RSA public/private key encryption in Swift
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Latest commit 6160bd5 Sep 21, 2018

README.md

SwiftyRSA

Maintainer(s): @ldiqual

Public key RSA encryption in Swift.

SwiftyRSA is used in the Scoop iOS app to encrypt driver license numbers before submitting them to Checkr through our API.

Installation

Swift 3.2 / 4.0+

With Cocoapods:

pod 'SwiftyRSA'

With Carthage:

github "TakeScoop/SwiftyRSA"

Swift 2.3

The swift-2.3 branch is built out of SwiftRSA 0.4.0 and is not actively maintained. If you'd like to use the latest features of SwiftyRSA, please use swift 3.0.

pod 'SwiftyRSA', :git => 'git@github.com:TakeScoop/SwiftyRSA.git', :branch => 'swift-2.3'

Objective-C

pod 'SwiftyRSA/ObjC'

Quick Start

Encrypt with a public key

let publicKey = try PublicKey(pemNamed: "public")
let clear = try ClearMessage(string: "Clear Text", using: .utf8)
let encrypted = try clear.encrypted(with: publicKey, padding: .PKCS1)

// Then you can use:
let data = encrypted.data
let base64String = encrypted.base64String

Decrypt with a private key

let privateKey = try PrivateKey(pemNamed: "private")
let encrypted = try EncryptedMessage(base64Encoded: "AAA===")
let clear = try encrypted.decrypted(with: privateKey, padding: .PKCS1)

// Then you can use:
let data = clear.data
let base64String = clear.base64String
let string = clear.string(using: .utf8)

Advanced Usage

Create a public/private key representation

With a DER file

let publicKey = try PublicKey(derNamed: "public")
let privateKey = try PrivateKey(derNamed: "private")

With a PEM file

let publicKey = try PublicKey(pemNamed: "public")
let privateKey = try PrivateKey(pemNamed: "private")

With a PEM string

let publicKey = try PublicKey(pemEncoded: str)
let privateKey = try PrivateKey(pemEncoded: str)

With a Base64 string

let publicKey = try PublicKey(base64Encoded: base64String)
let privateKey = try PrivateKey(base64Encoded: base64String)

With data

let publicKey = try PublicKey(data: data)
let privateKey = try PrivateKey(data: data)

With a SecKey

let publicKey = try PublicKey(reference: secKey)
let privateKey = try PrivateKey(reference: secKey)

Encrypt with a public key

let str = "Clear Text"
let clear = try ClearMessage(string: str, using: .utf8)
let encrypted = try clear.encrypted(with: publicKey, padding: .PKCS1)

let data = encrypted.data
let base64String = encrypted.base64Encoded

Decrypt with a private key

let encrypted = try EncryptedMessage(base64Encoded: base64String)
let clear = try encrypted.decrypted(with: privateKey, padding: .PKCS1)

let data = clear.data
let base64String = clear.base64Encoded
let string = try clear.string(using: .utf8)

Sign with a private key

SwiftyRSA can sign data with a private key. SwiftyRSA will calculate a SHA digest of the supplied String/Data and use this to generate the digital signature.

let clear = try ClearMessage(string: "Clear Text", using: .utf8)
let signature = clear.signed(with: privateKey, digestType: .sha1)

let data = signature.data
let base64String = signature.base64String

Verify with a public key

SwiftyRSA can verify digital signatures with a public key. SwiftyRSA will calculate a digest of the supplied String/Data and use this to verify the digital signature.

let signature = try Signature(base64Encoded: "AAA===")
let isSuccessful = try clear.verify(with: publicKey, signature: signature, digestType: .sha1)

Create a public/private RSA key pair

let keyPair = SwiftyRSA.generateRSAKeyPair(sizeInBits: 2048)
let privateKey = keyPair.privateKey
let publicKey = keyPair.publicKey

Export a key or access its content

let pem = try key.pemString()
let base64 = try key.base64String()
let data = try key.data()
let reference = key.reference
let originalData = key.originalData

Create public and private RSA keys

Use ssh-keygen to generate a PEM public key and a PEM private key. SwiftyRSA also supports DER public keys.

$ ssh-keygen -t rsa -f ~/mykey -N ''
$ cat ~/mykey > ~/private.pem
$ ssh-keygen -f ~/mykey.pub -e -m pem > ~/public.pem

Your keys are now in ~/public.pem and ~/private.pem. Don't forget to move ~/mykey and ~/mykey.pub to a secure place.

Under the hood

To enable using public/private RSA keys on iOS, SwiftyRSA uses a couple techniques like X.509 header stripping so that the keychain accepts them.

Click here for more details

When encrypting using a public key:

  • If the key is in PEM format, get rid of its meta data and convert it to Data
  • Strip the public key X.509 header, otherwise the keychain won't accept it
  • Add the public key to the keychain, with a random tag
  • Get a reference on the key using the key tag
  • Use SecKeyEncrypt to encrypt a ClearMessage using the key reference and the message data.
  • Store the resulting encrypted data to an EncryptedMessage
  • When the key gets deallocated, delete the public key from the keychain using its tag

When decrypting using a private key:

  • Get rid of PEM meta data and convert to Data
  • Add the private key to the app keychain, with a random tag
  • Get a reference on the key using the key tag
  • Use SecKeyDecrypt to decrypt an EncryptedMessage using the key reference and the encrypted message data
  • Store the resulting decrypted data to a ClearMessage
  • Delete private key from keychain using tag

Inspired from

License

This project is copyrighted under the MIT license. Complete license can be found here: https://github.com/TakeScoop/SwiftyRSA/blob/master/LICENSE