How to Encode and Decode Base64 Data in C ?

Base64 Decode Snippet in C

Base64 is a widely used encoding scheme that converts binary data into a string of printable ASCII characters. This is often necessary when transmitting binary data over channels that are not designed for its transmission, such as email or web pages.

Implementation Details

The provided code snippet implements both the encoding and decoding functionality of Base64 in C . The encoding function takes a buffer of binary data and its length, and returns a string containing the encoded data. The decoding function, on the other hand, takes a Base64-encoded string and returns a vector containing the decoded binary data.

To encode binary data, the snippet uses a series of steps:

1. It initializes an array of three bytes to store three consecutive bytes of the binary data.
2. It loops through the binary data buffer, reading three bytes at a time.
3. For each set of three bytes, it converts them into four 6-bit values and stores them in an array of four bytes.
4. It maps each 6-bit value to a character in the Base64 alphabet.
5. It appends the mapped characters to the encoded data string.

Decoding Base64-encoded data follows a similar process:

1. It initializes an array of four bytes to store the decoded data.
2. It loops through the encoded data string, reading four characters at a time.
3. For each set of four characters, it finds their corresponding values in the Base64 alphabet and converts them into four 6-bit values.
4. It splits the 6-bit values into three 8-bit bytes and stores them in the decoded data array.
5. It appends the decoded bytes to the vector containing the decoded binary data.

Usage

To use the provided code snippet, include the "base64.h" header file in your C program and use the following functions:

• base64_encode: Encodes a buffer of binary data into a Base64-encoded string.
• base64_decode: Decodes a Base64-encoded string into a vector of binary data.

Example

Here's an example of how to encode and decode Base64 data using the provided snippet:

#include "base64.h"

int main() {
  // Binary data to encode
  std::vector<BYTE> data = {0x12, 0x34, 0x56, 0x78};

  // Encode the data using Base64
  std::string encodedData = base64_encode(&data[0], data.size());

  // Print the encoded data
  std::cout << "Encoded Data: " << encodedData << std::endl;

  // Decode the Base64-encoded data
  std::vector<BYTE> decodedData = base64_decode(encodedData);

  // Print the decoded data
  std::cout << "Decoded Data:";
  for (BYTE byte : decodedData) {
    std::cout << " " << std::hex << (int)byte;
  }
  std::cout << std::endl;

  return 0;
}

This example will output the following:

Encoded Data: tEs=
Decoded Data: 12 34 56 78

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