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SELECT hex(HMAC('sha256', 'The quick brown fox jumps over the lazy dog', 'secret_key'));

┌─hex(HMAC('sha256', 'The quick brown fox jumps over the lazy dog', 'secret_key'))─┐
│ 31FD15FA0F61FD40DC09D919D4AA5B4141A0B27C1D51E74A6789A890AAAA187C                 │
└──────────────────────────────────────────────────────────────────────────────────┘

SELECT
    hex(HMAC('md5', 'message', 'key')) AS hmac_md5,
    hex(HMAC('sha1', 'message', 'key')) AS hmac_sha1,
    hex(HMAC('sha256', 'message', 'key')) AS hmac_sha256;

┌─hmac_md5─────────────────────────┬─hmac_sha1────────────────────────────────┬─hmac_sha256──────────────────────────────────────────────────────┐
│ 4E4748E62B463521F6775FBF921234B5 │ 2088DF74D5F2146B48146CAF4965377E9D0BE3A4 │ 6E9EF29B75FFFC5B7ABAE527D58FDADB2FE42E7219011976917343065F58ED4A │
└──────────────────────────────────┴──────────────────────────────────────────┴──────────────────────────────────────────────────────────────────┘

SELECT
    hmac('SHA256', 'message', 'key') = HMAC('sha256', 'message', 'key') AS same_result,
    HMAC('SHA256', 'message', 'key') = Hmac('Sha256', 'message', 'key') AS also_same;

┌─same_result─┬─also_same─┐
│           1 │         1 │
└─────────────┴───────────┘

-- Let's decrypt data we've previously encrypted with MySQL:
mysql> SET  block_encryption_mode='aes-256-ofb';
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT aes_encrypt('Secret', '123456789101213141516171819202122', 'iviviviviviviviv123456') as ciphertext;
+------------------------+
| ciphertext             |
+------------------------+
| 0x24E9E4966469         |
+------------------------+
1 row in set (0.00 sec)

SELECT aes_decrypt_mysql('aes-256-ofb', unhex('24E9E4966469'), '123456789101213141516171819202122', 'iviviviviviviviv123456') AS plaintext

┌─plaintext─┐
│ Secret    │
└───────────┘

-- Given equal input encrypt and aes_encrypt_mysql produce the same ciphertext:
SELECT encrypt('aes-256-ofb', 'Secret', '12345678910121314151617181920212', 'iviviviviviviviv') = aes_encrypt_mysql('aes-256-ofb', 'Secret', '12345678910121314151617181920212', 'iviviviviviviviv') AS ciphertexts_equal;

┌─ciphertexts_equal─┐
│                 1 │
└───────────────────┘

-- But encrypt fails when key or iv is longer than expected:
SELECT encrypt('aes-256-ofb', 'Secret', '123456789101213141516171819202122', 'iviviviviviviviv123');

Received exception from server (version 22.6.1):
Code: 36. DB::Exception: Received from localhost:9000. DB::Exception: Invalid key size: 33 expected 32: While processing encrypt('aes-256-ofb', 'Secret', '123456789101213141516171819202122', 'iviviviviviviviv123').

-- aes_encrypt_mysql produces MySQL-compatible output:
SELECT hex(aes_encrypt_mysql('aes-256-ofb', 'Secret', '123456789101213141516171819202122', 'iviviviviviviviv123')) AS ciphertext;

┌─ciphertext───┐
│ 24E9E4966469 │
└──────────────┘

-- Notice how supplying even longer IV produces the same result
SELECT hex(aes_encrypt_mysql('aes-256-ofb', 'Secret', '123456789101213141516171819202122', 'iviviviviviviviv123456')) AS ciphertext

┌─ciphertext───┐
│ 24E9E4966469 │
└──────────────┘

-- Re-using the table from the encrypt function example
SELECT comment, hex(secret) FROM encryption_test;

┌─comment──────────────┬─hex(secret)──────────────────────────────────┐
│ aes-256-gcm          │ A8A3CCBC6426CFEEB60E4EAE03D3E94204C1B09E0254 │
│ aes-256-gcm with AAD │ A8A3CCBC6426D9A1017A0A932322F1852260A4AD6837 │
└──────────────────────┴──────────────────────────────────────────────┘
┌─comment──────────────────────────┬─hex(secret)──────────────────────┐
│ aes-256-ofb no IV                │ B4972BDC4459                     │
│ aes-256-ofb no IV, different key │ 2FF57C092DC9                     │
│ aes-256-ofb with IV              │ 5E6CB398F653                     │
│ aes-256-cbc no IV                │ 1BC0629A92450D9E73A00E7D02CF4142 │
└──────────────────────────────────┴──────────────────────────────────┘

