nicwise / SwiftyRSA

RSA public/private key encryption in Swift

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

pod 'SwiftyRSA'

Usage

Encrypt

// With a PEM public key
let encrypted = try! SwiftyRSA.encryptString(str, publicKeyPEM: pemString)

// With a DER public key
let encrypted = try! SwiftyRSA.encryptString(str, publicKeyDER: derData)

Decrypt

let decrypted = try! SwiftyRSA.decryptString(str, privateKeyPEM: pemString)

Advanced Usage

Get a key instance

Note that the key reference will only be valid as long as the SwiftyRSA instance is alive.

let rsa = SwiftyRSA()

// Public key (PEM)
let pubPath   = bundle.pathForResource("public", ofType: "pem")!
let pubString = NSString(contentsOfFile: pubPath, encoding: NSUTF8StringEncoding, error: nil)! as String
let pubKey    = try! rsa.publicKeyFromPEMString(pubString)

// Public key (DER)
let pubPath = bundle.pathForResource("public", ofType: "der")!
let pubData = NSData(contentsOfFile: pubPath)!
let pubKey  = try! rsa.publicKeyFromDERData(pubData)

// Private key (PEM)
let privPath   = bundle.pathForResource("private", ofType: "pem")!
let privString = NSString(contentsOfFile: privPath, encoding: NSUTF8StringEncoding, error: nil)! as String
let privKey    = try! rsa.privateKeyFromPEMString(privString)

Use a key instance to encrypt/decrypt

// Encrypt
let encryptedString = try! rsa.encryptString(str, publicKey: pubKey)

// Decrypt
let decryptedString = try! rsa.decryptString(encrypted, privateKey: privKey)

Under the hood

When encrypting using a public key:

• If the key is in PEM format, get rid of meta data and convert to NSData
• Strip the ASN.1 data from the public key header (otherwise the keychain won't accept it)
• Add the public key to the app keychain, with a random tag
• Get a reference on the key using the key tag
• Convert clear text to NSData using UTF8
• Encrypt data with SecKeyEncrypt using the key reference
• Convert the resulting data to base64 and return it
• Delete public key from keychain using tag

When decrypting using a private key:

• Get rid of PEM meta data and convert to NSData
• Add the private key to the app keychain, with a random tag
• Get a reference on the key using the key tag
• Convert encrypted text to NSData from base64 string
• Decrypt data with SecKeyDecrypt using the key reference
• Convert the resulting data to String using UTF8
• Delete private key from keychain using tag

Inspired from

• http://blog.flirble.org/2011/01/05/rsa-public-key-openssl-ios/
• https://github.com/lancy/RSADemo

License

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