How do I export a public key that was generated using SecKeyGeneratePair to be used on a server?

Question

I generated a keeper using SecKeyGeneratePair.

        var publicKeyPtr, privateKeyPtr: Unmanaged?

        let publicKeyParameters: [String: AnyO         


        

Answer 1

SecItemCopyMatching is for you:

var dataPtr:Unmanaged<AnyObject>?
let query: [String:AnyObject] = [
    kSecClass: kSecClassKey,
    kSecAttrApplicationTag: "com.example.site.public",
    kSecReturnData: kCFBooleanTrue
]
let qResult = SecItemCopyMatching(query, &dataPtr)

// error handling with `qResult` ...

let publicKeyData = dataPtr!.takeRetainedValue() as NSData

// convert to Base64 string
let base64PublicKey = publicKeyData.base64EncodedStringWithOptions(nil)

Swift 4:

var dataPtr:CFTypeRef?
let query: [String: Any] = [
    kSecClass as String: kSecClassKey,
    kSecAttrApplicationTag as String: "com.example.site.public",
    kSecReturnData as String: true
]

let qResult = SecItemCopyMatching(query as CFDictionary, &dataPtr)

// error handling with `qResult` ...

let data = dataPtr as! Data
let base64PublicKey = data.base64EncodedString()

Note that the size of the data is 270, not the same as block size of the key. See this question on the crypto.stackexchange.com.