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SwiftyRSA

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+

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 => '[email protected]: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)

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