国赛babytree 赛题解析

WriteUp 9个月前 admin

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题目给了一个txt文件，里面是swift的抽象语法树。

文本很长而且是我不熟悉的swift语言，所以先了解一下swift的抽象语法树吧。

swift开发环境搭建：https://www.fatbobman.com/posts/swift-in-linux/

例子：

var str = "hello"

使用如下命令将switf文件转换为ast文件。

swiftc -dump-ast hello.swift

国赛babytree 赛题解析

如图就是一个初始化语句的ast结构：

◆pattern_binding_decl：初始化语句

◆pattern_named type=’String’ ‘str’：变量名称

◆value=”hello”：变量值

在题目给出的ast中，有类似的结构。

(pattern_binding_decl range=[re.swift:18:5 - line:18:15]
            (pattern_named type='String' 'key')
            Original init:
            (string_literal_expr type='String' location=re.swift:18:15 range=[re.swift:18:15 - line:18:15] encoding=utf8 value="345y" builtin_initializer=Swift.(file).String extension.init(_builtinStringLiteral:utf8CodeUnitCount:isASCII:) initializer=**NULL**)
            Processed init:
            (string_literal_expr type='String' location=re.swift:18:15 range=[re.swift:18:15 - line:18:15] encoding=utf8 value="345y" builtin_initializer=Swift.(file).String extension.init(_builtinStringLiteral:utf8CodeUnitCount:isASCII:) initializer=**NULL**))

          (var_decl range=[re.swift:18:9 - line:18:9] "key" type='String' interface type='String' access=fileprivate let readImpl=stored immutable)

所以这一块结构的意思就是：

var key = "345y"

再看一个例子：

var num = 10
if num == 10 {
    num = 100
}

国赛babytree 赛题解析

if语句

◆if_stmt：if语句

◆declref_expr：比较的对象

◆integer_literal_expr：比较的值

赋值语句

◆assign_expr：赋值语句

◆declref_expr：赋值的对象

◆integer_literal_expr：赋值的值

其他的对应关系就不列出了，可以自己写代码对照。

(call_expr type='()' location=re.swift:20:5 range=[re.swift:20:5 - line:20:17] nothrow
            (declref_expr type='(Any..., String, String) -> ()' location=re.swift:20:5 range=[re.swift:20:5 - line:20:5] decl=Swift.(file).print(_:separator:terminator:) function_ref=single)
            (argument_list labels=_:separator:terminator:
              (argument
                (vararg_expansion_expr implicit type='Any...' location=re.swift:20:11 range=[re.swift:20:11 - line:20:11]
                  (array_expr implicit type='Any...' location=re.swift:20:11 range=[re.swift:20:11 - line:20:11] initializer=**NULL**
                    (erasure_expr implicit type='Any' location=re.swift:20:11 range=[re.swift:20:11 - line:20:11]
                      (declref_expr type='Bool' location=re.swift:20:11 range=[re.swift:20:11 - line:20:11] decl=re.(file).top-level [email protected]:19:9 function_ref=unapplied)))))
              (argument label=separator
                (default_argument_expr implicit type='String' location=re.swift:20:10 range=[re.swift:20:10 - line:20:10] default_args_owner=Swift.(file).print(_:separator:terminator:) param=1))
              (argument label=terminator
                (default_argument_expr implicit type='String' location=re.swift:20:10 range=[re.swift:20:10 - line:20:10] default_args_owner=Swift.(file).print(_:separator:terminator:) param=2))
            )))))))

◆call_expr：函数调用

◆declref_expr：调用的函数，decl=Swift.(file).print(_:separator:terminator:)，这里调用的是print函数

◆argument：参数

print(result)

