How the DES_DECRYPT() function works in Mariadb?

The DES_DECRYPT() function is a string function that decrypts a string that was encrypted using the DES_ENCRYPT() function. It uses the Data Encryption Standard (DES) algorithm, which is a symmetric-key block cipher. It is useful for protecting sensitive data, such as passwords, credit card numbers, or personal information.

Syntax

The syntax of the DES_DECRYPT() function is as follows:

DES_DECRYPT(crypt_str [,key_str])

The crypt_str parameter is a binary string that represents the encrypted data. The key_str parameter is an optional string that specifies the key to use for decryption. If the key_str parameter is omitted, the DES_DECRYPT() function uses the same key that was used for encryption, which is stored in the des_key_file system variable.

The DES_DECRYPT() function returns a string that represents the decrypted data. If the crypt_str parameter is NULL, the DES_DECRYPT() function returns NULL. If the crypt_str parameter is not a valid encrypted string, the DES_DECRYPT() function returns NULL and generates a warning.

Examples

Example 1: Decrypting a string with the same key

In this example, we use the DES_DECRYPT() function to decrypt a string that was encrypted using the DES_ENCRYPT() function with the same key. We assume that the des_key_file system variable is set to a file that contains the key.

-- Encrypt a string with a key
SET @key = 'secret';
SET @plain = 'Hello, world!';
SET @crypt = DES_ENCRYPT(@plain, @key);

-- Decrypt the string with the same key
SELECT DES_DECRYPT(@crypt, @key) AS decrypted;

The output is:

+---------------+
| decrypted     |
+---------------+
| Hello, world! |
+---------------+

The DES_DECRYPT() function returns the original string that was encrypted using the DES_ENCRYPT() function with the same key.

Example 2: Decrypting a string with a different key

In this example, we use the DES_DECRYPT() function to decrypt a string that was encrypted using the DES_ENCRYPT() function with a different key. We assume that the des_key_file system variable is set to a file that contains the key.

-- Encrypt a string with a key
SET @key1 = 'secret';
SET @plain = 'Hello, world!';
SET @crypt = DES_ENCRYPT(@plain, @key1);

-- Decrypt the string with a different key
SET @key2 = 'wrong';
SELECT DES_DECRYPT(@crypt, @key2) AS decrypted;

The output is:

+-----------+
| decrypted |
+-----------+
| NULL      |
+-----------+

The DES_DECRYPT() function returns NULL and generates a warning, because the crypt_str parameter is not a valid encrypted string with the given key.

Example 3: Decrypting a string without a key

In this example, we use the DES_DECRYPT() function to decrypt a string that was encrypted using the DES_ENCRYPT() function without a key. We assume that the des_key_file system variable is set to a file that contains the key.

-- Encrypt a string without a key
SET @plain = 'Hello, world!';
SET @crypt = DES_ENCRYPT(@plain);

-- Decrypt the string without a key
SELECT DES_DECRYPT(@crypt) AS decrypted;

The output is:

+---------------+
| decrypted     |
+---------------+
| Hello, world! |
+---------------+

The DES_DECRYPT() function returns the original string that was encrypted using the DES_ENCRYPT() function without a key, because it uses the same key that was stored in the des_key_file system variable.

Related Functions

Some of the functions that are related to the DES_DECRYPT() function are:

• DES_ENCRYPT(): This function encrypts a string using the DES algorithm and returns a binary string. It is the inverse of the DES_DECRYPT() function. For example, DES_ENCRYPT('Hello, world!', 'secret') returns a binary string that can be decrypted using DES_DECRYPT() with the same key.
• AES_ENCRYPT(): This function encrypts a string using the Advanced Encryption Standard (AES) algorithm and returns a binary string. It is similar to the DES_ENCRYPT() function, but it uses a more secure and modern algorithm. For example, AES_ENCRYPT('Hello, world!', 'secret') returns a binary string that can be decrypted using AES_DECRYPT() with the same key.
• AES_DECRYPT(): This function decrypts a string that was encrypted using the AES_ENCRYPT() function. It uses the AES algorithm, which is a symmetric-key block cipher. It is similar to the DES_DECRYPT() function, but it uses a more secure and modern algorithm. For example, AES_DECRYPT(AES_ENCRYPT('Hello, world!', 'secret'), 'secret') returns Hello, world!.

Conclusion

The DES_DECRYPT() function is a useful function for decrypting a string that was encrypted using the DES_ENCRYPT() function. It uses the DES algorithm, which is a symmetric-key block cipher. It can be used for protecting sensitive data, such as passwords, credit card numbers, or personal information. The DES_DECRYPT() function accepts a binary string that represents the encrypted data and an optional string that specifies the key to use for decryption. It returns a string that represents the decrypted data. The DES_DECRYPT() function is compatible with other string functions, such as DES_ENCRYPT(), AES_ENCRYPT(), and AES_DECRYPT().