SELECT comment, decrypt('aes-256-cfb128', secret, '12345678910121314151617181920212') AS plaintext FROM encryption_test

-- Notice how only a portion of the data was properly decrypted, and the rest is gibberish since either `mode`, `key`, or `iv` were different upon encryption.
┌─comment──────────────┬─plaintext──┐
│ aes-256-gcm          │ OQ�E
                             �t�7T�\���\�   │
│ aes-256-gcm with AAD │ OQ�E
                             �\��si����;�o�� │
└──────────────────────┴────────────┘
┌─comment──────────────────────────┬─plaintext─┐
│ aes-256-ofb no IV                │ Secret    │
│ aes-256-ofb no IV, different key │ �4�
                                        �         │
│ aes-256-ofb with IV              │ ���6�~        │
│aes-256-cbc no IV                │ �2*4�h3c�4w��@
└──────────────────────────────────┴───────────┘

CREATE TABLE encryption_test
(
    `comment` String,
    `secret` String
)
ENGINE = MergeTree;

INSERT INTO encryption_test VALUES
('aes-256-ofb no IV', encrypt('aes-256-ofb', 'Secret', '12345678910121314151617181920212')),
('aes-256-ofb no IV, different key', encrypt('aes-256-ofb', 'Secret', 'keykeykeykeykeykeykeykeykeykeyke')),
('aes-256-ofb with IV', encrypt('aes-256-ofb', 'Secret', '12345678910121314151617181920212', 'iviviviviviviviv')),
('aes-256-cbc no IV', encrypt('aes-256-cbc', 'Secret', '12345678910121314151617181920212'));

SELECT comment, hex(secret) FROM encryption_test;

┌─comment──────────────────────────┬─hex(secret)──────────────────────┐
│ aes-256-ofb no IV                │ B4972BDC4459                     │
│ aes-256-ofb no IV, different key │ 2FF57C092DC9                     │
│ aes-256-ofb with IV              │ 5E6CB398F653                     │
│ aes-256-cbc no IV                │ 1BC0629A92450D9E73A00E7D02CF4142 │
└──────────────────────────────────┴──────────────────────────────────┘

INSERT INTO encryption_test VALUES
('aes-256-gcm', encrypt('aes-256-gcm', 'Secret', '12345678910121314151617181920212', 'iviviviviviviviv')),

('aes-256-gcm with AAD', encrypt('aes-256-gcm', 'Secret', '12345678910121314151617181920212', 'iviviviviviviviv', 'aad'));

SELECT comment, hex(secret) FROM encryption_test WHERE comment LIKE '%gcm%';

┌─comment──────────────┬─hex(secret)──────────────────────────────────┐
│ aes-256-gcm          │ A8A3CCBC6426CFEEB60E4EAE03D3E94204C1B09E0254 │
│ aes-256-gcm with AAD │ A8A3CCBC6426D9A1017A0A932322F1852260A4AD6837 │
└──────────────────────┴──────────────────────────────────────────────┘

-- Let's create a table where user_id is the unique user id, encrypted is an encrypted string field, iv is an initial vector for decrypt/encrypt.
-- Assume that users know their id and the key to decrypt the encrypted field:
CREATE TABLE decrypt_null
(
    dt DateTime,
    user_id UInt32,
    encrypted String,
    iv String
)
ENGINE = MergeTree;

-- Insert some data:
INSERT INTO decrypt_null VALUES
('2022-08-02 00:00:00', 1, encrypt('aes-256-gcm', 'value1', 'keykeykeykeykeykeykeykeykeykey01', 'iv1'), 'iv1'),
('2022-09-02 00:00:00', 2, encrypt('aes-256-gcm', 'value2', 'keykeykeykeykeykeykeykeykeykey02', 'iv2'), 'iv2'),
('2022-09-02 00:00:01', 3, encrypt('aes-256-gcm', 'value3', 'keykeykeykeykeykeykeykeykeykey03', 'iv3'), 'iv3');

-- Try decrypt with one key
SELECT
    dt,
    user_id,
    tryDecrypt('aes-256-gcm', encrypted, 'keykeykeykeykeykeykeykeykeykey02', iv) AS value
FROM decrypt_null
ORDER BY user_id ASC

┌──────────────────dt─┬─user_id─┬─value──┐
│ 2022-08-02 00:00:00 │       1 │ ᴺᵁᴸᴸ   │
│ 2022-09-02 00:00:00 │       2 │ value2 │
│ 2022-09-02 00:00:01 │       3 │ ᴺᵁᴸᴸ   │
└─────────────────────┴─────────┴────────┘