这段代码中，调用了print函数，打印的是result的值，result是Bool类型的数据，所以程序会输出true或者false。

(pattern_binding_decl range=[re.swift:19:5 - line:19:33]
            (pattern_named type='Bool' 'result')
            Original init:
            (call_expr type='Bool' location=re.swift:19:18 range=[re.swift:19:18 - line:19:33] nothrow
              (declref_expr type='(String, String) -> Bool' location=re.swift:19:18 range=[re.swift:19:18 - line:19:18] decl=re.(file)[email protected]:1:6 function_ref=single)
              (argument_list
                (argument
                  (declref_expr type='String' location=re.swift:19:24 range=[re.swift:19:24 - line:19:24] decl=re.(file).top-level [email protected]:17:9 function_ref=unapplied))
                (argument
                  (declref_expr type='String' location=re.swift:19:30 range=[re.swift:19:30 - line:19:30] decl=re.(file).top-level [email protected]:18:9 function_ref=unapplied))
              ))
            Processed init:
            (call_expr type='Bool' location=re.swift:19:18 range=[re.swift:19:18 - line:19:33] nothrow
              (declref_expr type='(String, String) -> Bool' location=re.swift:19:18 range=[re.swift:19:18 - line:19:18] decl=re.(file)[email protected]:1:6 function_ref=single)
              (argument_list
                (argument
                  (declref_expr type='String' location=re.swift:19:24 range=[re.swift:19:24 - line:19:24] decl=re.(file).top-level [email protected]:17:9 function_ref=unapplied))
                (argument
                  (declref_expr type='String' location=re.swift:19:30 range=[re.swift:19:30 - line:19:30] decl=re.(file).top-level [email protected]:18:9 function_ref=unapplied))
              )))

          (var_decl range=[re.swift:19:9 - line:19:9] "result" type='Bool' interface type='Bool' access=fileprivate let readImpl=stored immutable)

result变量就在call语句块的上方，可以分析出result是初始化的变量，用来初始化result变量的是一个call语句，调用的函数是check，参数分别是data和key。

var result = check(data, key)

(pattern_binding_decl range=[re.swift:18:5 - line:18:15]
            (pattern_named type='String' 'key')
            Original init:
            (string_literal_expr type='String' location=re.swift:18:15 range=[re.swift:18:15 - line:18:15] encoding=utf8 value="345y" builtin_initializer=Swift.(file).String extension.init(_builtinStringLiteral:utf8CodeUnitCount:isASCII:) initializer=**NULL**)
            Processed init:
            (string_literal_expr type='String' location=re.swift:18:15 range=[re.swift:18:15 - line:18:15] encoding=utf8 value="345y" builtin_initializer=Swift.(file).String extension.init(_builtinStringLiteral:utf8CodeUnitCount:isASCII:) initializer=**NULL**))

          (var_decl range=[re.swift:18:9 - line:18:9] "key" type='String' interface type='String' access=fileprivate let readImpl=stored immutable)

再往上可以找到key的定义。

var key = "345y"

(pattern_binding_decl range=[re.swift:17:5 - line:17:39]
            (pattern_named type='String' 'data')
            Original init:
            (subscript_expr type='<null>'
              (member_ref_expr type='@lvalue [String]' location=re.swift:17:28 range=[re.swift:17:16 - line:17:28] decl=Swift.(file).CommandLine.arguments
                (type_expr type='CommandLine.Type' location=re.swift:17:16 range=[re.swift:17:16 - line:17:16] typerepr='CommandLine'))
              (argument_list
                (argument
                  (integer_literal_expr type='Int' location=re.swift:17:38 range=[re.swift:17:38 - line:17:38] value=1 builtin_initializer=Swift.(file).Int.init(_builtinIntegerLiteral:) initializer=**NULL**))
              ))
            Processed init:
            (load_expr implicit type='String' location=re.swift:17:37 range=[re.swift:17:16 - line:17:39]
              (subscript_expr type='@lvalue String' location=re.swift:17:37 range=[re.swift:17:16 - line:17:39] decl=Swift.(file).Array extension.subscript(_:) [with (substitution_map generic_signature=<Element> (substitution Element -> String))]
                (inout_expr implicit type='inout Array<String>' location=re.swift:17:16 range=[re.swift:17:16 - line:17:28]
                  (member_ref_expr type='@lvalue [String]' location=re.swift:17:28 range=[re.swift:17:16 - line:17:28] decl=Swift.(file).CommandLine.arguments
                    (type_expr type='CommandLine.Type' location=re.swift:17:16 range=[re.swift:17:16 - line:17:16] typerepr='CommandLine')))
                (argument_list
                  (argument
                    (integer_literal_expr type='Int' location=re.swift:17:38 range=[re.swift:17:38 - line:17:38] value=1 builtin_initializer=Swift.(file).Int.init(_builtinIntegerLiteral:) initializer=**NULL**))
                ))))

