CryptoAPI RSA：CryptDecrypt仅在第一次解密，其他调用返回NTE_BAD_DATA

Question

我已经编写了对自定义长度的内存缓冲区进行加密/解密的程序。加密结束得很好；但是我的解密代码只能在任何缓冲区位置解密一次数据，这与块条目相对应。其他块的解密以NTE_BAD_DATA结尾。

您对此有何建议？

这是我的加密代码：

void CWinRSA::FinishEncrypt(const char* pcbRawData, const size_t nDataSize, char** ppcbEcrData, size_t& rnEcrSize) const
{
    if (m_hProvider == NULL)
    {
        throw ("Cannot encrypt data with wrong provider!!");
    }

    if (m_hKey == NULL)
    {
        throw ("Cannot encrypt data with a wrong key!!");
    }

    size_t nBlockLength = GetBlockLength();
    size_t nPaddingSize = nBlockLength - 11;

    size_t nRemain = nDataSize % nBlockLength;
    size_t nBlockProcess = (nDataSize / nPaddingSize + (nRemain != 0 ? 1 : 0));

    size_t nResultSize = nBlockProcess * nBlockLength;

    (*ppcbEcrData) = new char[nResultSize];

    DWORD dwBufferLength = nBlockLength;
    DWORD dwDataLength;

    for (int iBlock = 0; iBlock < nBlockProcess - 1; iBlock++)
    {
        memcpy((*ppcbEcrData) + (iBlock * nBlockLength),
            pcbRawData + (iBlock * nPaddingSize), nPaddingSize);

        dwDataLength = nPaddingSize;

        if (!CryptEncrypt(m_hKey, NULL, FALSE, 0,
            (BYTE*)((*ppcbEcrData) + (iBlock * nBlockLength)),
            &dwDataLength, dwBufferLength))
        {
            throw ("Cannot encrypt data!!");
        }
    }

    memcpy((*ppcbEcrData) + ((nBlockProcess - 1) * nBlockLength),
        pcbRawData + ((nBlockProcess - 1) * nPaddingSize), (nRemain ? nRemain : nPaddingSize));

    dwDataLength = (nRemain ? nRemain : nPaddingSize);

    if (!CryptEncrypt(m_hKey, NULL, TRUE, 0,
        (BYTE*)((*ppcbEcrData) + ((nBlockProcess - 1) * nBlockLength)),
        &dwDataLength, dwBufferLength))
    {
        throw ("Cannot encrypt data!!");
    }

    rnEcrSize = nResultSize;
}

解密：

void CWinRSA::FinishDecrypt(const char* pcbRawData, const size_t nDataSize, char** ppcbDecData, size_t& rnDecSize) const
{
    if (m_hProvider == NULL)
    {
        throw ("Cannot decrypt data with wrong provider!!");
    }

    if (m_hKey == NULL)
    {
        throw ("Cannot decrypt data with a wrong key!!");
    }

    size_t nBlockLength = GetBlockLength();

    if ((nDataSize % nBlockLength) != 0)
    {
        throw ("Cannot decrypt data!! Probably data is corrupted!!");
    }

    size_t nPaddingSize = nBlockLength - 11;
    size_t nBlockProcess = nDataSize / nBlockLength;

    size_t nResultSize = nBlockProcess * nPaddingSize;

    (*ppcbDecData) = new char[nResultSize];

    DWORD dwDataLength;

    char* pcbComputeResult = new char[nBlockLength];

    for (int iBlock = 0; iBlock < nBlockProcess - 1; iBlock++)
    {
        memcpy(pcbComputeResult, pcbRawData + (iBlock * nBlockLength), nBlockLength);

        if (!CryptDecrypt(m_hKey, NULL, FALSE, 0, (BYTE*)pcbComputeResult, &dwDataLength))
        {
            throw ("Cannot decrypt data!!");
        }

        memcpy((*ppcbDecData) + (iBlock * nPaddingSize), pcbComputeResult, nPaddingSize);
    }

    memcpy(pcbComputeResult, pcbRawData + ((nBlockProcess - 1) * nBlockLength), nBlockLength);

    if (!CryptDecrypt(m_hKey, NULL, TRUE, 0, (BYTE*)pcbComputeResult, &dwDataLength))
    {
        DWORD dwError = GetLastError();

        throw ("Cannot decrypt data!!");
    }

    memcpy((*ppcbDecData) + ((nBlockProcess - 1) * nPaddingSize), pcbComputeResult, nPaddingSize);

    rnDecSize = ((nBlockProcess - 1) * nPaddingSize) + dwDataLength;

    delete[] pcbComputeResult;
    pcbComputeResult = NULL;
}

Answer 1

RSA不能以这种方式使用。实际上，它不是分组密码（或流密码）。我的理解是，除了一条“短”消息外，它实际上没有任何密码用途，因此，从密钥解密一次后库就失败了，这也不足为奇。

如果需要保护任意大小的数据，请使用RSA为流或分组密码（如AES）交换对称密钥。

Answer 2

我找到了答案。在所有解密调用之前，我必须使用块长度（以字节为单位）初始化dwDataLength。

dwDataLength = nBlockLength;

if (!CryptDecrypt(m_hKey, NULL, TRUE, 0, (BYTE*)pcbComputeResult, &dwDataLength))
{
     DWORD dwError = GetLastError();

     throw ("Cannot decrypt data!!");
}

整个解密方法

void CWinRSA::FinishDecrypt(const char* pcbRawData, const size_t nDataSize, char** ppcbDecData, size_t& rnDecSize) const
{
    if (m_hProvider == NULL)
    {
        throw ("Cannot decrypt data with wrong provider!!");
    }

    if (m_hKey == NULL)
    {
        throw ("Cannot decrypt data with a wrong key!!");
    }

    size_t nBlockLength = GetBlockLength();

    if ((nDataSize % nBlockLength) != 0)
    {
        throw ("Cannot decrypt data!! Probably data is corrupted!!");
    }

    size_t nPaddingSize = nBlockLength - 11;
    size_t nBlockProcess = nDataSize / nBlockLength;

    size_t nResultSize = nBlockProcess * nPaddingSize;

    (*ppcbDecData) = new char[nResultSize];

    DWORD dwDataLength;

    char* pcbComputeResult = new char[nBlockLength];

    for (int iBlock = 0; iBlock < nBlockProcess - 1; iBlock++)
    {
        memcpy(pcbComputeResult, pcbRawData + (iBlock * nBlockLength), nBlockLength);

        dwDataLength = nBlockLength;

        if (!CryptDecrypt(m_hKey, NULL, FALSE, 0, (BYTE*)pcbComputeResult, &dwDataLength))
        {
            throw ("Cannot decrypt data!!");
        }

        memcpy((*ppcbDecData) + (iBlock * nPaddingSize), pcbComputeResult, nPaddingSize);
    }

    memcpy(pcbComputeResult, pcbRawData + ((nBlockProcess - 1) * nBlockLength), nBlockLength);

    dwDataLength = nBlockLength;

    if (!CryptDecrypt(m_hKey, NULL, TRUE, 0, (BYTE*)pcbComputeResult, &dwDataLength))
    {
        throw ("Cannot decrypt data!!");
    }

    memcpy((*ppcbDecData) + ((nBlockProcess - 1) * nPaddingSize), pcbComputeResult, nPaddingSize);

    rnDecSize = ((nBlockProcess - 1) * nPaddingSize) + dwDataLength;

    delete[] pcbComputeResult;
    pcbComputeResult = NULL;
}