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test(kas): fix stale unwrapKey HKDF salt round-trip test #40

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test(kas): fix stale unwrapKey HKDF salt round-trip test #40

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53 changes: 36 additions & 17 deletions OpenTDFKitTests/KASRewrapClientTests.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -29,13 +29,13 @@ final class KASRewrapClientTests: XCTestCase {
let components = jwt.split(separator: ".")
XCTAssertEqual(components.count, 3, "JWT should have 3 parts: header.payload.signature")

let headerData = Data(base64URLDecoded: String(components[0]))!
let header = try JSONSerialization.jsonObject(with: headerData) as! [String: String]
let headerData = try XCTUnwrap(Data(base64URLDecoded: String(components[0])))
let header = try XCTUnwrap(try JSONSerialization.jsonObject(with: headerData) as? [String: String])
XCTAssertEqual(header["alg"], "ES256")
XCTAssertEqual(header["typ"], "JWT")

let payloadData = Data(base64URLDecoded: String(components[1]))!
let payload = try JSONSerialization.jsonObject(with: payloadData) as! [String: Any]
let payloadData = try XCTUnwrap(Data(base64URLDecoded: String(components[1])))
let payload = try XCTUnwrap(try JSONSerialization.jsonObject(with: payloadData) as? [String: Any])
XCTAssertNotNil(payload["requestBody"])
XCTAssertNotNil(payload["iat"])
XCTAssertNotNil(payload["exp"])
Expand All @@ -49,7 +49,7 @@ final class KASRewrapClientTests: XCTestCase {

let components = jwt.split(separator: ".")
let signingInput = "\(components[0]).\(components[1])".data(using: .utf8)!
let signatureData = Data(base64URLDecoded: String(components[2]))!
let signatureData = try XCTUnwrap(Data(base64URLDecoded: String(components[2])))

let signature = try P256.Signing.ECDSASignature(rawRepresentation: signatureData)
let publicKey = signingKey.publicKey
Expand All @@ -64,11 +64,11 @@ final class KASRewrapClientTests: XCTestCase {
let jwt = try client.createSignedJWT(requestBody: requestBody, signingKey: signingKey)

let components = jwt.split(separator: ".")
let payloadData = Data(base64URLDecoded: String(components[1]))!
let payload = try JSONSerialization.jsonObject(with: payloadData) as! [String: Any]
let payloadData = try XCTUnwrap(Data(base64URLDecoded: String(components[1])))
let payload = try XCTUnwrap(try JSONSerialization.jsonObject(with: payloadData) as? [String: Any])

let iat = payload["iat"] as! Int
let exp = payload["exp"] as! Int
let iat = try XCTUnwrap(payload["iat"] as? Int)
let exp = try XCTUnwrap(payload["exp"] as? Int)

XCTAssertEqual(exp - iat, 60, "Token should expire 60 seconds after issuance")
}
Expand Down Expand Up @@ -166,16 +166,22 @@ final class KASRewrapClientTests: XCTestCase {
}
}

func testKeyUnwrappingWithValidKeys() throws {
/// Round-trips a random 256-bit key through HKDF(`sealSalt`) → AES-GCM seal →
/// `unwrapKey(salt: unwrapSalt)` and asserts the recovered key matches.
/// The seal and unwrap salts must agree for the GCM tag to verify, mirroring
/// the KAS session-key derivation. `unwrapSalt == nil` exercises `unwrapKey`'s
/// default (NanoTDF v12 salt).
private func assertUnwrapRoundTrip(sealSalt: Data, unwrapSalt: Data?,
file: StaticString = #filePath, line: UInt = #line) throws
{
let clientPrivateKey = P256.KeyAgreement.PrivateKey()
let sessionPrivateKey = P256.KeyAgreement.PrivateKey()

let sharedSecret = try sessionPrivateKey.sharedSecretFromKeyAgreement(with: clientPrivateKey.publicKey)

// Use empty salt/info to match KAS implementation
let symmetricKey = sharedSecret.hkdfDerivedSymmetricKey(
using: SHA256.self,
salt: Data(),
salt: sealSalt,
sharedInfo: Data(),
outputByteCount: 32,
)
Expand All @@ -195,10 +201,23 @@ final class KASRewrapClientTests: XCTestCase {
wrappedKey: wrappedKey,
sessionPublicKey: sessionPrivateKey.publicKey.compressedRepresentation,
clientPrivateKey: clientPrivateKey.rawRepresentation,
salt: unwrapSalt,
)

let unwrappedKeyData = unwrappedKey.withUnsafeBytes { Data(Array($0)) }
XCTAssertEqual(unwrappedKeyData, testKeyData, "Unwrapped key should match original key")
XCTAssertEqual(unwrappedKeyData, testKeyData, "Unwrapped key should match original key",
file: file, line: line)
}

/// NanoTDF: `unwrapKey` defaults (salt == nil) to the v12 session-key salt
/// (`CryptoConstants.hkdfSalt`), matching the KAS `rewrap_dek` derivation.
func testKeyUnwrappingNanoTDFDefaultSalt() throws {
try assertUnwrapRoundTrip(sealSalt: CryptoConstants.hkdfSalt, unwrapSalt: nil)
}

/// Standard (Base) TDF: empty HKDF salt on both the seal and the unwrap.
func testKeyUnwrappingStandardTDFEmptySalt() throws {
try assertUnwrapRoundTrip(sealSalt: Data(), unwrapSalt: Data())
}

func testKeyUnwrappingWithInvalidWrappedKeyFormat() {
Expand Down Expand Up @@ -284,15 +303,15 @@ final class KASRewrapClientTests: XCTestCase {

let encoder = JSONEncoder()
let jsonData = try encoder.encode(keyAccess)
let json = try JSONSerialization.jsonObject(with: jsonData) as! [String: Any]
let json = try XCTUnwrap(try JSONSerialization.jsonObject(with: jsonData) as? [String: Any])

XCTAssertEqual(json["type"] as? String, "remote")
XCTAssertEqual(json["protocol"] as? String, "kas")
XCTAssertEqual(json["url"] as? String, "https://kas.example.com")
XCTAssertEqual(json["header"] as? String, header.base64EncodedString())
}

func testRewrapRequestEntryWithDefaultAlgorithm() throws {
func testRewrapRequestEntryWithDefaultAlgorithm() {
let policyBody = "test policy".data(using: .utf8)!
let policy = KASRewrapClient.Policy(body: policyBody.base64EncodedString())

Expand Down Expand Up @@ -329,7 +348,7 @@ final class KASRewrapClientTests: XCTestCase {
}
"""

let jsonData = jsonString.data(using: .utf8)!
let jsonData = try XCTUnwrap(jsonString.data(using: .utf8))
let decoder = JSONDecoder()
let response = try decoder.decode(KASRewrapClient.RewrapResponse.self, from: jsonData)

Expand All @@ -355,7 +374,7 @@ final class KASRewrapClientTests: XCTestCase {
}
"""

let jsonData = jsonString.data(using: .utf8)!
let jsonData = try XCTUnwrap(jsonString.data(using: .utf8))
let decoder = JSONDecoder()
let response = try decoder.decode(KASRewrapClient.RewrapResponse.self, from: jsonData)

Expand Down
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