Generate base64 url-encoded X.509 format 2048-bit RSA public key with Swift?

Question

Working in Apple Swift for iOS. I have to generate this for the backend as it\'s a secure app.

I\'m new to security and certificates and have been searching for a da

Answer 1

If the public key is already in your keychain, you can look up the public key and return the data as base64 with something similar to the following:

// Create dictionary to specify attributes for the key we're
// searching for.  Swift will automatically bridge native values 
// to to right types for the SecItemCopyMatching() call.
var queryAttrs = [NSString:AnyObject]() 
queryAttrs[kSecClass] = kSecClassKey 
queryAttrs[kSecAttrApplicationTag] = publicKeyTag
queryAttrs[kSecAttrKeyType] = kSecAttrKeyTypeRSA
queryAttrs[kSecReturnData] = true

var publicKeyBits = Unmanaged?()
SecItemCopyMatching(queryAttrs, &publicKeyBits)

// Work around a compiler bug with Unmanaged types
//  the following two lines should simply be 
//  let publicKeyData : NSData = publicKeyRef!.takeRetainedValue() as NSData
let opaqueBits = publicKeyBits?.toOpaque() 
let publicKeyData = Unmanaged.fromOpaque(opaqueBits).takeUnretainedValue()

let publicKeyBase64 = publicKeyData.base64EncodedData(NSDataBase64EncodingOptions.Encoding64CharacterLineLength)

If you need to generate the keypair and store it in the keychain, use something along these lines:

// Create dictionaries to specify key attributes.  Swift will
// automatically bridge native values to to right types for the
// SecKeyGeneratePair() call.
var pairAttrs = [NSString:AnyObject]()
var privateAttrs = [NSString:AnyObject]()
var publicAttrs = [NSString:AnyObject]()

privateAttrs[kSecAttrIsPermanent] = true
privateAttrs[kSecAttrApplicationTag] = privateKeyTag

publicAttrs[kSecAttrIsPermanent] = true
publicAttrs[kSecAttrApplicationTag] = publicKeyTag

pairAttrs[kSecAttrKeyType] = kSecAttrKeyTypeRSA
pairAttrs[kSecAttrKeySizeInBits] = 2048
pairAttrs[(kSecPrivateKeyAttrs.takeUnretainedValue() as! String)] = privateAttrs
pairAttrs[(kSecPublicKeyAttrs.takeUnretainedValue() as! String)] = publicAttrs

var publicKeyPtr = Unmanaged?()
var privateKeyPtr = Unmanaged?()

let status = SecKeyGeneratePair(pairAttrs, &publicKeyPtr, &privateKeyPtr)

Note: publicKeyTag and privateKeyTag are strings used to identify the key in the keystore. Apple recommends reverse-dns notation (com.company.key.xxx), but as long as they are unique, all should be good.