          (var_decl range=[re.swift:17:9 - line:17:9] "data" type='String' interface type='String' access=fileprivate let readImpl=stored immutable)

这里是data的定义，data是有一个subscript_expr语句块定义的，subscript_expr其实是在去数组的下标，这里取的是arguments[1]，也就是第二个命令行参数。

var data = CommandLine.arguments[1]

(if_stmt range=[re.swift:16:1 - line:21:1]
        (binary_expr type='Bool' location=re.swift:16:32 range=[re.swift:16:4 - line:16:35] nothrow
          (dot_syntax_call_expr implicit type='(Int, Int) -> Bool' location=re.swift:16:32 range=[re.swift:16:32 - line:16:32] nothrow
            (declref_expr type='(Int.Type) -> (Int, Int) -> Bool' location=re.swift:16:32 range=[re.swift:16:32 - line:16:32] decl=Swift.(file).Int extension.>= function_ref=single)
            (argument_list implicit
              (argument
                (type_expr implicit type='Int.Type' location=re.swift:16:32 range=[re.swift:16:32 - line:16:32] typerepr='Int'))
            ))
          (argument_list implicit
            (argument
              (member_ref_expr type='Int' location=re.swift:16:26 range=[re.swift:16:4 - line:16:26] decl=Swift.(file).Array extension.count [with (substitution_map generic_signature=<Element> (substitution Element -> String))]
                (load_expr implicit type='[String]' location=re.swift:16:16 range=[re.swift:16:4 - line:16:16]
                  (member_ref_expr type='@lvalue [String]' location=re.swift:16:16 range=[re.swift:16:4 - line:16:16] decl=Swift.(file).CommandLine.arguments
                    (type_expr type='CommandLine.Type' location=re.swift:16:4 range=[re.swift:16:4 - line:16:4] typerepr='CommandLine')))))
            (argument
              (integer_literal_expr type='Int' location=re.swift:16:35 range=[re.swift:16:35 - line:16:35] value=2 builtin_initializer=Swift.(file).Int.init(_builtinIntegerLiteral:) initializer=**NULL**))
          ))

在往上是一个if语句，操作符是 >=（extension.>=），操作数一个是argument.count()，一个是2,所以这一块的意思就是比较命令行参数是否大于等于2。

if CommandLine.arguments.count >= 2 {

}

国赛babytree 赛题解析

在往上就是top_level_code_decl，顶层表达式了，如图所示，这个程序真是由一个func_decl和一个top_level_code_decl组成，我们已经分析完了下面的top_level_code_decl：

func check(encoded: String, keyValue:String) -> Bool {
    
}

if CommandLine.arguments.count >= 2 {
    let data = CommandLine.arguments[1]
    let key = "345y"
    let result = check(encoded: data, keyValue: key)
    print(result)
}

(func_decl range=[re.swift:1:1 - line:14:1] "check(_:_:)" interface type='(String, String) -> Bool' access=internal
    (parameter_list range=[re.swift:1:11 - line:1:49]
      (parameter "encoded" type='String' interface type='String')
      (parameter "keyValue" type='String' interface type='String'))
    (result
      (type_ident
        (component id='Bool' bind=Swift.(file).Bool)))
    (brace_stmt range=[re.swift:1:59 - line:14:1]

