Add hotp.v

hotp.v

@@ -0,0 +1,44 @@
+module votp
+
+import encoding.base32
+import regex
+
+
+struct Hotp {
+	secret string
+	digits int
+	digest string
+}
+
+pub fn new_hotp(secret string, digits int, digest string) Hotp {
+	return Hotp{secret: secret, digits: digits, digest: digest}
+}
+
+pub fn (h Hotp) generate_hotp(counter int) string {
+	msg := u64_to_bytes(counter)
+	key := h.secret.to_upper()
+	query := r' '
+	mut re := regex.regex_opt(query) or { return "NAH!" }
+	res := re.replace(key, r'')
+	new_key := base32.decode(missing_pad(res).bytes()) or { return "SOMETHING_WENT_WRONG!" }
+	hash := get_hash(msg, new_key, h.digest)
+	offset := hash[(hash.len)-1] & 0xf
+	bin_code := (int(hash[offset])&0x7f)<<24 |
+		(int(hash[offset+1])&0xff)<<16 |
+		(int(hash[offset+2])&0xff)<<8 |
+		(int(hash[offset+3]) & 0xff)
+	code := bin_code % int_pow(10, h.digits)
+	return code.str()
+}
+
+
+pub fn (h Hotp) verify(otp int, counter int) bool{
+	totp := new_hotp(h.secret, h.digits, h.digest)
+	code := totp.generate_hotp(counter)
+	if code == otp.str() {
+		return true
+	}
+	return false
+}
+
+