Unable to load RSA-PSS public key in iOS using SecKeyCreateWithData

I have an issue with a key I have generated for the rsa-pss-sha512 signing algorithm: I cannot load it into my iOS code using SecKeyCreateWithData().

Here is how I created it with:

% openssl genpkey -algorithm rsa-pss -pkeyopt rsa_keygen_bits:2048 -out DEV-v3-rsapss-private.pem
% openssl rsa -in DEV-v3-rsapss-private.pem -pubout > DEV-v3-rsapss-public.pem

In the code below I try to load the base64 part of the public key at step (1).

I have converted the public key to DER with:

% openssl rsa -pubin -in DEV-v3-rsapss-public.pem -out DEV-v3-rsapss-public.der -outform DER

In the code below I try to load the raw data of the DER at step (2).

I dump the ASN1 with:

% dumpasn1 -p -a DEV-v3-rsapss-public.der

and try to load the raw bytes of this ASN1 at step 3

All attempts end up with:

Optional(Swift.Unmanaged<__C.CFErrorRef>(_value: Error Domain=NSOSStatusErrorDomain Code=-50 "RSA public key creation from data failed" UserInfo={numberOfErrorsDeep=0, NSDescription=RSA public key creation from data failed}))

However I can successfully load a standard RSA key created with:

% openssl genrsa -out DEV-v3-rsa-private.pem 2048
% openssl rsa -in DEV-v3-rsa-private.pem -pubout > DEV-v3-rsa-public.pem

but I cannot use this private key when signing on my backend with the rsa-pss-sha512 algorithm. It complains about padding.

What am I missing?

import SwiftUI

struct ContentView: View {
    var body: some View {
        VStack {
            Image(systemName: "globe")
                .imageScale(.large)
                .foregroundStyle(.tint)
            Text("Hello, world!")
        }
        .padding()
        .onAppear() {

            // Step 1 ----------------------------
            let publicKeyPEMBase64 = "MIIBIDALBgkqhkiG9w0BAQoDggEPADCCAQoCggEBAKm6i5I/9PH+MQmhCCD8MSFGr+sGBiI6CPevojO7EGOAkJRnuEW3dAVAGiv8pUjyDV5pO7erjT1PNDLWBW28QSwuk+Ff8W4qOhlEUb/pZjimzhVMqz+59bYPtQN1GmhnuQRY9UpobQ6dSChnXGZ7fsTRE1V8XKeUujJr2uT/sU+OmDZh19S4wyiNDpEDmDSvFIEHeYWz48yPckZHr4hYp0p//1MGez9X7tiIDPV9gM2N9FZGmh3XCS93Pdr3Z86Cz0IxUeEBL9t4xspXl3kDvABkpji7oyK+Lbm1Q/fCIVwlMdT2QLmHrO2oLcqAfCMOAke4Zdd+FbHOBdGtNAwWGQMCAwEAAQ=="
            
            guard let publicKeyPEMData = Data(base64Encoded: publicKeyPEMBase64) else {
                NSLog("could not decode base64 of public key")
                return
            }
            createKey(publicKeyData: publicKeyPEMData, logPrefix: "(1)")
            