上方函数的大体结构为：参数，返回值和一个表达式。

(parameter_list range=[re.swift:1:11 - line:1:49]
      (parameter "encoded" type='String' interface type='String')
      (parameter "keyValue" type='String' interface type='String'))

参数分别为encoded和keyValue，都是String类型。

(result
      (type_ident
        (component id='Bool' bind=Swift.(file).Bool)))

返回值为Bool类型。

(brace_stmt range=[re.swift:1:59 - line:14:1]
      (pattern_binding_decl range=[re.swift:2:5 - line:2:33]
      (var_decl range=[re.swift:2:9 - line:2:9] "b" type='[UInt8]' interface type='[UInt8]' access=private readImpl=stored writeImpl=stored readWriteImpl=stored)
      (pattern_binding_decl range=[re.swift:3:5 - line:3:34]
      (var_decl range=[re.swift:3:9 - line:3:9] "k" type='[UInt8]' interface type='[UInt8]' access=private readImpl=stored writeImpl=stored readWriteImpl=stored)
      (pattern_binding_decl range=[re.swift:4:5 - line:4:25]
      (var_decl range=[re.swift:4:9 - line:4:9] "r0" type='UInt8' interface type='UInt8' access=private readImpl=stored writeImpl=stored readWriteImpl=stored)
      (var_decl range=[re.swift:4:13 - line:4:13] "r1" type='UInt8' interface type='UInt8' access=private readImpl=stored writeImpl=stored readWriteImpl=stored)
      (var_decl range=[re.swift:4:17 - line:4:17] "r2" type='UInt8' interface type='UInt8' access=private readImpl=stored writeImpl=stored readWriteImpl=stored)
      (var_decl range=[re.swift:4:21 - line:4:21] "r3" type='UInt8' interface type='UInt8' access=private readImpl=stored writeImpl=stored readWriteImpl=stored)
      (for_each_stmt range=[re.swift:5:5 - line:12:5]
      (return_stmt range=[re.swift:13:5 - line:13:198]

下方的语句块中又包含了3个定义变量的语句，1个for循环，1个返回语句。

(pattern_binding_decl range=[re.swift:2:5 - line:2:33]
        (pattern_named type='[UInt8]' 'b')
        Original init:
        (call_expr type='[UInt8]' location=re.swift:2:19 range=[re.swift:2:13 - line:2:33] nothrow
          (constructor_ref_call_expr type='(String.UTF8View) -> [UInt8]' location=re.swift:2:19 range=[re.swift:2:13 - line:2:19] nothrow
            (declref_expr implicit type='(Array<UInt8>.Type) -> (String.UTF8View) -> Array<UInt8>' location=re.swift:2:19 range=[re.swift:2:19 - line:2:19] decl=Swift.(file).Array extension.init(_:) [with (substitution_map generic_signature=<Element, S where Element == S.Element, S : Sequence> (substitution Element -> UInt8) (substitution S -> String.UTF8View))] function_ref=single)
            (argument_list implicit
              (argument
                (type_expr type='[UInt8].Type' location=re.swift:2:13 range=[re.swift:2:13 - line:2:19] typerepr='[UInt8]'))
            ))
          (argument_list
            (argument
              (member_ref_expr type='String.UTF8View' location=re.swift:2:29 range=[re.swift:2:21 - line:2:29] decl=Swift.(file).String extension.utf8
                (declref_expr type='String' location=re.swift:2:21 range=[re.swift:2:21 - line:2:21] decl=re.(file).check(_:_:)[email protected]:1:14 function_ref=unapplied)))
          ))
        Processed init:
        (call_expr type='[UInt8]' location=re.swift:2:19 range=[re.swift:2:13 - line:2:33] nothrow

