Add docs on column-level encryption

Fixes DOC-8057

Summary of changes:

- Add a new page, 'Column Level Encryption', to the security reference
  section

- Add links to the new page from our existing Encryption at Rest docs

src/current/_includes/v23.2/sidebar-data/reference.json

@@ -377,6 +377,12 @@
               "/${VERSION}/security-reference/encryption.html"
             ]
           },
+          {
+            "title": "Column Level Encryption",
+            "urls": [
+              "/${VERSION}/column-level-encryption.html"
+            ]
+          },
           {
             "title": "PKI and TLS",
             "urls": [

src/current/v23.2/column-level-encryption.md

@@ -0,0 +1,200 @@
+---
+title: Column Level Encryption
+summary: SQL users are required to pass encryption keys when reading from or writing to specific columns
+toc: true
+docs_area: reference.sql
+---
+
+CockroachDB v23.2 and later support _column level encryption_. Using this feature, you can encrypt one or more of the columns in each row of a database table.
+
+Column level encryption can be useful for compliance scenarios such as adhering to PCI or GDPR.
+
+Once a column is encrypted, SQL users are required to pass an encryption key when reading from or writing to that column. This prevents users without the encryption key from taking actions like the following:
+
+- Reading sensitive information (like _personally identifiable information_ ([PII](https://en.wikipedia.org/wiki/Personal_data))) when accessing the tables.
+- Adding or updating records without encrypting the specified columns.
+
+{{site.data.alerts.callout_info}}
+The "column-level encryption" feature described on this page specifically refers to either symmetric-key encryption or public-key encryption of data, **not** hashing functions operating on data.
+{{site.data.alerts.end}}
+
+{% include enterprise-feature.md %}
+
+## Available Functions
+
+### `encrypt` and `encrypt_iv`
+
+The `encrypt` and `encrypt_iv` functions encrypts a column's data with a given key and cipher method. For more information, see [Cryptographic functions]({% link {{ page.version.version }}/functions-and-operators.md %}#cryptographic-functions).
+
+For usage examples, see:
+
+- [Encrypt using the `encrypt` function](#encrypt-using-the-encrypt-function).
+- [Encrypt using the `encrypt_iv` function](#encrypt-using-the-encryptiv-function).
+
+These functions require an [enterprise license]({% link {{ page.version.version }}/enterprise-licensing.md %}). If you do not have an enterprise license, you will see an error message like the following if you try to use them:
+
+~~~
+ERROR:  encrypt(): use of pgcrypto cipher functions requires an enterprise license. see https://cockroachlabs.com/pricing for details on how to enable enterprise features
+~~~
+
+{{site.data.alerts.callout_info}}
+For more information about whether to use the `encrypt` or `encrypt_iv` variants of this function, see [Whether to use `encrypt` or `encrypt_iv`?](#whether-to-use-encrypt-and-decrypt-or-encrypt_iv-and-decrypt_iv).
+{{site.data.alerts.end}}
+
+### `decrypt` and `decrypt_iv`
+
+The `decrypt` and `decrypt_iv` functions decrypt an encrypted column's data with a given key and cipher method. For more information, see [Cryptographic functions]({% link {{ page.version.version }}/functions-and-operators.md %}#cryptographic-functions).
+
+For usage examples, see:
+
+- [Decrypt using the `decrypt` function](#encrypt-using-the-decrypt-function).
+- [Decrypt using the `decrypt_iv` function](#encrypt-using-the-decryptiv-function).
+
+These functions require an [enterprise license]({% link {{ page.version.version }}/enterprise-licensing.md %}). If you do not have an enterprise license, you will see an error message like the following if you try to use them:
+
+~~~
+ERROR:  decrypt(): use of pgcrypto cipher functions requires an enterprise license. see https://cockroachlabs.com/pricing for details on how to enable enterprise features
+~~~
+
+{{site.data.alerts.callout_info}}
+For more information about whether to use the `decrypt` or `decrypt_iv` variants of this function, see [Whether to use `encrypt` or `encrypt_iv`?](#whether-to-use-encrypt-and-decrypt-or-encrypt_iv-and-decrypt_iv).
+{{site.data.alerts.end}}
+
+## Security considerations
+
+### Whether to use `encrypt` and `decrypt` or `encrypt_iv` and `decrypt_iv`?
+
+Both `encrypt` and `decrypt` have `*_iv` variants: `encrypt_iv` and `decrypt_iv`.
+
+The benefits of using `encrypt_iv` and `decrypt_iv` include:
+
+- Avoid Repetition: If you use the same encryption key and method to encrypt the same plaintext multiple times without an IV, you'll get the same ciphertext every time. This repetition can provide a point of attack for someone trying to break the encryption. By using an IV, even the same plaintext will produce different ciphertexts, provided a different IV is used each time.
