How to implement Base64 encoding and decoding in php

Base64 algorithm is an encoding method that converts binary data into ASCII characters, so that the data can not be modified or damaged during transmission, and the true content of the data can also be hidden. In PHP, you can use built-in functions or manually write code to implement Base64 encoding and decoding.

1. Use of PHP built-in functions

PHP provides two built-in functions base64_encode() and base64_decode(), which can easily perform Base64 Codec. The following is how to use them:

Base64 encoding:

$encoded_data = base64_encode($data);

Among them, $data is the binary data that needs to be encoded, and $encoded_data is the encoded string. Different from other encoding methods (such as URL encoding), the Base64-encoded string may contain special characters such as "/" and " ", which need to be escaped when transmitted in the URL.

Base64 decoding:

$decoded_data = base64_decode($encoded_data);

Among them, $encoded_data is the encoded string and $decoded_data is the decoded binary data.

This method is the simplest implementation, but when processing large binary data (such as image files), it will occupy a large amount of memory and cause performance problems.

2. Manually write the Base64 algorithm

In order to process large binary data, we can manually write the implementation of the Base64 algorithm. The following is the code to manually implement Base64 encoding and decoding in PHP:

// Base64编码
function base64_encode_php($data) {
$base64_map = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
$base64_data = "";
$data_len = strlen($data);

for ($i = 0; $i < $data_len; $i += 3) {
    $chunk = ord(substr($data, $i, 3));
    $base64_data .= $base64_map[($chunk >> 2) & 0x3F];
    $base64_data .= $base64_map[(($chunk << 4) & 0x30) | ((ord(substr($data, $i + 1, 1)) >> 4) & 0x0F)];
    $base64_data .= (($i + 2) < $data_len) ? $base64_map[(ord(substr($data, $i + 1, 1)) << 2) & 0x3C | (ord(substr($data, $i + 2, 1)) >> 6) & 0x03] : "=";
    $base64_data .= (($i + 2) < $data_len) ? $base64_map[ord(substr($data, $i + 2, 1)) & 0x3F] : "=";
}

return $base64_data;
}


// Base64解码
function base64_decode_php($data) {
$base64_map = array(
    &#39;A&#39; => 0, &#39;B&#39; => 1, &#39;C&#39; => 2, &#39;D&#39; => 3, &#39;E&#39; => 4, &#39;F&#39; => 5, &#39;G&#39; => 6, &#39;H&#39; => 7,
    &#39;I&#39; => 8, &#39;J&#39; => 9, &#39;K&#39; => 10, &#39;L&#39; => 11, &#39;M&#39; => 12, &#39;N&#39; => 13, &#39;O&#39; => 14, &#39;P&#39; => 15,
    &#39;Q&#39; => 16, &#39;R&#39; => 17, &#39;S&#39; => 18, &#39;T&#39; => 19, &#39;U&#39; => 20, &#39;V&#39; => 21, &#39;W&#39; => 22, &#39;X&#39; => 23,
    &#39;Y&#39; => 24, &#39;Z&#39; => 25, &#39;a&#39; => 26, &#39;b&#39; => 27, &#39;c&#39; => 28, &#39;d&#39; => 29, &#39;e&#39; => 30, &#39;f&#39; => 31,
    &#39;g&#39; => 32, &#39;h&#39; => 33, &#39;i&#39; => 34, &#39;j&#39; => 35, &#39;k&#39; => 36, &#39;l&#39; => 37, &#39;m&#39; => 38, &#39;n&#39; => 39,
    &#39;o&#39; => 40, &#39;p&#39; => 41, &#39;q&#39; => 42, &#39;r&#39; => 43, &#39;s&#39; => 44, &#39;t&#39; => 45, &#39;u&#39; => 46, &#39;v&#39; => 47,
    &#39;w&#39; => 48, &#39;x&#39; => 49, &#39;y&#39; => 50, &#39;z&#39; => 51, &#39;0&#39; => 52, &#39;1&#39; => 53, &#39;2&#39; => 54, &#39;3&#39; => 55,
    &#39;4&#39; => 56, &#39;5&#39; => 57, &#39;6&#39; => 58, &#39;7&#39; => 59, &#39;8&#39; => 60, &#39;9&#39; => 61, &#39;+&#39; => 62, &#39;/&#39; => 63
);
$data_len = strlen($data);
$padding_count = substr_count($data, "=");
$binary_data = "";
$byte_count = 0;

for ($i = 0; $i < $data_len; $i++) {
    $char = $data[$i];

    if (isset($base64_map[$char])) {
        $byte_count++;
        $binary_data .= str_pad(decbin($base64_map[$char]), 6, "0", STR_PAD_LEFT);

        if ($byte_count == 4) {
            $byte_count = 0;

            $binary_data = substr($binary_data, 0, strlen($binary_data) - 8);
        }
    }
}

return substr($binary_data, 0, strlen($binary_data) - $padding_count * 8);
}

This code is mainly divided into two parts: Base64 encoding and Base64 decoding.

• In the Base64 encoding part, we first define a Base64 mapping table $base64_map, which is used to convert 6-bit binary data into corresponding Base64 characters. Then, for the input binary data, 3 bytes are taken out for processing at a time. For each 3-byte block of data, we will split it into 4 6-bit blocks. If the number of bytes currently processed is less than 3 bytes, the '=' character needs to be supplemented.

• In the Base64 decoding part, we first define a Base64 mapping table $base64_map, this time it is used to convert each Base64 character into 6-bit binary data. For the input Base64 string, we convert it to binary data and then convert it to ASCII characters in groups of 8 bits.

Although this method is relatively complex, it can greatly improve performance because it can process large amounts of data in chunks.

Summary

Whether you use PHP built-in functions or manually write the Base64 algorithm, you can easily perform Base64 encoding and decoding operations. For small binary data, using built-in functions is sufficient, but for processing large binary data, hand-writing algorithms can improve performance.

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