SecKeyRef to NSData

seckeyrefnsdata.c

// HELPER QUERIES

void queryValueToData(NSMutableDictionary *query, void * value) {
    query[(__bridge id)kSecValueRef] = (__bridge id)value ;
    query[(__bridge id)kSecReturnData] = @YES ;
}

void queryDataToValue(NSMutableDictionary *query, id data) {
    query[(__bridge id)kSecValueData] = data ;
    query[(__bridge id)kSecReturnRef] = @YES ;
}



NSMutableDictionary * rsa2048KeyQuery(NSData* tag) {
    NSMutableDictionary * rsaQuery = [[NSMutableDictionary alloc] init];
    
    rsaQuery[(__bridge id)kSecClass]              = (__bridge id)kSecClassKey;
    rsaQuery[(__bridge id)kSecAttrKeyType]        = (__bridge id)kSecAttrKeyTypeRSA ;
    rsaQuery[(__bridge id)kSecAttrApplicationTag] = tag ;
    rsaQuery[(__bridge id)kSecAttrKeySizeInBits]  = @(RSAKeySize2048);
    
    return rsaQuery;
}


OSStatus queryAddAndRemove(NSMutableDictionary * query, CFTypeRef * ref) {
    OSStatus sanityCheck;
    sanityCheck = SecItemAdd((__bridge CFDictionaryRef) query, ref);
    
    if(sanityCheck == errSecDuplicateItem) {
        // if it was already there, need to delete before we add
        (void) SecItemDelete((__bridge CFDictionaryRef) query);
        sanityCheck = SecItemAdd((__bridge CFDictionaryRef) query, ref);
    }
    
    // delete from Keychain
    (void) SecItemDelete((__bridge CFDictionaryRef) query);
    
    return sanityCheck;
}

// CONVERT BETWEEN SECKEYREF AND NSDATA

#define kPublicKeyTag "com.apple.sample.publickey"
static const uint8_t kFromKeyIdentifier[] = kPublicKeyTag;

NSData * dataFromKey(SecKeyRef givenKey) {
    
    
    // http://stackoverflow.com/questions/16748993/ios-seckeyref-to-nsdata
    NSData *publicTag = [[NSData alloc] initWithBytes:kFromKeyIdentifier
                                               length:sizeof(kFromKeyIdentifier)];
    
    // BUILD query
    NSMutableDictionary * queryPublicKey = rsa2048KeyQuery(publicTag);
    queryValueToData(queryPublicKey, givenKey);
    
    // MAKE query
    CFDataRef result;
    OSStatus sanityCheck = noErr;
    sanityCheck = queryAddAndRemove(queryPublicKey, (CFTypeRef *)&result);
    
    // SETUP result
    NSData * publicKeyBits = nil;
    if (sanityCheck == errSecSuccess) {
        publicKeyBits = CFBridgingRelease(result);
    }
    
    return publicKeyBits;
}



SecKeyRef keyFromData(NSData* data, CFTypeRef keyclass) {
    
    
    NSData *tag = [[NSData alloc] initWithBytes:kToKeyIdentifier
                                         length:sizeof kToKeyIdentifier];
    
    // BUILD query
    NSMutableDictionary * queryPublicKey = rsa2048KeyQuery(tag);
    queryPublicKey[(__bridge id)kSecAttrKeyClass] = (__bridge id)keyclass ;
    queryDataToValue(queryPublicKey, data);
    
    // MAKE query
    SecKeyRef keyRef = nil;
    (void) queryAddAndRemove(queryPublicKey, (CFTypeRef *)&keyRef);
    
    return keyRef;
}



// USE DER KEY DATA


int derEncodingGetSizeFrom(NSData* buf, int* iterator)
{
    const uint8_t* data = [buf bytes];
    int ret = 0;
    
    // parse TLV len
    int num_bytes = 1;
    int itr = *iterator;
    if (data[itr] > 0x80) {
        num_bytes = data[itr] - 0x80;
        itr++;
    }
    
    for (int i = 0 ; i < num_bytes; i++) { ret = (ret * 0x100) + data[itr + i]; }
    
    *iterator = itr + num_bytes;
    return ret;
}



int derSkipTagGetLength(NSData * der, int *iterator) {
    (*iterator)++; // skip T1
    return derEncodingGetSizeFrom(der, iterator); // skip L1
}

void derSkipNextTLV(NSData * der, int * iterator) {
    int size =     derSkipTagGetLength(der, iterator); // get + skip L
    
    (*iterator) += size; // skip Value
}

const void *publicKeyExponent(struct id_storage *sto) {
    
    if(sto == NULL || sto->publicKey == NULL) {
        return NULL;
    }
    
    NSData* pubkey = dataFromKey(sto->publicKey);
    if (pubkey == NULL) return NULL;
    
    int iterator = 0;
    
    /*
     Public Key Data Format
     T1,L1,V1[MODULUS_TAG,L2,V2,EXPONENT_TAG,L3,V3]
     */
    
    (void)derSkipTagGetLength(pubkey, &iterator); // skip L1
    
    derSkipNextTLV(pubkey, &iterator);
    
    int exp_size =     derSkipTagGetLength(pubkey, &iterator); // get + skip L2
    
    NSRange expRange = NSMakeRange(iterator, exp_size);
    NSData * expData = [pubkey subdataWithRange:expRange]; // get V2
    
    return CFBridgingRetain(expData);
}