Add test vectors for ECDH x963 style with KDF x963 (#9)

Tests/K1Tests/TestCases/ECDH/ECDH_X963_Tests.swift

@@ -0,0 +1,60 @@
+import Foundation
+@testable import K1
+import CryptoKit
+import XCTest
+
+private struct Vector: Codable {
+    let alicePrivateKey: String
+    let bobPrivateKey: String
+    let alicePublicKeyUncompressed: String
+    let bobPublicKeyUncompressed: String
+    let ecdhSharedKey: String
+    let x963KDFOutput: String
+}
+
+private struct ECDHX963Suite: Codable {
+    let vectors: [Vector]
+}
+
+
+final class ECDH_X963_Tests: XCTestCase {
+
+    func testECDH_X963_vectors() throws {
+        let fileURL = Bundle.module.url(forResource: "ecdh_secp256k1_x963_test", withExtension: ".json")
+        let data = try Data(contentsOf: fileURL!)
+        let suite = try JSONDecoder().decode(ECDHX963Suite.self, from: data)
+        try suite.vectors.forEach(doTest)
+    }
+}
+
+extension ECDH_X963_Tests {
+
+    fileprivate func doTest(_ vector: Vector) throws {
+        let alice = try PrivateKey(hex: vector.alicePrivateKey)
+        let bob = try PrivateKey(hex: vector.bobPrivateKey)
+        try XCTAssertEqual(alice.publicKey.rawRepresentation(format: .uncompressed).hex, vector.alicePublicKeyUncompressed)
+        try XCTAssertEqual(bob.publicKey.rawRepresentation(format: .uncompressed).hex, vector.bobPublicKeyUncompressed)
+
+        let ab = try alice.sharedSecretFromKeyAgreement(with: bob.publicKey)
+        let ba = try bob.sharedSecretFromKeyAgreement(with: alice.publicKey)
+        XCTAssertEqual(ab, ba, "Alice and Bob should be able to agree on the same secret")
+
+        let sharedSecretData = ab.withUnsafeBytes {
+            Data($0)
+        }
+        XCTAssertEqual(sharedSecretData.hex, vector.ecdhSharedKey)
+
+        let ab_x963 = ab.x963DerivedSymmetricKey(using: SHA256.self, sharedInfo: Data(), outputByteCount: 32)
+        let ba_x963 = ba.x963DerivedSymmetricKey(using: SHA256.self, sharedInfo: Data(), outputByteCount: 32)
+
+        XCTAssertEqual(ab_x963, ba_x963, "KDF between secrets should be the same")
+
+        let x963Data = ab_x963.withUnsafeBytes {
+            Data($0)
+        }
+        XCTAssertEqual(x963Data.hex, vector.x963KDFOutput)
+    }
+
+
+
+}