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

With Cocoapods:

pod 'SwiftyRSA'

With Carthage:

github "TakeScoop/SwiftyRSA"

Usage

Encrypt

// String
let encryptedString = try! SwiftyRSA.encryptString(str, publicKeyPEM: pemString)

// Data
let encryptedData = try! SwiftyRSA.encryptData(data, publicKeyPEM: pemString)

// With a DER key
let encryptedString = try! SwiftyRSA.encryptString(str, publicKeyDER: derData)
let encryptedData = try! SwiftyRSA.encryptData(data, publicKeyDER: pemString)

Decrypt

// String
let decryptedString = try! SwiftyRSA.decryptString(str, privateKeyPEM: pemString)

// Data
let decryptedData = try! SwiftyRSA.decryptData(data, privateKeyPEM: pemString)

Sign

SwiftyRSA can sign data with a private key. SwiftyRSA will calculate an SHA1 digest of the supplied String/NSData and use this to generate the digital signature.

// String
let signatureString = try! SwiftyRSA.signString(str, privateKeyPEM: pemString)

// Data
let signatureData = try! SwiftyRSA.signData(data, privateKeyPEM: pemString)

Verify

SwiftyRSA can verify digital signatures with a public key. SwiftyRSA will calculate a digest (default is SHA1) of the supplied String/NSData and use this to verify the digital signature.

// String
let verificationResult = try! SwiftyRSA.verifySignatureString(str, signature: sigString, publicKeyPEM: pemString)
if (verificationResult) {
    // verification was successful
}

// Data
let verificationResult = try! SwiftyRSA.verifySignatureData(data, signature: sigData, publicKeyPEM: String)
if (verificationResult) {
    // verification was successful
}

Alternate digest algorithms

SHA1 is the default digest algorithm. Alternate algorithms can be specified by supplying a value for the digestMethod parameter:

let digestSignature = try! rsa.signData(data, privateKey: privKey, digestMethod: .SHA256)
let result = try! rsa.verifySignatureData(data, signatureData: digestSignature, publicKey: pubKey, digestMethod: .SHA256)

Advanced Usage

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.

Get a key instance

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

import SwiftyRSA

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)
let encryptedData = try! rsa.encryptData(data, publicKey: pubKey)

// Decrypt
let decryptedString = try! rsa.decryptString(str, privateKey: privKey)
let decryptedData = try! rsa.decryptData(data, privateKey: privKey)

Sign or verify an existing digest

let rsa = SwiftyRSA()
let digestSignature = try! rsa.signDigest(digest, privateKey: privKey, digestMethod: .SHA1)

let verificationResult = try! rsa.verifySignatureData(digest, signature: digestSignature, publicKey: pubKey, digestMethod: .SHA1)
if (verificationResult) {
    // verification was successful
}

Use with Objective-C

@import SwiftyRSA;

NSString* str = @"ClearText";

NSBundle* bundle = [NSBundle bundleForClass:self.class];

NSString* pubPath = [bundle pathForResource:@"swiftyrsa-public" ofType:@"pem"];
NSString* pubString = [NSString stringWithContentsOfFile:pubPath encoding:NSUTF8StringEncoding error:nil];

NSString* privPath = [bundle pathForResource:@"swiftyrsa-private" ofType:@"pem"];
NSString* privString = [NSString stringWithContentsOfFile:privPath encoding:NSUTF8StringEncoding error:nil];

NSString* encrypted = [SwiftyRSA encryptString:str publicKeyPEM:pubString padding:kSecPaddingPKCS1 error:nil];
NSString* decrypted = [SwiftyRSA decryptString:encrypted privateKeyPEM:privString padding:kSecPaddingPKCS1 error:nil];

NSString* signature = [SwiftyRSA signString:str privateKeyPEM:privString digestMethod:DigestTypeSHA256 error:&error];
VerificationResult* result = [SwiftyRSA verifySignatureString:str signature:signature publicKeyDER:pubData digestMethod:DigestTypeSHA256 error:&error];
if (result.boolValue) {
    // verification was successful
} 

NSData* digestSignature = [rsa signData:data privateKey:privKey digestMethod:DigestTypeSHA256 error:&error];
VerificationResult* result = [rsa verifySignatureData:data signatureData:digestSignature publicKey:pubKey digestMethod:DigestTypeSHA256 error:&error];
if (result.boolValue) {
    // verification was successful
}   

NSData* digest = [data SHA256];
NSData* digestSignature = [rsa signDigest:digest privateKey:privKey digestMethod:DigestTypeSHA256 error:&error];
VerificationResult* result = [rsa verifySignatureData:digest signature:digestSignature publicKey:pubKey digestMethod:DigestTypeSHA256 error:&error];
if (result.boolValue) {
    // verification was successful
}

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