feat: add TOTPGenerator (RFC 6238)

2026-05-22 14:44:50 +02:00
parent 3b71a92089
commit 3af6c9ad31
2 changed files with 84 additions and 0 deletions
@@ -0,0 +1,50 @@
+import Foundation
+import CryptoKit
+
+public enum TOTPGenerator {
+    public static func generate(config: TOTPConfig, at date: Date = Date()) -> String {
+        let counter = UInt64(date.timeIntervalSince1970) / UInt64(config.period)
+        let keyBytes = base32Decode(config.secret)
+        let counterBytes = withUnsafeBytes(of: counter.bigEndian, Array.init)
+        let symKey = SymmetricKey(data: keyBytes)
+        let hmacBytes: [UInt8]
+        switch config.algorithm {
+        case .sha1:
+            hmacBytes = Array(HMAC<Insecure.SHA1>.authenticationCode(for: counterBytes, using: symKey))
+        case .sha256:
+            hmacBytes = Array(HMAC<SHA256>.authenticationCode(for: counterBytes, using: symKey))
+        case .sha512:
+            hmacBytes = Array(HMAC<SHA512>.authenticationCode(for: counterBytes, using: symKey))
+        }
+        let offset = Int(hmacBytes[hmacBytes.count - 1] & 0x0f)
+        let truncated = ((Int(hmacBytes[offset]) & 0x7f) << 24)
+            | (Int(hmacBytes[offset + 1]) << 16)
+            | (Int(hmacBytes[offset + 2]) << 8)
+            |  Int(hmacBytes[offset + 3])
+        let otp = truncated % Int(pow(10.0, Double(config.digits)))
+        return String(format: "%0\(config.digits)d", otp)
+    }
+
+    public static func secondsRemaining(config: TOTPConfig, at date: Date = Date()) -> Int {
+        let elapsed = Int(date.timeIntervalSince1970) % config.period
+        return config.period - elapsed
+    }
+
+    private static func base32Decode(_ input: String) -> [UInt8] {
+        let alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
+        let s = input.uppercased().filter { alphabet.contains($0) }
+        var result: [UInt8] = []
+        var buffer = 0
+        var bitsLeft = 0
+        for char in s {
+            guard let idx = alphabet.firstIndex(of: char) else { continue }
+            buffer = (buffer << 5) | alphabet.distance(from: alphabet.startIndex, to: idx)
+            bitsLeft += 5
+            if bitsLeft >= 8 {
+                bitsLeft -= 8
+                result.append(UInt8((buffer >> bitsLeft) & 0xff))
+            }
+        }
+        return result
+    }
+}