+- Defend Against Pattern Analysis: Without an IV, if two users have the same SSN or piece of data, their encrypted values will also be the same. An attacker can exploit these patterns. By using different IVs for each encryption, the encrypted values will be different even if the plaintext values are the same.
+- Cipher Block Chaining (CBC) Mode: Many encryption algorithms, like AES, operate on blocks of data. In modes like CBC, the previous block of ciphertext is used as an IV for the encryption of the next block. This means that even if there are patterns in the plaintext, they won't appear in the ciphertext. However, for the first block, there is no previous block of ciphertext, so an IV is used. This is another way IVs help in breaking up patterns in the ciphertext.
+- Mitigate Replay Attacks: Since the IV is typically random and changed for every encryption, it makes replay attacks more difficult. An attacker can't simply take an old piece of encrypted data and send it again, as the IV will likely have changed.
+
+The drawbacks of using `encrypt_iv` and `decrypt_iv` include:
+
+- Storage: You need to store the IV alongside the ciphertext. It's common practice to prepend or append the IV to the ciphertext before storing it. Unlike the encryption key, the IV doesn't need to be kept secret, but it does need to be known for decryption.
+- Randomness: It's crucial that IVs are random and not predictable. If an attacker can predict the next IV, some of the security benefits are negated.
+- Unique IVs with the Same Key: While IVs need to be random, it's also essential that the same IV isn't used twice with the same encryption key. Doing so can leak information about the plaintext.
+
+You will need to assess your risk profile to determine which functions to use.
+
+### How AES variants are determined
+
+The actual AES variant (AES-128, AES-192, or AES-256) is determined by the length of the encryption key you provide in the functions:
+
+- AES-128: 16-byte key
+- AES-192: 24-byte key
+- AES-256: 32-byte key
+
+Keys have to be 16-, 24-, or 32-byte lengths and map to the corresponding AES encryption strength.
+
+## Performance considerations
+
+[XXX](): write stuff based on Dikshant's comments
+
+## Examples
+
+### Setup
+
+The examples in this section operate on the following table.
+
+{% include_cached copy-clipboard.html %}
+~~~ sql
+CREATE TABLE IF NOT EXISTS users (
+    user_id UUID DEFAULT uuid_generate_v4() PRIMARY KEY,
+    name VARCHAR(255),
+    encrypted_ssn BYTES,
+    ssn_iv BYTES
+);
+~~~
+
+### Encrypt using the `encrypt` function
+
+{% include_cached copy-clipboard.html %}
+~~~ sql
+INSERT
+INTO
+    users (name, encrypted_ssn)
+VALUES
+    (
+        'John Doe',
+        encrypt(
+            '123-45-6789'::BYTES,
+            'your_secret_key'::BYTES,
+            'aes'
+        )
+    );
+~~~
+
+### Encrypt using the `encrypt_iv` function
+
+{% include_cached copy-clipboard.html %}
+~~~ sql
+WITH
+    iv AS (SELECT gen_random_bytes(16) AS iv)
+INSERT
+INTO
+    users (name, encrypted_ssn, ssn_iv)
+SELECT
+    'Jane Doe',
+    encrypt_iv(
+        '987-65-4321'::BYTES,
+        'your_secret_key'::BYTES,
+        iv,
+        'aes'
+    ),
+    iv
+FROM
+    iv;
+~~~
+
+### Decrypt using the `decrypt` function
+
+{% include_cached copy-clipboard.html %}
+~~~ sql
+SELECT
+    name,
+    convert_from(
+        decrypt(
+            encrypted_ssn,
+            'your_secret_key'::BYTES,
+            'aes'
+        ),
+        'UTF8'
+    )
+        AS ssn
+FROM
+    users
+WHERE
+    name = 'John Doe';
+~~~
+
+### Decrypt using the `decrypt_iv` function
+
+{% include_cached copy-clipboard.html %}
+~~~ sql
+SELECT
+    name,
+    convert_from(
+        decrypt_iv(
+            encrypted_ssn,
+            'your_secret_key'::BYTES,
+            ssn_iv,
+            'aes'
+        ),
+        'UTF8'
+    )
+        AS ssn
+FROM
+    users
+WHERE
+    name = 'Jane Doe';
+~~~
+
+## See also
+
++ [Encryption at Rest]({% link {{ page.version.version }}/encryption.md %})
++ [Cryptographic functions]({% link {{ page.version.version }}/functions-and-operators.md %}#cryptographic-functions)

src/current/v23.2/encryption.md

@@ -97,3 +97,8 @@ To check that the new key is active, use the stores report page in the DB Consol
 To disable encryption, specify `key=plain`. The data keys will be stored in plaintext and new data will not be encrypted.
 
 To rotate keys, specify `key=/path/to/my/new-aes-128.key` and `old-key=/path/to/my/old-aes-128.key`. The data keys will be decrypted using the old key and then encrypted using the new key. A new data key will also be generated.
+
+## See also
+
++ [Column Level Encryption]({% link {{ page.version.version }}/column-level-encryption.md %})
++ [Cryptographic functions]({% link {{ page.version.version }}/functions-and-operators.md %}#cryptographic-functions)