第一个定义变量的语句，变量名为b，类型是一个[UInt8]数组，这个数组是由ebcoded（decl=re.(file).check(:🙂[email protected]）转换过来的。

var b = [UInt8](encoded.utf8)

(pattern_binding_decl range=[re.swift:3:5 - line:3:34]
        (pattern_named type='[UInt8]' 'k')
        Original init:
        (call_expr type='[UInt8]' location=re.swift:3:19 range=[re.swift:3:13 - line:3:34] nothrow
          (constructor_ref_call_expr type='(String.UTF8View) -> [UInt8]' location=re.swift:3:19 range=[re.swift:3:13 - line:3:19] nothrow
            (declref_expr implicit type='(Array<UInt8>.Type) -> (String.UTF8View) -> Array<UInt8>' location=re.swift:3:19 range=[re.swift:3:19 - line:3:19] decl=Swift.(file).Array extension.init(_:) [with (substitution_map generic_signature=<Element, S where Element == S.Element, S : Sequence> (substitution Element -> UInt8) (substitution S -> String.UTF8View))] function_ref=single)
            (argument_list implicit
              (argument
                (type_expr type='[UInt8].Type' location=re.swift:3:13 range=[re.swift:3:13 - line:3:19] typerepr='[UInt8]'))
            ))
          (argument_list
            (argument
              (member_ref_expr type='String.UTF8View' location=re.swift:3:30 range=[re.swift:3:21 - line:3:30] decl=Swift.(file).String extension.utf8
                (declref_expr type='String' location=re.swift:3:21 range=[re.swift:3:21 - line:3:21] decl=re.(file).check(_:_:)[email protected]:1:33 function_ref=unapplied)))
          ))
        Processed init:
        (call_expr type='[UInt8]' location=re.swift:3:19 range=[re.swift:3:13 - line:3:34] nothrow

同上，接着定义一个变量k。

var k = [UInt8](keyValue.utf8)

(pattern_binding_decl range=[re.swift:4:5 - line:4:25]
        (pattern_typed type='UInt8'
          (pattern_named type='UInt8' 'r0')
          (type_ident
            (component id='UInt8' bind=Swift.(file).UInt8)))
        (pattern_typed type='UInt8'
          (pattern_named type='UInt8' 'r1')
          (type_ident
            (component id='UInt8' bind=Swift.(file).UInt8)))
        (pattern_typed type='UInt8'
          (pattern_named type='UInt8' 'r2')
          (type_ident
            (component id='UInt8' bind=Swift.(file).UInt8)))
        (pattern_typed type='UInt8'
          (pattern_named type='UInt8' 'r3')
          (type_ident
            (component id='UInt8' bind=Swift.(file).UInt8))))

      (var_decl range=[re.swift:4:9 - line:4:9] "r0" type='UInt8' interface type='UInt8' access=private readImpl=stored writeImpl=stored readWriteImpl=stored)

      (var_decl range=[re.swift:4:13 - line:4:13] "r1" type='UInt8' interface type='UInt8' access=private readImpl=stored writeImpl=stored readWriteImpl=stored)

      (var_decl range=[re.swift:4:17 - line:4:17] "r2" type='UInt8' interface type='UInt8' access=private readImpl=stored writeImpl=stored readWriteImpl=stored)

      (var_decl range=[re.swift:4:21 - line:4:21] "r3" type='UInt8' interface type='UInt8' access=private readImpl=stored writeImpl=stored readWriteImpl=stored)

接下来的语句块中定义了四个未初始化的变量r0, r1, r2, r3，类型是UInt8。

var r0, r1, r2, r3:UInt8

(dot_syntax_call_expr implicit type='(Int, Int) -> ClosedRange<Int>' location=re.swift:5:15 range=[re.swift:5:15 - line:5:15] nothrow
            (declref_expr type='(Int.Type) -> (Int, Int) -> ClosedRange<Int>' location=re.swift:5:15 range=[re.swift:5:15 - line:5:15] decl=Swift.(file).Comparable extension.... [with (substitution_map generic_signature=<Self where Self : Comparable> (substitution Self -> Int))] function_ref=double)
            (argument_list implicit
              (argument
                (type_expr implicit type='Int.Type' location=re.swift:5:15 range=[re.swift:5:15 - line:5:15] typerepr='Int'))
            ))
          (argument_list implicit

