Function sha224_hex 

pub fn sha224_hex(input: &str) -> String

Compute SHA224 hash and return as lowercase hex string.

This is the standard hash function used by the Trojan protocol.

Example

use trojan_auth::sha224_hex;

let hash = sha224_hex("password123");
assert_eq!(hash.len(), 56); // SHA224 = 224 bits = 28 bytes = 56 hex chars