Sodium

Swift-Sodium

Swift-Sodium provides a safe and easy to use interface to perform common cryptographic operations on iOS and OSX.

It leverages the Sodium library, and although Swift is the primary target, the framework can also be used in Objective C.

Usage

Add Sodium.framework as a dependency to your project, and import the module:

import Sodium

The Sodium library itself doesn't have to be installed on the system: the repository already includes a precompiled library for armv7, armv7s, arm64, as well as for the iOS simulator.

It targets Swift 4, introduced in Xcode 9.0.

The libsodium-ios.a file has been generated by the dist-build/ios.sh script. The libsodium-osx.a file has been generated by the dist-build/osx.sh script.

Running these scripts on Xcode 9.0 (9A235) on the revision 94550cefd5921c09a1ea352c759851b7ad0e592b of libsodium generates files identical to the ones present in this repository.

Public-key Cryptography

Authenticated Encryption

let sodium = Sodium(())!
let aliceKeyPair = sodium.box.keyPair()!
let bobKeyPair = sodium.box.keyPair()!
let message = "My Test Message".data(using:.utf8)!

let encryptedMessageFromAliceToBob: Data =
    sodium.box.seal(message: message,
                    recipientPublicKey: bobKeyPair.publicKey,
                    senderSecretKey: aliceKeyPair.secretKey)!

let messageVerifiedAndDecryptedByBob =
    sodium.box.open(nonceAndAuthenticatedCipherText: encryptedMessageFromAliceToBob,
                    senderPublicKey: aliceKeyPair.publicKey,
                    recipientSecretKey: bobKeyPair.secretKey)

seal() automatically generates a nonce and prepends it to the ciphertext. open() extracts the nonce and decrypts the ciphertext.

Optionally, Box provides the ability to utilize a user-defined nonce via seal(message: recipientPublicKey: senderSecretKey: nonce:).

The Box class also provides alternative functions and parameters to deterministically generate key pairs, to retrieve the nonce and/or the authenticator, and to detach them from the original message.

Anonymous Encryption (Sealed Boxes)

let sodium = Sodium()
let bobKeyPair = sodium.box.keyPair()!
let message = "My Test Message".data(using:.utf8)!

let encryptedMessageToBob =
    sodium.box.seal(message: message, recipientPublicKey: bobKeyPair.publicKey)!

let messageDecryptedByBob =
    sodium.box.open(anonymousCipherText: encryptedMessageToBob,
                    recipientPublicKey: bobKeyPair.publicKey,
                    recipientSecretKey: bobKeyPair.secretKey)

seal() generates an ephemeral keypair, uses the ephemeral secret key in the encryption process, combines the ephemeral public key with the ciphertext, then destroys the keypair. The sender can not decrypt the resulting ciphertext. open() extracts the public key and decrypts using the recipient's secret key. Message integrity is verified, but the sender's identity cannot be correlated to the ciphertext.

Public-key signatures

Detached signatures

let sodium = Sodium()
let message = "My Test Message".data(using:.utf8)!
let keyPair = sodium.sign.keyPair()!
let signature = sodium.sign.signature(message: message, secretKey: keyPair.secretKey)!
if sodium.sign.verify(message: message,
                      publicKey: keyPair.publicKey,
                      signature: signature) {
    // signature is valid
}

Attached signatures

let sodium = Sodium()
let message = "My Test Message".data(using:.utf8)!
let keyPair = sodium.sign.keyPair()!
let signedMessage = sodium.sign.sign(message: message, secretKey: keyPair.secretKey)!
if let unsignedMessage = sodium.sign.open(signedMessage: signedMessage, publicKey: keyPair.publicKey) {
    // signature is valid
}

Secret-key authenticated encryption

Authenticated encryption for a sequence of messages

let sodium = Sodium()
let message1 = "Message 1".data(using:.utf8)!
let message2 = "Message 2".data(using:.utf8)!
let message3 = "Message 3".data(using:.utf8)!

let secretkey = sodium.secretStream.xchacha20poly1305.key()!

