# Encryption functions

Percona Server for MySQL 8.0.28-20 adds encryption functions and variables to manage the encryption range. The functions may take an algorithm argument. Encryption converts plaintext into ciphertext using a key and an encryption algorithm.

You can also use the user-defined functions with the PEM format keys generated externally by the OpenSSL utility.

A digest uses plaintext and generates a hash value. This hash value can verify if the plaintext is unmodified. You can also sign or verify on digests to ensure that the original plaintext was not modified. You cannot decrypt the original text from the hash value.

When choosing key lengths, consider the following:

* Encryption strength increases with the key size and, also, the key generation time.

* If performance is important and the functions are frequently used, use symmetric encryption. Symmetric encryption functions are faster than asymmetric encryption functions. Moreover, asymmetric encryption has restrictions on the maximum length of a message being encrypted. For example, for RSA the algorithm maximum message size is the key length in bytes (key length in bits / 8) minus 11.

The following table and sections describe the functions. For examples, see function examples.

| Function Name                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------|
| [asymmetric_decrypt(algorithm, crypt_str, key_str)](#asymmetric_decryptalgorithm-crypt_str-key_str) |
| [asymmetric_derive(pub_key_str, priv_key_str)](#asymmetric_derivepub_key_str-priv_key_str) |
| [asymmetric_encrypt(algorithm, str, key_str)](#asymmetric_encryptalgorithm-str-key_str) |
| [asymmetric_sign(algorithm, digest_str, priv_key_str, digest_type)](#asymmetric_signalgorithm-digest_str-priv_key_str-digest_type) |
| [asymmetric_verify(algorithm, digest_str, sig_str, pub_key_str, digest_type)](#asymmetric_verifyalgorithm-digest_str-sig_str-pub_key_str-digest_type) |
| [create_asymmetric_priv_key(algorithm, (key_len | dh_parameters))](#create_asymmetric_priv_keyalgorithm-key_len--dh_parameters)   |
| [create_asymmetric_pub_key(algorithm, priv_key_str)](#create_asymmetric_pub_keyalgorithm-priv_key_str)  |
| [create_dh_parameters(key_len)](#create_dh_parameterskey_len)  |
| [create_digest(digest_type, str)](#create_digestdigest_type-str)  |

The following table describes the Encryption threshold variables which can be used to set the maximum value for a key length based on the type of encryption.

| Variable Name                     |
|-----------------------------------|
| [encryption_udf.dh_bits_threshold](#encryption_udfdh_bits_threshold)  |
| [encryption_udf.dsa_bits_threshold](#encryption_udfdsa_bits_threshold) |
| [encryption_udf.rsa_bits_threshold](#encryption_udfrsa_bits_threshold) |

## Install component_encryption_udf

Use the [Install Component Statement](https://dev.mysql.com/doc/refman/8.0/en/install-component.html) to add the component_encryption_udf component. The functions and variables are available. The user-defined functions and the Encryption threshold variables are auto-registered. There is no requirement to invoke `CREATE FUNCTION ... SONAME ...`.

The `INSERT` privilege on the `mysql.component` system table is required to run the `INSTALL COMPONENT` statement. To register the component, the operation adds a row to this table.

The following is an example of the installation command:

```{.bash data-prompt="mysql>"}
mysql> INSTALL COMPONENT 'file://component_encryption_udf';
```

!!! note

    If you are Compiling Percona Server for MySQL from Source, the Encryption UDF component is built by default when Percona Server for MySQL is built. Specify the `-DWITH_ENCRYPTION_UDF=OFF` cmake option to exclude it.

## User-defined functions described

## asymmetric_decrypt(*algorithm, crypt_str, key_str*)

Decrypts an encrypted string using the algorithm and a key string.

### Returns

A plaintext as a string.

### Parameters

The following are the function’s parameters:

* algorithm - the encryption algorithm supports RSA to decrypt the string.

* key_str - a string in the PEM format. The key string must have the following attributes:

  * Valid

  * Public or private key string that corresponds with the private or public key string used with the asymmetric_encrypt function.

