AES Encryption and Decryptionbb

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AI summary
The document provides a C++ example of using the OpenSSL library to encrypt and decrypt a QString using AES in CBC mode. It details the conversion of QString to a standard string for encryption, the initialization of the AES key and IV, and the process of encrypting and decrypting data. It emphasizes the importance of secure key management and notes that the example does not handle padding for input strings that are not multiples of the AES block size.
Tags
Cryptography
OpenSSL
Qt Framework
Last edited time
Jan 20, 2024 01:42 AM
The QString class in Qt provides a Unicode character string. It can be converted to and from standard C++ string types. If you want to encrypt and decrypt a QString using the OpenSSL library, you'll first need to convert it to a format that OpenSSL can use (like a standard string or byte array), and then convert it back to a QString after the operation.
Here's an example of how you might modify the provided C++ code to work with QStrings. Note that this assumes that your QString contains plain ASCII characters. If your QString contains Unicode characters, you'll need to handle the conversion to and from bytes differently.
In this example, qStringPlainText is converted to a std::string using the QString::toStdString method, then copied to the plain_text array using memcpy. After the decryption, the decrypted_text array is converted back to a QString using QString::fromStdString.
Please note that this example code is for demonstration purposes only. It doesn't handle padding for input strings that are not a multiple of the AES block size. Also, always use secure and random keys and IVs in a real-world scenario.

Note:

The AES_cbc_encrypt function is part of the OpenSSL library, which is a robust, full-featured open-source toolkit that implements the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols, as well as a full-strength general-purpose cryptography library.
The function AES_cbc_encrypt specifically is used for encrypting or decrypting using the AES (Advanced Encryption Standard) in CBC (Cipher Block Chaining) mode.
Here's the function prototype:
Let's break down the parameters:
  • in: A pointer to the input data (plaintext for encryption, or ciphertext for decryption). This should be a sequence of bytes. The length should be a multiple of the AES block size (16 bytes).
  • out: A pointer to the output data (ciphertext after encryption, or plaintext after decryption). The out buffer must be at least length bytes long.
  • length: The length of the in buffer, in bytes. This should be a multiple of the AES block size (16 bytes).
  • key: A pointer to an AES_KEY structure that has been filled by AES_set_encrypt_key or AES_set_decrypt_key.
  • ivec: A pointer to the initialization vector (IV). This should be an array of AES_BLOCK_SIZE bytes. For CBC mode, it is important that the IV is unique for each invocation with the same key. For encryption, the IV is usually chosen randomly and is transmitted to the decrypting party (typically prefixed to the ciphertext). For decryption, the IV must be the same as the one used for encryption.
  • enc: If this is AES_ENCRYPT, encryption is performed. If this is AES_DECRYPT, decryption is performed.
Remember that correct use of these cryptographic functions requires a good understanding of cryptography. Misuse can lead to insecure systems even if the cryptography itself is sound. It's generally recommended to use higher-level interfaces that are harder to misuse when dealing with cryptography.
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