/* stream encryption */

let stream_enc = sodium.secretStream.xchacha20poly1305.initPush(secretKey: secretkey)!
let header = stream_enc.header()
let encrypted1 = stream_enc.push(message: message1)!
let encrypted2 = stream_enc.push(message: message2)!
let encrypted3 = stream_enc.push(message: message3, tag: .FINAL)!

/* stream decryption */

let stream_dec = sodium.secretStream.xchacha20poly1305.initPull(secretKey: secretkey, header: header)!
let (message1_dec, tag1) = stream_dec.pull(cipherText: encrypted1)!
let (message2_dec, tag2) = stream_dec.pull(cipherText: encrypted2)!
let (message3_dec, tag3) = stream_dec.pull(cipherText: encrypted3)!

Authenticated encryption for independent messages

let sodium = Sodium()
let message = "My Test Message".data(using:.utf8)!
let secretKey = sodium.secretBox.key()!
let encrypted: Data = sodium.secretBox.seal(message: message, secretKey: secretKey)!
if let decrypted = sodium.secretBox.open(nonceAndAuthenticatedCipherText: encrypted, secretKey: secretKey) {
    // authenticator is valid, decrypted contains the original message
}

Hashing

Deterministic hashing

let sodium = Sodium()
let message = "My Test Message".data(using:.utf8)!
let h = sodium.genericHash.hash(message: message)

Keyed hashing

let sodium = Sodium()
let message = "My Test Message".data(using:.utf8)!
let key = "Secret key".data(using:.utf8)!
let h = sodium.genericHash.hash(message: message, key: key)

Streaming

let sodium = Sodium()
let message1 = "My Test ".data(using:.utf8)!
let message2 = "Message".data(using:.utf8)!
let key = "Secret key".data(using:.utf8)!
let stream = sodium.genericHash.initStream(key: key)!
stream.update(input: message1)
stream.update(input: message2)
let h = stream.final()

Short-output hashing (SipHash)

let sodium = Sodium()
let message = "My Test Message".data(using:.utf8)!
let key = sodium.randomBytes.buf(length: sodium.shortHash.KeyBytes)!
let h = sodium.shortHash.hash(message: message, key: key)

Random numbers generation

let sodium = Sodium()
let randomData = sodium.randomBytes.buf(length: 1000)!
let seed = "0123456789abcdef0123456789abcdef".data(using:.utf8)!
let stream = sodium.randomBytes.deterministic(length: 1000, seed: seed)!

Password hashing

let sodium = Sodium()
let password = "Correct Horse Battery Staple".data(using:.utf8)!
let hashedStr = sodium.pwHash.str(passwd: password,
                                  opsLimit: sodium.pwHash.OpsLimitInteractive,
                                  memLimit: sodium.pwHash.MemLimitInteractive)!

if sodium.pwHash.strVerify(hash: hashedStr, passwd: password) {
    // Password matches the given hash string
} else {
    // Password doesn't match the given hash string
}

if sodium.pwHash.strNeedsRehash(hash: hashedStr,
                                opsLimit: sodium.pwHash.OpsLimitInteractive,
                                memLimit: sodium.pwHash.MemLimitInteractive) {
    // Previously hashed password should be recomputed because the way it was
    // hashed doesn't match the current algorithm and the given parameters.
}

Key exchange

let sodium = Sodium()
let aliceKeyPair = sodium.keyExchange.keyPair()!
let bobKeyPair = sodium.keyExchange.keyPair()!

let sessionKeyPairForAlice = sodium.keyExchange.sessionKeyPair(publicKey: aliceKeyPair.publicKey,
    secretKey: aliceKeyPair.secretKey, otherPublicKey: bobKeyPair.publicKey, side: .CLIENT)!
let sessionKeyPairForBob = sodium.keyExchange.sessionKeyPair(publicKey: bobKeyPair.publicKey,
    secretKey: bobKeyPair.secretKey, otherPublicKey: aliceKeyPair.publicKey, side: .SERVER)!

let aliceToBobKeyEquality = sodium.utils.equals(sessionKeyPairForAlice.tx, sessionKeyPairForBob.xx) // true
let bobToAliceKeyEquality = sodium.utils.equals(sessionKeyPairForAlice.rx, sessionKeyPairForBob.tx) // true

Authentication tags

The sodium.auth.tag() function computes an authentication tag (HMAC) using a message and a key. Parties knowing the key can then verify the authenticity of the message using the same parameters and the sodium.auth.verify() function.

