Grabble / 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

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 => '[e-mail]:TakeScoop/SwiftyRSA.git', :branch => 'swift-2.3'

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

Get a public/private key reference

With a DER file

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

With a PEM file

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

With data

let publicKey = try PublicKey(data: data)

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 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

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
• https://github.com/btnguyen2k/swift-rsautils

License

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