可以看到(decl=Swift.(file).Comparable extension….),说明这是一个for-in循环。

(argument
              (integer_literal_expr type='Int' location=re.swift:5:14 range=[re.swift:5:14 - line:5:14] value=0 builtin_initializer=Swift.(file).Int.init(_builtinIntegerLiteral:) initializer=**NULL**))
(argument
              (binary_expr type='Int' location=re.swift:5:25 range=[re.swift:5:18 - line:5:26] nothrow
                (dot_syntax_call_expr implicit type='(Int, Int) -> Int' location=re.swift:5:25 range=[re.swift:5:25 - line:5:25] nothrow
                  (declref_expr type='(Int.Type) -> (Int, Int) -> Int' location=re.swift:5:25 range=[re.swift:5:25 - line:5:25] decl=Swift.(file).Int extension.- function_ref=double)
                  (argument_list implicit
                    (argument
                      (type_expr implicit type='Int.Type' location=re.swift:5:25 range=[re.swift:5:25 - line:5:25] typerepr='Int'))
                  ))
                (argument_list implicit
                  (argument
                    (member_ref_expr type='Int' location=re.swift:5:20 range=[re.swift:5:18 - line:5:20] decl=Swift.(file).Array extension.count [with (substitution_map generic_signature=<Element> (substitution Element -> UInt8))]
                      (load_expr implicit type='[UInt8]' location=re.swift:5:18 range=[re.swift:5:18 - line:5:18]
                        (declref_expr type='@lvalue [UInt8]' location=re.swift:5:18 range=[re.swift:5:18 - line:5:18] decl=re.(file).check(_:_:)[email protected]:2:9 function_ref=unapplied))))
                  (argument
                    (integer_literal_expr type='Int' location=re.swift:5:26 range=[re.swift:5:26 - line:5:26] value=4 builtin_initializer=Swift.(file).Int.init(_builtinIntegerLiteral:) initializer=**NULL**))
                )))

循环的范围是从0到b.count-4。

for i in 0...b.count-4 {

}

国赛babytree 赛题解析

紧跟着的是六条赋值语句。

国赛babytree 赛题解析

展开发现首尾的赋值语句格式相似,中间四条赋值语句格式相似,所以我们应该只需要仔细分析两种不同格式中的各一种。

国赛babytree 赛题解析

(load_expr implicit type='UInt8' location=re.swift:6:30 range=[re.swift:6:29 - line:6:32]
                (subscript_expr type='@lvalue UInt8' location=re.swift:6:30 range=[re.swift:6:29 - line:6:32] decl=Swift.(file).Array extension.subscript(_:) [with (substitution_map generic_signature=<Element> (substitution Element -> UInt8))]
                  (inout_expr implicit type='inout Array<UInt8>' location=re.swift:6:29 range=[re.swift:6:29 - line:6:29]
                    (declref_expr type='@lvalue [UInt8]' location=re.swift:6:29 range=[re.swift:6:29 - line:6:29] decl=re.(file).check(_:_:)[email protected]:2:9 function_ref=unapplied))
                  (argument_list
                    (argument
                      (declref_expr type='Int' location=re.swift:6:31 range=[re.swift:6:31 - line:6:31] decl=re.(file).check(_:_:)[email protected]:5:9 function_ref=unapplied))
                  )))

这是第一个赋值语句的结构,做的事情是用b数组的值填充r0到r3。

r0, r1, r2, r3 = b[i], b[i+1], b[i+2], b[i+3]