Authentication tags are not signatures: the same key is used both for computing and verifying a tag. Therefore, verifiers can also compute tags for arbitrary messages.

let sodium = Sodium()
let input = "test".data(using:.utf8)!
let key = sodium.auth.key()!
let tag = sodium.auth.tag(message: input, secretKey: key)!
let tagIsValid = sodium.auth.verify(message: input, secretKey: key, tag: tag)

Key derivation

The sodium.keyDerivation.derive() function generates a subkey using an input (master) key, an index, and a 8 bytes string identifying the context. Up to (2^64) - 1 subkeys can be generated for each context, by incrementing the index.

let sodium = Sodium()
let secretKey = sodium.keyDerivation.keygen()!

let subKey1 = sodium.keyDerivation.derive(secretKey: secretKey,
                                          index: 0, length: 32,
                                          context: "Context!")
let subKey2 = sodium.keyDerivation.derive(secretKey: secretKey,
                                          index: 1, length: 32,
                                          context: "Context!")

Utilities

Zeroing memory

let sodium = Sodium()
var dataToZero = "Message".data(using:.utf8)!
sodium.utils.zero(&dataToZero)

Constant-time comparison

let sodium = Sodium()
let secret1 = "Secret key".data(using:.utf8)!
let secret2 = "Secret key".data(using:.utf8)!
let equality = sodium.utils.equals(secret1, secret2)

Padding

let sodium = Sodium()
var data = "test".toData()!

// make data.count a multiple of 16
sodium.utils.pad(data: &data, blockSize: 16)!

// restore original size
sodium.utils.unpad(data: &data, blockSize: 16)!

Constant-time hexadecimal encoding

let sodium = Sodium()
let data = "Secret key".data(using:.utf8)!
let hex = sodium.utils.bin2hex(data)

Hexadecimal decoding

let sodium = Sodium()
let data1 = sodium.utils.hex2bin("deadbeef")
let data2 = sodium.utils.hex2bin("de:ad be:ef", ignore: " :")

Constant-time base64 encoding

let sodium = Sodium()
let b64 = sodium.utils.bin2base64("data".toData()!)!
let b64_2 = sodium.utils.bin2base64("data".toData()!, variant: .URLSAFE_NO_PADDING)!

Base64 decoding

let data1 = sodium.utils.base642bin(b64)
let data2 = sodium.utils.base642bin(b64, ignore: " \n")
let data3 = sodium.utils.base642bin(b64_2, variant: .URLSAFE_NO_PADDING, ignore: " \n")

Helpers to build custom constructions

Only use the functions below if you know that you absolutely need them, and know how to use them correctly.

Unauthenticated encryption

The sodium.stream.xor() function combines (using the XOR operation) an arbitrary-long input with the output of a deterministic key stream derived from a key and a nonce. The same operation applied twice produces the original input.

No authentication tag is added to the output. The data can be tampered with; an adversary can flip arbitrary bits.

In order to encrypt data using a secret key, the SecretBox class is likely to be what you are looking for.

In order to generate a deterministic stream out of a seed, the RandomBytes.deterministic_rand() function is likely to be what you need.

let sodium = Sodium()
let input = "test".data(using:.utf8)!
let key = sodium.stream.key()!
let (output, nonce) = sodium.stream.xor(input: input, secretKey: key)!
let twice = sodium.stream.xor(input: output, nonce: nonce, secretKey: key)!

XCTAssertEqual(input, twice)