ncryptf Swift

OS / Swift	Build Status
Linux 5.0
MacOS 5.0

A library for facilitating hashed based KDF signature authentication, and end-to-end encrypted communication with compatible API’s.

Installing

This library can be installed via Swift Package Manager by adding the following dependency

dependencies: [
    .package(url: "https://github.com/ncryptf/ncryptf-swift.git", , .upToNextMinor(from: "0.2.0")),
],

Testing

MacOS

MacOS tests run via the swift test command

swift test

Linux

Linux tests can be run either locally, or through the provided docker container

Local Testing

apt install libsodium-dev
swift test

Docker Testing

If you’re working on a platform that doesn’t support swift or XCTestCase, you run the test suite through Docker

First, build the docker image

docker build --tag ncryptf --compress --squash .

Then the tests can be run as follows:

docker run -it -v${PWD-.}:/package ncryptf swift test

HMAC+HKDF Authentication

HMAC+HKDF Authentication is an Authentication method that allows ensures the request is not tampered with in transit. This provides resiliance not only against network layer manipulation, but also man-in-the-middle attacks.

At a high level, an HMAC signature is created based upon the raw request body, the HTTP method, the URI (with query parameters, if present), and the current date. In addition to ensuring the request cannot be manipulated in transit, it also ensures that the request is timeboxed, effectively preventing replay attacks.

The library itself is made available by importing the following struct:

Supporting API’s will return the following payload containing at minimum the following information.

{
    "access_token": "7XF56VIP7ZQQOLGHM6MRIK56S2QS363ULNB5UKNFMJRQVYHQH7IA",
    "refresh_token": "7XF56VIP7ZQQOLGHM6MRIK56S2QS363ULNB5UKNFMJRQVYHQH7IA",
    "ikm": "bDEyECRvKKE8w81fX4hz/52cvHsFPMGeJ+a9fGaVvWM=",
    "signing": "7v/CdiGoEI7bcj7R2EyDPH5nrCd2+7rHYNACB+Kf2FMx405und2KenGjNpCBPv0jOiptfHJHiY3lldAQTGCdqw==",
    "expires_at": 1472678411
}

After extracting the elements, we can create signed request by doing the following:

let auth = try? Authorization(
    httpMethod: httpMethod,
    uri: uri,
    token: token,
    date: Date(),
    payload: payload
)

if auth = auth {
    let header = auth.getHeader()!
}

A trivial full example is shown as follows:

let token = Token(
    accessToken: "7XF56VIP7ZQQOLGHM6MRIK56S2QS363ULNB5UKNFMJRQVYHQH7IA",
    refreshToken: "7XF56VIP7ZQQOLGHM6MRIK56S2QS363ULNB5UKNFMJRQVYHQH7IA",
    ikm: Data(base64Encoded: "bDEyECRvKKE8w81fX4hz/52cvHsFPMGeJ+a9fGaVvWM=")!,
    signature: Data(base64Encoded: "7v/CdiGoEI7bcj7R2EyDPH5nrCd2+7rHYNACB+Kf2FMx405und2KenGjNpCBPv0jOiptfHJHiY3lldAQTGCdqw==")!,
    expiresAt: Date(timeIntervalSinceReferenceDate: 1472678411)
)

let date = Date()

let auth = try? Authorization(
    httpMethod: "POST",
    uri: "/api/v1/test",
    token: token,
    date: date,
    payload: "{\"foo\":\"bar\"}".data(using: .utf8, allowLossyConversion: false)
)

if auth = auth {
    let header = auth.getHeader()!
}

Note that the date property should be pore-offset when calling Authorization to prevent time skewing.

The payload parameter in Authorization:init should be a JSON serializable string.

Version 2 HMAC Header

The Version 2 HMAC header, for API’s that support it can be retrieved by calling:

if auth = auth {
    let header = auth.getHeader()!
}

Version 1 HMAC Header

For API’s using version 1 of the HMAC header, call Authorization with the optional version parameter set to 1 for the 6th parameter.

let auth = try? Authorization(
    httpMethod: httpMethod,
    uri: uri,
    token: token,
    date: Date(),
    payload: payload,
    version: 1
)

if auth = auth {
    let header = auth.getHeader()!
}

This string can be used in the Authorization Header

Date Header

The Version 1 HMAC header requires an additional X-Date header. The X-Date header can be retrieved by calling authorization.getDateString()

Encrypted Requests & Responses

This library enables clients to establish and trusted encrypted session on top of a TLS layer, while simultaniously (and independently) providing the ability authenticate and identify a client via HMAC+HKDF style authentication.

The rationale for this functionality includes but is not limited to:

1. Necessity for extra layer of security
2. Lack of trust in the network or TLS itself (see https://blog.cloudflare.com/incident-report-on-memory-leak-caused-by-cloudflare-parser-bug/)
3. Need to ensure confidentiality of the Initial Key Material (IKM) provided by the server for HMAC+HKDF authentication
4. Need to ensure confidentiality of user submitted credentials to the API for authentication

The primary reason you may want to establish an encrypted session with the API itself is to ensure confidentiality of the IKM to prevent data leakages over untrusted networks to avoid information being exposed in a Cloudflare like incident (or any man-in-the-middle attack). Encrypted sessions enable you to utilize a service like Cloudflare should a memory leak occur again with confidence that the IKM and other secure data would not be exposed.

Generating Keys

To encrypt, decrypt, sign, and verify messages, you’ll need to be able to generate the appropriate keys. Internally, this library uses libsodium-swift to perform all necessary cryptography functions.

Encrytion Keys

Encryption uses a sodium crypto box. A keypair can be generated as follows:

let kp = Utils.generateKeypair()

Signing Keys

Encryption uses a sodium signature. A keypair can be generated as follows:

let kp = Utils.generateSigningKeypair()

Encrypted Request Body

Payloads can be encrypted as follows:

import CryptoSwift // For .bytes alias

    let payload = """
{
    "foo": "bar"
}
"""

guard var Request = try? Request(
    secretKey: kp.secretKey
) else {
    // Handle init errors
}

guard let cipher = try? request!.encrypt(
    request: payload.data(using: .utf8, allowLossyConversion: false)!,
    publicKey: publicKey // 32 byte public key from server
) else {
    // Handle errors
}

// Do your HTTP request here

Note that you need to have a pre-bootstrapped public key to encrypt data. For the v1 API, this is typically this is returned by /api/v1/server/otk.

Decrypting Responses

Responses from the server can be decrypted as follows:

import CryptoSwift // For .bytes alias

guard let response = try? Response(
    secretKey: kp.secretKey
) else {
    // Handle initialization errors
}

guard let decrypted = try? response!.decrypt(
    response: Data(base64Encoded: "")!.bytes, // The raw body provided in the servers http response
) else {
    // Handle errors
}

V2 Encrypted Payload

Verison 2 works identical to the version 1 payload, with the exception that all components needed to decrypt the message are bundled within the payload itself, rather than broken out into separate headers. This alleviates developer concerns with needing to manage multiple headers.

The version 2 payload is described as follows. Each component is concatanated together.

Segment	Length
4 byte header DE259002 in binary format	4 BYTES
Nonce	24 BYTES
The public key associated to the private key	32 BYTES
Encrypted Body	X BYTES
Signature Public Key	32 BYTES
Signature or raw request body	64 BYTES
Checksum of prior elements concatonated together	64 BYTES