            // Step 2 ----------------------------
            let publicKeyDerRawBytes = [UInt8]([0x30, 0x82, 0x01, 0x20, 0x30, 0x0b, 0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x0a, 0x03, 0x82, 0x01, 0x0f, 0x00, 0x30, 0x82, 0x01, 0x0a, 0x02, 0x82, 0x01, 0x01, 0x00, 0xa9, 0xba, 0x8b, 0x92, 0x3f, 0xf4, 0xf1, 0xfe, 0x31, 0x09, 0xa1, 0x08, 0x20, 0xfc, 0x31, 0x21, 0x46, 0xaf, 0xeb, 0x06, 0x06, 0x22, 0x3a, 0x08, 0xf7, 0xaf, 0xa2, 0x33, 0xbb, 0x10, 0x63, 0x80, 0x90, 0x94, 0x67, 0xb8, 0x45, 0xb7, 0x74, 0x05, 0x40, 0x1a, 0x2b, 0xfc, 0xa5, 0x48, 0xf2, 0x0d, 0x5e, 0x69, 0x3b, 0xb7, 0xab, 0x8d, 0x3d, 0x4f, 0x34, 0x32, 0xd6, 0x05, 0x6d, 0xbc, 0x41, 0x2c, 0x2e, 0x93, 0xe1, 0x5f, 0xf1, 0x6e, 0x2a, 0x3a, 0x19, 0x44, 0x51, 0xbf, 0xe9, 0x66, 0x38, 0xa6, 0xce, 0x15, 0x4c, 0xab, 0x3f, 0xb9, 0xf5, 0xb6, 0x0f, 0xb5, 0x03, 0x75, 0x1a, 0x68, 0x67, 0xb9, 0x04, 0x58, 0xf5, 0x4a, 0x68, 0x6d, 0x0e, 0x9d, 0x48, 0x28, 0x67, 0x5c, 0x66, 0x7b, 0x7e, 0xc4, 0xd1, 0x13, 0x55, 0x7c, 0x5c, 0xa7, 0x94, 0xba, 0x32, 0x6b, 0xda, 0xe4, 0xff, 0xb1, 0x4f, 0x8e, 0x98, 0x36, 0x61, 0xd7, 0xd4, 0xb8, 0xc3, 0x28, 0x8d, 0x0e, 0x91, 0x03, 0x98, 0x34, 0xaf, 0x14, 0x81, 0x07, 0x79, 0x85, 0xb3, 0xe3, 0xcc, 0x8f, 0x72, 0x46, 0x47, 0xaf, 0x88, 0x58, 0xa7, 0x4a, 0x7f, 0xff, 0x53, 0x06, 0x7b, 0x3f, 0x57, 0xee, 0xd8, 0x88, 0x0c, 0xf5, 0x7d, 0x80, 0xcd, 0x8d, 0xf4, 0x56, 0x46, 0x9a, 0x1d, 0xd7, 0x09, 0x2f, 0x77, 0x3d, 0xda, 0xf7, 0x67, 0xce, 0x82, 0xcf, 0x42, 0x31, 0x51, 0xe1, 0x01, 0x2f, 0xdb, 0x78, 0xc6, 0xca, 0x57, 0x97, 0x79, 0x03, 0xbc, 0x00, 0x64, 0xa6, 0x38, 0xbb, 0xa3, 0x22, 0xbe, 0x2d, 0xb9, 0xb5, 0x43, 0xf7, 0xc2, 0x21, 0x5c, 0x25, 0x31, 0xd4, 0xf6, 0x40, 0xb9, 0x87, 0xac, 0xed, 0xa8, 0x2d, 0xca, 0x80, 0x7c, 0x23, 0x0e, 0x02, 0x47, 0xb8, 0x65, 0xd7, 0x7e, 0x15, 0xb1, 0xce, 0x05, 0xd1, 0xad, 0x34, 0x0c, 0x16, 0x19, 0x03, 0x02, 0x03, 0x01, 0x00, 0x01])

            let publicKeyDerData = Data(publicKeyDerRawBytes)
            createKey(publicKeyData: publicKeyDerData, logPrefix: "(2)")
            
            // Step 3 ----------------------------
            let publicKeyAsn1RawBytes = [UInt8]([0x00, 0x92, 0x59, 0xAA, 0x05, 0xC1, 0xF7, 0x8B, 0x33, 0xC2, 0x22, 0xEB, 0x87, 0x62, 0x97, 0x12, 0x68, 0x7E, 0x83, 0x94, 0x17, 0xCE, 0x5F, 0x1F, 0x5E, 0xB7, 0x37, 0x21, 0x3E, 0x0F, 0xE9, 0x35, 0xAE, 0x84, 0xC4, 0x4D, 0x75, 0xDC, 0xCC, 0x9D, 0x48, 0x4C, 0x03, 0xF6, 0xD2, 0x34, 0xED, 0xAF, 0x7E, 0xA2, 0x26, 0x2C, 0xB6, 0xBD, 0x61, 0x55, 0xC3, 0xE0, 0xB4, 0xB4, 0xA7, 0x66, 0xF6, 0xB4, 0xD7, 0x80, 0xFE, 0x93, 0xD6, 0x85, 0xF8, 0xD6, 0xD3, 0x07, 0x04, 0x69, 0x4E, 0x41, 0xDA, 0x13, 0x50, 0x51, 0xB2, 0x01, 0xEA, 0xD0, 0x25, 0x51, 0x40, 0x68, 0x14, 0x21, 0xDF, 0xFB, 0x41, 0xE2, 0x0F, 0x6D, 0x5D, 0x57, 0x74, 0x2C, 0x58, 0xA9, 0x7D, 0xBF, 0x9E, 0x9F, 0xF7, 0xEC, 0xA3, 0xB8, 0x53, 0x85, 0x18, 0x60, 0x94, 0x94, 0xAC, 0x08, 0xAD, 0x19, 0xDA, 0x1B, 0x8E, 0x18, 0x4D, 0xD3, 0x5B, 0x22, 0x95, 0xA7, 0x9E, 0xCC, 0x2A, 0x32, 0xA8, 0x43, 0xCE, 0x50, 0xD3, 0x0C, 0xFF, 0x90, 0x1A, 0x59, 0xCB, 0xF6, 0x0A, 0xAE, 0x60, 0x12, 0x8C, 0x23, 0xC8, 0xBD, 0x01, 0xD2, 0xC9, 0x87, 0x81, 0xC8, 0x87, 0x91, 0x86, 0x6D, 0x6A, 0x4F, 0x35, 0xBB, 0xAA, 0x65, 0x7D, 0xCA, 0x6E, 0x4E, 0x60, 0x5B, 0xB7, 0x4C, 0x18, 0xED, 0x0B, 0x95, 0xE7, 0x88, 0x06, 0x97, 0x23, 0xF2, 0x96, 0x66, 0x0A, 0x84, 0x01, 0x9B, 0x23, 0x8C, 0x78, 0x3F, 0xA3, 0xCC, 0x3B, 0xC7, 0xDD, 0x8A, 0xAC, 0xDA, 0x0B, 0x26, 0x2A, 0x8A, 0x2C, 0xA7, 0x45, 0xEB, 0x81, 0x58, 0xB3, 0x17, 0xE1, 0xEC, 0x02, 0x8C, 0x21, 0x39, 0x4D, 0xEE, 0xD9, 0x74, 0x2E, 0x7C, 0x0A, 0x13, 0xAA, 0xCA, 0x7A, 0xEE, 0xF7, 0x92, 0x60, 0xF9, 0xD5, 0x10, 0xBD, 0x05, 0x55, 0x04, 0xD1, 0x0D, 0xCF, 0xAA, 0x1D, 0xA7, 0x9D, 0x62, 0x61])