国赛babytree 赛题解析

第二个赋值语句,首先是一个取下标,取的是b[i+0]。

国赛babytree 赛题解析

接着是一个运算语句块。

国赛babytree 赛题解析

初步看出是用r2异或一个表达式。

该表达式是另一个表达式 & 0xff得到。

国赛babytree 赛题解析

接着又是加运算。

一个是k[0]。

国赛babytree 赛题解析

一个是r0 >> 4。

综上,第二个赋值语句:

b[i+0] = r2 ^ ((k[0] + (r0 >> 4)) & 0xff)

同理可以分析出接下来的几条赋值语句。

b[i+1] = r3 ^ ((k[1] + (r1 >> 2)) & 0xff)
b[i+2] = r0 ^ k[2]
b[i+3] = r1 ^ k[3]
k[0], k[1], k[2], k[3] = k[1], k[2], k[3], k[0]

for循环之后就是返回语句。

国赛babytree 赛题解析

返回语句由一条判断语句组成，操作符是==。

国赛babytree 赛题解析

第一个参数是b数组。

第二个参数是一个给定的数组。

[88, 35, 88, 225, 7, 201, 57, 94, 77, 56, 75, 168, 72, 218, 64, 91, 16, 101, 32, 207, 73, 130, 74, 128, 76, 201, 16, 248, 41, 205, 103, 84, 91, 99, 79, 202, 22, 131, 63, 255, 20, 16]

return (b == [88, 35, 88, 225, 7,  201, 57, 94, 77, 56, 75, 168, 72, 218, 64, 91, 16, 101, 32, 207, 73, 130, 74, 128, 76, 201, 16, 248, 41, 205, 103, 84, 91, 99, 79, 202, 22, 131, 63, 255, 20, 16])

re.swift

func check(encoded: String, keyValue:String) -> Bool {
    var b = [UInt8](encoded.utf8)
    var k = [UInt8](keyValue.utf8)
    var r0, r1, r2, r3:UInt8
    for i in 0...b.count-4 {
        r0 = b[i]
        r1 = b[i+1]
        r2 = b[i+2]
        r3 = b[i+3]
        b[i+0] = r2 ^ ((k[0] + (r0 >> 4)) & 0xff)
        b[i+1] = r3 ^ ((k[1] + (r1 >> 2)) & 0xff)
        b[i+2] = r0 ^ k[2]
        b[i+3] = r1 ^ k[3]
        let temp = k[0]
        k[0] = k[1]
        k[1] = k[2]
        k[2] = k[3]
        k[3] = temp
    }
    return (b == [88, 35, 88, 225, 7,  201, 57, 94, 77, 56, 75, 168, 72, 218, 64, 91, 16, 101, 32, 207, 73, 130, 74, 128, 76, 201, 16, 248, 41, 205, 103, 84, 91, 99, 79, 202, 22, 131, 63, 255, 20, 16])
}

if CommandLine.arguments.count >= 2 {
    let data = CommandLine.arguments[1]
    let key = "345y"
    let result = check(encoded: data, keyValue: key)
    print(result)
}

解题脚本

b = [88, 35, 88, 225, 7,  201, 57, 94, 77, 56, 75, 168, 72, 218, 64, 91, 16, 101, 32, 207, 73, 130, 74, 128, 76, 201, 16, 248, 41, 205, 103, 84, 91, 99, 79, 202, 22, 131, 63, 255, 20, 16]
k = [121, 51, 52, 53] //换位后的key
for i in range(len(b)-4, -1, -1):
    k[1], k[2], k[3], k[0] = k[0], k[1], k[2], k[3]
    r1 = k[3] ^ b[i+3]
    r0 = k[2] ^ b[i+2]
    r3 = ((k[1] + (r1 >> 2)) & 0xff) ^ b[i+1]
    r2 = ((k[0] + (r0 >> 4)) & 0xff) ^ b[i]
    b[i], b[i+1], b[i+2], b[i+3] = r0, r1, r2, r3
for i in b:
    print(chr(i), end='')