otp-cj OTP 库:HOTP/TOTP 实现(RFC 4226/6238)、Base32 编解码、otpauth URI 生成及 README

2026-08-21 08:43:24 +08:00
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+package simcu::otp.core
+
+/**
+ * HOTP（HMAC-based One-Time Password, RFC 4226）。
+ * 公式：HOTP(K,C) = Truncate(HMAC-SHA1(K, C)) mod 10^digits
+ */
+public class Hotp {
+    /// 生成一次性密码（默认 6 位）。counter 为 8 字节大端计数。
+    public static func generate(secret: Array<Byte>, counter: Int64): String {
+        generate(secret, counter, 6)
+    }
+
+    /// 生成一次性密码，指定位数。counter 为 8 字节大端计数。
+    public static func generate(secret: Array<Byte>, counter: Int64, digits: Int64): String {
+        // counter → 8 字节大端
+        var counterBytes = Array<Byte>(8, repeat: 0)
+        var c = counter
+        var i = 7
+        while (i >= 0) {
+            counterBytes[i] = UInt8(c & 0xff)
+            c = c >> 8
+            i -= 1
+        }
+        let hmac = HmacSha1(secret)
+        let hs = hmac.compute(counterBytes)
+        let offset = Int64(hs[19]) & 0x0f
+        let binCode = ((Int64(hs[offset]) & 0x7f) << 24) |
+            (Int64(hs[offset + 1]) << 16) |
+            (Int64(hs[offset + 2]) << 8) |
+            Int64(hs[offset + 3])
+        let mod = pow10(digits)
+        let code = binCode % mod
+        padLeft(code.toString(), digits)
+    }
+
+    private static func pow10(n: Int64): Int64 {
+        var r: Int64 = 1
+        var i = 0
+        while (i < n) {
+            r *= 10
+            i += 1
+        }
+        r
+    }
+
+    private static func padLeft(s: String, width: Int64): String {
+        var r = s
+        while (r.size < width) {
+            r = "0" + r
+        }
+        r
+    }
+}