            let publicKeyAsn1Data = Data(publicKeyAsn1RawBytes)
            createKey(publicKeyData: publicKeyAsn1Data, logPrefix: "(3)")
        }
    }
    
    func createKey(publicKeyData: Data, logPrefix: String) {
        let attributes: [NSObject : NSObject] = [
                kSecAttrKeyType: kSecAttrKeyTypeRSA,
                kSecAttrKeyClass: kSecAttrKeyClassPublic,
            ]

        var error: Unmanaged<CFError>?
        guard let secPublicKey = SecKeyCreateWithData(publicKeyData as CFData, attributes as CFDictionary, &error) else {
            NSLog("\(logPrefix): \(String(describing: error))")
            return
        }

        NSLog("\(logPrefix): sucessfully created key \(secPublicKey)")
    }
}

Solution

The exported RSA public key is in X.509/SPKI format, while SecKeyCreateWithData() requires the public key in PKCS#1 format.

The X.509/SPKI key can be converted into the PKCS#1 format using OpenSSL as follows, e.g. PEM encoded:

openssl rsa -pubin -RSAPublicKey_out -in <spki.pem> -out <public_pkcs1.pem>

The posted key converted to PKCS#1 format in this way is:

With this format, the import is now successful:

import Foundation

func createKey(publicKeyData: Data, logPrefix: String) {
        let attributes: [NSObject : NSObject] = [
                kSecAttrKeyType: kSecAttrKeyTypeRSA,
                kSecAttrKeyClass: kSecAttrKeyClassPublic,
        ]

        var error: Unmanaged<CFError>?
        guard let secPublicKey = SecKeyCreateWithData(publicKeyData as CFData, attributes as CFDictionary, &error) else {
                print("\(logPrefix): \(String(describing: error))")
                return
        }

        print("\(logPrefix): sucessfully created key \(secPublicKey)")
 }

let publicKeyPEMBase64 = "MIIBCgKCAQEAqbqLkj/08f4xCaEIIPwxIUav6wYGIjoI96+iM7sQY4CQlGe4Rbd0BUAaK/ylSPINXmk7t6uNPU80MtYFbbxBLC6T4V/xbio6GURRv+lmOKbOFUyrP7n1tg+1A3UaaGe5BFj1SmhtDp1IKGdcZnt+xNETVXxcp5S6Mmva5P+xT46YNmHX1LjDKI0OkQOYNK8UgQd5hbPjzI9yRkeviFinSn//UwZ7P1fu2IgM9X2AzY30VkaaHdcJL3c92vdnzoLPQjFR4QEv23jGyleXeQO8AGSmOLujIr4tubVD98IhXCUx1PZAuYes7agtyoB8Iw4CR7hl134Vsc4F0a00DBYZAwIDAQAB"         
let publicKeyPEMData = Data(base64Encoded: publicKeyPEMBase64)! 
createKey(publicKeyData: publicKeyPEMData, logPrefix: "(1)")

with the output:

(1): sucessfully created key <SecKeyRef algorithm id: 1, key type: RSAPublicKey, version: 4, 2048 bits (block size: 256), exponent: {hex: 10001, decimal: 65537}, modulus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addr: 0x6000029bc3a0>

which corresponds to the correct key as a comparison of public exponent and modulus with the original key in an ASN.1 parser shows.