1 Reply by johnot

(2 replies, posted in wolfSSL)

After further testing and investigation, I've discovered that the encryption and decryption works just fine. I'm actually trying to port parts of this code from adb to wolfssl:
https://cs.android.com/android/platform … 28_gcm.cpp

I've zeroed down the problem to my copy pasta of SPAKE2 from boringssl, needed for pairing authentication in adb. The encryption/decryption must be failing because the key received from SPAKE2_process_msg is wrong.

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2 Reply by johnot

(21 replies, posted in wolfSSL)

Try this.

Create a callback for the peer verification to bypass the failure. Returning 1 allows the client to accept any certificate, hence bypassing the certificate verification failure.

int wolfssl_verify_cb(int, WOLFSSL_X509_STORE_CTX*)
{
    return 1;
}

void your_function()
{
    // ...
    SSL_CTX_set_verify(ssl_ctx, SSL_VERIFY_PEER | SSL_VERIFY_FAIL_IF_NO_PEER_CERT, wolfssl_verify_cb);
    // ...
}

NOTE: From my experience, wolfSSL uses the callback provided through `SSL_CTX_set_verify`, not `SSL_CTX_set_cert_verify_callback`. I haven't dug through the code completely, but those functions set 2 different variables. I believe the CB variable in `SSL_CTX_set_verify` is the one that gets called when the verification fails.

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3 Topic by johnot

(2 replies, posted in wolfSSL)

Hi there,

I'm trying to replicate the functions 

 EVP_AEAD_CTX_seal

and 

 EVP_AEAD_CTX_open

in order to send (and receive) data to a server using BoringSSL. However, the server fails to decrypt the data. It seems like wolfSSL doesn't have any directly compatible functions. Here's my approach:

[UPDATE]: I posted decryption code earlier instead of encryption code, my bad.

// Original code using BoringSSL
size_t Encrypt(bssl::ScopedEVP_AEAD_CTX context, const uint8_t* in, size_t in_len, uint8_t* out, size_t out_len)
{
    size_t written_sz;
    std::vector<uint8_t> nonce(EVP_AEAD_nonce_length(EVP_AEAD_CTX_aead(context.get())), 0);

    if (!EVP_AEAD_CTX_seal(context.get(), out, &written_sz, out_len, nonce.data(),
                                        nonce.size(), in, in_len, nullptr, 0)) {
        std::cerr  << "Failed to encrypt" << std::endl;
        return 0;
    }
    
    return written_sz;
}

and

// Code ported to use wolfSSL
// key_g = { preset key }
size_t Decrypt(wolfssl::UniquePtr<WOLFSSL_EVP_CIPHER_CTX> encryptContext,
                                   const uint8_t* in, size_t in_len, uint8_t* out, size_t out_len)
{
    int written_sz, ret, taglen = 16;
    std::vector<uint8_t> nonce(EVP_CIPHER_iv_length(EVP_aes_128_gcm()), 0);

    ret = EVP_EncryptInit(encryptContext.get(), EVP_aes_128_gcm(), key_g, nonce.data());

    assert(ret == SSL_SUCCESS))

    ret = EVP_EncryptUpdate(encryptContext.get(), out, &written_sz, in, (int)in_len);

    if (ret != WOLFSSL_SUCCESS){
        std::cerr  << "Failed to encrypt" << std::endl;
        return 0;
    }

    ret = EVP_EncryptFinal(encryptContext.get(), out, &written_sz);

    if (ret != WOLFSSL_SUCCESS || written_sz != in_len){
        std::cerr  << "Failed to encrypt" << std::endl;
        return 0;
    }

    unsigned char tag[taglen]
    // the last 16 bytes are the tag. Copy the tag into those last 16 bytes as boringssl does
    assert((in_len + taglen) == out_len);
    assert(EVP_CIPHER_CTX_ctrl(encryptContext.get(), EVP_CTRL_GCM_GET_TAG, taglen, (void*)tag) == SSL_SUCCESS);
    memcpy((void*)(out + in_len), tag, taglen);

    return written_sz + taglen; // bssl returns sizeof(encryptedData) + taglen
}

I tried analyzing the encrypted data for bssl and figured out that authTag, which is 16 bytes (depending on cipher I suppose), is appended to the end of the encryption data. I tried following a similar scheme since wolfSSL didn't have the functions out of the box.

However, the server fails to decrypt the data. Can anybody help out?

Thanks in advance

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