Question

How to hash a string with SHA-256 in PHP

Answer 1

function sha256(string $input): string {
    // hash() returns a lowercase hex string by default
    return hash('sha256', $input);
}

$input = "PHP programming language";
$hash = sha256($input);

echo $hash . PHP_EOL;



/*
run:

2d4cfd679f3faa497d21fc551e081cd49da5f1c386f76eb70845e3d0ebc208e0

*/

 

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Answer 2

declare(strict_types=1);

/**
 * Computes a SHA-256 hash for a string.
 *
 * Why SHA-256?
 * - Built into PHP.
 * - Produces a fixed-length hexadecimal string.
 * - Commonly used for checksums and data verification.
 * - More appropriate than rolling your own hash function.
 *
 * Important:
 * - Hashing is not encryption.
 * - A hash is intended to identify data, not recover it.
 * - Different inputs can theoretically produce the same hash
 *   (called a collision), although collisions are extremely
 *   unlikely with SHA-256.
 *
 * @param string $text The input string to hash.
 *
 * @return string The SHA-256 hash as a hexadecimal string.
 */
function hashString(string $text): string
{
    return hash('sha256', $text);
}

/*
 * Example input string.
 *
 * In a real application, this value might come from:
 * - User input
 * - A file
 * - A database
 * - An API request
 */
$text = 'Hello, World!';

/*
 * Compute the hash value.
 */
$hashValue = hashString($text);

echo "Original string: {$text}" . PHP_EOL;
echo "SHA-256 hash  : {$hashValue}" . PHP_EOL;

/*
 * Demonstrate hash comparison.
 *
 * Identical strings should produce identical hashes.
 */
$anotherText = 'Hello, World!';

$hash1 = hashString($text);
$hash2 = hashString($anotherText);

if ($hash1 === $hash2) {
    echo PHP_EOL;
    echo "Hashes match." . PHP_EOL;

    /*
     * IMPORTANT:
     *
     * A matching hash does not mathematically guarantee
     * that two inputs are identical because all hash
     * functions have the possibility of collisions.
     *
     * For SHA-256, collisions are extraordinarily unlikely,
     * but when exact equality matters, compare the original
     * values as well.
     */
    if ($text === $anotherText) {
        echo "Strings are identical." . PHP_EOL;
    }
}

/*
 * Professional guidance:
 *
 * Good uses for hashing:
 * - Data integrity verification
 * - File checksums
 * - Cache keys
 * - Digital fingerprints
 * - Detecting changes in data
 *
 * Password storage:
 * - Do NOT use hash() directly.
 * - Use password_hash() and password_verify().
 *
 * Example:
 *
 * $passwordHash = password_hash($password, PASSWORD_DEFAULT);
 *
 * if (password_verify($password, $passwordHash)) {
 *     // Password is correct.
 * }
 *
 * Password hashing requires specialized algorithms such as
 * bcrypt or Argon2, which are provided by PHP's password API.
 */


/*
run:

Original string: Hello, World!
SHA-256 hash  : dffd6021bb2bd5b0af676290809ec3a53191dd81c7f70a4b28688a362182986f

Hashes match.
Strings are identical.

*/

 

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