OpenSSL RSA in Swift. Get a public key into a String

Does exist any example on Swift 3 with basic RSA Security Framework operations(macosx)?

There’s no official Apple samples that meets these criteria. The standard sample I point folks to is iCryptoCompatibility, but that’s in Objective-C. OTOH, the core code would be relatively simple to port to Swift, or you could just add the NSOperation subclasses to your project and then call them from Swift via bridging.

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—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

I did "c" working sample as you recommended.

Have some difficulties to port in swift 3

        var bio = BIO_new(BIO_s_mem());
        var ret = PEM_write_bio_RSAPublicKey(bio, rsaKeyPair);

        var keylen = BIO_ctrl(bio,BIO_CTRL_PENDING,0,nil)// BIO_pending(bio);
      
        var pem_key = calloc(keylen+1, 1); / Null-terminate */
        BIO_read(bio, pem_key, Int32(keylen));
        let cT1 = String(cString: pem_key), 
        print(cT1)//printf("%s", pem_key);

to port nulled-string pem-key into String(Line 8).

The error is: Cannot invoke initializer for type 'String' with an argument list of type '(cString: UnsafeMutableRawPointer?)'. Overloads for 'String' exist with these partially matching parameter lists: (cString: UnsafePointer<CChar>), (cString: UnsafePointer<UInt8>).

How to get String from pem_key at line 8?

Swift 3 does not, in general, allow you to convert pointers of one type to pointers of a different type. The rules of the road here are outlined in SE-0107 UnsafeRawPointer API, which puts Swift’s type aliasing rules on a firm footing. I strongly recommend you read the UnsafeRawPointer Migration doc before going further.

In this case,

calloc

returns a raw pointer, that is, a pointer to memory whose type isn’t specified.

String(cString:)

, OTOH, expects a C string pointer, that is, a pointer to a

CChar

, and you can’t just freely cast between the two. You can convert a raw pointer to a typed pointer, but you have to be careful when you do so because it can be very easy to run into aliasing problems. Here’s an example of code that actually compiles.

let cT1 = String(cString: pem_key!.assumingMemoryBound(to: CChar.self))

However, there are better options. My preferred option in situations like this is to allocate the memory with the right type in Swift and then pass its address to the underlying read function. For example.

var buffer = [CChar](repeating: 0, count: keylen)
BIO_read(bio, &buffer, Int32(buffer.count))
let cT1 = String(cString: buffer)

Finally, I have to stress that, if you’re working with a low-level C API like OpenSSL, you’re really going to need to understanding Swift’s pointer rules, as discussed in the docs I referenced above.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

YEs. Thanks a lot. Made me happy for a couple of days) Wish you that too..