SQL Data Encryption Challenge

In many applications, sensitive data stored in databases needs to be protected from unauthorized access. This challenge focuses on implementing a basic form of data encryption directly within SQL to safeguard sensitive fields. Successfully completing this will demonstrate your understanding of data security principles and SQL's capabilities in handling such tasks.

Problem Description

Your task is to implement a mechanism for encrypting and decrypting sensitive string data stored in a database table using SQL. You will need to create functions or procedures that can take a plaintext string and return its encrypted version, and vice-versa. The encryption method should be deterministic for simplicity, meaning the same input will always produce the same output.

Key Requirements:

• Encryption Function: Create a SQL function (or equivalent stored procedure) that accepts a plaintext string and returns its encrypted representation.
• Decryption Function: Create a SQL function (or equivalent stored procedure) that accepts an encrypted string and returns its original plaintext representation.
• Deterministic Encryption: The encryption process must be deterministic.
• Basic Transformation: The encryption should involve a simple, reversible transformation of the input string characters. For example, shifting characters by a fixed amount (like a Caesar cipher) or substituting characters based on a predefined mapping.

Expected Behavior:

• Encrypting a given string should produce a consistent, seemingly random, but reversible output.
• Decrypting the output of the encryption function should yield the original plaintext string.
• Attempting to decrypt a string that was not encrypted using the corresponding function should ideally produce an error or a clearly unreadable result.

Edge Cases to Consider:

• Empty strings.
• Strings containing special characters, numbers, and different cases (uppercase/lowercase).
• Maximum string length limitations (if any are imposed by the chosen encryption method).

Examples

Example 1: Simple Caesar Cipher Encryption

Assume a Caesar cipher with a shift of +3.

Input: PLAINTEXT_DATA = 'SECRET'

Output (for Encryption Function): ENCRYPTED_DATA = 'VHFUHW'

Explanation: Each letter in 'SECRET' is shifted 3 positions forward in the alphabet. S -> V, E -> H, C -> F, R -> U, E -> H, T -> W.

Input: ENCRYPTED_DATA = 'VHFUHW'

Output (for Decryption Function): PLAINTEXT_DATA = 'SECRET'

Explanation: Each letter in 'VHFUHW' is shifted 3 positions backward in the alphabet. V -> S, H -> E, F -> C, U -> R, H -> E, W -> T.

Example 2: Encryption with a Character Map

Assume a custom mapping for encryption: 'a' -> 'z', 'b' -> 'y', ..., 'z' -> 'a' 'A' -> 'Z', 'B' -> 'Y', ..., 'Z' -> 'A' Numbers and special characters remain unchanged.

Input: PLAINTEXT_DATA = 'Hello World 123!'

Output (for Encryption Function): ENCRYPTED_DATA = 'Svyyq Dliow 123!'

Explanation: 'H' becomes 'S', 'e' becomes 'v', 'l' becomes 'y', 'o' becomes 'l', space remains space, 'W' becomes 'D', 'r' becomes 'i', 'd' becomes 'w', numbers and '!' remain unchanged.

Input: ENCRYPTED_DATA = 'Svyyq Dliow 123!'

Output (for Decryption Function): PLAINTEXT_DATA = 'Hello World 123!'

Explanation: The decryption process reverses the character map. 'S' becomes 'H', 'v' becomes 'e', 'y' becomes 'l', 'l' becomes 'o', etc.

Constraints

• The encryption and decryption functions must be implemented using standard SQL syntax, compatible with common relational database systems (e.g., PostgreSQL, MySQL, SQL Server, Oracle).
• The maximum length of a string to be encrypted is 255 characters.
• The encryption algorithm should be simple enough that its computational complexity for both encryption and decryption is linear with respect to the length of the input string (O(n)).
• The implemented solution should be able to handle ASCII characters.

Notes

• This challenge focuses on demonstrating encryption within SQL, not on creating a cryptographically secure solution. Real-world applications require much more robust encryption methods.
• Consider using SQL's built-in string manipulation functions (e.g., SUBSTRING, REPLACE, ASCII, CHAR) to implement your transformations.
• For the character mapping example, you might explore using CASE statements or a separate lookup table within your SQL implementation.
• Think about how you would apply this to an actual table. For instance, you might have a Users table with a Password or CreditCardNumber column that you want to encrypt.