UInt8 Array Swift to const char* C

I have the following function

public func encryptWithRSAKey(_ data: String, rsaKeyRef: SecKey, padding: SecPadding) -> [UInt8]? {

    let blockSize = SecKeyGetBlockSize(rsaKeyRef)
    var messageEncrypted = [UInt8](repeating: 0, count: blockSize)
    var messageEncryptedSize = blockSize

    var status: OSStatus!

    status = SecKeyEncrypt(rsaKeyRef, SecPadding.OAEP, data, data.count, &messageEncrypted, &messageEncryptedSize)

    if status != noErr {
        print("\(logClassName): Encryption Error!")

    return messageEncrypted


the output is encryptedMessage = [9,43,128...] 128 length

and I have to send the result into a C function

void STDCALL CpProxyAvOpenhomeOrgCredentials1BeginSet(THandle aHandle, const char* aId, const char* aUserName, const char* aPassword, uint32_t aPasswordLen, OhNetCallbackAsync aCallback, void* aPtr)
    CpProxyAvOpenhomeOrgCredentials1C* proxyC = reinterpret_cast<CpProxyAvOpenhomeOrgCredentials1C*>(aHandle);
    ASSERT(proxyC != NULL);
    Brh buf_aId(aId);
    Brh buf_aUserName(aUserName);
    Brh buf_aPassword;
    buf_aPassword.Set((const TByte*)aPassword, aPasswordLen);
    FunctorAsync functor = MakeFunctorAsync(aPtr, (OhNetFunctorAsync)aCallback);
    proxyC->BeginSet(buf_aId, buf_aUserName, buf_aPassword, functor);

What is the way for encoding messageEncrypted in swift to const char* aPassword in C

1 answer

  • answered 2017-11-12 19:49 Martin R

    A C function

    void cfunc(const char* aPassword, uint32_t aPasswordLen);

    is imported to Swift as

    public func cfunc(_ aPassword: UnsafePointer<Int8>!, _ aPasswordLen: UInt32)

    For an array, withUnsafeBufferPointer() gives you a pointer to the (contiguous) element storage. Due to the different signedness (Int8 vs UInt8), the pointer must be "rebound". Example:

    let encryptedMessage: [UInt8] = [9, 43, 128]
    encryptedMessage.withUnsafeBufferPointer {
        $0.baseAddress!.withMemoryRebound(to: Int8.self, capacity: encryptedMessage.count) {
            cfunc($0, UInt32(encryptedMessage.count))