# 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.

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()`

.