This code defines a static C++ function `_encrypt_buffer` that performs...

September 5, 2025 at 02:14 PM

static int _encrypt_buffer(const char* payload, size_t len, 
    char* outBuffer, size_t& outLen, string& outHash)
{
    int result = 0;

    const size_t maxLen = outLen;

    outLen = 0;
    outHash = "";

    sfCrypto::sfCreds encCreds;
    encCreds.setKeypair(kAgentPrivateKey, kAgentCert);
    encCreds.setPeerCert(kMeaCert);

    sfEncryptStream encryptStream;
    result = encryptStream.init(encCreds, 0, ENC_BLOCK_SIZE);
    if (!result)
    {
        bool doFlush = false;
        size_t encLen = maxLen;
        result = encryptStream.encrypt(payload, len, outBuffer, encLen, doFlush);

        while (!result && doFlush)
        {
            outLen += encLen;
            encLen = maxLen - outLen;
            result = encryptStream.flush(outBuffer + outLen, encLen, doFlush);
        }

        if (!result)
        {
            outLen += encLen;
            encLen = maxLen - outLen;
            int result = encryptStream.finalize(outBuffer + outLen, encLen, outHash);
            if (result == 0) 
                outLen += encLen;
        }
    }
    encryptStream.close();

    return result;
}

This code defines a static C++ function _encrypt_buffer that performs encryption on a given payload. Let's break it down to understand its purpose and behavior step-by-step:

Function Parameters

payload: A const char* representing the input data to be encrypted.
len: The size (in bytes) of the input payload.
outBuffer: A char* buffer where the encrypted output will be stored.
outLen: A reference to a variable holding the size of the output buffer. Returns the final length of the encrypted data.
outHash: A reference to a std::string that will store a hash (presumably for integrity verification) of the encrypted output.

Function Purpose

The function encrypts the input payload using a cryptographic operation and stores the encrypted data in outBuffer. It also computes a hash of the encrypted data for integrity or verification purposes.

If the encryption function encounters a scenario where it needs to process the buffer incrementally (e.g., due to block-based encryption), the function handles that by iterating and flushing the data until the operation is finalized.

Breakdown of Core Behavior

Setting Up Creds and Encryption Stream:
- Creates a credentials object encCreds of type sfCrypto::sfCreds.
- Loads a keypair (private key and certificate) into the credentials object via setKeypair.
- Sets the peer certificate (this might be used to encrypt data for a specific recipient).
- Initializes an encryption stream object encryptStream using the credentials and a predefined encryption block size (ENC_BLOCK_SIZE).
Initializing Encryption:
- Calls encryptStream.init to initialize the encryption context. If this fails (result is non-zero), the function stops.
Processing the Encryption:
- Encrypts the input payload and writes the encrypted data into outBuffer. The encLen variable keeps track of how much encrypted data is written.
- Handles incremental encryption by flushing (if necessary) until all data has been processed.
Finalizing Encryption:
- Once all data has been encrypted and flushed, calls encryptStream.finalize.
- The finalize method writes any remaining data into the buffer and generates the associated hash of the encrypted output, storing it in outHash.
Closing the Stream:
- Ensures that the encryption stream is closed with encryptStream.close() to release resources.
Returning the Result:
- Returns the result of the encryption operation (0 on success, a non-zero error code otherwise).

Key Concepts in This Code

Encryption Stream: The code seems to use a block-based encryption mechanism, where data may need to be processed incrementally. This accommodates situations where the output buffer may fill up before all input data is processed.
Cryptographic Hash: During the finalization step, a hash of the encrypted buffer is computed. This is likely used for verifying data integrity or detecting tampering.
Error Handling: The function relies on the result variable to check the success or failure of the encryption steps.

Summary

The _encrypt_buffer function takes input data (payload), encrypts it, and writes the encrypted data to a provided output buffer (outBuffer). Along the way, it supports incremental/block encryption and computes a hash of the encrypted output for integrity purposes. The function returns 0 if all operations are successful or a non-zero error code to indicate failure.

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