## asymmetric_derive(*pub_key_str, priv_key_str*)

Derives a symmetric key using a public key generated on one side and a private key generated on another.

### asymmetric_derive output

A key as a binary string.

### asymmetric_derive parameters

The `pub_key_str` must be a public key in the PEM format and generated using the Diffie-Hellman (DH) algorithm.

The `priv_key_str` must be a private key in the PEM format and generated using the Diffie-Hellman (DH) algorithm.

## asymmetric_encrypt(*algorithm, str, key_str*)

Encrypts a string using the algorithm and a key string.

### asymmetric_encrypt output

A ciphertext as a binary string.

### asymmetric_encrypt parameters

The parameters are the following:

* algorithm - the encryption algorithm supports RSA to encrypt the string.

* str - measured in bytes. The length of the string must not be greater than the key_str modulus length in bytes - 11 (additional bytes used for PKCS1 padding)

* key_str - a key (either private or public) in the PEM format

## asymmetric_sign(*algorithm, digest_str, priv_key_str, digest_type*)

Signs a digest string using a private key string.

### asymmetric_sign output

A signature is a binary string.

### asymmetric_sign parameters

The parameters are the following:

* algorithm - the encryption algorithm supports either RSA or DSA to encrypt the string.

* digest_str - the digest binary string that is signed. Invoking create_digest generates the digest.

* priv_key_str - the private key used to sign the digest string. The key must be in the PEM format.

* digest_type - the OpenSSL version installed on your system determines the available hash functions. The following table lists these functions:

    | OpenSSL 1.0.2 | OpenSSL 1.1.0 | OpenSSL 1.1.1 | OpenSSL 3.0.x |
    |---|---|---|---|
    | md5 | md5 | md5 | md5 |
    | sha1 | sha1 | sha1 | sha1 |
    | sha224 | sha224 | sha224 | sha224 |
    | sha384 | sha384 | sha384 | sha384 |
    | sha512 | sha512 | sha512 | sha512 |
    | md4 | md4 | md4 | md4 |
    | sha | md5-sha1 | md5-sha1 | md5-sha1 |
    | ripemd160 | ripemd160 | ripemd160 | sha512-224 |
    | whirlpool | whirlpool | sha512-224 | sha512-256 |
    |  | blake2b512 | sha512-256 | sha3-224 |
    |  | blake2s256 | whirlpool | sha3-256 |
    |  |  | sm3 | sha3-384 |
    |  |  | blake2b512 | sha3-512 |
    |  |  | blake2s256 |  |
    |  |  | sha3-224 |  |
    |  |  | sha3-384 |  |
    |  |  | sha3-512 |  |
    |  |  | shake128 |  |
    |  |  | shake256 |  |

## asymmetric_verify(*algorithm, digest_str, sig_str, pub_key_str, digest_type*)

Verifies whether the signature string matches the digest string.

### asymmetric_verify output

A `1` (success) or a `0` (failure).

### asymmetric_verify parameters

The parameters are the following:

* algorithm - supports either ‘RSA’ or ‘DSA’.

* digest_str - invoking create_digest generates this digest binary string.

* sig_str - the signature binary string. Invoking asymmetric_sign generates this string.

* pub_key_str - the signer’s public key string. This string must correspond to the private key passed to asymmetric_sign to generate the signature string. The string must be in the PEM format.

* digest_type - the supported values are listed in the digest type table of create_digest

## create_asymmetric_priv_key(*algorithm, (key_len | dh_parameters)*)

Generates a private key using the given algorithm and key length for RSA or DSA
or Diffie-Hellman parameters for DH. For RSA or DSA, if needed, execute `KILL
[QUERY|CONNECTION] <id>` to terminate a long-lasting key generation. The
DH key generation from existing parameters is a quick operation. Therefore, it
does not make sense to terminate that operation with `KILL`.

### create_asymmetric_priv_key output

The key as a string in the PEM format.

### create_asymmetric_priv_key parameters

The parameters are the following:

* algorithm - the supported values are ‘RSA’, ‘DSA’, or ‘DH’.

* key_len - the supported key length values are the following:

    * RSA - the minimum length is 1,024. The maximum length is 16,384.

