Convert SecKeyRef to EC_KEY in iOS

Question

I'm creating CSR from openSSL but due to OpenSSL isn't storing keys in secure enclave so I chooses objective C to create key pair (private key and public key) in secure enclave and send to OpenSSL for X509 certificate. I get successfully public key in NSData and then convert const unsigned char * bitsOfKeyDataPublicKey = (unsigned char *) [publicKey bytes]; and then create public key EC_KEY*_ec_keyPublic = d2i_EC_PUBKEY(NULL,&bitsOfKeyDataPublicKey, publicKeyLegnth);. But For Private key we get SecKeyRef from objective c so for creation EC_Key how can we convert private key or is this any way to convert or use private key ? Looking for response. Thanks

Answer 1

You can change private key from SecKeyRef to NSData

Example:

- (NSData *)getPrivateKeyBits {
    OSStatus sanityCheck = noErr;
    NSData * privateKeyBits = nil;

    NSMutableDictionary * queryPrivateKey = [[NSMutableDictionary alloc] init];

    // Set the public key query dictionary.

    [queryPrivateKey setObject:(id)kSecClassKey forKey:(id)kSecClass];
    [queryPrivateKey setObject:_privateTag forKey:(id)kSecAttrApplicationTag];
    [queryPrivateKey setObject:(id)kSecAttrKeyTypeEC forKey:(id)kSecAttrKeyType];
    [queryPrivateKey setObject:[NSNumber numberWithBool:YES] forKey:(id)kSecReturnData];

    // Get the key bits.
    sanityCheck = SecItemCopyMatching((__bridge CFDictionaryRef)queryPrivateKey, (void *)&privateKeyBits);

    if (sanityCheck != noErr) {
        privateKeyBits = nil;
    }
    else if (sanityCheck == errSecItemNotFound) {
        privateKeyBits = nil;
    }

    return privateKeyBits;
}

Don't forget to use the _privateTag used for generating private key

now you can use:

const unsigned char *bitsOfKeyDataPrivateKey = (unsigned char *) [[self getPrivateKeyBits] bytes];
EC_KEY *_ec_keyPrivate = d2i_EC_PUBKEY(NULL,&bitsOfKeyDataPrivateKey, privateKeyLegnth);