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