    * DSA - the minimum length is 1,024. The maximum length is 9,984.

    !!! note 
 
        The key length limits are defined by OpenSSL. To change the maximum key length, use either encryption_udf.rsa_bits_threshold or encryption_udf.dsa_bits_threshold.

* dh_parameters - Diffie-Hellman (DH) parameters. Invoking create_dh_parameter creates the DH parameters.

## create_asymmetric_pub_key(*algorithm, priv_key_str*)

Derives a public key from the given private key using the given algorithm.

### create_asymmetric_pub_key output

The key as a string in the PEM format.

### create_asymmetric_pub_key parameters

The parameters are the following:

* algorithm - the supported values are ‘RSA’, ‘DSA’, or ‘DH’.

* priv_key_str - must be a valid key string in the PEM format.

## create_dh_parameters(*key_len*)

Creates parameters for generating a Diffie-Hellman (DH) private/public key pair.
If needed, execute `KILL [QUERY|CONNECTION] <id>` to terminate the generation of long-lasting parameters.

Generating the DH parameters can take more time than generating the RSA keys or
the DSA keys.
OpenSSL defines the parameter length limits. To change the
maximum parameter length, use encryption_udf.dh_bits_threshold.

### create_dh_parameters output

A string in the PEM format and can be passed to create_asymmetric_private_key.

### create_dh_parameters parameters

The parameters are the following:

* key_len - the range for the key length is from 1024 to 10,000. The default value is 10,000.

## create_digest(*digest_type, str*)

Creates a digest from the given string using the given digest type. The digest string can be used with asymmetric_sign and asymmetric_verify.

### create_digest output

The digest of the given string as a binary string

### create_digest parameters

The parameters are the following:

* digest_type - the OpenSSL version installed on your system determines the available hash functions. The following table lists these functions:

    | OpenSSL 1.0.2 | OpenSSL 1.1.0 | OpenSSL 1.1.1 | OpenSSL 3.0.x |
    |---|---|---|---|
    | md5 | md5 | md5 | md5 |
    | sha1 | sha1 | sha1 | sha1 |
    | sha224 | sha224 | sha224 | sha224 |
    | sha384 | sha384 | sha384 | sha384 |
    | sha512 | sha512 | sha512 | sha512 |
    | md4 | md4 | md4 | md4 |
    | sha | md5-sha1 | md5-sha1 | md5-sha1 |
    | ripemd160 | ripemd160 | ripemd160 | sha512-224 |
    | whirlpool | whirlpool | sha512-224 | sha512-256 |
    |  | blake2b512 | sha512-256 | sha3-224 |
    |  | blake2s256 | whirlpool | sha3-256 |
    |  |  | sm3 | sha3-384 |
    |  |  | blake2b512 | sha3-512 |
    |  |  | blake2s256 | sm3 |
    |  |  | sha3-224 | blake2b512 |
    |  |  | sha3-384 | blake2s256 |
    |  |  | sha3-512 | blake2b512 |
    |  |  | shake128 | blake2s256 |
    |  |  | shake256 |  |

* str - String used to generate the digest string.

### Encryption threshold variables

The maximum key length limits are defined by OpenSSL. Server administrators can limit the maximum key length using the encryption threshold variables.

The variables are automatically registered when component_encryption_udf is installed.

| Variable Name                    |
|----------------------------------|
| encryption_udf.dh_bits_threshold |

### `encryption_udf.dh_bits_threshold`

The variable sets the maximum limit for the create_dh_parameters user-defined function and takes precedence over the OpenSSL maximum length value.

| Option       | Description      |
|--------------|------------------|
| command-line | Yes              |
| scope        | Global           |
| data type    | unsigned integer |
| default      | 10000            |

The range for this variable is from 1024 to 10,000. The default value is 10,000.

### encryption_udf.dsa_bits_threshold

The variable sets the threshold limits for create_asymmetric_priv_key user-defined function when the function is invoked with the DSA parameter and takes precedence over the OpenSSL maximum length value.

| Option       | Description      |
|--------------|------------------|
| command-line | Yes              |
| scope        | Global           |
| data type    | unsigned integer |
| default      | 9984             |

The range for this variable is from 1,024 to 9,984. The default value is 9,984.

