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TOTP-algorithm/Rust-TOTP-algoritm.md

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+# Implementation of the TOTP algorithm in Rust
+
+```Rust
+use base32::decode;
+use chrono::Utc;
+use sha1::{digest::Update, Digest, Sha1};
+
+const INTERVAL: u64 = 30;
+const TOTP_KEY: &str = "BOMY6BV5BWVJEWJ4ZLDYKN3LSIS736B3";
+
+fn generate() {
+    // Pre-process data
+    let epoch = Utc::now().timestamp() as u64;
+    let msg = epoch / INTERVAL;
+    let bytes_msg = msg.to_be_bytes();
+
+    let key_decoded = decode(base32::Alphabet::RFC4648 { padding: false }, TOTP_KEY).unwrap();
+
+    // HMAC-SHA1
+    let mut key_pad = key_decoded.clone();
+    key_pad.resize(64, 0);
+
+    let i_key_pad: Vec<u8> = key_pad.iter().map(|&x| x ^ 0x36).collect();
+    let o_key_pad: Vec<u8> = key_pad.iter().map(|&x| x ^ 0x5C).collect();
+
+    let mut i_key_pad_msg = Vec::new();
+    i_key_pad_msg.extend_from_slice(&i_key_pad);
+    i_key_pad_msg.extend_from_slice(&bytes_msg);
+
+    let i_key_pad_msg_hashed = Sha1::new().chain(&i_key_pad_msg).finalize();
+
+    let mut o_key_pad_msg = Vec::new();
+    o_key_pad_msg.extend_from_slice(&o_key_pad);
+    o_key_pad_msg.extend_from_slice(&i_key_pad_msg_hashed);
+
+    let hmac_result = Sha1::new().chain(&o_key_pad_msg).finalize();
+
+    // TOTP Algorithm
+    let start = (hmac_result[19] & 0xF) as usize;
+    let raw_bytes: [u8; 4] = hmac_result[start..start + 4].try_into().unwrap();
+    let raw_token = u32::from_be_bytes(raw_bytes);
+    let raw_token = raw_token & 0x7F_FF_FF_FF;
+    let token = raw_token % 1_000_000;
+
+    println!("{:06}", token);
+}
+
+```