, 16, 840, 1, 101, 3, 4, 3, 18] else { // id-ml-dsa-65 (RFC 9881)
19        throw ASN1Error.invalidASN1Object(reason: "not an ML-DSA-65 key: \(oid)")
20    }
21    let bits = try ASN1BitString(derEncoded: key)
22    return try MLDSA65.PublicKey(rawRepresentation: bits.bytes)
23}
24