### encryption_udf.rsa_bits_threshold

The variable sets the threshold limits for the create_asymmetric_priv_key user-defined function when the function is invoked with the RSA parameter and takes precedence over the OpenSSL maximum length value.

| Option       | Description      |
|--------------|------------------|
| command-line | Yes              |
| scope        | Global           |
| data type    | unsigned integer |
| default      | 16384            |

The range for this variable is from 1,024 to 16,384. The default value is 16,384.

### Examples

Code examples for the following operations:

* set the threshold variables

* create a private key

* create a public key

* encrypt data

* decrypt data

```{.bash data-prompt="mysql>"}
-- Set Global variable
mysql> SET GLOBAL encryption_udf.dh_bits_threshold = 4096;

-- Set Global variable
mysql> SET GLOBAL encryption_udf.rsa_bits_threshold = 4096;
```

```{.bash data-prompt="mysql>"}
-- Create private key
mysql> SET @private_key = create_asymmetric_priv_key('RSA', 3072);

-- Create public key
mysql> SET @public_key = create_asymmetric_pub_key('RSA', @private_key);

-- Encrypt data using the private key (you can also use the public key)
mysql> SET @ciphertext = asymmetric_encrypt('RSA', 'This text is secret', @private_key);

-- Decrypt data using the public key (you can also use the private key)
-- The decrypted value @plaintext should be identical to the original 'This text is secret'
mysql> SET @plaintext = asymmetric_decrypt('RSA', @ciphertext, @public_key);
```

Code examples for the following operations:

* generate a digest string

* generate a digest signature

* verify the signature against the digest

```{.bash data-prompt="mysql>"}
-- Generate a digest string
mysql> SET @digest = create_digest('SHA256', 'This is the text for digest');

-- Generate a digest signature
mysql> SET @signature = asymmetric_sign('RSA', @digest, @private_key, 'SHA256');

-- Verify the signature against the digest
-- The @verify_signature must be equal to 1
mysql> SET @verify_signature = asymmetric_verify('RSA', @digest, @signature, @public_key, 'SHA256');
```

Code examples for the following operations:

* generate a DH parameter

* generates two DH key pairs

* generate a symmetric key using the public_1 and the private_2

* generate a symmetric key using the public_2 and the private_1

```{.bash data-prompt="mysql>"}
 -- Generate a DH parameter
 mysql> SET @dh_parameter = create_dh_parameters(3072);

 -- Generate DH key pairs
 mysql> SET @private_1 = create_asymmetric_priv_key('DH', @dh_parameter);
 mysql> SET @public_1 = create_asymmetric_pub_key('DH', @private_1);
 mysql> SET @private_2 = create_asymmetric_priv_key('DH', @dh_parameter);
 mysql> SET @public_2 = create_asymmetric_pub_key('DH', @private_2);

-- Generate a symmetric key using the public_1 and private_2
-- The @symmetric_1 must be identical to @symmetric_2
mysql> SET symmetric_1 = asymmetric_derive(@public_1, @private_2);

-- Generate a symmetric key using the public_2 and private_1
-- The @symmetric_2 must be identical to @symmetric_1
mysql> SET symmetric_2 = asymmetric_derive(@public_2, @private_1);
```

Code examples for the following operations:

* create a private key using a `SET` statement

* create a private key using a  `SELECT` statement

* create a private key using an `INSERT` statement

```{.bash data-prompt="mysql>"}
mysql> SET @private_key1 = create_asymmetric_priv_key('RSA', 3072);
mysql> SELECT create_asymmetric_priv_key('RSA', 3072) INTO @private_key2;
mysql> INSERT INTO key_table VALUES(create_asymmetric_priv_key('RSA', 3072));
```

## Uninstall component_encryption_udf

You can deactivate and uninstall the component using the [Uninstall Component statement](https://dev.mysql.com/doc/refman/8.0/en/uninstall-component.html).

```{.bash data-prompt="mysql>"}
mysql> UNINSTALL COMPONENT 'file://component_encryption_udf';
```